UBC_1983_A1 R49
Content
NON-METALLIC
INCLUSIONS
ELECTROSLAG REFINED
IN
INGOTS
by FIDEL Ing.
Quim. Met., U n i v e r s i d a d
M.Sc,
REYES-CARMONA Nacional
The U n i v e r s i t y o f I l l i n o i s
A THESIS SUBMITTED
Autdnoma de M d x i c o ,
a t U r b a n a - C h a m p a i g n , 1978
IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE
STUDIES
Department o f M e t a l l u r g i c a l E n g i n e e r i n g
We
accept
this
t h e s i s as c o n f o r m i n g
to the r e q u i r e d
standard
THE UNIVERSITY OF BRITISH COLUMBIA January
©
Fidel
1976
19 83
Reyes-Carmona, 1983
In p r e s e n t i n g
t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the
requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it
f r e e l y a v a i l a b l e f o r reference
and study.
I further
agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s
thesis
f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . understood t h a t copying o r p u b l i c a t i o n o f t h i s f o r f i n a n c i a l gain
It is thesis
s h a l l n o t be allowed without my
permission.
F i d e l Reyes-Carmona
Department o f M e t a l l u r g i c a l E n g i n e e r i n g
The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date
E-6
(3/81)
March 21, 1983
written
ABSTRACT
The
o b j e c t i v e of
non-metallic chemically to the
this
inclusions
transformed,
final
1020,
were r e f i n e d by
e l e c t r o d e s was
removed and
4340 and
two
electrode
when t h e
are
t i p by
and
by
the
the
how
and electrodes
and
200
the
deoxidation
practices,
transformed
Inclusions
liquid
No
origin
in
the
are
slag at
d i s s o l v e d i n the
formed.
i n c l u s i o n s are
these
found t h a t i n c l u s i o n s i n
presence of
of e l e c t r o d e
i n mould
alloys.
chemically
entirely
mm
R e f i n i n g of
AISi
i t was
droplet i s completely as
and
electrodes
the
matrix
ingot inclusions
and
i t is
concluded
e i t h e r d i s s o l v e d or
removed
slag. The
on
mm
thermal gradients.
they are
a l l electrode
the
CaSiAlBa
p h y s i c a l l y and
were i d e n t i f i a b l e that
(7.5
s l a g systems.
research
a l t e r e d by
film
(Ni-Mo-V) s t e e l
done u n d e r d i f f e r e n t
Through t h i s
liquid
physically
c o n t r o l l e d from
rotor
ESR-units
namely p u r e A l , C a S i ,
chemically
to investigate
( i n c l u s i o n s ) are
diameter) under d i f f e r e n t
electrode
was
ESR-product.
Several
the
research
e f f e c t s o f the
chemical
composition
were t r a c e d d u r i n g i n c l u s i o n s was
refining
d e t e r m i n e d by
m e t a l samples d u r i n g m e a s u r e d by
the
slag with of the and
and
without
liquid
hence the
pool
deoxidizers and
chemistry
e x t r a c t i n g s l a g and
refining.
The
total
vacuum f u s i o n t e c h n i q u e ,
ingot of
liquid
oxygen c o n t e n t chemical
was
analyses
ii
of
s l a g by
spectrophotometric
a n a l y s i s by analysis. the
SEM
and
The
The
EPMA and
assays
deoxidation
and
chemical
techniques,
by
were u s e d t o f o r m u l a t e
precipitation
composition
slags.
inclusions and
The
The
i s the
of cooperative
2
+
3
[Ca]
+
(A1 0 )
+
3
The potential
composition
i n low
o f complex
Al-Ca-Si
silica
30 wt%
2
i n ESR
deoxidation practice
slags
Al 0 2
ingots takes
r e a c t i o n s between s l a g
3
an
and
2
wt%)
efficient
20 wt%
p l a c e by
and
Si0
(>10.0
system t o perform
CaF ,
ingots
the
CaO. process
deoxidizers i n
the
sequences:
[Al]
2
slag
slag
50 wt%
deoxidation
following
the
i s predictable i n high
deoxidation
corroborate
mechanisms.
precipitation
t h e most a p p r o p r i a t e
and
of inclusions i n refined
the e l e c t r o d e or the
content
micro-
x-ray ( c r y s t a l l o g r a p h i c )
a r e more s t r o n g l y i n f l u e n c e d by than
electron
(FeO)
t
( A l ^ )
+
(FeO)
t
(CaO)
Fe
[Ca]
t
3
+
(CaO
Fe
+ 2
[Al]
p r e c i p i t a t i o n r e a c t i o n s a r e c o n t r o l l e d by i n the melt,
thus
the
transitions
t o be
the
oxygen
expected
are : Al 0 «FeO 2
3
+ MnS An
+ MnS
I I I or
I I -»• c t - A l 0 2
(Ca, Mn)
excessive
+ Y
3
I I o r I I I -»• x C a 0 « y
Ca
+
* X CaO* (y - ^)
r a i s e s the A l content
Al 0 2
3
A l ^
CaS
to:
(A1 0 )* 2
+ MnS
S -*• x C a 0 « y A l ^
deoxidation with
ingot according X Ca
3
+ | X
[Al]
in
the
iii
R a d i a l i n c l u s i o n s i z e d i s t r i b u t i o n as w e l l as arm
spacings i n samples e x t r a c t e d
i n g o t s were determined.
I t was
from l i q u i d p o o l
found t h a t the
s i z e obeys the normal d i s t r i b u t i o n and v a r i a t i o n of the i n c l u s i o n Hence the i n c l u s i o n
s i z e along
composition and
l o c a l s o l i d i f i c a t i o n c o n d i t i o n s and thermochemical c o n d i t i o n s .
dendrite and
inclusion
there
i s a normal
radial
distances.
s i z e i s a f u n c t i o n of a l s o of the
local
iv TABLE OF CONTENTS Page Abstract
i
Table of Contents
iv
L i s t of F i g u r e s
ix
L i s t of Tables
xvii
L i s t of Symbols
xix
Chapter I II
INTRODUCTION
1
LITERATURE REVIEW
4
2.1 2.2
L i t e r a t u r e Survey on E l e c t r o d e Inclusions L i t e r a t u r e Survey on S l a g - L i q u i d Metal R e a c t i o n s and t h e i r I n f l u e n c e on the ESR Ingot Chemistry 2.2.1 2.2.2 2.2.3 2.2.4
2.3
P r i n c i p l e s of the Reaction Scheme i n the ESR Process On the Nature of the ESR R e a c t i o n Scheme Thermodynamic Approach of the ESR S l a g Systems O v e r a l l View on the M o d e l l i n g of ESR Reactions
General N u c l e a t i o n and Growth of I n clusions 2.3.2.1 2.3.2*2
2.3.3
Homogeneous Nucleation Heterogeneous Nucleation
Growth of I n c l u s i o n s
12 12 18 32 34
P r e c i p i t a t i o n of I n c l u s i o n s 2.3.1 2.3.2
4
36 * ....
36 39 39 42 43
V
Chapter
Page 2.3.4 2.3.5 2.3.6
Sulfides . . . Specific Sulfides Oxisulfides 2.3.6.1 2.3.6.2 2.3.6.3
2.3.7
III
The Fe-O-S System The Fe-O-S-Mn E q u i l i brium The Fe-O-S-Si-Mn Equilibrium
53 55 62 66
Aluminates Calcium Aluminates Complex Oxides
66 76 90
I n c l u s i o n s i n ESR-Ingots
94
NATURE OF THE PROBLEM
106
3.1 3.2
106
3.3 3.4 3.5
IV
47 51 53
Oxides 2.3.7.1 2.3.7.2 2.3.7.3
2.4
„
I n c l u s i o n s i n the E l e c t r o d e The Chemical I n f l u e n c e o f the ESR components on the Composition of Inclusions The P r e c i p i t a t i o n o f I n c l u s i o n s from L i q u i d Pool to Ingot D i s t r i b u t i o n o f I n c l u s i o n s During Solidification E s t a b l i s h m e n t of the Proposal and O b j e c t i v e s Sought Through t h i s Research
108 I l l 113 115
EXPERIMENTAL WORK AND TECHNIQUES
116
4.1 4.2 4.3 4.4
116 118 121 122
4.5 4.6
Experimental Procedure Analysis of Inclusions T o t a l Oxygen A n a l y s i s I n c l u s i o n E x t r a c t i o n Method 4.4.1 Apparatus and Experimental Procedure C r y s t a l l o g r a p h i c X-ray A n a l y s i s o f Extracted Inclusions Atomic A b s o r p t i o n A n a l y s i s (Spectrophotometry)
123 126 ?
127
vi Chapter 4.7 V
Page Metallographic
RESULTS AND 5.1
DISCUSSION
-^8 •
Mechanism by which E l e c t r o d e are E l i m i n a t e d 5.1.1 5.1.2
5.1.2.2
5.1.3
130 Inclusions 130
Behavior of O x i s u l f i d e I n c l u s ions i n 1 0 2 0 M.S. Electrode Tips *. , . . Removal of Oxide and S u l f i d e I n c l u s i o n s i n 4 340 and Rotor Steels 5.1.2.1
5.2
Analysis
Removal of Oxides and Sulfides i n 4340 electrodes Calcium Aluminum S i l i cates i n a Rotor ( N i Cr-Mo) S t e e l
F i n a l Remarks About the moval Mechanism
Re-
The Chemical I n f l u e n c e of the E l e c t r o d e , Slag and D e o x i d i z e r on the Chemical Composition of I n c l u s i o n s .. 5.2.1
D e s c r i p t i o n of Experimental Findings 5.2.1.1
5.2.1.2 5.2.1.3
5.2.1.4
P r e l i m i n a r y Studies on the E f f e c t of the Slag and the Deoxidation I n t e r m i t t e n t CaSi A d d i t i o n s and the Rea c t i o n Scheme R e f i n i n g of 1 0 2 0 M.S., 2 0 0 mm Diameter Ingots Deoxidized C o n t i n uously with A l 1 0 2 0 M.S. Ingots Deo x i d i z e d Continuously with a CaSi A l l o y ... .....
130 141
144 146 148
151 151
151 157
159 164
5.2.1.5
C o r r o b o r a t i o n and Ext e n s i o n o f Previous F i n d i n g s t o a 4340 S t e e l CaSi ( c o n t i n u ously) Deoxidized
D i s c u s s i o n o f R e s u l t s i n Terms of E l e c t rode and S l a g Composition, Related t o the Second Question 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5
The E f f e c t o f the E l e c t r o d e on the I n c l u s i o n Composition of ESR Ingots E l u c i d a t i o n o f the E f f e c t o f S l a g and D e o x i d i z e r s (preliminary studies) , P r e l i m i n a r y D i s c u s s i o n on the Deoxidation Mechanism Comprehensive D i s c u s s i o n on the Deoxidation Mechanism F i n a l Remarks
F i n d i n g s and D i s c u s s i o n Related t o the T h i r d Question 5.4.1
D e s c r i p t i o n of Experimental Results 5.4.1.1 5.4.1.2 5.4.1.3 5.4.1.4
5.4.2 5.4.3
The I n c l u s i o n Mean Diameter F i n d i n g s from I n d i v i d u a l Experiments Complimentary Studies Summary o f E x p e r i mental F i n d i n g s
P r e c i p i t a t i o n of Inclusions i n the Fe-Al-Ca-O-S (Mn) system D i s c u s s i o n of R e s u l t s » 5.4.3.1 5.4.3.2
N u c l e a t i o n Growth and F l o t a t i o n of Inclusions . . . Comparison between T h e o r e t i c a l and Experimental Results...*
viii Chapter VI
Page THE RADIAL DISTRIBUTION OF INCLUSIONS IN CaSi AND A l DEOXIDIZED INGOTS 6.1 6.2 6.3
VII VIII
Experimental D e t a i l s and Techniques...... Experimental F i n d i n g s D i s c u s s i o n of R e s u l t s
2
2
3
223 2
2
2 2
4
5
CONCLUSIONS
228
SUGGESTIONS FOR FUTURE WORK
2 32
LIST OF REFERENCES
235
FIGURES
251
TABLES
3
APPENDIX . . . ........
5
1
374
ix LIST OF FIGURES Figure
Page
1.
Schematic i l l u s t r a t i o n of an ESR system
2.
P r e d i c t e d and measured temperature p r o f i l e s f o r a 1018 MS e l e c t r o d e 25 mm i n diameter
252
Manganese c o n t e n t o f the metal f o r u n i v a r i a n t e q u i l i b r i u m y - i r o n + "MnO" + "MnS" + l i q u i d (1) f o r Fe-Mn-S-0 s y s tem and u n i v a r i a n t e q u i l i b r i u m Y + "MnS" + l i q u i d s u l f i d e f o r Fe-Mn-S system
253
U n i v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 system i n the presence o f y - i r o n and Mn(Fe)0 phases
254
Univariant e q u i l i b r i a involving s o l i d metal and Mn(Fe)0 i n the Fe-Mn-S-0 system bonded w i t h t e r n a r y Fe-Mn-0 and Fe-S-0 terminal-phase f i e l d s (e) , ,(p) , (f) , (n), (g) and (h)
255
L o c a t i o n o f the p l a n e s i n the quaternary (FeO-MnO-MnS-Si0 ) system
256
E q u i l i b r i u m phases i n t h r e e planes o f the FeO-MnO-MnS-SiC^ system. a) MnS-FeO2MnO«Si02, b) MnS-2FeO«Si0 -2MnO«Si0 and c) MnS-FeO-MnO
256
Behavior o f i n c l u s i o n s e n r i c h e d i n Mn and S i as a f u n c t i o n o f temperature
257
Schematic i l l u s t r a t i o n o f changes i n i n c l u s i o n composition i n a 1020 MS e l e c t rode produced v i a a c i d e l e c t r i c f u r a n c e . . . .
258
Wt. % A l and wt. % Ca and wt. % 0 i n l i q u i d i r o n a t u n i t A l 0 and CaO a c t i v i t y 3
259
Isothermal Fe-Al-Ca-0 p r e c i p i t a t i o n (Henrian a c t i v i t i e s ) diagram
260
3.
-
4.
5.
6.
i
r
o
....
n
2
7.
2
8. 9.
10.
2
11.
251
2
X
Figure 12. 13.
Page Ternary A l 0 ~ ( C a , X ) 0 - S i 0 diagram 2
3
2
inclusion 261
Slag chemical composition used i n the ,.(34,53,83) , a. • 4.past and p r e s e n t i n v e s t i g ation
262
14.
Schematic i l l u s t r a t i o n of the ESR arrangement used i n t h i s i n v e s t i g a t i o n
26 3
15.
Schematic i l l u s t r a t i o n of the " i n c l u s i o n extractor"
264
16.
T y p i c a l i n c l u s i o n s from 1020 MS ( o p t i c a l microscopy) *
265
17.
Deformed i n c l u s i o n s i n 1020 MS and t h e i r
18.
19.
20.
21.
22. 23.
24. 25.
electrodes electrodes
X-ray spectrum a n a l y s i s
(SEM)
...
266
M a c r o s t r u c t u r e of a 1020 MS e l e c t r o d e t i p where l i q u i d f i l m , p a r t i a l l y molten and f u l l y r e c r y s t a l l i z e d areas are shown
267
M a c r o s t r u c t u r e s o f a 4340 e l e c t r o d e t i p . D r o p l e t , l i q u i d f i l m , p a r t i a l l y molten, f u l l y and p a r t i a l l y r e c r y s t a l l i z e d zones are shown
268
M a c r o s t r u c t u r e o f a r o t o r (Ni-Cr-Mo) s t e e l . L i q u i d f i l m , and p a r t i a l l y molten areas are shown
269
Schematic i l l u s t r a t i o n o f 1020 MS e l e c t r o d e tip (acid e l e c t r i c furnace produced) s u b j e c t e d t o ESR-thermal g r a d i e n t s
270
M u l t i p h a s e ( r e l a t i v e l y grown) i n c l u s i o n s i n a 1020 MS e l e c t r o d e t i p
271
S i n g l e phase i n c l u s i o n s i n p a r t i a l l y and f u l l y molten r e g i o n s i n a 1020 e l e c t r o d e tip
272
Complex Ca-Al-Si-Mn i n c l u s i o n s l o c a t e d i n the l i q u i d f i l m and d r o p l e t s
273
Spectrum X-ray a n a l y s i s o f Ca-Al-Si-Mn i n c l u s i o n s i n a 1020 MS e l e c t r o d e l o c a t e d i n the l i q u i d f i l m and d r o p l e t s
274
xi Figure 26.
27.
28.
29.
30.
31.
32.
33
34.
35.
36.
37.
Page Changes i n i n c l u s i o n chemical composition i n a 4 340 e l e c t r o d e t i p s u b j e c t e d t o ESR thermal g r a d i e n t s
275
Changes i n i n c l u s i o n chemical composition i n a 4340 e l e c t r o d e t i p with a strong r e c r y s t a l l i z e d region
276
Behavior of oxide i n c l u s i o n s i n a e l e c t rode t i p of a r o t o r s t e e l subjected t o ESR thermal g r a d i e n t s
277
.
Aluminum s i l i c a t e s i n a 4340 ESR i n g o t 75 mm i n diamter. Precipitated inclusions in a l o c a l i z e d region
278
I n f l u e n c e o f CaSi and FeO i n t e r m i t t e n t a d d i t i o n s on the oxygen content of a 1020 M.S. (RIII-W)
279
Changes i n oxygen content i n a 1020 MS i n g o t as a r e s u l t o f CaSi and FeO i n t e r m i t t e n t a d d i t i o n s (RII-W)
280
Changes i n s l a g chemical composition i n a 1020 MS (RIII-W) as a r e s u l t of CaSi and FeO i n t e r m i t t e n t a d d i t i o n s
281
Changes i n s l a g chemical composition as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s of CaSi and FeO i n s l a g d u r i n g r e f i n i n g (RII-W)
282,283
Changes i n i n g o t chemical composition as a r e s u l t of CaSi and FeO a d d i t i o n s i n s l a g during r e f i n i n g (RIII-W)
284
E f f e c t of CaSi and FeO a d d i t i o n s i n the s l a g on the chemical composition of a 1020 MS i n g o t (RII-W)
285
Changes i n i n c l u s i o n composition and s i z e i n a 1020 MS i n g o t (RIII-W) as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s o f CaSi and FeO i n the s l a g
286
Chemical a n a l y s i s o f s l a g samples i n R I - I l .
287
xii Figure
Page
38.
Ingot chemical a n a l y s i s i n R I - l l
288
39.
S l a g chemical a n a l y s i s (wt. %) i n a cont i n u o u s l y A l d e o x i d i z e d 1020 MS i n g o t (RII-Il)
289
40.
Slag chemical a n a l y s i s
290
41.
I n c l u s i o n mean diameter and t o t a l oxygen content i n a c o n t i n u o u s l y (Al) d e o x i d i z e d ingot, (RII-Il)
291
42.
T o t a l oxygen content and i n c l u s i o n mean diameter i n i n g o t (RII-I2)
292
43.
I n c l u s i o n chemical composition (at. %) as a f u n c t i o n o f c o n t i n u o u s l y i n c r e a s i n g deoxidation rates i n RII-Il
293
I n c l u s i o n chemical composition (at. %) as a f u n c t i o n of the i n g o t h e i g h t (or continuously increasing deoxidation r a t e s ) i n RII-I2
294
45.
Ingot chemical a n a l y s i s i n R I I - I l
295
46.
Ingot chemical a n a l y s i s i n RII-I2
296
47.
"Alumina g a l a x i e s " , (EPMA), a s s o c i a t e d t o MnS I I i n i n c i p i e n t aluminum d e o x i d i z e d i n g o t s , ( R I I - I l and RII-I2)
297
"Alumina g a l a x i e s " (EPMA) and MnS I I i n A l deoxidized ingots
29 8
Faceted alumina (a-A^C^) i n samples from l i q u i d p o o l and i n g o t d e o x i d i z e d with A l ..
299
Calcium aluminates low i n Ca from h i g h l y A l d e o x i d i z e d i n g o t s . A l , Ca and S composition RII-I2
300
Composition dependence o f s u l f i d e phases on the Ca:Al r a t i o i n the oxide phase ( R I I - I l )
301
44.
48. 49. 50.
51.
(wt. %) i n R I I - I l . . .
xiii Page
Figure 52.
5 3
•
54.
55.
56.
Composition dependence o f s u l f i d e phases on Ca-aluminate i n c l u s i o n s phases i n RII-I2 .. 302 Segregated m a t e r i a l i n an A l d e o x i d i z e d i n g o t ( l i q u i d pool) . . Dependence o f "FeO" contents i n s l a g on the Ai2 0-.:CaO r a t i o i n s l a g o f a c o n t i n u ously A l deoxidized ingot (RII-Il) Dependence o f "FeO" contents i n s l a g on the A ^ O ^ t C a O r a t i o i n s l a g o f a c o n t i n u o u s l y A l d e o x i d i z e d i n g o t (RII-I2)
3
0
3
3
04
3
05
Changes i n t o t a l oxygen content and i n c l u s i o n mean diameter i n a c o n t i n u o u s l y CaSi deoxidized ingot (RIII-Il)
306
I n c l u s i o n mean diameter and t o t a l oxygen content i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t (RIII-I2)
307
58.
I n c l u s i o n chemical composition as a f u n c t i o n of d e o x i d a t i o n r a t e s i n R I I I - I l
308
59.
I n c l u s i o n chemical composition as a funct i o n o f d e o x i d a t i o n r a t e s i n RIII-I2
309
60.
Changes i n s l a g chemical composition i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t (RIIIIl)
310
Changes i n s l a g chemical composition i n a continuously CaSi d e o x i d i z e d i n g o t (RIII12)
311
Changes i n A l and S i i n R I I I - I l as a consequence o f c o n t i n u o u s l y i n c r e a s i n g CaSi deoxidation rates
312
Changes i n i n g o t composition as a consequence o f c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n RIII-I2
313
57.
61.
62.
63.
XIV
Figure 64.
65.
66.
67.
68.
69.
Page Dependence o f "FeO" contents i n s l a g samples on the d e o x i d a t i o n r a t e s i n RIII-Il •
314
Dependence o f "FeO" contents i n s l a g samples on the d e o x i d a t i o n r a t e s i n RIII-I2
315
S u l f u r (as s u l f i d e s ) content i n i n c l u s i o n s as a f u n c t i o n of the Ca:Al r a t i o i n the Ca-aluminate i n c l u s i o n phases i n R I I I - I l ..
316
S u l f u r (as s u l f i d e s ) content i n i n c l u s i o n s as a f u n c t i o n o f the Ca:Al r a t i o i n the Ca-aluminate i n c l u s i o n phases i n RIII-I2 ..
317
Chemical composition o f i n c l u s i o n s (as Ca:Al r a t i o s ) as a r e s u l t o f c o n t i n u o u s l y i n c r e a s i n g d e o x i d a t i o n r a t e s i n RIII-I2, (a) and s u l f u r (as s u l f i d e ) i n i n c l u s i o n s i n Ca-aluminates, (b) . s
318
Segregate e n r i c h e d i n A l , Ca and S i i n a sample e x t r a c t e d from the l i q u i d p o o l of i n g o t R I I I - I l
319
S l a g chemical a n a l y s i s o f a 4340 i n g o t c o n t i n u o u s l y d e o x i d i z e d w i t h a CaSi a l l o y , [R-4340 (1)]
320
71.
Ingot chemical composition i n R-4340 ( 1 ) . . .
321
72.
I n c l u s i o n s i z e d i s t r i b u t i o n and t o t a l oxygen content i n R-4340 (1)
322
Changes i n "FeO" contents i n the s l a g as a consequence o f the c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n R-4340(1)
323
I n c l u s i o n chemical composition (as Ca:Al r a t i o s i n a t . %) i n samples o f l i q u i d p o o l and i n g o t i n R-4340 (1)
324
I n c l u s i o n composition as Ca:Al r a t i o s and S content i n R-4340 (1)
325
70.
73.
74.
75.
XV
Page
Figure I n c l u s i o n composition (oxide and s u l f i d e phases i n a r o t o r s t e e l d e o x i d i z e d with S i based a l l o y s , namely: Ca-65 wt.% S i , Al-65% S i and "Hypercal". R-RS(I), R-RS(II) and R-RS(III)
326
77.
Segregate e n r i c h e d i n A l , Ca and S i from the A l S i d e o x i d i z e d i n g o t , R-RS(II)
327
78 .
I n c l u s i o n p r e c i p i t a t i o n sequence i n a s t e e l c o n t a i n i n g two l e v e l s o f s u l f u r
328
79.
S t a t i s t i c a l determination c l u s i o n diameter
329
80.
C e - d i s t r i b u t i o n i n a i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l
330
81.
Ce and La d i s t r i b u t i o n i n an i n c l u s i o n of a sample e x t r a c t e d from the l i q u i d p o o l . La and Ce come from a RE w i r e l o c a t e d i n the q u a r t z t u b i n g
331
A l , Ca and Zr d i s t r i b u t i o n s i n an i n c l u s i o n of a sample e x t r a c t e d from the l i q u i d p o o l . Zr was i n the q u a r t z t u b i n g
332
D i s t r i b u t i o n o f oxide formers i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d pool
333
76.
82.
83.
84.
85.
86.
87.
of the mean i n -
,
D i s t r i b u t i o n o f o x i d e - s u l f i d e former i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l
334
Inclusion d i s t r i b u t i o n i n a dendritic s t r u c t u r e o f 1020 MS samples taken from l i q u i d pool during r e f i n i n g
335
Inclusion d i s t r i b u t i o n i n a dendritic s t r u c t u r e o f a 4 34 0 sample from the l i q u i d pool
336
Isothermal (1823 K) p r e c i p i t a t i o n (Fe, A l , Ca, 0, S) diagram a t 0.1 a c t i v i t y o f aluminum
337
xvi Figure 88.
Page E f f e c t o f the a c t i v i t y o f A l ( h = 0.001, 0.01 and 0.1) on the " p r e c i p i t a t i o n sequence" o f Ca-aluminates
338
E f f e c t o f the a c t i v i t y of S (h = 0.01, 0.01 and 0.001) on the " p r e c i p i t a t i o n sequence" o f Ca-aluminates
339
Arrangement o f aluminates i n r e l a t i v e l y low CaSi d e o x i d i z e d ESR-ingots
340
T y p i c a l arrangement o f i n c l u s i o n s i n a r e l a t i v e l y low CaSi or high A l deoxidized ingots
341
X A1 0_• Y CaO/CaS i n t e r f a c e i n an ESR i n g o t , R-RS ( I I I ) , d e o x i d i z e d with "hypercal". X-ray spectrum analyses are a l s o i n c l u d e d
342,343
93.
Secondary DAS i n a round 1020 MS ESR i n g o t
344
94.
Secondary DAS i n a 1020 MS ESR i n g o t
345
95.
Secondary DAS i n a 4340 ESR i n g o t
346
96.
R a d i a l s i z e d i s t r i b u t i o n of i n c l u s i o n s i n an A l d e o x i d i z e d i n g o t , (RII-I2)
347
Radial i n c l u s i o n size d i s t r i b u t i o n i n a low CaSi d e o x i d i z e d i n g o t ( R I I I - I l )
348
Radial i n c l u s i o n size d i s t r i b u t i o n i n a 200 mm ESR i n g o t CaSi d e o x i d i z e d , ( R I I I - I l )
349
Radial i n c l u s i o n size d i s t r i b u t i o n i n a 4340 (ESR) i n g o t CaSi d e o x i d i z e d
350
89.
90. 91.
92.
97. 98. 99.
A 1
2
(200 mm
i n diameter)
xvii
L I S T OF
TABLES Page
Table I. II.
III. IV.
V. VI. VII.
VIII. IX. X.
XI.
Correction factor
to the
Stokes'
351
Law
Thermochemical data f o r a) I n v a r i a n t e q u i l i b r i a i n Fe-S-0 s y s t e m and b) E s t i m a t e d d a t a f o r i n v a r i a n t e q u i l i b r i a i n Fe-Mn-0, Fe-Mn-S and Mn-S-Q t e r n a r y systems
353
Estimated data for i n v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 q u a t e r n a r y s y s t e m
355
C a l c u l a t e d and p u b l i s h e d f r e e f o r F e - O - C a - A l s y s t e m a t 1823
356
E q u i l i b r i u m constants reactions
energy d a t a K (1550°C)...
for deoxidation
Equations f o r i n v a r i a n t e q u i l i b r i a i s o t h e r m a l (Fe-O-Ca-Al) system
357
i n the
Chemical a n a l y s i s o f e l e c t r o d e s used this research
in
E x p e r i m e n t s and t h e i r this investigation
in
f e a t u r e s used
Chemical c o m p o s i t i o n of d e o x i d i z e r s used i n the p r e s e n t i n v e s t i g a t i o n a)
I n c l u s i o n c o m p o s i t i o n as a r e s u l t o f r e m e l t i n g 4340 e l e c t r o d e s i n a s m a l l E S R - f u r n a c e (75 mm i n d i a m e t e r )
b)
Slag-deoxidizer effect composition
on
inclusion
c)
I n c l u s i o n c h e m i c a l c o m p o s i t i o n o f 4340 e l e c t r o d e s u s e d i n t h e s m a l l ESRfurnace
C h e m i c a l e f f e c t o f s l a g and e l e c t r o d e s u r f a c e p r e p a r a t i o n on i n c l u s i o n c o m p o s i t i o n . (A 1020 MS and a r o t o r (Ni-Cr-Mo) s t e e l were r e f i n e d i n t h e 200 mm i n d i a m e t e r E S R - f u r n a c e t h r o u g h s e v e r a l s l a g s y s t e m s ). .
358
359
360
361
362
362
362
xviii Page
Table XII.
XIII.
Slag chemical a n a l y s i s o f ESR (Ni-Cr-Mo) i n g o t s d e o x i d i z e d with S i based d e o x i dizers Chemical with: a) b) c)
XIV.
XV. XVI.
a n a l y s i s of ingots deoxidized
the Al-65% S i a l l o y the Ca-65% S i a l l o y and the CaSiAlBa (hypercal) a l l o y
D e r i v e d equations f o r i n v a r i a n t ( i s o t h e r m a l ) e q u i l i b r i a i n the Fe-O-Ca-Al-S system Computed compositions i n Table XV and e ^ and e * =
XVII.
365 366 367
T y p i c a l data recorded from EPMA a n a l y s i s of i n c l u s i o n s . a) l i q u i d p o o l and b) i n g o t
C
364
1
368 369
370
based on data g i v e n
= - 25,
e ^ 0
= -62
-40
3
7
1
3
7
2
Computed compositions i n the Fe-Ca-Al0-S system by u s i n g i n f o r m a t i o n i n Table XV, v a r i a b l e e~r
(-535, -400, -300, Al -250 and -200) i n a d d i t i o n t o the e = -62 and e = -110 Q
C
a
s
XVIII.
E f f e c t o f i n i t i a l number of i n c l u s i o n s on growth d u r i n g c o o l i n g o f l i q u i d metal
373
xix LIST OF SYMBOLS a c t i v i t y o f the i component
l
'A' s p e c i e s i n s l a g
(A)
'A' element i n s o l u t i o n i n l i q u i d iron r a t i o of A t o B s p e c i e s
[A], A A: B A
(g)'
A
(l)' (s) A
deoxidant, composition o f which i s Al-65 wt.% S i . (Table IX)
AlSi
A l
'A' s p e c i e s i n gaseous, l i q u i d or s o l i d state
alumina as a primary d e o x i d a t i o n product
2°3*
atomic p e r c e n t
at. %
i o n i c species with e i t h e r a p o s i t i v e or negative v a l e n c e allotropic
a-Fe a-Al 0 2
state of iron
corundum; i t i s a l s o g i v e n as 'A' when i t i s r e f e r r e d t o as a p a r t o f the Ca-aluminates p r e c i p i t a t i o n sequence
3
degrees i n the C e l s i u s grade) s c a l e
(centi-
s u p e r s a t u r a t i o n r a t i o i n terms of c o n c e n t r a t i o n s
C:C»
(1)'(s)
and C A 3
2
l i q u i d o r s o l i d CaO s t o i c h i o m e t r i c Ca-aluminates as g i v e n by the pseudo b i n a r y (CaO-Al 0 ) phase diagram, i.e., 2
3
CaO«Al 0 ,
CaO-2Al 0 ,
CaO«6Al 0 ,
12CaO«7Al 0
2
3
2
2
3
3CaO«2Al 0 2
3
3
2
3
and
XX
(CaO) *
p e r i p h e r a l phase on a c a l c i u m aluminate oxide i n c l u s i o n
(Ca,Mn)S
double
CaS
phase heterogeneously precipitated on a Ca-aluminate phase
(CaS)*
p e r i p h e r a l c a l c i u m s u l f i d e phase i n e q u i l i b r i u m w i t h the CaO from the Ca-aluminate and oxygen and sulfur i n solution in iron
s u l f i d e w i t h Ca and
Mn
deoxidant, composition of which i s given i n Table (IX)
CaSi CaSiAlBa
deoxidant ("hypercal"), composition of which i s given i n Table IX
DAS
d e n d r i t e arm
DAS
secondary
11
D c 6„ or Fe
6-iron
spacing
d e n d r i t e arm
spacing
c r i t i c a l drag f o r c e particle
on a
a l l o t r o p i c state
iron
of
spherical
electron
e i
i n t e r a c t i o n c o e f f i c i e n t ; the e l e ment f o r which the a c t i v i t y coe f f i c i e n t i s being c a l c u l a t e d i s designated j and the element c a u s i n g the e f f e c t i s d e s i g nated i .
EPMA
electron-probe-micro
f
Henrian
FeO"
activity
i r o n oxide,
(Fe O) x
analyses
coefficient
xxi Fe(x,y,z)-0-S
pseudo t e r n a r y i n c l u s i o n phase diagrams w i t h an oxide and a s u l f i d e p h a s e ; ( H i l t y and c o ,(129) workers)
f^
liquid fraction
GR
product thermal
of growth r a t e by gradients
Y, k, or 8-Al C>2
a l l o t r o p i c s t a t e s o f the alumina
Y^
a c t i v i t y c o e f f i c i e n t of species A
h^
Henrian
HIC
hydrogen induced
HSLA
high s t r e n g t h low a l l o y
kV
excitation
K
a b s o l u t e degrees(absolute) s c a l e
2
Kg t o n
£
- 1
£^ L
cracking steel
voltage i n k i l o v o l t s i n the K e l v i n
d e o x i d a t i o n r a t e i n kilograms of deoxidant per (metric) tonne of remelted i n g o t liquid
1
a c t i v i t y of s p e c i e s A
oxisulfide
l i q u i d metal and L„
l i n e s d i v i d i n g the t e r n a r y i n e l u s i o n and s l a g compositions suggesting the formation of low m e l t i n g phases, F i g u r e s (12) and (13)
X
wave l e n g t h i n X-rays
m(CaO) • nfA^O.j)
m and n are c o e f f i c i e n t s o f the Ca-aluminate phases which are e q u i v a l e n t t o those i n the CaOA l 0 pseudo-binary phase diagram 2
3
xxii manganese s u l f i d e type III
MnS(I,II,III)
I, I I , or
y
viscosity
yA
specimen c u r r e n t d e n s i t y i n (EPMA) microamperes u n i t l e n g t h , microns
ym
oxide of the type Mn(Fe)0 o,
"o",
or o x i
concentration
ppm
R I I I - I l and
( 1 0 2 0 ) ESR i n g o t s A l - d e o x i d i z e d (200 mm i n diameter)
RII-I2 RIII-I2
R-43040 (1) R-RS(I), R-RS(II) R-RS(III)
million
i n g o t s i n which CaSi and FeO were added ( 2 0 0 mm i n diameter)
RII-W, RIII-W R I I - I l and
i n p a r t s per
and
( 1 0 2 0 ) ESR i n g o t s CaSi ( 2 0 0 mm i n diameter) ( 4 3 4 0 ) ESR i n g o t CaSi ( 2 0 0 mm i n diameter)
deoxidized deoxidized
Rotor (Ni-Cr-Mo) s t e e l d e o x i d i z e d with C a S i , A l S i CaSiAlBa a l l o y s
and
P
density
a
interfacial
u
r e s u l t i n g vector
V
velocity
+
degree of accuracy (plus or minus) i n chemical a n a l y s i s less
<
-«-
or
s
or ^
=
< tension velocity
vector
than
reaction in equilibrium approximately gaseous phase
ACKNOWLEDGEMENTS
I would l i k e t o express my s i n c e r e g r a t i t u d e t o my s u p e r v i s o r Dr. A l e c M i t c h e l l f o r h i s c o n c i s e a d v i s e .
I am
a l s o t h a n k f u l t o P r o f e s s o r s R. B u t t e r s and B. Hawbolt f o r t h e i r c o n t r i b u t i o n s and d i s c u s s i o n s d u r i n g t h i s work.
I
a l s o a p p r e c i a t e the t e c h n i c a l a s s i s t a n c e o f A. L a c i s , G. S i d l a , R. Cardeno, H. Tump, R. McLeod and M. Mager. I would l i k e t o thank the Banco de Mexico, Consejo N a c i o n a l de C i e n c i a y T e c h n o l o g i a N a c i o n a l Autonoma de Mexico
(CONACyT), U n i v e r s i d a d
(Departamento de M e t a l u r g i a de
l a UNAM) and the Department o f M e t a l l u r g i c a l E n g i n e e r i n g of the U n i v e r s i t y o f B r i t i s h Columbia f o r the f i n a n c i a l given d u r i n g my p r o f e s s i o n a l s t u d i e s .
support
The author i s a l s o
g r a t e f u l f o r the f i n a n c i a l a s s i s t a n c e o f the American Iron and S t e e l I n s t i t u t e
( P r o j e c t No. 32-445).
T h i s work i s s p e c i a l l y brothers
and
s i s t e r s and
reach my
goal.
dedicated
everyone who
t o my
has
parents,
contributed
to
1 CHAPTER I INTRODUCTION In
today's technology
where there i s the demand f o r
e x t r a - h i g h - q u a l i t y m a t e r i a l s , there are o n l y three ary
steelmaking p r o c e s s e s capable o f f u l f i l l i n g
q u i r e d s t r i n g e n t standards
the r e -
1) E l e c t r o n Beam M e l t i n g (EBM),
2) Vacuum A r c R e f i n i n g (VAR) and (ESR).
second-
3) E l e c t r o s l a g R e f i n i n g
The p r o p e r t i e s r e s u l t i n g from any o f the above p r o -
c e s s e s can be c a t e g o r i z e d a s :
crystal structure,
chemical
homogeneity, s u l f u r and phosphorus c o n t e n t and i n c l u s i o n chemistry and s i z e d i s t r i b u t i o n .
The EBM and the VAR p r o -
cesses o f f e r the lowest gas content.
The v e r s a t i l i t y i n
c o n t r o l and o p e r a t i o n , c r y s t a l s t r u c t u r e , r e l a t i v e cal
electri-
e f f i c i e n c y and r e p r o d u c i b i l i t y are the main f e a t u r e s o f
the ESR p r o c e s s . * Research
c a r r i e d o u t s i n c e 1967
has w i d e l y demonstrated
t h a t the ESR-process o f f e r s d e f i n i t e advantages over v e n t i o n a l p r a c t i c e and i n some r e s p e c t s a l s o o f f e r s tages over other secondary
steelmaking p r a c t i c e s .
conadvan-
The con-
tinuous demand f o r h i g h q u a l i t y m a t e r i a l s has i n c r e a s e d s i n c e 1967.
From 1960 t o 1973 the western world i n c r e a s e d
i t s ESR p r o d u c t i o n from 2 600 t o about 120 000
tonne/year
and i t i s f o r e c a s t t o i n c r e a s e t o 600 000 tonneVyear i n 1985. The
S o v i e t Union's p r o d u c t i o n i s about three times t h a t
* First
I n t . Symp. on ESR
2 of the Western world.
T h i s marked i n c r e a s e i n p r o d u c t i o n
i n d i c a t e s the a c c e p t a b i l i t y of the products manufactured the
by
ESR-technology. M a t e r i a l s produced f o r p a r t i c u l a r purposes such as
r o t o r s used i n thermal and n u c l e a r e l e c t r i c a l p l a n t s ,
land-
i n g gear used i n a i r c r a f t , crank s h a f t s used i n l a r g e v e s s e l s , gun b a r r e l s , s u p e r a l l o y s used i n t u r b i n e b l a d e s , h i g h q u a l i t y t o o l and b a l l b e a r i n g s t e e l s , e t c . are examples o f the wide v a r i e t y o f m a t e r i a l s produced by the ESR-process.
These components are s u b j e c t
to d r a s t i c
temperature and environmental c o n d i t i o n s and/or to dynamic s t r e s s e s .
These two adverse c o n d i t i o n s by them-
s e l v e s generate m i c r o c r a c k s which are u s u a l l y a s s o c i a t e d w i t h chemical inhomogeneities and/or with i n c l u s i o n s i n the metal m a t r i x . I n c l u s i o n s p l a y a major r o l e i n f a i l u r e s under described situations.
the
Thus t h e i r index o f s p h e r i c i t y ,
degree o f cohesion with the metal matrix, i n t e r p a r t i c l e d i s t a n c e , volume f r a c t i o n , s i z e d i s t r i b u t i o n ,
plasticity,
thermal c o n t r a c t i o n and expansion c o e f f i c i e n t s w i t h r e s p e c t to the m a t r i x and chemistry are the parameters determine the s e r v i c e l i f e ,
which
i n terms of i n c l u s i o n s , f o r
a given material. The p o t e n t i a l of the ESR-process, because of i t s v e r satility,
can be extended to o t h e r types o f uses such as
3 E l e c t r o s l a g C a s t i n g (ESC) I t i s important
and E l e c t r o s l a g Welding
(ESW).
to note t h a t w h i l e these p r o c e s s e s
very r a r e l y used i n North America,
are
i n the S o v i e t Union's
technology they are w i d e l y p r a c t i c e d . The ESR process because of i t s m u l t i p l e degrees
of
freedom a l s o o f f e r s a wide range of parameters to be modif i e d and improved without modifying the standard f u r n a c e . To o p t i m i z e the mechanical
p r o p e r t i e s which are
r e l a t e d to i n c l u s i o n s i n a ESR-product, a s e r i e s of
strictly inter-
a c t i o n s between a l l the components of the process should be e v a l u a t e d , i . e . e l e c t r o d e , s l a g , d e o x i d i z e r and f y i n g i n g o t should a l l be c o n s i d e r e d .
solidi-
I f the mechanisms
by which i n c l u s i o n s are formed are known, then the
ESR-
process c a p a b i l i t i e s and r e s t r i c t i o n s i n t h i s r e s p e c t can be d e f i n e d .
4 CHAPTER II LITERATURE REVIEW 2.1
L i t e r a t u r e Survey on E l e c t r o d e From the thermal p o i n t of view
should be c o n s i d e r e d
as one
Inclusions the e l e c t r o d e t i p
of the sources by which
one
p a r t of the t o t a l heat produced by the s l a g i s consumed, Figure
(1).
T h i s amount of thermal energy which i s t r a n s -
f e r r e d from the s l a g to the e l e c t r o d e p l a y s s e v e r a l r o l e s : 1.
I t i s p r i m a r i l y converted to s e n s i b l e heat, thus
producing a f i n e l i q u i d f i l m which afterwards w i l l droplets, 2. and
form
and I t a l s o determines the temperature g r a d i e n t s
below the slag/gas
interface.
above
Thus, i t e s t a b l i s h e s
amount of p o s s i b l e s u r f a c e o x i d a t i o n and
the
the d i s s o l u t i o n
of c e r t a i n second phase p a r t i c l e s or i n c l u s i o n s i n the e l e c trode . (1-5) T h e o r e t i c a l and
experimental
s t u d i e s have been per-
formed to determine whether i n c l u s i o n s from the e l e c t r o d e e l i m i n a t e d before
are
or a f t e r the metal d r o p l e t i s formed.
Heat and mass t r a n s f e r models have a l s o been developed to p r e d i c t the maximum i n c l u s i o n diameter which can be s o l v e d under g i v e n
dis-
ESR-conditions. (6)
M i t c h e l l , J o s h i and
Cameron
have s t u d i e d the temp-
e r a t u r e d i s t r i b u t i o n above the slag/gas l a b o r a t o r y ESR
furnace.
interface in a
They have i n d i c a t e d t h a t gradients
the r a d i a l
i n a larger electrode-ingot
came s i g n i f i c a n t .
Their
c o n f i g u r a t i o n b<
r e s u l t s a l s o suggest
s o l u t i o n o f second phase p a r t i c l e s tent
temperature
that di;
to a varying
ex-
i s feasible. (7)
Maulvault
and E l l i o t t
who
have d e v e l o p e d a one
d i m e n s i o n a l model have t a k e n i n t o a c c o u n t t h e cal
movement o f t h e e l e c t r o d e .
w h i c h have b e e n b a s e d file,
Their
i n an assumed
verti-
computations,
parabolic
pro-
h a v e shown a r e a s o n a b l e a g r e e m e n t w i t h t h e expe
mentally
(37 mm
diameter electrode)
determined
values
(8) M e n d r y k o w s k i e t a l . ' s work fied the
one-dimensional-heat electrode
part
immersed
found t h a t w h i l e n e i t h e r vection play tions, the
sults
model and
a simpli-
considering
i n the s l a g have
also
r a d i a t i o n n o r gas p h a s e
a major r o l e ,
the convective
electrode
flow
by u s i n g
f o r a given
set of
con-
condi-
heat t r a n s f e r from the s l a g t o
i s i n d e e d more s i g n i f i c a n t .
suggest that conduction along
Their r e -
the e l e c t r o d e
pre
d o m i n a t e s a s t h e h e a t - t r a n s f e r - c o n t r o l l i n g mechanism. (9)
Tacke e t a l . f o r m e d a t U.B.C.
along (6,10) have
t h e l i n e s w i t h work p e r coupled
two m o d e l s
(one
6
to determine the s l a g temperature and the other to determine the heat f l u x e s ) t o c a l c u l a t e the e l e c t r o d e temperature, i t s m e l t i n g p r o f i l e and i t s depth o f immersion i n the s l a g .
I t has been claimed t h a t computed
v a l u e s o b t a i n e d by t h i s two-dimensional flow are i n agreement with the experimental e f f e c t was"also t h e o r e t i c a l l y yzed.
findings.
The r a d i a l
and e x p e r i m e n t a l l y
anal-
These r e s u l t s i n agreement with M i t c h e l l e t
(6)
al.
show t h a t the temperature g r a d i e n t s become
steeper i n the e l e c t r o d e nearer the l i q u i d f i l m . A r e p r e s e n t a t i v e example o f t y p i c a l g r a d i e n t s i n an e l e c t r o d e are shown i n F i g u r e
(2).
I t i s important
to mention t h a t i n a l l the above models the thermal energy spent f o r r e c r y s t a l l i z a t i o n or g r a i n growth, as shown by s e v e r a l r e s e a r c h e r s ^ ' 11-14)
n
Q
t
j
3 e e n
considered. The
i n c l u s i o n d i s s o l u t i o n phenomenon has a l s o
been approached by s e v e r a l r e s e a r c h e r s from the mass
(12) t r a n s f e r view p o i n t ,
Kay and Pomfret
f i r s t r e s e a r c h e r s t o have suggested
were the
and modelled the
d i s s o l u t i o n o f oxide i n c l u s i o n s ( s i l i c a and alumina) i n the e l e c t r o d e f i l m under normal ESR c o n d i t i o n s . They c l a i m t h a t
7 although i n c l u s i o n s can be d i s s o l v e d as a r e s u l t of l i q u i d f i l m - l i q u i d slag i n t e r a c t i o n during formation
stage,
t h e i r computed values
r a t e would o n l y r e q u i r e the time t h a t spends before
i t becomes l i q u i d .
d i s s o l u t i o n of alumina and meters were 4 and
20
ym,
silica
the
droplet
for dissolution an e l e c t r o d e
Mitchell
material
Their c a l c u l a t i o n s
for
i n c l u s i o n s whose d i a -
were performed under the
sumption t h a t thermodynamic e q u i l i b r i u m a t the t i p / s l a g i n t e r f a c e was
the
reached a t 1800
and
as-
electrode
2000°C.
based on heat t r a n s f e r c a l c u l a t i o n ^ '
has
r e c a l c u l a t e d the d i s s o l u t i o n of i n c l u s i o n s (12) u s i n g the c o n d i t i o n s o f Pomfret and Kay . Mitchell's r e s u l t s show t h a t even by u s i n g a two-fold
superheating (8)
(70°
C) above t h a t found by Mendrikowski e t a l .
s o l u t i o n i s p r e d i c t e d below 1600° C.
no
Hence the i n c l u s i o n -
d i s s o l u t i o n mechanism i n the s o l i d e l e c t r o d e t i p was considered
not
to s t r o n g l y i n f l u e n c e the o v e r a l l i n c l u s i o n
removal. (16) Hajra and
Ratnam
f e r c a l c u l a t i o n s and ESR-furnace.
have a l s o performed mass t r a n s experimental r e s e a r c h
T h e i r approach was
previously described with M i t c h e l l ' s
works.
in a
laboratory
on the same b a s i s as
Their results
show t h a t slag/metal
i n agreement
reactions play
important r o l e i n the e l e c t r o d e - i n c l u s i o n removal. a l s o found t h a t oxide p a r t i c l e s c h a r a c t e r i s t i c of e l e c t r o d e were not t r a c e d i n the
ingot.
the
an They
the
8 Experimental and
t h e o r e t i c a l work, so f a r des-
c r i b e d , has o n l y been concerned with l a b o r a t o r y
ESR
(17) furnaces.
Medovar e t a l .
800
mm
- 1200
also reported
that, i n
consumable e l e c t r o d e s r e f i n e d by
ESR,
the i n c l u s i o n removal o c c u r s i n the molten metal or i n the p r o c e s s of d r o p l e t formation.
film
They have a l s o
i n d i c a t e d t h a t i n c l u s i o n s i n d r o p l e t s d i f f e r e d from those i n the e l e c t r o d e . shape, s i z e s and
They c l a i m t h a t the i n c l u s i o n
d i s t r i b u t i o n i n the s o l i d
were s i m i l a r i n nature to those i n the ESR
Research c a r r i e d out on a q u a n t i t a t i v e b a s i s i n the e l e c t r o d e d u r i n g cated
claimed
has
'
suggested t h a t i n c l u s i o n s
r e f i n i n g are s p e c i f i c a l l y l o they have a w e l l
defined
Based on these f i n d i n g s i t has
t h a t i n c l u s i o n s are mechanically
c a l l y removed by
ingot. (19 20)
i n the S o v i e t Union
i n the l i q u i d f i l m and
size distribution.
droplets
and
been
chemi-
the s l a g . (19)
On
the other hand Roshchin e t a l
w i t h other
investigators^ ''have
due
"high temperature h e a t i n g "
to the
1
i n agreement established
that
manganese s u l f i d e s
9 are f i r s t l y
spherodized and afterwards d i s s o l v e d .
I t has
(19) been observed
that s i l i c a t e
i n c l u s i o n s were
sphero-
d i z e d , transformed and s l i g h t l y enlarged, i n c o n t r a d i c t i o n to s e v e r a l i n v e s t i g a t o r s ' r e s e a r c h reach the l i q u i d f i l m .
The
1
3
^
b e f o r e they
same c o n t r a d i c t i o n i s found
with r e s p e c t to second phase p r e c i p i t a t e s .
While some
r e s e a r c h e r s b e l i e v e t h a t d i s s o l u t i o n occurs i n the stage^
solid
o t h e r s have r e p o r t e d t h a t t h i s takes p l a c e i n
the l i q u i d stage
and s t i l l others ^
t h a t they do not d i s s o l v e and
have
suggested
serve as n u c l e a t i n g agents
i n the r e f i n i n g i n g o t . Roshchin e t a l . ' s work was
performed
u s i n g o p t i c a l and o p t i c a l - q u a n t i t a t i v e d i s t r i b u t i o n ) techniques.
exclusively
(inclusion
These r e s e a r c h e r s c l a i m t h a t
s i m u l a t e d heat t r e a t e d samples
(under an i n e r t atmo-
sphere) s u b j e c t e d to s e v e r a l p e r i o d s of time and e r a t u r e ranges, served i n a c t u a l Other
produced
size
temp-
e q u i v a l e n t r e s u l t s t o those
ob-
ESR-electrodes. (13)
studies
i n l i n e with the p r e v i o u s work,
u s i n g d i f f e r e n t schedules have agreed with the above f i n d ings.
The major disadvantage
of these simulated e x p e r i -
ments i s t h a t the c a l c u l a t e d thermal g r a d i e n t s ^ the time-temperature
and
schedules are so d i f f e r e n t to t h a t
experienced by the e l e c t r o d e t i p s t h a t a s e l f - c o n s i s t e n t
c o n c l u s i o n cannot be
derived,
(15) Studies
c a r r i e d out on a q u a n t i t a t i v e b a s i s
oxygen content and
i n c l u s i o n chemical a n a l y s i s ) have
mined t h a t i n c l u s i o n s are d i s s o l v e d i n the l i q u i d
(total deter-
film.
These a n a l y t i c a l s t u d i e s however were performed e x c l u s i v e l y on. m a t e r i a l belonging The
to the molten
family.
idea which supports the e x i s t e n c e
r e o x i d a t i o n due
to continuous i n c l u s i o n d i s s o l u t i o n , from
the heat a f f e c t e d r e g i o n to the e l e c t r o d e has
a l s o been p r o p o s e d
1
3
^.
The
these i n c l u s i o n s , however, was
not
Theoretical s t u d i e s ^ ' ^ ' ^ ^ electrode-mold
of a continuous
liquid
film,
chemical nature of investigated.
indicate that for a
diameter c o n f i g u r a t i o n some
given
superheating
i s expected at the e l e c t r o d e t i p , although f o r a s h o r t of time.
On
period
t h i s b a s i s i t has
been a n t i c i p a t e d t h a t i f (18) i n c l u s i o n s c o n t a c t the s l a g or e a r l i e r i f they are s i l i c a type, t h e i r d i s s o l u t i o n r a t e should be extremely high (21) f o r a l l common s l a g - i n c l u s i o n combinations (22) Paton e t a l .
have a l s o suggested t h a t the
l i q u i d u s - s o l i d u s l e n g t h of each a l l o y system and trode-steelmaking
p r a c t i c e a l s o p l a y an important
T h e i r s t u d i e s were performed on and
a gradual
served.
The
1200
mm
diameter
d i s s o l u t i o n of s u l f i d e s was critical
intrinsic
the e l e c role. electrodes
( o p t i c a l l y ) ob-
length at which changes i n s u l f u r con-
c e n t r a t i o n s were observed was
about one
centimeter above
the
"fusion l i n e . " (23)
Zhengbang e t a l . ' s s t u d i e s
based on the
con-
95 c e n t r a t i o n s of a r t i f i c i a l
Zr
0
2
i n c l u s i o n s have shown that
the chemistry of i n c l u s i o n s during gradually
from the e l e c t r o d e to the
the ESR ingot.
p r o c e s s change Other
research-
ers c l a i m t h a t the major r e a c t i o n s i t e where i n c l u s i o n s from the e l e c t r o d e are e l i m i n a t e d i s a t the l i q u i d f i l m (23 24) (15) slag interface ' . Mitchell who has r e f i n e d electrodes
containing
c a l c i u m aluminum s i l i c a t e s has
p o r t e d small i n c l u s i o n s i n the
liquid film,
the
re-
composition
of which d i d not correspond to the s t o i c h i o m e t r i c 2FeO«Si0 phase.
2
2.2
L i t e r a t u r e Review on S l a g - L i q u i d Metal and
2.2.1
t h e i r I n f l u e n c e on the ESR Ingot
P r i n c i p l e s o f the R e a c t i o n Among the c o n v e n t i o n a l
Reactions
12
Chemistry
Scheme i n the ESR
Process
and secondary steelmaking
prac-
t i c e s the ESR-process r e p r e s e n t s one of the most complex metallurgical reactors. study
The degree of d i f f i c u l t y
inits
a r i s e s because r e a c t i o n s take p l a c e a t s i t e s
(elect-
r o d e - s l a g , d r o p l e t - s l a g and l i q u i d p o o l i n t e r f a c e s ) which have separate
and d i s t i n c t chemical
and e l e c t r o c h e m i c a l r e -
(26 2 7 )
gimes
'
.
The d r o p l e t , due t o i t s s i z e
sees no
p o t e n t i a l d i f f e r e n c e between i t and the surrounding
slag
t h e r e f o r e i t r e a c t s under the thermochemical c o n d i t i o n s d i c t a t e d by the s l a g . and
The e l e c t r o d e
(liquid film) - slag
the molten l i q u i d p o o l - s l a g i n t e r f a c e s r e a c t almost
e n t i r e l y by imposed e l e c t r o c h e m i c a l p o t e n t i a l s . a t these and
Reactions
s i t e s are c o n t r o l l e d by the s u r f a c e environments
they are not d i r e c t l y i n f l u e n c e d by the s l a g
chemistry.
I t i s worthwhile t o mention t h a t the above p a t t e r n s are mainly a p p l i e d t o DC-ESR and t o a g i v e n extent to the AC-ESR (26) (2728) operation . Several researchers ' have suggested t h a t even i n t h i s l a t t e r o p e r a t i n g mode
slag-metal ex-
change and s u r f a c e s are r u l e d by the p o l a r i z a t i o n (28 29 ) " Several studies t i a l behavior
'
on the c u r r e n t
behavior.
density-poten-
have shown t h a t s i n c e there i s not a l i n e a r
r e l a t i o n s h i p between these parameters used i n ESR, then p o l a r i z a t i o n e x i s t s .
f o r DC and AC ranges Schwerdtfeger s 1
(28) studies
have a l s o shown t h a t a f t e r the l i m i t i n g
r e n t i s approached
f o r a g i v e n s l a g system
cur-
a plateau i s
reached.
T h i s l i m i t i n g c u r r e n t can be
i n c r e a s e d again
i f the p o t e n t i a l i s markedly i n c r e a s e d . tude o f the l i m i t i n g c u r r e n t potential relationship
has
only
Thus, the magni-
from t h i s c u r r e n t
density-
given a c l e a r i n d i c a t i o n that
2+ a s u r f a c e s a t u r a t i o n i n Fe
r e s u l t s i n the s e p a r a t i o n
of
an i r o n - r i c h phase which remains f i x e d on the anode s u r face by
i n t e r f a c i a l tension f o r c e s ^ ^ . 3
incomplete i r r e v e r s i b i l i t y i n the s l a g and
leads to a net
Therefore, "FeO"
this
production
a l s o to a net s o l u t i o n of aluminum or
cal-
cium i n the i r o n . Besides the r e c t i f i c a t i o n of AC c u r r e n t caused by i n t e r (30 32) f a c i a l e f f e c t s there i s evidence ' i n the l i t e r a t u r e which e s t a b l i s h e s t h a t r e c t i f i c a t i o n due to c u r r e n t p a s s i n g 2+ through the slag-skin/mould bulk,
i n c r e a s e s the Fe
i n the s l a g
thus r a i s i n g a l l o x i d a t i o n r a t e s i n the
ESR-reaction
(33) scheme.
Hawkins e t a l .
have shown t h a t i f 5% - 30%
the t o t a l c u r r e n t i s passed through the mould w i t h an c i e n c y of 2% f o r the anodic
reaction
of oxygen would occur, under normal (29) I t has been s p e c u l a t e d
of
effi-
a r i s e of about 40
ppm
ESR-conditions.
t h a t the mechanism which con-
t r o l s t h i s type of r e c t i f i c a t i o n i s the presence of s m a l l arc c o n t a c t s which pass through the s l a g - s k i n i n t o the s l a g . (27) Mitchell temperature and the
reaction
has a l s o i n d i c a t e d t h a t due high c u r r e n t - d e n s i t y slag-metal scheme
is
probably
not
a
to the
high
interface
well-defined
14 Faradaic i n t e r f a c e . sible
Thus e l e c t r o l y t i c
o n l y to the extent p e r m i t t e d by
r e a c t i o n s are possuch p o l a r i z a t i o n
phenomena. (28 The
30)
suggested FeU) Ca
2 +
* + 2e
' Fe
r e a c t i o n scheme i s as f o l l o w s : + 2e
2 +
* Ca
,
(1) (2)
X
Ca t (Ca) s l a g or [Ca] and at h i g h c u r r e n t d e n s i t i e s :
(3)
X
Al
3 +
Fe I t has
2 +
+ 3e
t
+ 2e
t .Fe
[Al]
(4) (5)
( £ )
a l s o been c l a r i f i e d t h a t other r e a c t i o n s with
higher decomposition p o t e n t i a l s than those allowed above scheme w i l l not take
by
the
place. (26)
From the above r e a c t i o n scheme t h a t d u r i n g the anodic h a l f c y c l e adjacent gen
to the metal s u r f a c e
i t has been
envisaged
i r o n oxides w i l l
form
e i t h e r by d i s c h a r g e of oxy-
i o n s or by d i s s o l u t i o n of Fe which w i l l r e p l a c e Ca-ions
locally.
T h i s leads to a high i r o n oxide a c t i v i t y
(
a F e 0
^
W 1
th
consequent d i s s o l u t i o n of oxygen i n t o the i r o n b u l k . 2+ 3+
Simult-
aneously
the
FeO
or Fe
(or Fe
) w i l l be t r a n s p o r t e d by
hydrodynamic regime i n t o the bulk of the s l a g c a u s i n g a ual
grad-
i n c r e a s e i n the a„ . The c a t h o d i c h a l f c y c l e w i l l d i s FeO charge A l 3+ , Ca 2+ or Fe 2+ . Any of these ions w i l l contribute to reduce the a _ in the slag. I t can also be established that i f in this n
last e l e c t r o c h e m i c a l r e a c t i o n there i s not s u f f i c i e n t
Ca
2+
or
15
(33) a slag deoxidation i s
i f Ca i s e x t e n s i v e l y evaporated necessary
to a v o i d the e l e c t r o d e s a c r i f i c i a l
Up t o t h i s p o i n t i n t h i s review
deoxidation.
only the r e a c t i o n s as
a r e s u l t o f the i n h e r e n t e l e c t r o c h e m i c a l nature of the ESRprocess
have been c o n s i d e r e d .
There are, however, other (38)
types o f r e a c t i o n s i n v o l v i n g the s l a g
atmosphere
inter-
f a c e which a l s o a f f e c t i t s o v e r a l l r e a c t i o n p a t t e r n s .
Holz-
gruber ( ^ 34
has claimed
that i f remelting
i s c a r r i e d out
under a pure oxygen atmosphere the oxygen content ranges from 1.8 t o 3.8 times t h a t o b t a i n e d atmosphere. content try.
In t h i s work
i n ingots
under an argon
i t i s a l s o shown t h a t oxygen
i n ESR-ingots i s very dependent on the s l a g chemis(1 37)
S e v e r a l r e s e a r c h e r s have e s t a b l i s h e d
v
'
' that i f
r e m e l t i n g i s not c a r r i e d out under an i n e r t atmosphere and if
the s l a g i s not d e o x i d i z e d then the oxygen content (and
the l o s s of r e a c t i v e elements) i n the i n g o t can only be c o n t r o l l e d by the s l a g (oxygen p o t e n t i a l ) . results (38)
a l s o i n favour o f the above theory
the lowest oxygen content s l a g chemistry
Miska e t a l . ' s show t h a t
i s c o n t r o l l e d s t r i c t l y by the
and i n t e r m e d i a t e oxygen contents
i n f l u e n c e d by the s l a g - e l e c t r o d e
are strongly
chemistry.
While some r e s e a r c h e r s ( 3 8 ) have found t h a t the i n t r o d u c t i o n o f oxygen i n t o the s l a g i s a mass t r a n s f e r c o n t r o l l e d process
others d ' 3 3 ) b e l i e v e t h a t i n a d d i t i o n t o t h i s
mechanism there i s an "oxygen s i n k " face) which a c t s as a d r i v i n g f o r c e .
(at the slag-metal
inter-
I t i s thought t h a t the
d e s u l f u r i z a t i o n r e a c t i o n i s c o n t r o l l e d by t h i s dual mech(1, 12)
anism
I t i s g e n e r a l l y accepted i n t r o d u c t i o n of i r o n oxide
t h a t there
i s a continuous
i n t o the melt, due t o the
continuous o x i d a t i o n of the e l e c t r o d e s u r f a c e . has p o i n t e d out t h a t the ESR-reaction
Mitchell
v
p a t t e r n i s more
s t r o n g l y i n f l u e n c e d by t h i s phenomenon than by the oxygen i n t r o d u c e d as a r e s u l t o f r e a c t i o n s t a k i n g p l a c e a t the slag-atmosphere i n t e r f a c e .
Other s t u d i e s have a l s o
shown t h a t by r e f i n i n g e l e c t r o d e s with d i f f e r e n t (36,39)
o
r
different surface preparation
wise e q u i v a l e n t ESR-conditions,
under o t h e r -
d i f f e r e n t composition
d i f f e r e n t mechanical p r o p e r t i e s a r e observed. havior
chemistry
or
T h i s be-
although i t i s i n d i r e c t , has been a t t r i b u t e d t o
the i n t r o d u c t i o n o f v a r i o u s q u a n t i t i e s of i r o n oxide
into
the s l a g as ( e l e c t r o d e ) s c a l i n g . (40 41) There a r e r e p o r t s i n the l i t e r a t u r e ' i n d i c a t e t h a t the e v a p o r a t i o n
x
'
' which
of gaseous f l u o r i d e com-
pounds i n c e r t a i n s l a g systems a l s o a f f e c t s the r e a c t i o n pattern.
The r e a c t i o n :
(A1 0 ) + 3 ( C a F ) 2
2
3
l a r g e l y c o n t r i b u t e s t o s h i f t the A l 0 : C a O r a t i o . 2
r e a c t i o n becomes very
(8)
t 3(CaO) + 2A1F +
3
important where the c a l c i u m
a c t i v i t i e s are l e s s than 10
-2 (42, 43)
Mitchell
This oxide (36)
17 has p o i n t e d out t h a t i n order to t r a c e the a c t u a l s h i f t i n g i n the chemical
composition
the CaF« and A l F ^ 3
p a r t i c u l a r l y i n s l a g s where
have about the same vapour p r e s s u r e ,
a n a l y s i s i n the 0
2-
:F
-
r a t i o as w e l l as the Ca
2+
: Al
an
3+
should be considered. Complementary r e a c t i o n s are: (CaF ) + H 0 2
2
t
( g )
(CaO)
+ 2HF+
(9)
and 2(CaF ) + 2
Chouldhury e t a l .
K i i i i )
(Si0 ) 2
±n
t
(CaO)
+ SiF^
a r e c e n t communication have
p o i n t e d out t h a t by r e m e l t i n g i n g o t s with low current
(10)
the S i l o s s e s from an a c i d i c s l a g are
frequency negligible.
They n o t i c e , however, t h a t f o r a s l a g where the CaO:Si0
2
r a t i o i s g r e a t e r than 4, S i l o s s e s r i s e to 65% d u r i n g r e melting. gations
T h i s f i n d i n g i s a l s o supported (40, 45)
.
t h a t r e a c t i o n (9)
m
i n previous
.. , , „. ^, . (39) T o b i a s ' and Bhat's work
can be c o n s i d e r e d
of oxygen i n the system.
investi-
suggests
as an a d d i t i o n a l source
In t h i s work
although
i s not c l e a r l y s p e c i f i e d , i t i s c o n s i d e r e d
a mechanism
t h a t moisture
as a condensed phase i n moulds, water vapour from the atmosphere or c h e m i c a l l y bonded moisture i n the f l u x markedly a l t e r s the recovery of t i t a n i u m and
s i l i c o n i n ESR-ingots.
2.2.2
On the Nature of the ESR-reaction
Scheme
A g r e a t d e a l of a t t e n t i o n has been d e d i c a t e d to i n v e s t i g a t e the o r i g i n , sequence and consequence o f the r e a c t i o n s i n the ESR-process.
The major o b j e c t i v e o f these
s t u d i e s have been to c o n t r o l the i n g o t composition out s a c r i f i c i n g i t s chemical
integrity.
I t i s c o n v e n t i o n a l l y accepted
t h a t the
broadest
c l a s s i f i c a t i o n of r e a c t i o n s t a k i n g p l a c e d u r i n g can be s u b d i v i d e d Reactions
with-
refining
as f o l l o w s : which are c o n t r o l l e d by the oxygen p o t e n t i a l
[Me] + [0]
(11)
* (MeO)
and r e a c t i o n s as a r e s u l t of the exchange between
two
liquids: [Me] + (MO) t
(MeO) + [M]
(12)
Among the r e a c t i o n s comprised i n the f i r s t category,
type
(11), a r e : [Ca] + [0] t
(CaO)
2[A1] + 3[0] t
'
( 4 8
6
(A1 0 ) 2
[Si] + 2 [ 0 ] t
(Si0 )
[Ti] + 2[0] t
(Ti0 )
2
(11-i)
)
( 3 6
3
'
4 8
"
5 2
'
6 2 )
(26, 33,35,36,49-51,63,64)
2
( 5 2
2
'
5
8
m i r I -*• /i-i ^ \ (26,33,35.36,63,64) x[Fe] + y[o] (Fe 0 ) ' ' ' • ' x y t
2(Ti 0 )
[Ti] + 2 ( T i 0 )
t
( T i 0 ) + (TiO)
2
2
2
2
n
_
i
i
i
)
. (11-v) (11-vi)
( 5 2 )
3
3
(
(11-iv)
)
[Ti] + 3 ( T i 0 )
(11-ii)
( 5 2 )
(11-vii)
The group of r e a c t i o n s of the k i n d (12) the
so c a l l e d d e o x i d a t i o n (FeO) t-
[Mn]+
subdivided i n
s
r e a c t i o n s , (12a),
namely:
(MnO) + Fe (57,59-61)
(12-i)
[Si]+ 2(FeO) t
( S i 0 ) + 2Fe d,57,60,61)
[Til + 2 (FeO) t
( T i 0 ) + 2Fe (52,58,60)
(12-ii)
2
(12-iii)
2
2[A1]+ 3(FeO) t [Ca] + (FeO) t and
±
( A 1 0 ) + 3Fe (35,48,57,60) 2
(12-iv)
3
(CaO) + Fe
(12-v)
( 6 2 )
the exchange r e a c t i o n s which a l s o i n v o l v e the r e a c t i v e
species,
(12-b):
3[Ti] + 2(A1 0 ) t 2
3
2[Ti] + (Si0 ) t
3(Ti0 )
2(Ti0 )
2
+ 2 [ T i ] (52,58)
2
3 [ S i ] + 2(A1,0-) t ^
+ 4[A1] (18,39,46-51)
2
3(SiCO
J
+
4[A
Z
(12-vii)
i]d/44,46,47,49,55) (12-viii)
2[Mn] + ( S i 0 ) t
2(MnO) + [ S i ] ( /56,57,76)
2[A1]
( A l ^ )
44
2
+ 3(MnO) J
+
Other r e a c t i o n s i n c l u d e d in laboratory
3
[Mn]
(ESW) experiments are (12-C): ( C u C l ) + [Al] t
Cu +
2
3(Cu 0) + 2[A1] t 2
2
0
Cu +
3
(Al 0 ) 2
S i + 2(Fe O)
(MnO) + Fe t
2 Fe +
C + (Fe O) t
CO
x
(A1C1 )
N i + (FeO)
( S i 0 ) + 2 Fe t
( g )
(12-ix) (12-x)
( 5 7 )
i n t h i s c a t e g o r y observed
( N i 0 ) + Fe t
(12-vi)
(Si0 ) 9
+ Fe
3
-(^1)
20
Although the d e p i c t e d
c a t e g o r i z a t i o n of the
reaction
scheme has been presented i n an o v e r s i m p l i f i e d manner i t s t h e o r e t i c a l basis
should be enunciated to e s t a b l i s h •
the r e a c t i n g c o n d i t i o n s under which i t takes p l a c e
and
the governing r e a c t i n g mechanism. A wide range of o p i n i o n s
and
sometimes
c o n t r o v e r s i a l r e s u l t s are found i n the
apparently
literature in re-
gard to the approach p r e d i c t i n g the E S R - r e a c t i o n sequence. While some i n v e s t i g a t o r ' s work
(63)
support the theory
there e x i s t s a s t a t e of e q u i l i b r i u m ,
other
studies
that
(58)
(33)
based i n thermodynamic data and
experimental
r e s u l t s have
found t h a t e i t h e r a "dynamic e q u i l i b r i u m " or k i n e t i c f a c t o r s govern the r e a c t i o n p a t t e r n .
I t i s w e l l recognized^®^
t h a t i f an ESR-furnace i s c o n s i d e r e d
s t r i c t l y as a
even i n the absence of e l e c t r o c h e m i c a l (65
such t h a t t r u e thermal e q u i l i b r i u m and
hence i t should be
operates under three
f a c t o r s , i t s nature i s 66)
'
i s never reached
instead considered
as a r e a c t o r which
d i f f e r e n t regimes, namely:
unsteady s t a t e which holds f o r about three
times
i n g o t diameter from bottom.
2)
for
time
and
3)
of
the
refining
stage
most
of
which
the is
refining at
the
end
Other p e c u l i a r i t i e s o f the ESR the r e a c t i o n sequence are caused by
i t s r a d i a l and
reactor
a quasi-steady
p r o c e s s which
the
1)
an
the state hot
top
time.
influence
i t s hydrodynamic regime v e r t i c a l temperature g r a d i e n t s
(30
'
65,67)^
Thus, s t r i c t l y
speaking an a c t u a l s t a t e of e q u i l
brium i s not reached because of the changing thermal cond t i o n s , hence i n f l u e n c i n g i t s chemical n a t u r e .
From t h i s
d e s c r i p t i o n and from the e l e c t r o c h e m i c a l p r i n c i p l e s a l ready d e s c r i b e d
i t can be seen t h a t the r e a c t i o n scheme
must be c o n s i d e r e d a c c o r d i n g to both thermal regime i t s resulting kinetic factors. p o r t e d by Kay's s t u d i e s d ' reaction pattern.
4 8
)
o
and
These i d e a s have been sup the behavior o f the
n
In t h i s work
ESR
i t has been suggested
t h a t s l a g - m e t a l composition r e l a t i o n s h i p s are governed by (33) kinetic factors.
Hawkins e t a l .
have c l e a r l y shown
t h a t t h i s p a r t i c u l a r s t a t e o f e q u i l i b r i u m i s not unique but i t can be r e p r e s e n t e d as a thermal-parameter denominated " c h a r a c t e r i s t i c temperature." was
T h i s parameter
c a l c u l a t e d on a thermochemical b a s i s i n d i c a t e s
the system may
see simultaneous r e a c t i o n s a t t h e i r
responding thermal r e g i o n s .
Although t h i s
which that cor-
"characteris-
t i c temperature" as a parameter does not have any p h y s i c a l meaning
i t does r e p r e s e n t the unsteady
thermal-chemi
c a l behavior of the ESR p r o c e s s . (33 61) I t has been proposed actions
are
the
result
' of
that o v e r a l l a
well defined
of steps which i n v o l v e mass t r a n s f e r t i o n and hydrodynamic
(ESR) r e -
(diffusion,
series convec-
flow) and chemical f a c t o r s (reorgan
z a t i o n o f the r e l a t i v e p o s i t i o n o f i o n s , atoms or mole-
cules).
The
i s r u l e d by:
k i n e t i c aspect of e l e c t r o a c t i v e the a c t i v i t i e s of r e a c t i n g
interfaces
species
on
both
s i d e s of t h i s s i t e , d i f f u s i o n c o e f f i c i e n t s , temperature and
concentration
gradients
extending from the
inter(33)
face to the
l i q u i d i r o n or s l a g b u l k .
Hawkins
have a l s o suggested t h a t a t h r e e f o l d - s t a g e
et a l .
reaction
se-
quence can be envisaged, namely i)
Transport of reactants
to the s l a g - m e t a l i n t e r -
face.
T h i s s t e p i s a t t a i n e d by d i f f u s i o n and
of the
two
c o n t r i b u t i n g phases
i i ) • Electrochemical
liquid
metal).
r e a c t i o n s which i n v o l v e
e l e c t r o n exchange p r o c e s s , iii)
(Slag and
convection
the
and
T r a n s p o r t of r e a c t i n g products away from
interface.
This
Experimental
(ESW)
work
( ^ 6
has
shown t h a t
dependent upon the
products a t the e l e c t r o a c t i v e i n t e r f a c e s . found t h a t l i q u i d m i s c i b l e
the reaction
I t has
been
r e a c t i o n products r e a d i l y
are e f f i c i e n t l y t r a n s p o r t e d
reacting interface.
away from
the
Gaseous r e a c t i o n p r o d u c t s which
are formed at the e l e c t r o - a c t i v e i n t e r f a c e r e a c t i o n by
the
step i s again r u l e d as stage ( i ) .
r a t e of r e a c t i o n i s s t r o n g l y
d i f f u s e and
ion-
slow
the
i n t e r f e r i n g with the d i f f u s i o n products
through the boundary l a y e r .
And
solid reaction
u c t s a l s o slow the r e a c t i o n r a t e by b l o c k i n g area a v a i l a b l e f o r r e a c t i o n .
Patchet
(^D
off
has
prodthe
also
i n v e s t i g a t e d " i n d u s t r i a l cases" component e l e c t r o d e and
i n ESW
s l a g systems.
these experiments t h a t r e a c t i o n s can taneously
and
involving multiI t i s noted i n
take p l a c e
simul-
they a l t e r the composition of the r e f i n e d (28
product.
Work c a r r i e d out by
57,
has
suggested t h a t although the process operates under
5 8
(chemical
in
and
agreement
'
33,
a
)
several investigators w i t h Patchet's f i n d i n g s
k i n e t i c ) dual regime, the s t a r t i n g thermo-
dynamic c o n d i t i o n s a t l e a s t can be used to i n i t i a t e c a l c u l a t i o n s i n v o l v e d i n p r e d i c t i n g the equilibrium" conditions.
On
et a l .
t h a t during
have r e p o r t e d
the other
metal drops l e a v i n g the e l e c t r o d e
"dynamic hand, Cooper
AC-melting;
i n terms of s u l f u r ,
reach chemical e q u i l i b i r u m with the s l a g and extent
that
of the r e a c t i o n s between l i q u i d pool and
They a l s o c l a i m t h a t the
r e a c t i o n s which o c c u r r e d
at t h i s
to minor temperature and
Hawkins e t al.(58)
who
differences
T h i s apparent
d i c t i o n i s c l a r i f i e d by M i t c h e l l
( 2 7
'
3 0
'
4 1
?
contraand
have e s t a b l i s h e d that although
an a c t u a l thermodynamic e q u i l i b r i u m may
not be
attained
i n i n d u s t r i a l ESR-operation; the k i n e t i c s of the c e s s , however, are so f a v o r a b l e brium i s reached. s l a g s and
only
( l a t t e r ) s i t e were
compositional
w i t h those of the e l e c t r o d e .
the
slag
were almost n e g l i g i b l e .
due
the
I t has
pro-
t h a t a s t a t e c l o s e to e q u i l i -
a l s o been found t h a t low. v i s c o s i t y
h i g h l y e f f e c t i v e r e a c t i n g area enable
the
r e a c t i o n s to reach
such a s t a t e of n e a r - e q u i l i b r i a
6378) .
Several studies
shown t h a t
on C a F ~ A l 0 2
2
although t h i s s l a g system has
concentrations
of A l , S i and Mn
tendency to achieve
3
'
s l a g s have
high
viscosity
i n ESR-ingots have the
(
6 3 ,
'
6 9
7 0
^
have a l s o found
t h a t r e g a r d l e s s of the number of e l e c t r o c h e m i c a l k i n e t i c parameters of the ESR-process, a simple chemical
has
or thermo-
( e q u i l i b r i u m ) approach i s s u f f i c i e n t to p r e (71)
d i e t the f i n a l i n g o t composition. s t u d i e d the S i - S i 0 t h a t i f there
2
Mitchell
r e a c t i o n , has
i s a constant
the s l a g i n which y°
i s high
a l s o sug-
i r o n oxide
source i n
then i t i s f e a s i b l e
t h a t the e f f e c t i v e oxygen p o t e n t i a l w i l l be t h a t of Fe-FeO e q u i l i b r i u m . which supports the and
53
the t h e o r e t i c a l e q u i l i b r i u m .
Other r e s e a r c h e r s
gested
'
(168)
'
who
(49
Petersen's
Perhaps (ESR)
(72, 73)_
the most t y p i c a l work
e q u i l i b r i u m theory I n
the
^h^g
W O
rk
i s Holzgruber
i t has been es-
t a b l i s h e d t h a t s u l f u r removal i s e n t i r e l y dependent upon the s l a g chemistry.
Other s t u d i e s along
of the p r e v i o u s work
a l s o c a r r i e d out by Miska e t
was
the
lines
(38) al.
•
.
These r e s e a r c h e r s
Holzgruber e t a l . ' s p r o p o s a l . obtained
by r e m e l t i n g
deoxidizer who
have a l s o agreed with Miska e t a l . ' s f i n d i n g s
low a l l o y s t e e l u s i n g A l as a
were not i d e n t i c a l to Holzgruber e t a l . ' s
used d i f f e r e n t e l e c t r o d e chemistry
practices.
and
Si-deoxidation
They have a t t r i b u t e d these d i f f e r e n c e s to
the d e o x i d a t i o n
p r a c t i c e and a l s o t o the presence of
Mn and A l i n the e l e c t r o d e . been s t u d i e d under s e v e r a l
The S i - S i C ^ r e a c t i o n has (ESR) s l a g systems.
g r u b e r ^ ^ , Holzgruber and P l o c k i n g e r 7 5
Holz-
^ *^ and Miska 7
(38) and
Wahlster
furnaces
have found t h a t i n i n d u s t r i a l
ESR-
t h i s r e a c t i o n reaches a s t a t e of e q u i l i b r i u m .
(75) influence of several a l l o y s and the i n f l u e n c e (38) of the A1 C>2 i n the s l a g i s a l s o shown. Kusamichi (77) The
2
et a l . ' s f i n d i n g s
i n agreement with p r e v i o u s work,
have a l s o shown t h a t the S i - S i C ^ behavior i s l i n e a r l y r e l a t e d t o the b a s i c i t y index of the s l a g . there
Although
are i n d i c a t i o n s of the v a l i d a t i o n of the thermo-
chemical e q u i l i b r i u m achieved d u r i n g should be p o i n t e d
refining i t
out t h a t t h i s e q u i l i b r i u m i s very
temperature-dependent^ ^. 48
Retelsdorf
and Winterhager
^ ^ 9
f
Boucher
and
(79) Jager and Kuhnelt
have s t u d i e d the A l - A ^ O ^ r e -
a c t i o n and conclude t h a t the A l and the oxygen content from ESR-ingots indeed f o l l o w the t h e o r e t i c a l (thermodynamic)
equilibrium.
(46 47 49-51) Abundant i n f o r m a t i o n ' ' ' exists i n the l i t e r a t u r e which e s t a b l i s h e s the v a l i d i t y of the v
(83) equilibirum-reaction
theory.
Rehak e t a l . ' s s t u d i e s
on the A l and S i d i s t r i b u t i o n i n ESR-ingots
a l s o favour
the thermodynamic approach of the ESR-reaction system.
They c l a i m t h a t r e a c t i o n s i n v o l v i n g these s p e c i e s are r u l e d by the e l e c t r o d e composition and by the i n d i v i d u a l a c t i v i t y of the components of the s l a g . (76) Holzgruber and P l o c k i n g e r ' s
work
and Choudhury
(44) et a l . ' s
are a l s o i n agreement with Holzgruber and (72
Petersen's
73) '
.
T h e i r thermodynamic approach on
s l a g chemistry as a f u n c t i o n of the a c i d i t y - b a s i c i t y concept and A l d e o x i d a t i o n
techniques
in industrial
p r a c t i c e , c l e a r l y r e v e a l t h a t indeed e q u i l i b r i u m i s reached. Kamardin e t a l . low
who have r e f i n e d 0.38 wt. % carbon
a l l o y Cr-Mo s t e e l s d e o x i d i z e d
with aluminum
have
concluded t h a t d e s p i t e t h e i r approximate method t o c a l c u l a t e the a c t i v i t y of the s l a g components
(by means o f
t e r n a r y diagrams o f the CaD-A^O^-SiG^-system) , the pred i c t i o n o f the A l and S i - c o n c e n t r a t i o n s
i n r e f i n e d ingots
can be estimated u s i n g a thermodynamic treatment. The p r e v i o u s phasized gory
d e s c r i p t i o n has e s s e n t i a l l y been
on r e a c t i o n o f the type
which i n v o l v e s r e a c t i n g
has a l s o been e x t e n s i v e l y of t h e i r study
( 1 1 ) . The other
s p e c i e s between two
studied.
i s t h a t they l a r g e l y
a l t e r the c h e m i s t r y o f
em-
liquids
The importance c o n t r i b u t e to
i n d u s t r i a l ESR - i n g o t s .
m o d i f i c a t i o n of the i n g o t chemistry
cate-
The
( " l o n g i t u d i n a l seg-
27 r e g a t i o n " ) becomes more c r i t i c a l where h i g h a c t i v i t y r e a c t i v e elements i s p r e s e n t . r o l e p l a y e d by
the T i
Because of the
in either superalloys
s t a b i l i z e d s t a i n l e s s s t e e l s , a considerable
of
important or T i -
e f f o r t has
been devoted to understand the mechanism by which a homogeneous l o n g i t u d i n a l T i - d i s t r i b u t i o n i s reached in refined ingots.
Although there are evidences i n
1-4. a. literature
71,
t h e r e are
(37, • few
74)
. . . . ,. ^ , which i n d i c a t e the mechanism,
s t u d i e s which c l e a r l y r e v e a l
(46 studies
48, •
it.
Pateisky's
47) '
have shown t h a t the r e a c t i o n
(12-vi)
indeed a t t a i n s e q u i l i b r i u m .
It i s also indicated
this equilibrium
a f f e c t e d by
i s strongly
Krucinski's
ment w i t h P a t e i s k y ' s
have a l s o i n d i c a t e d t h a t
brium.
studies
also pointed
out
that Ti-oxides
i s the r e a c t i o n
have remelted ingots
tility
the
(11-vi and
11-vii)
studied
A l l i b e r t et a l .
under S i C ^ - s l a g s
'
'
'
of lower v o l a -
have shown t h a t t h i s r e a c t i o n does f o l l o w i t s
stoichiometric slope
has
from the i n d u s t r i a l (47 49 55)
been e x t e n s i v e l y
(12-viii).
equili-
of lower valency i n
Another i n t e r e s t i n g r e a c t i o n viewpoint which has
the
Krucinski
s l a g s h o u l d be c o n s i d e r e d , i . e . r e a c t i o n s
who
i n agree-
(12-vi) a c t u a l l y reaches a s t a t e of In a d d i t i o n to the above f a c t s
that
the thermal (52)
reaction conditions.
reaction
the
i s 0.781
ratio.
The
[Al] vs
[Si] p l o t whose
indeed c o r r o b o r a t e s t h i s f a c t and
also
i n d i c a t e s the r e v e r s i b i l i t y which i s reached as a manif e s t a t i o n of a s t a t e o f e q u i l i b r i u m .
Kay's
studies^
suggest t h a t t h i s r e a c t i o n i s not i n f l u e n c e d by the oxygen p o t e n t i a l .
This conclusion
i s a l s o supported
by O p r a v i l (81) . Choudhury e t a l . (78) who have r e f i n e d ingots
(2300 mm
i n diameter) u s i n g 2.5 Hz AC. ESR
s t u d i e d the r e a c t i o n
(12-ix).
ment with Holzgruber s
Their r e s u l t s
have
i n agree-
and Holzgruber and P l o c k i n g e r s
1
1
^
c l e a r l y show t h a t the s l a g b a s i c i t y p l a y s a s i g n i f i c a n t r o l e i n the Si-Mn d i s t r i b u t i o n i n ESR-ingots.
Choudhury s 1
r e s u l t s a l s o show t h a t the type of c u r r e n t does not i n f l u e n c e the i n g o t c h e m i s t r y .
I t i s a l s o p o i n t e d out
t h a t Mn l o s s e s take p l a c e o n l y when the CaOtSiC^ r a t i o i n the s l a g i s l e s s than 3.
They a l s o c l a i m t h a t
the continuous A l - a d d i t i o n d u r i n g r e f i n i n g and
Mn are unavoidable.
The s t o i c h i o m e t r y
despite
the l o s s of S i of t h i s r e a c t i o n
was not i n v e s t i g a t e d . (37) Buzek and Hlineny recovery
rates
concerned w i t h the low Mn-
(50-58%) have used i s o t o p i c oxygen
18 {O
} above the s l a g t o determine the r e a c t i o n mechanism.
T h e i r f i n d i n g s * i n d i c a t e t h a t by A l - d e o x i d a t i o n proved Mn-recovery i s a t t a i n e d .
Although they have not s p e c i -
f i c a l l y e s t a b l i s h e d i t s thermodynamic behavior i n d i c a t e i t s high e f f e c t i v e n e s s . reduction-oxidation
im-
they d i d
They c l a i m t h a t the
mechanism i s r u l e d by the r e a c t i o n
(12-x). Regarding the has
s o - c a l l e d deoxidation
suggested the use
of extreme care i n any
s i n c e s e v e r a l r e a c t i o n s may has
been p o i n t e d
instances action
out t h a t r e a c t i o n
( 1 2 - i i ) may
has
a well-defined
(8).
^
approach
operate s i m u l t a n e o u s l y .
be c o n t r o l l e d by r e a c t i o n
(12-i)
r e a c t i o n s , Kay
It
i n some
Since the
re-
e q u i l i b r i u m constant
of a v a l u e c l o s e to u n i t y i n the range of ESR-temperatures, Fraser
has
date i t s mechanism.
d e l i b e r a t e l y s e l e c t e d i t to
He has
may
proceed to the
and
subsequently r e v e r s e
the s l a g - i n g o t
quently
noted t h a t t h i s r e a c t i o n
l e f t a t the e l e c t r o d e - s l a g
This proposal
steady s t a t e c o n d i t i o n s
d i f f e r e n c e between the two Mitchell the type
( 3 0 )
has
extended t h i s p r o p o s a l
are an
h
the A l d i s t r i b u t i o n s by
fre-
the
thermal
to r e a c t i o n s
of
i n d i c a t i o n of the
"deoxidation
a
v
e
studied
the S i , T i ,
r e f i n i n g i n g o t s under
have found a " s a t i s f a c t o r y " stab-
of these elements.
a t t a i n e d during on
which are
the
(12-vi).
s e v e r a l s l a g systems ility
l e d to
major e l e c t r o a c t i v e s i t e s .
K r i c h e v e c e t a l . (^O) and
has
observed i n r e a c t i o n s of t h i s type are a con-
sequence of a dynamic balance c r e a t e d by
Mn
interface
a t the h i g h e r temperature of
interface.
b e l i e f t h a t the
eluci-
They c l a i m t h a t these f i n d i n g s "practical" equilibrium
refining. reactions"
conditions
T h e i r s t u d i e s were performed (12-iv).
30
As d e s c r i b e d i n p r e v i o u s s e c t i o n s
the formation of
i r o n oxide d u r i n g r e f i n i n g i s almost unavoidable, e i t h e r as a r e s u l t of e l e c t r o c h e m i c a l r e a c t i o n s or as a r e s u l t of the r e a c t i o n s between the s l a g and the atmosphere d u r i n g r e f i n i n g . • These sources o f i r o n o x i d e i n c o n j u n c t i o n with the oxide on the e l e c t r o d e s u r f a c e b e f o r e and d u r i n g r e f i n i n g ,
formed
i n the presence of the oxide
components of the s l a g generate a l i q u i d with e x t e n s i v e (1 immiscibility
38 '
.
t o u n i t y a t very low
"FeO"
binary
(CaF ~FeO) ^ , 2
Al 0 ~FeO) ^ 2
'
82) Hence, the
F
e
0
concentrations.
rapidly
S t u d i e s on
t e r n a r y (CaF -CaO-FeO) ^ *,
and i n quaternary
3
rises
a
1
2
(CaF ~ 2
(CaF -Al 0 -CaO-Al 0 -FeO) ^ 2
2
3
2
3
systems have shown t h i s b e h a v i o r . A CaF
2
s l a g can permit very l i t t l e oxygen b e f o r e i t
becomes o x i d i z i n g with r e s p e c t to i r o n .
Consequently,
any
element which forms an o x i d e more s t a b l e would then be o x i d i z e d from the metal i n t o the s l a g . more c r i t i c a l where r e a c t i v e metals T i are p r e s e n t .
T h i s f a c t becomes
such as A l , S i , Zr, and
S e v e r a l techniques have been proposed such a problem:
1) A complete
to overcome
removal of s c a l e on the
e l e c t r o d e s u r f a c e and the use of an i n e r t atmosphere (74) (He or N ) , 2) p a i n t i n g the e l e c t r o d e s u r f a c e a f t e r s c a l e i s removed w i t h an A l or a magnesia-alumina s p i n e l (38) p a i n t to prevent o x i d a t i o n of the e l e c t r o d e , 3) en2
r i c h i n g electrodes i n oxidable Zr, A l , S i , e t c . , oxide
(FeAl or FeSi) ^ ^ 84
(CaF -Ca>
( 8 5
2
(83)
such as
4) continuous a d d i t i o n s of a)
formers as elements
alloys
elements
strong
( A l , S i , T i , Zr, e t c . ) , and
b) f e r r o
c) s l a g - d e o x i d i z e r composites
' >. 8 6
(34)
Holzgruber
suggests t h a t
use of a p r o t e c t i v e atmosphere d a t i o n i s achieved
i n a d d i t i o n to
a more e f f i c i e n t
i f a deoxidizer
the
deoxi-
( A l , S i or T i ) i s added
i n a s l a g system which does not c o n t a i n i t s oxide. Other . (39 , 46, 55, 60) . _ ^ researchers ' ' ' have proposed t h a t i f an element i s prone to o x i d a t i o n
l i k e T i , S i , Zr,
during
ESR-process then a d d i t i o n s of i t s r e s p e c t i v e oxide vents i t s l o s s e s .
Kay's
^
f i n d i n g s i n d i c a t e t h a t by
f i n i n g a l l o y s which c o n t a i n A l , T i and oxide
slags
Zr i n f r e e - t i t a n i u m
As the amount of Ti02 i n the s l a g i n c r e a s e s
the d e o x i d a t i o n
i s only c a r r i e d out by A l and
and
a l s o found t h a t by adding 15%
Zr.
The
the Si-decrement i n the i n g o t are con-
t r o l l e d by the exchange r e a c t i o n
containing
re-
the three elements i n the e l e c t r o d e a c t as
deoxidizers.
Al-increment
pre-
Ti0
2
(12-viii).
0.5% Zr.0
2
Kay
to the s l a g
has initially
i s s u f f i c i e n t to p r o t e c t the Zr
con-
(79)
t e n t of the r e f i n e d a l l o y .
Jager e t a l .
t h a t the e f f e c t of the A l - c o n t e n t
from the e l e c t r o d e or
a d e o x i d i z e r i s very dependent upon the s l a g The
net content
of A l t r a n s p o r t e d
have shown as
chemistry.
i n t o the i n g o t i s almost
constant f o r a given A^O^-content the s l a g
(up to 24 wt. %) i n
and a l s o f o r a g i v e n CaO: S i 0
ratio
2
(up t o 2 ) .
If these two parameters a r e i n c r e a s e d the n e t A l - c o n t e n t of the ESR-ingot
increases d r a s t i c a l l y
hence l e a d i n g t o (78)
d e l e t e r i o u s mechanical (79) and Jager e t a l . proved
properties.
Chouldhury e t a l .
have claimed t h a t by u s i n g an "im-
technique" a maximum A l content of 0.01 wt %
can be a t t a i n e d i n i n d u s t r i a l
125 tonnes
ESR-ingots.
In these two communications the d e o x i d a t i o n r a t e s , how(55) ever, a r e not g i v e n .
Kajioka e t a l .
have s t u d i e d the
e f f e c t o f A l - d e o x i d a t i o n under s e v e r a l s l a g systems, namely CaF ~CaO, C a F - A l 0 2
2
2
and C a F - A l 0 - C a O - S i 0 . They have
3
2
2
3
2
found
t h a t d e o x i d a t i o n r a t e s between 0.05 t o 0.1 wt. % A l produce the b e s t " r e s u l t s " , i n the i n g o t .
i . e . an almost
steady
Al-distribution (34)
On the other hand, Holzgruber
proposes
a d e o x i d a t i o n r a t e o f 6.2 wt. % A l . 2.2.3
Thermodynamic Approach o f the ESR-Slag Systems Another important
area o f the ESR-slag
thermo chemical approach. important,
In t h i s f i e l d
system i s i t s
although
very
very l i t t l e i n f o r m a t i o n has been r e p o r t e d .
(45) Mitchell A1 0 2
has found t h a t i n the common system CaO +
+ Si0
3
2
+ CaF
2
there a r e only three f l u o r i d e - c o n t a i n i n g
compounds other than the i n d i v i d u a l f l u o r i d e s , i . e . C
11 7 ' 3 3 A
F
C
A
F
a
n
d
C
9 3 ' S
F
w
n
e
r
e
c
' ' A
F
a
n
d
s
stand f o r
33 CaO, has
A 1 0 , CaF 2
3
2
and
Si0
respectively.
2
This
been taken as an i n d i c a t i o n t h a t the C a F
s i d e r e d as an
observation may
2
be
con-
i n e r t d i l u e n t i n h i g h l y b a s i c areas of
these systems, s i n c e the acid-base i n t e r a c t i o n s i n v o l v i n g 20 would be 54) who 30 wt.
stronger
than those f o r F .
(53 A l l i b e r t et a l . '
have remelted a l l o y s through 70 wt. %
% A1 0 2
3
with 0,
2,
5,
10,
and
15 wt.
C a F
% Si0
p e c t i v e l y , have a p p l i e d M i t c h e l l ' s c r i t e r i a .
2
res-
2
Their
f i n d i n g s show t h a t the acid-base i n t e r a c t i o n s i n the ernary
CaO
+ A l ^ O ^ + Si0
2
+ CaF
same as those i n the t e r n a r y
are approximately
2
CaO
+ A^O^
'
+ SiC^
s
Y
quatthe
s t e m
f
d i l u t e d i n the C a F . There are o t h e r i n d i c a t i o n s i n the 1 -4. t.. *_ , ^ • , (38, 58, 88 , 89) l i t e r a t u r e which a l s o support t h i s theory (14 53 54) 2
A l l i b e r t et a l .
'
'
a l s o suggest an a l t e r n a t e method
f o r r e a c t i o n s r e l a t e d p r i m a r i l y to b a s i c i t y , i . e . the C a O / S i 0 r a t i o concept which i s s t r o n g l y supported i n the (34, 49-51, 72-76) . , . , . (38) German l i t e r a t u r e ' ' . Miska and Whalster 2
M
who
have s t u d i e d
the C a F - C a O - A l 0 - S i 0 - F e O system 2
2
3
found t h a t i f the A l 0 : C a O r a t i o i s g r e a t e r 2
the C a F
2
than
3
a t ESR-temperatures remains i n e r t and
composition behaves as i t were i n the C a O - A l 0 2
Chai's and fluxes
Eagar's s t u d i e s o n
have
2
3.0,
the
slag
binary.
3
CaF ~metal oxide welding 2
have concluded t h a t the o x i d i z i n g p o t e n t i a l of
these types of s l a g s i s reduced o n l y by these s p e c i e s
i n the C a F
2 <
The
the d i l u t i o n
a d d i t i o n of C a F
2
of
i n these
34
s l a g systems has i d e s and
almost no e f f e c t on the more s t a b l e
hence the C a F
2
was
v i r t u a l l y considered
ox-
as a
diluent. 2.2.4
O v e r a l l View on the M o d e l l i n g
of ESR-Reactions
(57) A r e c e n t work
has
c l e a r l y revealed
understanding of the E S R - r e a c t i o n system.
the
I t has
i n d i c a t e d above t h a t there are e s s e n t i a l l y two proach the r e a c t i o n p a t t e r n . r e a c t o r and
the
These are the
current been
ways to
equilibrium
" s i n g l e - s t a g e r e a c t o r " concepts.
e q u i l i b r i u m - r e a c t o r method i s by
f a r a simpler
The
approach.
I t i s supported by the i d e a t h a t an a c t u a l s t a t e of brium i s reached d u r i n g r e f i n i n g ,
as p r e v i o u s l y
equili-
indi-
cated.
I t s p r i n c i p l e i s to
a
s l a g w i t h an e l e c t r o d e of a given composition
(ESR)
ap-
(thermodynamically) e q u i l i b r a t e This
technique i n t r i n s i c a l l y assumes a unique e q u i l i b r i u m tempe r a t u r e and ume.
a mass t r a n s f e r flow through a f i x e d s l a g v o l -
These two
major assumptions
as a l r e a d y
indicated,
are not n e c e s s a r i l y t r u e . The t a c t and pointed
second approach c o n s i d e r s
a t r a n s i t i o n a l phase con-
a "lumped m a s s - t r a n s f e r c o e f f i c i e n t . "
I t has
out t h a t although t h i s model resembles the
e q u i l i b r i u m nature of the process
non-
i t r e l i e s on a mass-
t r a n s f e r c o e f f i c i e n t which does not have a t h e o r e t i c a l background i n i t s computation.
Another disadvantage of
been
t h i s technique i s t h a t r e a c t i o n s o f the type
i t i s not able to account f o r (12). M i t c h e l l has a l s o p o i n t e d out 2+
t h a t both techniques r e l y on the Fe i n p u t datum.
c o n c e n t r a t i o n s as an
T h i s parameter, however, i s unknown and has
to be determined e x p e r i m e n t a l l y . As d e s c r i b e d here, these two concepts have both advantages
and disadvantages.
N e v e r t h e l e s s , i t can be un-
m i s t a k e a b l y seen t h a t the main o b j e c t i v e of these two a l t e r n a t i v e s i s to p r e d i c t and c o n t r o l the i n g o t chemical homogeneity .
36 2.3
P r e c i p i t a t i o n of
2.3.1
General
Inclusions
Since endogeneous i n c l u s i o n s are no longer as f o r e i g n p a r t i c l e s
but
" n a t u r a l " components of
today's technology demands from m e t a l l u r g i s t s
considered steel,
skillful
c o n t r o l of them to y i e l d products which c o u l d f u l l y i s f y the r e q u i r e d s t r i n g e n t standards.
sat-
A v a s t amount of
(90-98) r e s e a r c h has been devoted d e o x i d i z e r s and
to study the e f f e c t s of
deoxidation
techniques
i s known t h a t s i n c e elemental liquid iron at
(0.168 and
0.20
o r d i n a r y steelmaking
i n the p a s t .
oxygen i s h i g h l y s o l u b l e i n
wt.
% a t the monotectic
d e o x i d i z e r can be s e l e c t e d to maintain
oxygen content
to a g i v e n l e v e l .
with is has
The
first
s u l f u r i n the melt.
i n p a r t i c u l a r cases The
capability
simultaneously
second important requirement
i t s a b i l i t y to be removed from the melt once o x i d a t i o n taken p l a c e . „
. ..
..
. ,.
(99-106) .
S o l i d i f i c a t i o n - p r e c i p i t a t i o n studies shown t h a t the
tinuous
have
i n c l u s i o n p r e c i p i t a t i o n sequence, as a
measure of the degree of d e o x i d a t i o n
and
the
requirement
d e o x i d i z e r i s o b v i o u s l y a high
to r e a c t with oxygen and
and
temperatures r e s p e c t i v e l y ) , then
an a p p r o p r i a t e
expected from any
It
processes.
i s a s e r i e s of con-
These comprise the n u c l e a t i o n , growth
e l i m i n a t i o n of the d e o x i d a t i o n
products.
The
nucle-
a t i o n phenomena can be homogeneous or heterogeneous
and
i t can take p l a c e i n the l i q u i d stage or during fication.
To homogeneously n u c l e a t e a phase
sary t o o r i g i n a t e
solidi-
i t i s neces-
a s u p e r s a t u r a t i o n and i t can be reached
by u n d e r c o o l i n g o f the s p e c i e s i n s o l u t i o n ,
by a d d i t i o n s (9
of e i t h e r a d e o x i d i z e r or oxygen and during
solidification
If there a r e some s o l i d p a r t i c l e s i n a melt where deoxida t i o n products ation
can d i f f u s e t o
(precipitation) At steelmaking
then a heterogeneous n u c l e -
occurs.
temperature some oxides, o x i s u l f i d e s and
s u l f i d e s a r e g e n e r a l l y found
i n s o l u t i o n with l i q u i d
Once s o l i d i f i c a t i o n s t a r t s , s e g r e g a t i o n
(due to incomplete
d i f f u s i o n i n the s o l i d ) i n the i n t e r d e n d r i t i c As soon as t h i s i n t e r d e n d r i t i c cipitation clusions
liquid
l i q u i d i s saturated
takes p l a c e .
c o n t i n u e s u n t i l the s o l i d u s
i s reached. further
of i n c l u s i o n s
steel.
occurs. pre-
P r e c i p i t a t i o n of i n temperature o f the melt
Under p a r t i c u l a r circumstances
as w i l l be
d e s c r i b e d , p r e c i p i t a t i o n takes p l a c e a t even lower
temperature ranges.
I n c l u s i o n s i z e , shape, q u a n t i t y and
d i s t r i b u t i o n i s p r i n c i p a l l y given by the s o l i d i f i c a t i o n r a t e and by the s o l u b i l i t y i n the l i q u i d s t e e l
.
of certain
chemical
species
Maximum s o l u b i l i t y o f these
s p e c i e s i n f l u e n c e s the p r e c i p i t a t i o n sequence d u r i n g dification. solubility
soli-
As an a p r i o r i r u l e , f o r s p e c i e s which have low i n liquid steel
precipitation
c i p i e n t s o l i d i f i c a t i o n i s observed.
s t a r t s when i n -
These types o f i n -
38 e l u s i o n s w i l l have longer time f o r growth. O x i - s u l f i d e s and
s u l f i d e s which are p r e c i p i t a t e d as
a r e s u l t of monotectic r e a c t i o n s are i n c l u d e d i n t h i s
cate-
gory.
high
On the other hand, i f s o l u b i l i t y i s r e l a t i v e l y
p r e c i p i t a t i o n takes p l a c e at the l a s t stage of c a t i o n and
hence these phases are c o n f i n e d to
solidifilocalized
areas. While i n the f i r s t case i n c l u s i o n s are g l o b u l a r , large ond
and
group
have l a r g e i n t e r p a r t i c l e d i s t a n c e s , i n the i n c l u s i o n s are very
around g r a i n s or d e n d r i t e s .
small and u s u a l l y l o c a t e d
S i n g l e phase or composite
f i l m s around d e n d r i t e s are a l s o i n c l u d e d i n t h i s kind.
The
second
s o l u b i l i t y of some s p e c i e s i n l i q u i d s t e e l
a l t e r the s u l f i d e chemistry
sec-
and
, . (90,106,107) sequence and s i z e '
can
hence i t s p r e c i p i t a t i o n
2.3.2
Nucleation
2.3.2.1
Homogeneous N u c l e a t i o n
According
and Growth of I n c l u s i o n s
to the homogeneous n u c l e a t i o n theory
posed by Volmer and Weber-Becker the f o r m a t i o n
and
pro-
Doring^®^'^
o f a new phase from a l i q u i d phase
occurs
o n l y i f s u p e r s a t u r a t i o n e x i s t s i n the parent phase. , , (99,101,110,111) e r a l researchers ' • the i n t e r f a c i a l saturation Popel^
1 1
^
interfacial
tension
(a)
Sev-
. i T x. have r e v e a l e d t h a t
and the degree of super-
(C:C») of a melt i n f l u e n c e the n u c l e a t i o n r a t e . has c a l c u l a t e d the r a t e s o f n u c l e a t i o n f o r t e n s i o n s ranging
from 180 to 100 ergs/cm
and s u p e r s a t u r a t i o n r a t i o s from 1 t o 10.
2
His s t u d i e s
show t h a t f o r systems (FeO-MnO) where the a = 180 ergs/cm , 2
28 he obtained
a n u c l e a t i o n r a t e of about 10
a t i o n r a t i o s as low as .1.5.
a t super s a t u r -
With C:C°° r a t i o s o f about 10, 35
the n u c l e a t i o n r a t e s were i n c r e a s e d to 10
.
On the other
hand i n systems (FeO-MnO-Si0 ) where the i n t e r f a c i a l 2
t e n s i o n i s about 700 ergs/cm
2
i n c l u s i o n s i s extremely small
the n u c l e a t i o n r a t e o f -79 (10 ) for supersaturation
40
r a t i o s of l e s s than 3.
I t becomes a p p r e c i a b l e , however,
a t C:C°° r a t i o s of about 10. about 1000
ergs/cm
2
For i n t e r f a c i a l
t e n s i o n s of
as i n the CaO-A^O^-SiC^ system,
homogeneous n u c l e a t i o n of i n c l u s i o n s becomes very cult.
diffi-
These c o n c l u s i o n s are s i g n i f i c a n t f o r d e o x i d a t i o n
d u r i n g c o o l i n g and
solidification.
During
c o o l i n g of a
w e l l - d e o x i d i z e d melt which does not c o n t a i n any i n c l u s i o n s there i s a p o s s i b i l i t y interfacial
of formation of an oxide with
t e n s i o n , e.g.
T u r p i n and c l a s s i c a l theory
Elliot
FeO'A^O^ and
FeO-rich
lower
silicates.
u s i n g Volmer and Weber's ^^8)
obtained
an e x p r e s s i o n f o r c r i t i c a l
super-
s a t u r a t i o n i n terms of the f r e e energy f o r homogeneous n u c l e ation.
They have found t h a t h e r c y n i t e was
formed i n i r o n
melts where thermodynamically alumina should have p r e cipitated.
Thus, they
suggested t h a t s u p e r s a t u r a t i o n i s
r e q u i r e d t o produce homogeneously n u c l e a t e d Chipman ^
X 1 1
^
has
alumina phases.
suggested t h a t both A l ^ O ^ and
p r e c i p i t a t e simultaneously
FeO'A^O-j
may
i f there i s not complete mixing (112-113)
i n the melt.
McLean and Ward
have i n d i c a t e d t h a t
h e r c y n i t e may
a l s o p r e c i p i t a t e a f t e r an i n i t i a l alumina p r e -
41 c i p i t a t i o n when the metal i s d e p l e t e d brium i n t h i s case is between A^O^,
in A l .
The
FeO-A^O^
equili-
dissolved (99)
oxygen and
the l i q u i d i r o n .
shows t h a t i f the c r i t i c a l nucleate
A^O^
Turpin*s
and
E l l i o t ' s work
f r e e energy to homogeneously
were much g r e a t e r than t h a t f o r h e r c y n i t e ,
the p r e c i p i t a t i o n s of the l a t t e r phase becomes more f e a sible.
These r e s e a r c h e r s
concentrations
have a l s o concluded t h a t a t high
of d e o x i d i z e r or a l t e r n a t i v e l y of oxygen
r e l a t i v e to normal bath compositions i n e q u i l i b r i u m with pure oxide e f f e c t and
i s r e q u i r e d to overcome the s u r f a c e
tension
thus to p r e c i p i t a t e phases homogeneously.
They have a l s o p o i n t e d out t h a t the common method of adding the d e o x i d i z e r to a molten p o o l p r o v i d e s s a t u r a t i o n to form very c l u s i o n was
sufficient
small i n c l u s i o n s .
super-
T h i s con-
a l s o reached by Turkdogan ^^1)
showed
t h a t i f the deoxidant i s assumed to be evenly d i s t r i b u t e d i n the melt b e f o r e n u c l e a t i o n . then the s u p e r s a t u r a t i o n
at-
t a i n e d would be an order of magnitude l e s s than t h a t necessary f o r homogeneous n u c l e a t i o n .
He
therefore
postulated
t h a t the d i s s o l u t i o n of d e o x i d i z e r i n l i q u i d s t e e l
takes
a f i n i t e time d u r i n g which c e r t a i n r e g i o n s of the melt are expected
to be very r i c h i n s o l u t e c o n c e n t r a t i o n .
these r e g i o n s
l i q u i d metal a t t a i n s s u f f i c i e n t l o c a l
super-
s a t u r a t i o n f o r homogeneous n u c l e a t i o n . I n v e s t i g a t i o n s c a r r i e d out by Von
Bogdandy^ ^' on 114
In
n u c l e a t i o n of aluminum c o n t a i n i n g phases showed t h a t when the deoxidant i s c a r e f u l l y i n t r o d u c e d
i n t o the melt
the
i n c l u s i o n s form i n a l a y e r at a d e f i n i t e time and l o c a t i o n . They have p o s t u l a t e d t h a t very h i g h s u p e r - s a t u r a t i o n
ratios
14 (10 ) are r e q u i r e d f o r homogeneous n u c l e a t i o n of these oxides. These values are s e v e r a l o r d e r s of magnitude (99) higher
2.3.2.2
than those obtained
Heterogeneous
In a c t u a l p r a c t i c e
by
Turpin
Nucleation l a r g e degrees o f
supersaturation
are not r e q u i r e d i f the p r e c i p i t a t i o n of i n c l u s i o n s take
, . , s u r .f a c e s (115)
-i
p l a c e on s o l i d
From the above d i s c u s s i o n i t i s e v i d e n t t h a t
nucle-
a t i o n of i n c l u s i o n s i n s t e e l i s not the r a t e c o n t r o l l i n g step because high s u p e r s a t u r a t i o n
i s reached near
r e g i o n s where the d e o x i d i z e r s are t r a n s p o r t e d l i q u i d pool.
These n u c l e i are u n i f o r m l y
to s t i r r i n g of the melt f u r t h e r oxides
the
i n t o the
d i s t r i b u t e d due
(during r e f i n i n g ) and p r e c i p i t a t e
as c o o l i n g and
solidification
takes p l a c e .
However, the presence of p r e - e x i s t i n g i n c l u s i o n s from electrodes
( i f any), make heterogeneous n u c l e a t i o n more
f a v o r a b l e where r e f i n i n g c o n d i t i o n s are not optimum.
2.3.3
Growth of
Inclusions
By u s i n g Shewman's f o r m u l a t i o n ^ among the phenomena which c o n t r i b u t e clusions gots gen
from n u c l e i
(2-4 and
ym),
the
(0.1
ym)
can
see
to s i z e s found i n ESR
p r e c i p i t a t i o n on
i s the mechanism which i n the
the
nuclei
l e a s t amount of time
process.
The
in(oxy-
generate i n c l u s i o n s i z e s i n the range
a r i l y found i n the ESR
that
to growth of i n -
growth by d i f f u s i o n of s o l u t e s
d e o x i d i z e r s ) and
sees.) c o u l d
one
(^
1-2
ordin-
above c a l c u l a t i o n s 7
are very dependent on cm ). 5 - 3
(10
Turkdogan
) at the
the number of n u c l e i p r e s e n t u s e (
j
a
d i f f e r e n t number of
s t a r t i n g conditions
and
hence h i s
showed t h a t a d i f f e r e n t maximum r a d i u s (23
ym)
was
(6 sees ).
of
nuclei
calculations
inclusions
reached i n a s l i g h t l y h i g h e r p e r i o d The
(10
of
time
above i n f o r m a t i o n p l u s some o t h e r t h e o r (117)
e t i c a l c a l c u l a t i o n s performed by
Lindberg and
i n a s i m i l a r a p p l i c a t i o n of Wert's and
Torsell
Zener s model^ 1
1 1 8
^
c l e a r l y i n d i c a t e t h a t t h i s growth mechanism i s a very f a s t process. Experimental work performed by s e v e r a l r e (107 117 119 120) searchers ' ' ' agree w i t h p r e v i o u s c a l c u l a t i o n s . During c o o l i n g
and
solidification
the growth of
inclusions
becomes more s i g n i f i c a n t as p r e c i p i t a t i o n c o n t i n u e s on existing particles.
Iyengar^ ^ 1 2
has
pre-
formulated a model
44 to p r e d i c t the growth under the above c o n d i t i o n s .
His r e -
s u l t s have shown t h a t the time f o r completion of growth i s dependent on the i n i t i a l
s i z e of i n c l u s i o n s .
almost n e g l i g i b l e .
Thus, these
are c l e a r l y i d e n t i f i e d w i t h r e s u l t s found 27
de-
6 7 With 10 -10 nuclei/cm
creases with i n c r e a s e i n r a d i u s . the growth was
T h i s time
in
3
results E S R ' " ' '
2
1
'
30) '
l i q u i d p o o l s and
i n g o t s , i . e . growth i s almost
en-
t i r e l y achieved by d i f f u s i o n of s o l u t e s . (117 The
second phenomenon which has been observed
'
120-122) to l a r g e l y c o n t r i b u t e t o the growth of
inclusions
i n c o n v e n t i o n a l m e l t i n g p r a c t i c e s i s the c o l l i s i o n a l e s c e n c e mechanism.
T h i s mechanism i s s t r i c t l y
t o the motion o f oxide i n c l u s i o n s i n l i q u i d
co-
related
steel.
For a g i v e n s i z e d i s t r i b u t i o n of i n c l u s i o n s i n a melt there i s a d i s t r i b u t i o n of r i s i n g v e l o c i t i e s '
2 1
^.
The
l a r g e r i n c l u s i o n s w i l l l e v i t a t e more r a p i d l y than the s m a l l e r , ,,. . (117,122) ones and as a r e s u l t c o l l i s i o n may occur ' The c o a l e s c e n c e o f i n c l u s i o n s depends on
impact,
speed and angle, s u r f a c e p r o p e r t i e s such as s u r f a c e t e n s i o n , chemical composition l i q u i d or
and t h e i r p h y s i c a l s t a t e ( i . e .
solid).
I t has been observed
t h a t the motion of
inclusions
i n s t e e l f a l l s w i t h i n the v i s c o u s flow regime where the Reynolds number of the p a r t i c l e
i s l e s s than one.
This
45
includes
i n c l u s i o n s i z e s i n the 0-50 ym range.
condition, Stokes
1
Under t h i s
Law (13)
Ust = i s a p p l i c a b l e provided
the system i s c o n s i d e r e d
t o be d i -
l u t e and p a r t i c l e i n t e r a c t i o n can be n e g l e c t e d . a t i o n o f Stokes' L a w ^ tions:
126
^
depends upon the f o l l o w i n g
1) i n c o m p r e s s i b i l i t y o f the medium,
extent of the medium, velocity,
4) r i g i d i t y of i n c l u s i o n s ,
The parameter i n v o l v e d Ust = t e r m i n a l
condi-
2) i n f i n i t e
3) very small and c o n s t a n t
at the f l u i d - p a r t i c l e i n t e r f a c e and cles.
The d e r i v -
terminal
5) absence o f s l i p p i n g 6) s p h e r i c i t y o f p a r t i -
i n t h i s expression a r e :
v e l o c i t y according
t o Stokes' Law,
(cm/sec.) p
s
, p = density
pectively,
o f the p a r t i c l e and the medium r e s -
(g/cm ) 3
r - r a d i u s o f the sphere, (cm) y = v i s c o s i t y of the medium, The
above c o n d i t i o n s
in reality.
Corrections,
(g/cm. sec.)
are very d i f f i c u l t
however, can be a p p l i e d t o ac-
count f o r the d e v i a t i o n from i d e a l i t y . the a v a i l a b l e c o r r e c t i o n s . provided
to s a t i s f y
Table
(I) l i s t s
Stokes' Law i s a p p l i c a b l e ^
1 2 6
^
t h a t g r a v i t y i s the only e x t e r n a l f o r c e a c t i n g on
inclusions.
I f an i n c l u s i o n i s i n a melt
as i n the ESR
46
p r o c e s s , which i s i t s e l f spherical
i n motion, then the drag on a
p a r t i c l e i s g i v e n by: Dc = -6iryr (v-u)
where
v = velocity
(vector) of sphere
u = resulting velocity rounding
(14) due to g r a v i t y and
(vector) due t o movement o f the s u r -
fluid.
In order t o o b t a i n an e x p r e s s i o n f o r the v e l o c i t y of the i n c l u s i o n s i s necessary location
r e l a t i v e to a f i x e d c o o r d i n a t e system
t o know the r e s u l t i n g v e l o c i t y
it
(u) a t every
i n the melt.
Iyengar's
work' ^ 2 1
has c l e a r l y r e v e a l e d
through
e r a l mathematical approaches
t h a t growth of i n c l u s i o n s
any other mechanism i s almost
negligible.
sevby
47
2.3.4
Sulfides The
i d e a of "hot s h o r t n e s s " was
l a s t century.
conceived
i n the
T h i s t o p i c , however, r e c e i v e d more a t t e n t i o n (127
i n the e a r l y 30's
128) '
.
The
so c a l l e d
"steel
burning"
or "overheating phenomenon" has been s t u d i e d s i n c e then. Research through s u l f u r was
the years has l e d to the c o n c l u s i o n t h a t
l e s s d e t r i m e n t a l when manganese was
present.
Since then Mn has been used to modify the s u l f i d e phase. I f Mn
i s absent or p r e s e n t i n i n s u f f i c i e n t amounts
f o r m a t i o n o f FeS
i s almost
inevitable.
the
T h i s phase has
a
very low m e l t i n g p o i n t (1190° C) and when i t i s combined with i r o n or FeO phase
(940°C).
i t forms a lower m e l t i n g p o i n t e u t e c t i c T h i s e u t e c t i c p r e c i p i t a t e s between g r a i n s
(129-132) or d e n d r i t e s
. I f t h i s s t e e l i s to be heated
a u s t e n i t i c temperatures
f o r f u r t h e r mechanical
at
working
then g r a i n detachment o c c u r s ^ ^ " ^ ^ . T h i s problem (133) • (overheating") has been observed even i n ESR-materials.
Thus Mn
has the c a p a b i l i t y to modify the
phase from a l i q u i d temperatures the Mn:S
"FeS"
to a s o l i d
(1900- 1200°C) .
"MnS"
a t hot working
T h i s t r a n s i t i o n occurs where (92)
r a t i o i s h i g h e r than 4
s u l f i d e i n c l u s i o n s i n low carbon
.
The
i d e a l form f o r
s t e e l s i s to have a pure
MnS-phase which melts a t about 1610°C. k i n d s of MnS
sulfide
Three d i f f e r e n t (90 134) have been u s u a l l y r e p o r t e d ' , MnS I - I I I .
T h e i r s t a b i l i t y depends on the c o o l i n g r a t e and on chemistry of the melt (136-139) ^
T
^
e
t
r
a
n
s
-L i t
o
f
n
r
the o
m
type I to I I o c c u r s i f the oxygen content i n the s t e e l i s d i m i n i s h e d to l e s s than 100 ppm. II
The
t r a n s i t i o n of type
to I I I i s o b t a i n e d by the i n f l u e n c e of two
parameters,
a low oxygen content and a high a c t i v i t y of s u l f u r . has been r e p o r t e d t h a t the presence C a
(140
142)
p
r
o
m
0
4 -
and H i l l e r t ' ^ 3
tem
of C, S i , P, A l and
f o r m a t i o n of MnS
e
who
It
III.
Fredriksson
have s t u d i e d the Fe-O-S t e r n a r y s y s -
have claimed t h a t as a r e s u l t of a c o o p e r a t i v e -
eutectic reaction
where MnS
forms as a c r y s t a l l i n e phase
t o g e t h e r with the F e - r i c h phase, a MnS-type IV i s formed. The morphology o f these s u l f i d e s has g e n e r a l l y been desc r i b e d as g l o b u l a r , b r a n c h e d rod and i d i o m o r p h i c f o r type (93 I,
I I and I I I , r e s p e c t i v e l y
142) '
.
which they are formed i s as f o l l o w s . type I
The mechanism by Sulfide
inclusions
are u s u a l l y a s s o c i a t e d with o x i - s u l f i d e s
(eutectic
type) and are p r e c i p i t a t e d as a r e s u l t of a monotectic reaction. almost
Since p r e c i p i t a t i o n of s u l f i d e s takes p l a c e
s i m u l t a n e o u s l y with the deoxidaton process
an o x i d e ^ s u l f i d e and a s u l f i d e w i l l be formed.
(type I) e n r i c h e d phase
The phase which p r e c i p i t a t e s f i r s t i s (91 142)
r i c h e r i n oxygen than the second phase or
then
'
.
Rimmed
s e m i k i l l e d i n d u s t r i a l i n g o t s (with r e l a t i v e l y h i g h
oxygen content and low s u l f u r s o l u b i l i t y ) c o n t a i n t h i s
49 type of s u l f i d e .
Ingots which have been d e o x i d i z e d
the
t h e o r e t i c a l required
low
oxygen content and
deoxidation initially reaction ^
1 3
amount of aluminum w i l l have
high s u l f u r s o l u b i l i t y .
p r a c t i c e produces MnS
thought to be ^
.
II.
This
T h i s type
was
formed as a r e s u l t of a e u t e c t i c
More r e c e n t
ideas i n d i c a t e t h a t i t i s
o r i g i n a t e d by a c o o p e r a t i v e monotectic r e a c t i o n . also believed
with
It i s
that t h i s s u l f i d e p r e c i p i t a t e s at i n (91)
c i p i e n t s o l i d i f i c a t i o n stages. out
t h a t s i n c e alumina and
t o g e t h e r but
MnS
f o r the
frequently
to p r e c i p i t a t e MnS
These c o n d i t i o n s
observed
lower s u l f u r s o l u b i l i t y
are
I I I i n s t e e l s , than i n MnS
II.
are a t t a i n e d because of the excess of A l
This
s u l f i d e p r e c i p i t a t e s i n the e a r l y stages
of s o l i d i f i c a t i o n as a s i n g l e phase. that the
pointed
s u l f i d e (type I I ) .
Lower oxygen content and
in solution.
II are
has
as d i s t i n c t phases then the alumina phase
a c t s as a s u b s t r a t e
required
Kiessling
I t has
been o b s e r v e d ^
t h r e e types are p r e c i p i t a t e d i n between g r a i n s
or
dendrites. Recent c o m m u n i c a t i o n s ^ MnS
IV
'
1 4 3
^
which p r e s e n t s a "ribbon"
c a t i o n of e i t h e r I - I I I who
1 3 8
have s t u d i e d
( 1 3 9 )
or I I
the k i n e t i c s and
have suggested
pattern (
1
4
3
)
.
is a Ito et
that
modifial.
chemical i n f l u e n c e
(
1
3
9
of
melts on the MnS-shape
c l a i m t h a t type II r e s u l t s from
a e u t e c t i c r e a c t i o n and
type I and
III
(type N)
are
)
pre-
142
^
50 c i p i t a t e d from s o l i d s t e e l . given.
Steinmetz e t a l . d
4 3
A mechanism, however was not )
who have s t u d i e d the Fe-Mn-O
and the F e - S i - 0 systems a t 1500° and 1600°C
have shown
t h a t there are areas of s t a b i l i t y f o r the three MnS
types
when the [S] v s . [0] and the [S] v s . [Mn] are p l o t t e d . In t h i s work, i t i s a l s o proposed t h a t MnS-morphology
is
very dependent upon the l o c a l a c t i v i t y c o n d i t i o n s o f oxygen and the degree of d e o x i d a t i o n
( S i or Mn).
a s u c c e s s i o n of d i f f e r e n t c o n d i t i o n s
Thus, i f
i n terms of l o c a l
a c t i v i t y or degree o f d e o x i d a t i o n of melts
i s made then
a continuous s e r i e s of m o r p h o l o g i c a l changes i n MnS's would take p l a c e , i . e . from s p h e r i c a l
( o x i s u l f i d e ) a t h i g h oxy-
gen a c t i v i t i e s , r o d l i k e , d e n d r i t i c and " s k e l e t o n " shape a t medium oxygen a c t i v i t i e s and pseudo and h i g h l y talline last
(MnS) a t very low oxygen
"transition"
(MnS I I t o MnS
(local) a c t i v i t y .
crysThis
I I I ) has been observed
when a melt i s d e o x i d i z e d e i t h e r by A l , Ca or Ca-bearing (140,142,144,145) a l l ovc:
'
'
'
51
2.3.5
Specific
Sulfides
K i e s s l i n g and Lange
(91)
(92) and S a l t e r and P i c k e r i n g
have e s t a b l i s h e d t h a t double s u l f i d e s of the type are f r e q u e n t l y found. elements
Me r e p r e s e n t s any o f the f o l l o w i n g
T i , V, N i , Cr, Fe, Zr, Mg and Ca.
Pickering ^ h a v e
(Mn, Me)s
S a l t e r and
s t u d i e d the replacement o f Mn by Fe
i n the double s u l f i d e . 0.5 to 32 wt. % Fe.
They found t h a t i t ranges
from
The maximum s o l u b i l i t y l i m i t , however, (91)
d i s a g r e e s w i t h p r e v i o u s work performed by K i e s s l i n g (41.0).
The Cr s u b s t i t u t i o n f o r Mn i n these
has a l s o been s t u d i e d by these r e s e a r c h e r s .
,
sulfides While
Salter
(92) and P i c k e r i n g
have r e p o r t e d a replacement o f Mn by (91)
Cr ranging from 0-5 to 25 wt. % ( C r ) , K i e s s l i n g
who
has s t u d i e d these compounds i n s y n t h e t i c s u l f i d e s found a maximum replacement of 26 wt. % Cr.
has
Perhaps
the
most important double s u l f i d e which has become a f o c u s o f a t t e n t i o n with the advent o f the C a - i n j e c t i o n processes i s the (Ca, Mn)S. , .^
.
literature
There i s abundant i n f o r m a t i o n i n the
(140, 144, 158) '
'
...
^ , ,. ,
.
.
which e s t a b l i s h e s t h a t t h i s com-
pound i s p r e c i p i t a t e d on complex Ca-aluminates a p e r i p h e r a l envelope.
S a l t e r and P i c k e r i n g
forming d ^) 4
n
a
v
e
found t h a t s i n c e CaS i s isomorphous with the MnS (NaCl type o f l a t t i c e ) then e x t e n s i v e CaS s o l u b i l i t y i n MnS should be expected.
They have a l s o found a l i m i t e d s o l u b -
i l i t y of FeS
(4% Fe)
i n the above
l i n g and W e s t m a n ' ^
(CaS-MnS) system.
Kiess- ,
have determined the e x i s t e n c e of a
4
( t r i a n g u l a r shaped) m i s c i b i l i t y gap which shows a maximum
i m m i s c i b i l i t y a t approximately 120 0°C and a t 50
Ca + Mn,
(in at.%).
A t approximately 1000°C i t i s i n c r e a s e d
from 2 5 to 8 5 Ca/Ca + Mn.
These r e s e a r c h e r s
t h i s m i s c i b i l i t y gap
may
i.e.
r i c h phases.
C a - r i c h and Mn
d i v i d e the
ment with r e s p e c t to the Ca and Mn or MnS 6.0
phases.
wt.%
Mn
S a l t e r and from 1.0 ively.
(Ca, Mn)S
i n t o two
and
from 3.0
s o l u b i l i t i e s i n the
to 7.0
wt.
4
wt.
% f o r Mn
i n CaS
and
CaS
from 3.0
% Ca i n to 12.0
Ca i n MnS
to
MnS.
wt.
% and
respect-
Eklund s t u d i e s ' ^ ^ ^ supported by K i e s s l i n g and
man's f i n d i n g s o n
types
There i s c e r t a i n d i s a g r e e -
P i c k e r i n g ' * ^ r e p o r t from 1.0
to 19.0
suggest t h a t
Church e t a l . ' ^ ® ^ have r e p o r t e d
i n CaS
Ca/
West-
the i n i t i a t i o n of c o r r o s i o n i n i n c l u s -
i o n s , has a l s o i d e n t i f i e d the e x i s t e n c e of these phases. t h i s study i t i s shown t h a t while remains almost i n e r t severely attacked. l i n g and
the s u l f i d e phase e n r i c h e d
i n Ca
T h i s f i n d i n g i s i n agreement with
Westman's who
have a l s o observed the CaS
i t i o n to hydrogen s u l f i d e and sence of water.
Ca-sulfide enriched
in
In Mn
was Kiess-
decompos-
c a l c i u m hydroxide i n the
pre-
53 2.3.6
Oxisulfides
2.3.6.1
The
Fe-Q-S System
Rosenqvist and Dunicz
(161)
and
Turkdogan e t a l .
(162)
have determined the s o l u b i l i t y o f s u l f u r i n high p u r i t y iron.
I t i s e s t a b l i s h e d t h a t the maximum s o l u b i l i t y of
s u l f u r i n d e l t a - i r o n i s 0.18 wt.% a t 1365°C.
A t the same
temperature the gamma-iron holds o n l y 0.06 wt.%. bility
g e n e r a l l y decreases w i t h temperature but a l p h a -
i r o n a t 913°C holds 0.02 wt.%. has
The s o l u -
been s t u d i e d e x t e n s i v e l y .
The Fe-O-S t e r n a r y
system
H i l t y and C r a f t s ^ ^ ^ have 3
determined the l i q u i d u s s u r f a c e based on chemical and m e t a l l o graphic
analysis.
T h e i r r e s u l t s show t h a t the Fe-FeS-FeO
as the most important p a r t o f the Fe-O-S system i n the range o f p r a c t i c a l i n t e r e s t , i s c o n s t i t u t e d by a t e r n a r y e u t e c t i c a t 67 wt.% Fe, 24 wt.% S, 9 wt.% 0 920°C.
and about
A m i s c i b i l i t y gap which extends i n t o the system
from the Fe-0 s i d e to a s u l f u r content a t 21.5 wt.% a minimum p o i n t Fe,
with
( p l a i t p o i n t ) a t approximately 81.5 wt.%
16.5 wt.% S, 2 wt.% O and a t 1345°C.
The s o l u b i l i t y o f
oxygen i n i r o n a t s e v e r a l temperatures has a l s o been d e t e r mined by H i l t y and C r a f t s ^ ^ 3 ) ^
j t i s indicated that f o r
increasing s u l f u r concentrations
the oxygen content o f
i r o n f i r s t decreases s l i g h t l y up t o about 0.1% S and then increases r a p i d l y .
The s o l u b i l i t y o f s u l f u r i n i r o n as a
54 r e s u l t o f the oxygen i n f l u e n c e has been determined dogan e t a l .
166)^ T h e i r f i n d i n g s i n d i c a t e t h a t i n
the e q u i l i b r i u m Fe-S-O. s a t u r a t e d with w u s t i t e temperature
by Turk-
i n the
range between 913°C t o 1375°C, there i s a p r o -
nounced expansion on the s u l f u r s o l u b i l i t y curve which reaches a maximum o f 143 ppm o f S a t about v a l u e corresponds
1200°C.
This
to almost h a l f o f t h a t of the s o l i d u s on
the Fe-S diagram. Yarwood e t a l . ' ^ " ^
have proposed
an i n c l u s i o n pre-
c i p i t a t i o n model f o r the Fe-FeS-FeO system. mgs
Their f i n d -
4. - 4 . U 4-v, u (90,134,135, 163) i n agreement with other r e s e a r c h e r s ' ' ,
show t h a t the p r e c i p i t a t i o n sequence monotectic r e a c t i o n ,
as a r e s u l t o f the
i s indeed a f f e c t e d by the %0:%S r a t i o ,
(0:S), i n the a l l o y .
I f t h i s r a t i o i s g r e a t e r than 0.05.
i n c l u s i o n s w i l l have a wide range of compositions.
They a l s o
found t h a t w h i l e the maximum oxide content i n i n c l u s i o n s was
dependent on the i n i t i a l J m
was
not.
i J
0:S r a t i o , the minimum content
• (164-166)
Kor and Turkdogan's
ment w i t h Yarwood e t a l . ' s '
0 5
.
-it,
, •
i n qualitative ^
agree-
i n d i c a t e t h a t f o r 0:S
r a t i o s g r e a t e r than 0.12 two l i q u i d s form a t a g i v e n tempe r a t u r e and composition.
T h e i r experiments
on an a l l o y
con-
t a i n i n g 0.02% C and an 0:S r a t i o o f 0.29, c l e a r l y r e v e a l the presence o f the l i q u i d
oxysulfide.
55 2.3.6.2
The Fe-O-S-Mn
"Equilibrium"
H i l t y and C r a f t s ^ ter
1 2 9
'
i
n
t h e i r aim t o g a i n a b e t -
understanding of the d e o x i d a t i o n p r a c t i c e and the i n -
c l u s i o n chemistry
have
s t u d i e d the Fe-S-O,
Fe-S-Mn, Mn-O-S
and the Fe-O-Mn systems t o develop the Fe-O-S-Mn
system.
They have suggested t h a t the Fe-S-0 i s s t r o n g l y m o d i f i e d if
the Mn content i n the a l l o y
i s h i g h enough t o enhance
the p r e c i p i t a t i o n o f the s u l f u r - f r e e oxide and the oxygenfree sulfides,
s i m u l t a n e o u s l y with the s o l i d i f i c a t i o n of
the m e t a l l i c phase.
S e m i - q u a n t i t a t i v e work performed on
the Fe-O-S system
by these r e s e a r c h e r s
by adding 0.3% Mn
the i m m i s c i b i l i t y r e g i o n s from the Fe-O-S
and the Fe-S-Mn a r e encountered m i s c i b l e r e g i o n i s formed.
indicates
and hence a continuous im-
They propose
t h a t the metal
oxide and metal s u l f i d e e u t e c t i c s are i n i t i a l l y to
that
formed c l o s e
the i r o n c o r n e r , d i a g o n a l l y i n t e r s e c t the i m m i s c i b i l i t y
r e g i o n and meet the " t e r n a r y " e u t e c t i c .
I t was a l s o
t h a t the e u t e c t i c i n the m o d i f i e d t e r n a r y remained i n the same l o c a t i o n as i n the o r i g i n a l Fe-O-S Van V l a c k e t a l . ^ s h o r t n e s s " problem
1
3
^
almost
system.
a l s o concerned w i t h the "hot
have observed t h a t i f the Mn content
i s about 0.8% i n the Fe-O-S system, d u r i n g quenching
found
this alloy
originates
duplex o x i d e - s u l f i d e i n c l u s i o n s .
The
s u l f i d e phase e n r i c h e d i n Mn was a r e s u l t o f a primary crystallization.
I t was a l s o noted t h a t i f the Mn content
56 i n the t e r n a r y a l l o y
(Fe-O-S) was low then FeS and Mn-
r i c h oxide phases were p r e c i p i t a t e d . (164-166)
. m
Turkdogan and Kor
,
f
.. . _
a s e r i e s o f papers have compiled
i n f o r m a t i o n concerning the Fe-Mn-S-0 system.
thermodynamic Oxygen and
s u l f u r p o t e n t i a l diagrams which a r e i n v o l v e d i n t h i s q u a t e r (93) nary have been developed
'.
Turkdogan and Kor based
on H i l t y and C r a f t s o b s e r v a t i o n s ' * * ^ and on t h e o r e t i c a l 3
thermodynamic
data developed by Darken and Gurry
have p r o -
posed t o r e p r e s e n t the s t a b i l i t y phase f i e l d s f o r the Fe-Mn-S-0 system under s e v e r a l c o n d i t i o n s .
They have
esti-
mated t h e c o e x i s t e n c e o f gamma i r o n , Fe(Mn)0, FeS, Mn(Fe)S and a l i q u i d o x y s u l f i d e , £^ , as the e q u i l i b r i u m phases a t about 900°C, F i g u r e
( 3 ) . The a
mated t o be u n i t y and 0.4 r e s p e c t i v e l y
p
e
S
and a
(condensed) M
n
g
were e s t i -
and hence t h e e q u i l i _3
brium manganese i n gamma i r o n was computed
t o be lOppm (10
%).
The f o u r f o l d phase e q u i l i b r i u m i n v o l v i n g the gamma i r o n , Mn(Fe)0, Mn(Fe)S and l i q u i d o x y s u l f i d e
(£^), c o n s i d e r e d as
perhaps the most important u n i v a r i a n t e q u i l i b r i u m i n the quaternary
(Fe-O-S-Mn) system
has been estimated on the
premise o f an i d e a l l i q u i d o x y s u l f i d e s o l u t i o n , i . e . a + a + a _ + = i. They c l a i m t h a t s i n c e FeO FeS MnO MnS a
J
ideal
mixing behavior i s observed i n the FeO-FeS l i q u i d i n e q u i l i brium with gamma i r o n and MnO-MnS and s i n c e the FeO-MnO forms an i d e a l s o l u t i o n
then the i d e a l behavior c o n s i d e r e d i n
the FeO-FeS-MnO-MnS i s a reasonable assumption.
The behavior
of Mn i n i r o n under the above c o n d i t i o n s i s g i v e n i n F i g ure
(3) and Table ( I I ) . The r e a c t i o n scheme used t o e s t a b l i s h the phases i n -
v o l v e d i n such e q u i l i b r i a a r e :
M n 0
M n S
(s)
+
(s)
+
F e
F e
( s ) * FeO (s)
t
FeS
+ Mn
( 1 )
MnO
(s)
t MnO
MnS
( s )
t
M n S
+ Mn
( 1 )
(15)
( s )
(16)
( s )
< ) 17
(1)
(i)
( 1 8
I t has been e l u c i d a t e d t h a t i f a., _ = a.. _ s 1 MnS MnO
)
(be-
cause o f t h e i r low Fe i n s o l u t i o n and the Mn a c t i v i t i e s or atom f r a c t i o n s i n i r o n ) then an e x p r e s s i o n i s o b t a i n e d to r e p r e s e n t the Mn content o f s o l i d i r o n f o r t h i s
equili-
brium: 1 -N (K, + K_) ( — - — — ) + Mn
K-, + K. = 1 ; where N = atom
fraction.
By t a k i n g a., „ = 0.4 and a., = 0.5 a t the i n v a r i a n t MnS MnO 3
e q u i l i b r i u m l o c a t e d a t 900°C and u s i n g the above e x p r e s s i o n , the d o t t e d curve
i n Figure
(3) i s o b t a i n e d .
The Mn contents
o f gamma i r o n i n e q u i l i b r i u m w i t h s o l i d Mn(Fe)S and l i q u i d s u l f i d e , i n curve
(k) have been e s t a b l i s h e d u s i n g the "FeS"-
"MnS" phase diagram.
Raoult's
Law was assumed f o r the s o l u b -
i l i t y o f "FeS" i n "MnS". The curves
j and k show the s t r o n g e f f e c t o f oxygen on the
m e l t i n g p o i n t o f t h e o x y s u l f i d e phase i n the Fe-Mn-O-S (j) and
58 the
Fe-Mn-S (k) systems r e s p e c t i v e l y .
a l i q u i d phase l e s s than 10
I t i s seen t h a t w h i l e
(point A) i s formed when the Mn content i s % i n the former system ( j ) , the minimum Mn
content t o suppress the l i q u i d phase on the Fe-Mn-O-S system at
1200°C i s 1%.
The i n v a r i a n t e q u i l i b r i u m
(j)
which i n -
v o l v e s the gamma i r o n , Mn(Fe)0, Mn(Fe)S and the l i q u i d s u l f i d e phases
oxy-
i s the most important e q u i l i b r i u m i n the
Fe-Mn-O-S system by which the "hot s h o r t n e s s " can be avoided. Turkdogan and Kor have shown t h a t as long as the s t e e l cont a i n s Mn(Fe)0 and Mn(Fe)S i n e q u i l i b r i u m with the metal, a l i q u i d o x y s u l f i d e may
form between 900° and 1225°C
on the c o n c e n t r a t i o n o f Mn i n s o l u t i o n i n s t e e l . the
Mn-content i n s o l u t i o n
depending The h i g h e r
the h i g h e r i s the temperature
above which a l i q u i d phase i s p r e s e n t . (165 Experimental work performed by Kor and Turkdogan
'
166) have
clearly
shown
the
above
by
(0.34% Mn and 150 ppm S) a t about 900°C.
oxidizing
iron
They found a de-
p l e t i o n of Mn and accumulation of S i n the metal c l o s e t o the
scale-metal i n t e r f a c e .
These changes b r i n g about the
f o r m a t i o n of l i q u i d o x y s u l f i d e near the s u r f a c e above 900°C and the p r e c i p i t a t i o n of p y r r h o t i t e below 900°C. of
low i n t e r f a c i a l
tension
Because
the l i q u i d o x y s u l f i d e has been
seen to p e n e t r a t e i n t o the g r a i n boundaries i n the metal and the s c a l e .
They have a l s o observed t h a t most of the
l i q u i d phase i s found a t the s c a l e - m e t a l i n t e r f a c e . o b s e r v a t i o n s have a l s o been r e p o r t e d by other 1 6 9
)
These (130,
researchers
who have s t u d i e d more complex systems. Turkdogan and Kor who have taken as a b a s i s the i n -
formation and technique
used t o c o n s t r u c t f i g u r e
have extended t h e i r experimental table
( I I I ) , t o d e s c r i b e the Mn behavior
of other
(terminal) phase f i e l d s .
Mn-S-0 and Fe-Mn-O. low
and t h e o r e t i c a l
s o l u b i l i t y o f oxygen i n i r o n
the Fe-S-O, t h a t due t o the
stable deoxidation
u c t s i n commercial s t e e l s must be present. nary Fe-Mn-O-S system
data,
i n the presence
Namely
They have suggested
(4),
prod-
In the q u a t e r -
the Mn(Fe)0 has been taken as the
most s t a b l e oxide which i s p r e s e n t a t a l l temperatures o f interest.
As shown i n F i g u r e
(4),
the M n - p o t e n t i a l
i s given by two i n v a r i a n t s a t two temperatures, 900 and 1225°C: m-n-j
1) the i n v a r i a n t
g i v e n by the i n t e r s e c t i o n o f the
u n i v a r i a n t s which i s c o n s t i t u t e d by the gamma i r o n ,
Mn(Fe)0 as ( o x i ) , FeS, i^, "MnS" and the gaseous phase a t about 900°C and
2) the i n v a r i a n t given by the i n t e r s e c t i o n
of the u n i v a r i a n t s j , p and q.
The i n v o l v e d phases i n
t h i s e q u i l i b r i u m are an Fe/Mn s o l i d phase, "MnS", "MnO", l i q u i d oxide
(SL^) and l i q u i d metal
{l^) a t about
1225°C.
The most complete r e p r e s e n t a t i o n o f the phase changes i n c l u d i n g the l i q u i d , d e l t a and gamma i r o n developed Figure
by Kor and Turkdogan
(5).
The i n v a r i a n t VII
has a l s o been
^ and i t i s g i v e n i n r e p r e s e n t s the immiscible
r e g i o n i n the Fe-Mn-0 system
a t 1527°C.
I t i s important
to p o i n t o u t t h a t t h i s i n v a r i a n t was assumed t o be e q u i v a l e n t t o the Fe-0 m i s c i b i l i t y gap.
The phases i n e q u i l i -
brium a t V I I are d e l t a - i r o n , Mn(Fe)0, (£ ^) and l i q u i d metal previously described involved
"i^- •
system, a r e d e l t a - i r o n "MnO" a low s o l u b i l i t y product
oxide
The u n i v a r i a n t s V and VI were
i n Figure
i n the u n i v a r i a n t e
(Oxi), l i q u i d
(4).
The e q u i l i b r i u m phases
which are f o r the Fe-Mn-0 and l^-
Since
the "MnO" has
a t high M n - a c t i v i t i e s
(>1% Mn)
the e q u i l i b r i u m oxygen i n s o l u t i o n i s so low t h a t the s o l i dus
i n the Fe-Mn-0 i s almost e q u i v a l e n t
The
u n i v a r i a n t g was a l s o assumed e q u i v a l e n t
binary
system.
In g e n e r a l
g and f r e p r e s e n t liquid
t o the Fe-Mn system. t o the Fe-Mn
i t can be s a i d t h a t the u n i v a r i a n t s
the gamma t o d e l t a and the d e l t a t o
i r o n transformations
respectively.
The three
phase f i e l d s i n t h i s f i g u r e a r e the d e l t a - i r o n
new
+ Ox +
which i s l i m i t e d by the e - f u n i v a r i a n t s , the gamma-iron + Ox + £
2
which l i e s between
6 i r o n + Ox + g and f .
f';^ e u n i v a r i a n t s and the
which i s l o c a t e d between the u n i v a r i a n t s
The f - f ' u n i v a r i a n t s correspond t o the Fe-Mn-0
system a l r e a d y
described
i n Figure (4).
C r a f t s and H i l t y ' s w o r k '
2 9
' * ) on
i n c l u s i o n p r e c i p i t a t i o n diagrams representation
6 7
pseudo-equilibrium
has a l s o i n c l u d e d the
o f the Fe-O-Si-Mn-S system as a pseudo-
t e r n a r y , Fe(Mn, S i ) - 0 - S .
I t i s proposed t h a t t h i s
system
61
i s i n t e g r a t e d by metal-oxide,
m e t a l - s u l f i d e and s u l f i d e -
oxide m i s c i b i l i t y gaps which i n t e r s e c t themselves ucing an almost i s o m e t r i c i n t e r n a l t r i p l e
liquid
prodregion.
E q u i v a l e n t t o t h e i r proposed Fe(Mn)-0-S pseudo-ternary there are metal-oxide and metal s u l f i d e e u t e c t i c s which g i n a t e i n the metal corner and pass through f o l d immiscible
region.
ori-
the t h r e e -
These b i n a r y e u t e c t i c s c o n t i n u -
o u s l y decrease i n temperature u n t i l they reach the pseudotriple eutectic.
I t i s a l s o p o s t u l a t e d t h a t while the
above " t e r n a r y " i s u s e f u l t o r e p r e s e n t melts
silica
saturated
a pseudo t e r n a r y which c o u l d d e s c r i b e low S i t o Mn
r a t i o s should be d i f f e r e n t . fluxes s i l i c a
They c l a i m t h a t s i n c e the Mn
a s h i f t of the metal o x i d e - e u t e c t i c towards
the o x i d e c o r n e r o f the diagram would be expected.
I t has
a l s o been proposed t h a t s i n c e there i s s o l u b i l i t y between "MnS" and MnO-SiC^ may disappear
then the s u l f i d e - o x i d e m i s c i b i l i t y gap
and the pseudo-ternary e u t e c t i c would move
towards the oxide c o r n e r . granular higher
I t i s a n t i c i p a t e d t h a t more i n t e r -
s u l f i d e s are expected i n t h i s case than i n the
silicon
steels.
62
2.3.6.3
The Fe-Si-O-S-Mn
System
Other more complex systems have a l s o been g e n e r a l i z e d i n the m o d i f i e d p s e u d o - t e r n a r i e s , namely the F e ( S i ) - 0 - S , Fe(Mn, S i , h i g h A l ) - 0 - S , Fe(Mn, S i , low Al)-0-S and the Fe(Al,Ca)-0-S s y s t e m s
( 1 2 9 ,
1
6
7
)
.
The e x t e n s i v e e f f o r t d e d i c a t e d to c o n t r o l the "hots h o r t n e s s " problem i s c l e a r l y r e v e a l e d by C r a f t s and H i l t y (129) studies
.
I t i s seen t h a t the search f o r adequate de-
o x i d i z e r s which c o u l d promote the formation of h i g h m e l t i n g p o i n t phases has been the main aim.
The most common
f e a t u r e o f these diagrams i s t h a t the l a s t l i q u i d to solidify
i s a ternary e u t e c t i c .
as t h e i r authors have s t a t e d
These t e r n a r y diagrams
are n o t t r u e t e r n a r i e s and
hence "the r a t i o n a l i z a t i o n o f the problem i s i n t u i t i v e i n c h a r a c t e r and l i a b l e t o c o n s i d e r a b l e e r r o r , but should be h e l p f u l i n the e f f o r t t o b r i n g i n c l u s i o n s under c o n t r o l " . Silverman^ problem
a l s o concerned with the "hot s h o r t n e s s "
has s t u d i e d the Fe-Mn-Si-S-0
system.
He has
claimed t h a t i f the m e t a l l i c phase i s r e l a t i v e l y
neglected
the i n c l u s i o n chemistry o f the f i v e f o l d system can be reasonably w e l l r e p r e s e n t e d by the MnS-MnO-FeO-Si0 T h i s system was " s l i c e d " ,
as d e p i c t e d i n F i g u r e
t e r n a r y p l a n e s , shown i n F i g u r e are pseudo t e r n a r i e s FeO-MnO-MnS.
(7a-c).
2
system.
(6)
Two o f these
i n three planes
the 2FeO«Si0 -2MnO«Si0 -MnS and the
The t h i r d plane.
2
2
FeO-MnO•Si0 ~MnS 2
i s more d i f -
63
f i c u l t t o analyze because of i t s f i v e primary phase The
fields.
"A" area i s p r e s e n t i n the three planes and i t r e p -
r e s e n t s the "FeS" s t a b i l i t y
field.
The primary c r y s t a l l i z a t i o n 2MnO«Si0 -MnS-plane i s a s o l i d 2
2FeO«SiC>
2
and 2MnO«SiC> . 2
product on the 2FeO«SiC> 2
s o l u t i o n c o n s i s t i n g of
The second and t h i r d
products
are the FeS'-phase a t "A" and a mixture o f two i m m i s c i b l e l i q u i d s a t "B". as f o l l o w s : silicates
Silverman's o b s e r v a t i o n s can be summarized
1) The MnS-FeO-MnO•Si0
2
plane shows t h a t
liquid
e n r i c h e d i n "FeO" a l l o w more "MnS" i n s o l u t i o n
than l i q u i d
silicates
e n r i c h e d i n "MnO".
2)
This plane
a l s o shows t h a t "MnS" i s more s o l u b l e i n "FeO" than i n the l i q u i d
silicates
content o f the l i q u i d
i n t h i s plane.
s i l i c a t e decreases and the S i 0
t e n t i n c r e a s e s , the s o l u b i l i t y decreases.
3) As the "FeO"
o f "MnS" i n l i q u i d
2
con-
silicate
4) Samples from area "A" i n the MnS-FeO-MnO«Si0
2
plane suggest t h a t the "FeS"-phase s o l i d i f i e s as a e u t e c t i c a t about 910°C.
Silverman^
MnS i s f l u x e d by s i l i c a t e s
has concluded t h a t s i n c e
and oxides i n the planes s t u d i e d
then i n c l u s i o n s i n t h i s system are p a r t i a l l y and f i n i s h i n g
liquid
temperatures.
Van Vlack e t a l . ' s r e s e a r c h ' ^ i n l i n e with 3
work'^ ^ 9
at r o l l i n g
Silverman's
has s e m i - q u a n t i t a t i v e l y shown how the s i l i c o n
a f f e c t s the i n c l u s i o n chemical behavior i n v a r i o u s
systems.
64
In
t h i s work the m e t a l l i c phase n e g l e c t e d by Silverman i s
now
taken i n t o account.
Van V l a c k e t a l . ' s f i n d i n g s
be summarized i n the f o l l o w i n g p o i n t s :
can
1) I f s i l i c o n i s
added i n "small or moderate" q u a n t i t i e s to an Fe-S
alloy
u n d e t e c t a b l e changes i n i n c l u s i o n shape and composition w i l l be observed.
"FeS" was
the o n l y phase p r e s e n t .
Fe-S-0 a l l o y
s i l i c o n was
a l s o added.
n o n - m e t a l l i c phases were p r e s e n t . in
One
In t h i s a l l o y
2
3) I f s i l i c o n
i s added to a t e r n a r y Fe-Mn-S a l l o y whose Mn:S i n c l u s i o n s remain
(about
1200°C).
were observed.
solid at austenitic
ratio
(Mn,Fe)S
4) I f s i l i c o n and oxygen were added to (they generate the Fe-Mn-Si-S-0 system)
a l i q u i d phase s i l i c e o u s i n c h a r a c t e r was
observed.
a s s o c i a t e d with s a t u r a t e d MnS.
observed t h a t i f the S i : 0 r a t i o was
This
They a l s o
l a r g e r than t h a t
r e q u i r e d to form Si02 then a g l a s s y type of i n c l u s i o n formed d u r i n g c o o l i n g . was
smaller
On the o t h e r hand, i f t h i s
the g l a s s y phase disappeared.
a l s o observed t h a t i f oxygen was content then the l i q u i d
i n excess
composition was
phase was
was
ratio
Van V l a c k e t a l . of the
silicon
s h i f t e d from the
s i l i c e o u s range to a more o x i d i z i n g compositions. latter
was
temperatures
G l o b u l a r i n c l u s i o n s of the type
the Fe-Mn-S system
l i q u i d phase was
two
phase was e n r i c h e d
"FeS" and the other e n r i c h e d i n " S i 0 " .
3:1,
2) In an
This
s i m i l a r i n nature to t h a t encountered i n
the Fe-Mn-O-S-system.
T h i s f i n d i n g was
a l s o observed by
65 H i l t y and C r a f t s <
1 2 9
'
l 6 7 )
.
Van V l a c k e t a l . ' s work based on t h e i r own and a l s o on Silverman's work have
illustrated
the
(MnS-MnO-FeO-Si0 ~system)
phase
2
changes
l i q u i d phase u s i n g F i g u r e s (8 a-b) MnS-MnO-FeS-Si0 -system. 2
in
the
which r e p r e s e n t the
I t has been p o i n t e d out t h a t
although t h i s system i s q u a l i t a t i v e
i n c h a r a c t e r and
m e t a l l i c phase i s " t e m p o r a r i l y " ignored used
findings
the
approach
i n t h e i r experimental work indeed d e s c r i b e s phase
changes t o which the i n c l u s i o n s are s u b j e c t e d . et a l . d
3 (
^
have proposed
e n r i c h e d composition temperature
ranges)
ary e q u i l i b r i u m .
(C)
Van
Vlack
t h a t s i n c e the l i q u i d phase
v a r i e s from a s i l i c a e n r i c h e d composition
(A) to a
then the quaternary
can be r e p r e s e n t e d
MnO
(at h i g h
by a Mn0-Si0
2
Once the s o l u b i l i t y product f o r S i 0
the melt i s reached
the excess s i l i c o n goes i n t o
i n the metal and the excess oxygen r e a c t s with Mn MnO
the
(and l i m i t e d l y with i r o n to produce
FeO).
binin
2
solution to
produce
These r e -
a c t i o n products w i l l generate a composition B i n F i g u r e which f l u x e s the MnS, Figure
as i n d i c a t e d by Silverman's work i n
(76).
The r e s u l t i n g l i q u i d w i l l be composed of 50 % "MnS" about
(8)
1320°C
of "MnS" Rhodonite
at
and hence, d u r i n g s o l i d i f i c a t i o n a mixture
and a s i l i c a t e
either tephroite
(Mn0«Si0 ) depending o
(2MnO*Si0 ) or
on the MnO:Si0
2
9
ratio
will
p r e c i p i t a t e a t low a u s t e n i t i c temperature. have a l s o observed
Van Vlack e t a l . ^
and q u a l i t a t i v e l y p r e d i c t e d with
1 3 0
this
s i m p l i f i e d model t h a t the l i q u i d phase becomes a s i l i c e o u s g l a s s i f the l i q u i d c o n t a i n s an e x c e s s i v e amount o f s i l i c o n . Under t h i s c o n d i t i o n a l i q u i d
which i s r a p i d l y
can remain as a " g l a s s y " i n c l u s i o n a t room Composition
C
i n Figure
(8a)
solidified
temperature.
i s a t t a i n e d i f the oxygen
content exceeds the s i l i c o n content.
Under t h i s
circumstance
the l i q u i d phase d i s s o l v e s a c o n s i d e r a b l e amount of "MnS" and the excess oxygen may r e a c t with some Mn from the MnS. I t i s a l s o b e l i e v e d t h a t some o f the i r o n i s t r a n s f e r r e d i n t o the l i q u i d t o balance the s u l f u r . compositions
are sketched
i n Figure
These s h i f t s i n
(9). In subsequent
s o l i d i f i c a t i o n stages the f o r m a t i o n o f FeS i s expected. 2.3.7
Oxides
2.3.7.1
Aluminates
Experimental
and t h e o r e t i c a l s t u d i e s on the A l - 0 e q u i l i -
brium have been t r a c e d i n the l i t e r a t u r e s i n c e e a r l y i n t h i s century.
The d i f f i c u l t i e s presented i n determining the
thermodynamic e q u i l i b r i u m a r e o b v i o u s l y observed
i n F i g u r e (10).
This summarizes the e q u i l i b r i u m v a l u e s found by s e v e r a l researchers
( 1 7
° "
1
8
3
)
a t 1600°,
1800° and 1900° C.
l a t e s t e q u i l i b r i u m v a l u e s g i v e n by Gustafsson and
The
Melberg^ ^
.. - work , from s e v e r a, are summarized l r e s e a r c h e r s (176, 177, u
179—18 2) Gustafsson and Melberg
c l a i m t h a t t h i r d order
17
67 polynomial (regression) parameters should be i n c l u d e d i n the determination
of the i n v o l v e d a c t i v i t i e s where there e x i s t s
s t r o n g oxygen-metal
(Al or Ca)
interaction.
Their tech-
nique u n f o r t u n a t e l y o n l y works when b i n a r y oxygen-aluminum or oxygen-calcium systems are c o n s i d e r e d .
Sims^ ^ 9
has
p o i n t e d out t h a t the observed d i s c r e p a n c i e s can be r e c o n c i l e d on the b a s i s t h a t the oxide phase i n e q u i l i b r i u m with Fe-O-Al i s not pure A^O^
but i n s t e a d FeO'A^O^ and
t h i s s p i n e l phase w i l l always be p r e s e n t .
the
hence
Other s t u d i e s on
t h i s matter have shown t h a t by d e o x i d i z i n g a melt with aluminum at s e v e r a l l e v e l s served: melt
three g e n e r a l stages can be
1) I f i n s u f f i c i e n t aluminum i s added to an
ob-
iron
( i . e . there i s an excess o f oxygen i n s o l u t i o n ) f e r r o u s
oxide
and h e r c y n i t e should be p r e c i p i t a t e d
as d i c t a t e d by
(112-113) the FeO-Al^O^ e q u i l i b r i u m diagram mediate A l - l e v e l s *
(about
.
.
0.4-0.5% Al) a mixture of •
-a-
4-
^d83,
n i t e and alumina i s p r e c i p i t a t e d
184) '
n i t e phase w i l l be the major phase present high Al-contents found'
8 3
'
1 8 4 )
F a r r e l l ^^5)
steel
_. .
hercy-
.
The and
inter-
hercy3) At
i n an i r o n melt almost pure A^O^
is
.
According and
2) At
to the d e o x i d a t i o n diagram proposed by a
f n u
v
kin
e <
3 carbon or low
alloy
d e o x i d i z e d with aluminum, the s o l i d i f i c a t i o n of
m e t a l - o x i d e - s u l f i d e system s t a r t s by s o l i d i f y i n g crystals
(A^O^) i n s t e a d of metal.
As the
Hilty
oxide
temperature
the
68 decreases
s o l i d i f i c a t i o n o f metal and some oxide
takes
p l a c e s i m u l t a n e o u s l y u n t i l the metal-oxide b i n a r y e u t e c t i c i s reached.
S o l i d metal, s o l i d oxide and a phase r i c h i n
sulfide w i l l p a r t i a l l y precipitate i n further stages.
solidification
The remaining phase r i c h i n s u l f i d e w i l l
precipitate,
finally
i n the same manner as the Fe-O-S system, as
the temperature
approaches the t e r n a r y e u t e c t i c .
McLean
(112-113) and coworkers
who have s t u d i e d the thermodynamic
behavior of the Fe-O-Al system c l e a r thermochemical
have found t h a t there a r e
c o n d i t i o n s under which e i t h e r
A ^ O ^ o r h e r c y n i t e a r e formed.
In t h i s work
pure
i t has been
p o i n t e d o u t t h a t t o p r e v e n t the f o r m a t i o n o f h e r c y n i t e the oxygen a c t i v i t y a t 1600°C.
should be reduced
to l e v e l s below 0.058
A c t i v i t i e s o f oxygen equal t o 0.058 r e p r e s e n t
the l o c a t i o n o f the (A^O^-FeO• A^O^) t r a n s i t i o n p o i n t . S e v e r a l r e s e a r c h e r s have a l s o agreed
that k i n e t i c
fac-
t o r s a r e i n v o l v e d i n the FeO-FeO'A^O^-A^O^ p r e c i p i t a t i o n sequence.
T o r s e l l and O l e t t e ^
i n the submicron Hammar's'^^
1 2
^
s i z e s one second
have observed
a f t e r aluminum was added.
t h e o r e t i c a l p r e d i c t i o n s a r e i n agreement with
T o r s e l l * s and O l e t t e s f i n d i n g s . 1
Hammar s e x p e r i m e n t a l 1
work, however, d i d not f o l l o w such a b e h a v i o r . t h a t the f i r s t
*
inclusions
t r a n s f o r m a t i o n i s g i v e n by
He c l a i m s
FeO'A^O^dT
FeO'A^O-jCs) and i t i s very dependent o f the i n c l u s i o n
size.
T h i s t r a n s f o r m a t i o n has been t r a c e d 17 seconds a f t e r the Al-addition.
L a t e r d e o x i d a t i o n stages t r a n s f o r m the
F e O ' A ^ O ^ s ) t o almost pure A^O^.
The mechanisms proposed
to c o n t r o l these t r a n s f o r m a t i o n s a r e the simultaneous
dif-
f u s i o n o f oxygen from the p a r t i c l e and d i f f u s i o n of aluminum i n t o the p a r t i c l e .
Since, Hammar s r e s u l t s were not i n 1
agreement w i t h h i s theory
i t was proposed t h a t i n c l u s i o n s
may have a p e r i p h e r a l case of FeO-A^O^Csf which enclose the FeO « A 1 0 ( i f 2
thus d i f f u s i o n o f A l i n t o l i q u i d
3
ates was prevented.
precipit-
T h i s p r o p o s a l was indeed c o r r e c t ,
„ . ,. (184, 186-188) , . . , s i n c e EPMA-studies ' showed an e n r i c h e d A l - c a s e p n u
surrounding state.
the FeO'Al^O^ which was o r i g i n a l l y i n l i q u i d
Another i n t e r e s t i n g o b s e r v a t i o n t r a c e d by Hammar
was t h a t the FeO-phase was not detected one second a f t e r the (18 7) a d d i t i o n o f aluminum. t h a t a sharp decrease
Wadby and S a l t e r i n oxygen
have noted
as w e l l as pure alumina
i n c l u s i o n s a r e seen w i t h i n a p e r i o d o f 30 seconds. and D r i o l e s t u d i e s '
8 9
Cremer
^ on the i n f l u e n c e o f e l e c t r o m a g n e t i c
s t i r r i n g and the removal of i n c l u s i o n s , have e s t a b l i s h e d t h a t a f t e r 20 seconds o f the aluminum a d d i t i o n p a r t i c l e s were grown i n s i d e c l u s t e r s .
spherical
Hammar has a l s o ob-
served r e l a t i v e l y l a r g e FeO-A^O^ i n c l u s i o n s transforming t o pure A ^ O ^ i n t h e p e r i o d o f one t o three minutes a f t e r the a d d i t i o n o f A l i n t o the molten i r o n . * F e O « A l 0 i s not intended t o i n d i c a t e s t o i c h i o m e t r y and i n f a c t the F e O « A l 0 ( s ) would have a d i f f e r e n t A l 0 / F e O r a t i o 2
3
2
than
3
FeO«Al 0 (1). 2
3
2
3
70 Straube and P l o c k i n g e r ^ '
1 9 1
^
who
have s t u d i e d the p r e -
c i p i t a t i o n of alumina i n melts c o n t a i n i n g some manganese, have s t a t e d t h a t the primary d e o x i d a t i o n p r o d u c t s are lean i n alumina and c o n t a i n e s s e n t i a l l y Mn-oxides.
The
A^O^-
content i n c r e a s e d very r a p i d l y d u r i n g the next few u n t i l the composition reached t h a t of the s p i n e l A^O-j.
I t was
partially
seconds
(Fe,Mn)0«
observed t h a t i n c l u s i o n s were i n a f l u i d or
f l u i d state.
(18 7) Waudby e t a l . have a l s o agreed (190 191)
with Straube and P l o c k i n g e r ' s f i n d i n g s
'
.
Waudby
(187) et a l . noted t h a t once the s p i n e l type was formed i t r e a c t e d with A l i n f u r t h e r stages to produce i r r e g u l a r h i g h l y aluminous
i n c l u s i o n s which e n c l o s e d i r o n .
Morgan
(188) et a l .
who
have s t u d i e d the d e o x i d a t i o n e f f e c t on the
i n c l u s i o n chemistry have a l s o observed s i l i c a t e d e o x i d a t i o n products p e r i p h e r a l l y p r e c i p i t a t e d on A^O^ phases.
or FeO'A^O^
Waudby's and S a l t e r ' s experiments were performed
a t s e v e r a l A l - d e o x i d a t i o n l e v e l s , namely 0.05, and 0.5 wt.
%.
0.15,
0.3
T h e i r samples were quenched and heat t r e a t e d
afterwards f o r 7 days at 1150°C.
Under the above experimental
c o n d i t i o n s , i t was
found t h a t by d e o x i d i z i n g the i r o n
melt w i t h 0.5%
i n as c a s t c o n d i t i o n duplex h e r c y n i t e -
Al
alumina i n c l u s i o n s were observed.
A f t e r the heat t r e a t -
ment, however, i n c l u s i o n s d i s s o l v e d more oxygen u n t i l hercynite •has
equilibrium
composition
was
a l s o i d e n t i f i e d s i m i l a r compounds,
reached.
the
Hammar
(Fe,Ni) 'A^O^,
71 i r r e s p e c t i v e of the quenching time.
The o u t s t a n d i n g c r y s (183)
t a l l o g r a p h i c work performed by Watanabe and coworkers (192)
along the l i n e s of Sloman's and Evan's work inum d e o x i d i z e d melts
has c l e a r l y r e v e a l e d the nature of (183)
the t r a n s f o r m a t i o n i n the Fe-O-Al system. was
on alum-
T h e i r work
c a r r i e d out by m e l t i n g l e v i t a t e d samples under a p u r i -
f i e d Ar-atmosphere and s o l i d i f i e d under three cooling conditions.
The 0:A1
r a t i o was
different
1.45 which i s c l o s e
to the s t o i c h i o m e t r i c r a t i o found i n the A 1 0 2
3
phase.
Ex-
t r a c t e d i n c l u s i o n s from the m e t a l l i c m a t r i x were a n a l y z e d by X-ray (powder) d i f f r a c t i o n u s i n g Cr-Ka r a d i a t i o n . r e s u l t s showed t h a t s i n c e the F e O « A l 0 2
3
phase had
Their
inter-
p l a n a r spacing approximately e q u i v a l e n t t o the y ' - A ^ O ^ a ' ) then the y'-A^O^ was though to o r i g i n a t e from the s p i n e l phase, as f o l l o w s : F e O A l 0 -•• Y ' - A l 0 ( a ' ) -> y - A l 0 ( a ) l
2
3
The f i n a l Y
, -
2
A1 0 2
3
2
3
3
+
Y'-AljOg
i s o b t a i n e d a c c o r d i n g to the degree of
simultaneous m i g r a t i o n of i r o n and aluminum out and the o r i g i n a l F e O « A 1 0 2
3
phase.
s i n c e i n the p r o c e s s o f K - A 1 0 2
phase d i s a p p e a r s and Y ' - A 1 0 2
i s d e r i v e d from Y ' ~ 2 ° 3 ^ • a 1
i n t h e i r experiments a-Al 0 . 2
3
( b )
The a - A l 0 2
3
I t was 3
a l s o proposed t h a t
formation the F e 0 « A l 0 2
3
(b) shows up, then K - A 1 0 2
T n
e
third cooling
produced Y ' - A 1 0 2
3
into
phase was
3
3
condition
(b), 0 - A l O 2
3
and
the more abundant phase.
Hence, the o v e r a l l t r a n s f o r m a t i o n sequence
was
proposed
to be: FeO-Al 0 2
3
+ y ' - A l 0 (a') 2
-* 6 - A l 0 2
2
Since y' -A1 C> was was
A 1
+ ^' ~ 2 ° 3 A l
"*" * ~ 2 ° 3
( b )
A l
3
found i n a l l the c o o l i n g c o n d i t i o n s , i t
3
suggested t h a t the r a t e of t r a n s f o r m a t i o n from t o y '-A1 C> i s f a s t and t h a t the y '-A^C^
FeC"Al 0
3
a-Al 0
is relatively
2
2
3
2
3
2
studied.
(b) to
slow.
The morphology of Al C>
who
°3 > (a
2
a-Al 0 .
3
2
y'
3
3
type of i n c l u s i o n s has been widely
T o r s e l l and O l e t t e ^
1 2
^
were the f i r s t r e s e a r c h e r s
proposed t h a t i n a d d i t i o n to a l o c a l s u p e r s a t u r a t i o n , a
continuous d i f f u s i o n of aluminum and oxygen i n t o these r e g i o n s i s r e q u i r e d t o p r e c i p i t a t e the d e n d r i t i c type of inclusions.
Under these c o n d i t i o n s
t h a t d e n d r i t i c alumina was
i t has been proposed
a r e s u l t of a homogeneous n u c l e (189)
ation.
Cremier and D r i o l e
have suggested t h a t
alumina i n c l u s i o n s are products of heterogeneous T h i s type grows i n areas low i n d e o x i d i z e r .
spherical
nucleation.
Torsell
and
O l e t t e have a l s o proposed t h a t c l u s t e r s are not formed i n r e g i o n s e n r i c h e d i n aluminum. c l u s t e r s of alumina
I t i s also indicated
that
which are very commonly observed i n
aluminum d e o x i d i z e d melts
are formed due to c o l l i s i o n of
s i n g l e p a r t i c l e s as a r e s u l t o f thermal, mechanical or e l e c t r o m a g n e t i c a g i t a t i o n of the molten bath.
Cremier and
D r i o l e have concluded t h a t the importance
of magneto-hydro-
dynamic phenomena on the k i n e t i c s of d e o x i d a t i o n o f s t e e l i s mainly a p h y s i c o - c h e m i c a l p r o c e s s , i . e . shape and type of i n c l u s i o n s i n the Fe-Al-0 system are c o n t r o l l e d by the l o c a l flow and a c t i v i t y c o n d i t i o n s .
Steinmetz
et a l . '
8
4
^
who have s t u d i e d the above system under s e v e r a l c o n d i t i o n s ( i n d u c t i o n - s t i r r i n g , c o n v e c t i o n - f r e e and i n the gas phase) have a l s o agreed with t h a t p r o p o s a l .
They found t h a t w i t h
an oxygen supply h i g h enough compared to the supply of r e s p e c t i v e elements, cipitate.
l i q u i d phase o f h i g h F e O - a c t i v i t y p r e -
I t i s a l s o suggested
t h a t t h e i r growth i s a l -
most s t r i c t l y c o n t r o l l e d by the flow c o n d i t i o n s a t which the g i v e n r e g i o n i s s u b j e c t e d .
They c l a i m t h a t the s p h e r i -
c a l contours become u n s t a b l e and change t o " r o s e t t e s " and f i n a l l y t o d e n d r i t e shape as the " p h a s e - s p e c i f i c concent r a t i o n s " or " m a t e r i a l s flow" are changed.
The degree o f
l o c a l d e o x i d a t i o n and the type and shape of oxides and s u l f i d e s have a l s o been shown i n t h i s work. o f p l a t e - l i k e alumina
and the MnS
The a s s o c i a t i o n
I I I are g i v e n where the
l o c a l c o n c e n t r a t i o n of aluminum i s h i g h e r
(2 t o 3%).
At
i n t e r m e d i a t e d e o x i d a t i o n (0.25-1.0% A l ) a mixture of coarse s u l f i d e type I I and a c i c u l a r oxide i n the presence of s u l f i d e are found.
Between these two ranges
a mixture of MnS
I I and I I I i s expected
aluminum contents
(1.25-1.75% A l ) and a t very low
(0-0.25%) o x y s u l f i d e s , primary
I I and d e n d r i t i c oxides may be formed. Steinmetz
s u l f i d e s , type (184) et a l . have
74 a l s o proposed the mechanism a l r e a d y d e s c r i b e d f o r s u l f i d e s for
the alumina, i . e .
1) d e n d r i t e s and coarse g l o b u l a r
hercynite at high i n i t i a l
oxygen contents,
2)
initial
g l o b u l a r to " c o r a l " shape alumina f o r low oxygen contents under very d r a s t i c c o o l i n g c o n d i t i o n s . gen o n l y d e n d r i t i c A ^ O ^
i s expected.
Above 0.019% oxySlower growth i s r e -
q u i r e d f o r the b r a n c h e d - i r r e g u l a r shape alumina type.
They
have a l s o proposed t h a t under low i n i t i a l oxygen contents r a d i a t e d - c r y s t a l l i n e to compact n i t r i d e s are grown on the alumina. Braun e t a l . ^ stirring
l 9 3
^ , who have s t u d i e d the i n f l u e n c e of
time, s t i r r i n g r a t e and i n i t i a l oxygen i n i r o n melts
have c l a s s i f i e d the morphology of the alumina i n c l u s i o n s f i v e types, namely:
d e n d r i t i c , faceted,
s p h e r i c a l and c l u s t e r s . not
into
plate-like,
I t was found t h a t these types are
e x c l u s i v e l y found as a unique type but as a mixture f o r
a g i v e n s e t of experimental c o n d i t i o n s .
They have a l s o
observed t h a t i n c l u s i o n s which i n t e g r a t e the c l u s t e r s change from d e n d r i t i c to p l a t e - l i k e shapes a t low oxygen contents t o s p h e r i c a l a t high oxygen l e v e l s . Olette et
( 1 2 0 )
al. (
l 9 5
^
,
Braun e t a l .
(
1
9
3
)
,
T o r s e l l and
Okohira e t a l .
and Cremer and D r i o l e ^
1 8 9
^
(
1
9
4
)
,
Ooi
have agreed on the
mechanism by which alumina c l u s t e r s are formed, i . e . c o l l i s i o n and
coalescence o f s i n g l e p a r t i c l e s as a r e s u l t of f l u i d
motion i n the melt.
Ooi e t a l . 's s t u d i e s on n o n - s t i r r e d
75 and s t i r r e d melts
have shown t h a t under the former
condi-
t i o n d e n d r i t i c and alumina c l u s t e r s are the major t y p e s . S p h e r i c a l i n c l u s i o n s were almost absent. type o f experiment produced
Their
second
1) i n c l u s i o n s l a r g e r than
20 ym i n diameter with adhered p a r t i c l e s of about 0.5 2.0
-
ym i n diameter and 2) c l u s t e r s composed of v e r y small
s p h e r i c a l i n c l u s i o n s with the maximum diameter o f which about 2 ym.
Ooi e t a l . ^
1 9
~^
have c o r r o b o r a t e d the
was
"collision
coalescence and s i n t e r i n g theory" on the f o r m a t i o n o f alumina c l u s t e r s by measuring
the neck growth and assuming
volume
d i f f u s i o n as the c o n t r o l l i n g mechanism. H i l t y and C r a f t s ^
1 6 7
^
have found t h a t 0.5%
Mn
in liquid
i r o n enhances the A l - d e o x i d a t i o n power as much as f i v e times. McLean^
113
^
suggests t h a t Mn
lowers the oxygen and
the A l c o n c e n t r a t i o n f o r u n i v a r i a n t t r a n s i t i o n from Al 0 2
3
to
Sims^ ^ 9
h l ^ O ^ i
as suggested by P l o c k i n g e r
raises (Fe, Mn).
) and Waudby ^
has s t u d i e d the dual A l - S i d e o x i d a t i o n of melts
(0.4% A l and 0.5%
S i ) . He noted t h a t the i n c l u s i o n s are
c h a r a c t e r i s t i c o f those e x c l u s i v e l y d e o x i d i z e d with A l and s t r o n g e r d e o x i d a t i o n was Al-deoxidized.
reached than when the melt i s
Sims p o i n t s out t h a t i f s i l i c o n i s added
b e f o r e o r with the aluminum
one minute
o b t a i n the maximum c l e a n l i n e s s studies^
l 9
^
•
i s s u f f i c i e n t to
Waudby s and Wilson's 1
on p r o g r e s s i v e d e o x i d a t i o n o f iron-oxygen
melts by A l - S i a l l o y s
(0.3, 0.6
and 0.9%
A l - S i ) . have
1 8 7
\
76 found t h a t because o f the much more r a p i d f o r m a t i o n of alumina compared with s i l i c a ,
the alumina c o n t e n t o f
the i n c l u s i o n s p r o p o r t i o n a l l y i n c r e a s e with the A l - S i addition.
Hence, they concluded t h a t the dual
(Al-Si)
d e o x i d i z e r behaves i n a complex manner only when a melt is
(Al-Si) deoxidized i n r e l a t i v e l y c r i t i c a l
additions.
D e o x i d a t i o n of melts by l a r g e q u a n t i t i e s of A l - S i behave as c o n v e n t i o n a l a d d i t i o n s o f the s t r o n g e s t element deoxidizer.
As proposed by S i m s ^ ^ 9
c l u s t e r s i s expected.
i n the
formation o f alumina
G a t e l l i e r et a l . '
9
^
i n agree-
ment with Waudby's and Wilsons's and Sim's f i n d i n g s have noted t h a t i f aluminum i s f i r s t l y metal bath the s i l i c o n remains
i n t r o d u c e d t o the
as a p a s s i v e d e o x i d i z e r .
G a t e l l i e r e t a l . ' s t h e o r e t i c a l c o n s i d e r a t i o n have shown t h a t t h r e e d i f f e r e n t b e h a v i o r s might be observed, a t 1600°C: 3/4 1) I f the a / A l ° ° / alumina should be p r e c i p i t a t e d , 3 /4 2) i f a / A l " 1400/ pure SiC> p r e c i p i t a t e s and 3) i n the 3/4 a
s
6
0
i
a
2
i n t e r m e d i a t e range o f these s t a b i l i t y ranges a A
l
(600 S a c
/
i 1400), m u l l i t e i s the most s t a b l e phase.
2.3.7.2
Calcium aluminates
Although the use o f c a l c i u m as a d e o x i d i z e r and des u l f u r i z e r i n i r o n melts has become an a t t r a c t i v e
alternative
(198) s i n c e S p o n s e l l e r ' s and F l i n n ' s r e s e a r c h the foundry i n d u s t r y ,
i t s use i n
to d e s u l f u r i z e , i n o c u l a t e and to
77
enhance t h e s p h e r o i d i z a t i o n o f g r a p h i t e early has of
i n this
century.
been c o n s i d e r e d research
Sponseller's
t h a t has c o n c l u s i v e l y c o n t r i b u t e d
Al,
C/ N i , S and Au.
liquid
iron.
i t s i n t e r r e l a t e d e f f e c t s with
calcium
in liquid
1880°K.
At t h i s
1.87
-
( l 9 8 )
In
light
other
of Sponseller's
( 1 4 4
'
reducing Al,
1
5
5
'
1
9
7
'
9
9
_
2
0
2
) .
i t s vapour pressure
i s 0.032% a t
a t about
t o improve
1780°K
W
o
r
k
( 1 9 9 )
.
inten-
i t s solubility,
respect
i t s vapour p r e s s u r e 1
elements, i . e .
and F l i n n ' s f i n d i n g s
t o overcome t h e p r o b l e m o f d e n s i t y w i t h
years
also
i t s vapour p r e s s u r e i s
has been d e d i c a t e d
i r o n and t o d i m i n i s h
to the develop-
the s o l u b i l i t y of
atm. and i t b o i l s
( 1 9 9 )
pieces
They have
i r o n under p r e s s u r e
temperature
1.645
sive research
They f o u n d t h a t
since
and F l i n n ' s work
a s one o f t h e most f u n d a m e n t a l
ment o f t h e C a - t r e a t m e n t o f l i q u i d studied
has been used
to liquid
i n the l a s t
20
has been devoted t o
by a l l o y i n g
i t with
Ba o r a s m u l t i p l e m i x t u r e s o f v a r i o u s
S i , C,
elements,
CaAlSi,
(9 5) CaAlSiFe, the
CaAlBaFe, e t c .
who
has reviewed
s t a t e o f t h e a r t o f oxygen and i t s r e a c t i o n s w i t h
ferent deoxidizers, of
Philbrook
has d e s c r i b e d
C a - t r e a t m e n t up t o 19 77.
Sweden, t h e F i r s t Metallurgy
the current
dif-
understanding
I n June o f t h e same y e a r i n
I n t e r n a t i o n a l C o n f e r e n c e on I n j e c t i o n
took p l a c e .
In the proceedings o f t h i s
a new d i r e c t i o n on t h e d e o x i d a t i o n
meeting^ *^
practice i s clearly
9
seen.
78
Thermodynamic and k i n e t i c theory t o support the e x p e r i mental work, f i n a l l y g i v e c r e d i t t o the d e o x i d a t i o n capab i l i t y o f Ca-bearing m i x t u r e s .
The second conference on (97)
i n j e c t i o n p r o c e s s e s a l s o h e l d i n Sweden more, r e c o n f i r m s the advantages
i n 1 9 8 0 , once
( d e o x i d i z e r and d e s u l f u r -
i z e r ) and disadvantages (low y i e l d ) of i t s usage. i n a more r e c e n t communication
Holappa^ ^ 98
a l s o p r e s e n t s an o v e r a l l
view of the Ca-treatment i n the l a d l e . In a d d i t i o n t o the p r e v i o u s l y d e s c r i b e d advantages o f the usage o f Ca-bearing mixtures
the major a t t r i b u t e s o f
t h i s d e o x i d a t i o n p r a c t i c e i n terms o f i n c l u s i o n s a r e : 1)
the e l i m i n a t i o n o f c l u s t e r s and angular alumina i n -
c l u s i o n s which otherwise would be formed from the A l deoxidation p r a c t i c e ' ^ 4
1 6 8 ) ^ ) ^he t r a n s i t i o n o f 2
MnS type I I t o MnS I I I o r p e r i p h e r a l c a l c i u m s u l f i d e around C a - a l u m i n a t e s
( 1 4 4
'
1 4 5
'
1 4 7
'
1 6 8
'
1 9 7 ]
.
The presence
of the MnS I I I has been observed a t r e l a t i v e l y low Cacontent
(< 20 ppm) and the "CaS" a t much h i g h e r Cat
O A
,
.
,^
(157, 158, 168)
_ .
,
content (> 20 ppm) i n the melt ' • . I t has a l s o j. * • *.u T * . (146, 159, 160) _ . been r e p o r t e d i n the l i t e r a t u r e • • that i n a d d i t i o n t o the above c h a r a c t e r i s t i c s
TJ
e x c e l l e n t de-
79
(96—98) oxidation, desulfurization (157,
ation
158, 204)
'
'
processes. added"to ^ ( 2 0 4 ) t
and some dephosphoriz,
,
,
i
.
.
. .
a r e reached by the c a l c i u m i n j e c t i o n
Gaseous
and m e t a l l i c c a l c i u m has been
the s t e e l stream d u r i n g tapping ^ , ' p l u n g i n g ' 8
o
s n
r
ooting
i t as b u l l e t s i n t o
the metal bath.
When m e t a l l i c c a l c i u m i s added to the melt i t t u r n s i n t o vapour bubbles which r a p i d l y r i s e t o the metal s u r f a c e and subsequently r e a c t v i o l e n t l y with the s l a g and the oxygen i n the a i r producing c o n s i d e r a b l e f l a r e , s p l a s h i n g and fumes.
B u r n - o f f and r e a c t i o n s with the s l a g and l i n i n g
m a t e r i a l s reduce the y i e l d o f the Ca-treatment t o about 10-50% (
l
9
7
'
2
0 5 )
m
Thus, new means t o u t i l i z e c a l c i u m as
calcium-composite wires
(97)
o r i r o n tube c o n t a i n i n g Ca(155)
a l l o y s have been developed techniques o b v i o u s l y
.
In a d d i t i o n to these
the simultaneous d e o x i d i z e r a d d i t i o n s
(as mixtures of d e o x i d i z e r s with o r without s l a g s ) e i t h e r top or bottom blown i n t o the c o n v e r t e r have a l s o been industrially
practiced.
I t i s a general p r a c t i c e
in
c o n v e n t i o n a l steelmaking, to f i r s t l y d e o x i d i z e e f f i c i e n t l y the melt w i t h A l and secondly by the c a l c i u m t r e a t m e n t ^ . Regarding the mechanical p r o p e r t i e s , i t i s g e n e r a l l y accepted t h a t g l o b u l a r i n c l u s i o n s improve (92
of the mechanical p r o p e r t i e s
the a n i s o t r o p y
95-97)
'
. I t has been pro-
posed as a p r i o r i r u l e s t h a t e i t h e r a Ca:S r a t i o g r e a t e r than 1 . 2 5
(
1
5
3
)
or more than 2 0 - 3 0
ppm of C a
( l 5 1 )
i s required to
80 achieve the t r a n s i t i o n from the alumina
(clusters) to
c a l c i u m aluminates and the MnS I I t o a t l e a s t MnS I I I or t o p e r i p h e r a l c a l c i u m s u l f i d e s .
Gatellier et a l . '
have found i n experimental melts t h a t a complete of A l 0 2
3
(144) 9
7
^
elimination
as c l u s t e r s i s a t t a i n e d when the 0:Ca r a t i o
(wt %) i n i n c l u s i o n s i s about to be independent
three.
T h i s r u l e was found
of the i n g o t chemical composition.
(209) Faulring et a l .
have r e p o r t e d t h a t the n o z z l e b l o c k -
age by the aluminate type o f i n c l u s i o n s i s e l i m i n a t e d when the Ca:Al r a t i o
( i n wt.%) i s g r e a t e r than 0.14.
This
r a t i o r e p r e s e n t s compositions which c l o s e l y correspond (133) to the CaO • 2 A 1 0 2
3
phase.
gested t h a t "burning"
Boldy e t a l .
have sug-
which occurs even i n ESR-ingots
where the s u l f u r content i s u s u a l l y thousandths
of a
p e r c e n t might be e l i m i n a t e d o n l y by r a r e - e a r t h or Catreatments.
These r e s e a r c h e r s have r e p o r t e d t h a t the
problem was e l i m i n a t e d , i n c o n v e n t i o n a l p r a c t i c e
:
when
manganese s u l f i d e s were completely transformed t o CaS. (157 158) Japanese r e s e a r c h e r s drogen
'
who have s t u d i e d the hy-
induced c r a c k i n g (HIC) on p i p e l i n e s t e e l s
have
concluded t h a t a Ca:S r a t i o g r e a t e r than or equal t o 1.5 i s r e q u i r e d t o prevent the r e o x i d a t i o n of Ca d u r i n g the teeming
o f the melt.
t a n t or t o t a l l y
Under these c o n d i t i o n s high r e s i s -
i n s u s c e p t i b l e s t e e l s t o HIC were developed.
I t has a l s o been e s t a b l i s h e d t h a t Ca-aluminates
are a l s o
81 p r e s e n t i n s t e e l s produced v i a the b a s i c e l e c t r i c a r c furnace^ ^^. 2
T h e i r presence a r i s e s due t o the aluminum
which i s used as a d e o x i d i z e r and the b a s i c i t y of the s l a g or by the Ca-(Si) treatment.
While some work i n the
l i t e r a t u r e r e p o r t s the presence o f Ca-aluminates by the Ca-treatment 19 7
( 1 4 4
'
1 4 7
'
1 4 8
'
1 5 1
'
1 5 3
'
2 0 7 )
,
others
( 9 6
'
97
<
20 8) '
have shown t h a t complex c a l c i u m - a l u m i n u m - s i l i c a t e s (159)
are formed.
Church e t a l . ' s
s t u d i e s on a s t e e l
processed under two d i f f e r e n t c o n d i t i o n s , a i r melt and d e o x i d i z e d i n the l a d l e and carbon d e o x i d i z e d i n vacuum have found g l o b u l a r type o f i n c l u s i o n s .
( g a l a x i t e ) o x i d e s , s u l f i d e s and
stringer
In the s t e e l t r e a t e d under vacuum,
i n c l u s i o n s were s m a l l e r , fewer and were l e s s complex than i n t h a t t r e a t e d under a i r . These
inclusions consisted
o f a nucleous of g a l a x i t e surrounded by a C a - A l - S i matrix. Whereas the a i r melted s t e e l c o n t a i n e d (Mn, Ca)S around g l o b u l a r oxides and MnS
the
I with some Ca, Cr and Fe i n
s o l u t i o n , i n the s t e e l melted under vacuum o n l y the l a t t e r type was
observed.
The presence of s l a g i n some c o n v e n t i o n a l
processes and the chemistry of the d e o x i d i z e r s employed i n the Ca-treatment p l u s the chemistry o f the melt indeed c o m p l i c a t e the e l u c i d a t i o n of the mechanism(s) by which the i n c l u s i o n chemistry i s c o n t r o l l e d .
Ja*ger and H o l z -
(202) gruber
have found t h a t a l l o y s of Ca with A l , Mn o r S i
used as deoxidants i n 18-8
s t e e l s a f t e r the A l - t r e a t m e n t
i n c r e a s e the Ca y i e l d when 0.1 wt.%
(Ca + Ba) i s a l s o
present. CaO
D^type of i n c l u s i o n s c o n s i s t i n g of 40-60 ^2°3
and 60-40 wt.%
under t h i s
w
i
t
wt.%
p e r i p h e r a l CaS are found
h
treatment.
S a l t e r and P i c k e r i n g '
^
4 0
i n t h e i r s t u d i e s on
C-Cr
b e a r i n g s t e e l s dexodized with a CaSi a l l o y and H i l t y coworkers' ' 4 4
1 6 8
^ who
used C a S i , CaSiB'a and
and
CaSiBaAl
a l l o y s to d e o x i d i z e an i r o n melt and C a S i T i to d e o x i d i z e some c a s t i n g melts, have h i g h l i g h t e d the p r e c i p i t a t i o n scheme.
These r e s e a r c h e r s have found t h a t
inclusions
g e n e r a l l y obey the sequence of phases g i v e n by the pseudobinary Ca0-Al 0 2
diagram.
3
Although these phases d i d not
necessarily follow a stoichiometric relationship c a l c i i m aluminates i d e n t i f i e d were: CaO-2Al 0 2
3
(CA ), C a O - A l ^ 2
CaO*f>Al 0 2
(CA) , 12CaO• 7 A l 0 2
3
3
the
(CAg), (C A ). 1 2
7
S a l t e r and P i c k e r i n g have r e p o r t e d as an e x c e p t i o n a l case a Ca-aluminate
the composition of which corresponded
c l o s e l y to the C ^ A . 2
Pickering s^
o x i d a t i o n i n the l a d l e , of
reactions.
2 <
have
9
de-
have a l s o found the same sequence
In these s t u d i e s the C^A^
Faulring et a l . ^ ^ ^ (201, 207)
s t u d i e s on
1
7
and S a l t e r e t a l . '
4
was (
^
identified.
and o t h e r s
agreed t h a t f o r a g i v e n l e v e l of d e o x i -
d a t i o n with c a l c i u m
a mixture of a t l e a s t two
s t o i c h i o m e t r i c c a l c i u m aluminate phases
different
are found.
(144) H i l t y and coworkers
have approached
the i n -
c l u s i o n f o r m a t i o n mechanism as another p a r t i c u l a r case of the g e n e r a l theory t o e x p l a i n the metal-oxide
sulfide
83 co-precipitation. to
These r e s e a r c h e r s ' work c o i n c i d e n t a l l y
S a l t e r ' s and P i c k e r i n g • s
190,
210)
A^O^
S U
gg
( 1 4 0 J
( 1 4 7
'
1 4 8
'
t h a t s i n c e CaO s u b s t a n t i a l l y f l u x e s
e s t
then the CaO decreases
the m e l t i n g p o i n t of the
" A l 0 " to produce Ca-aluminates 2
and o t h e r s
3
range o f steelmaking
which melt w i t h i n the
temperatures.
Hilty et a l . ^ ^ ^ 8
propose t h a t the pseudo t e r n a r y e u t e c t i c i n t h e i r t e r n a r y ( m e t a l - o x i d e - s u l f i d e ) diagram should be moved c l o s e r t o the oxide corner and hence a h i g h e r m e l t i n g p o i n t " e u t e c t i c " should be expected.
The Ca-aluminate
p r e c i p i t a t i o n se-
quence g i v e n by H i l t y and F a r r e l l suggest t h a t t h i s i s m o d i f i e d by the s u l f u r content, i . e . while a s t e e l t a i n i n g 0.015% S p r e c i p i t a t e s
con-
( C A ) , a s t e e l with 0.005% S 2
and the same Ca- content ('v, 40 ppm) , i t w i l l
precipitate
(CA) . Laboratory and i n d u s t r i a l work performed
by
Takenouchi
(154) and Susuki described.
have agreed w i t h the r e s u l t s p r e v i o u s l y The shape c o n t r o l o f the Ca-aluminates
disappearance
and the
of the manganese s u l f i d e s was a l s o o b t a i n e d .
The d e o x i d i z e r used was a CaAl a l l o y as wires 4.8 and 7 mm diameter
s h i e l d e d with a s t e e l p l a t e 0.2 mm
Emi e t a l . ^
X
1
^
w
i n thickness.
h o have used the same d e o x i d i z e r and
technique, have r e p o r t e d e s s e n t i a l l y the same trend o f (144) r e s u l t s as t h a t g i v e n by H i l t y and F a r r e l l
.
The
s t o i c h i o m e t r i c C^A-y phase was c l e a r l y seen a t a p p r o x i mately
75-80 ppm o f Ca i n the (HSLA) s t e e l .
84 Researchers a t
(Wakayama works) Sumitomo Metal i n -
dustries i n Japan^^3) et a l . ' s and
Emi
i
a
o
n
g
et a l . ' s work
Ca treatment) have introduced b u l l e t shooter" L.D.
the l i n e s of Takenouchi (pipeline
The
the above r e s e a r c h . aluminates) and
i n the
CaO
to A^O^
The
presence of the
the e x t e r n a l
and
the C a - a l l o y by the " A l -
i n t o the S t e e l contained
converter.
steels
r a t i o was
160
ton
equivalent
internal
(A^O^-MnS and
CaS)
(Ca-
phases
have shown a c l e a r dependence on the t o t a l c a l c i u m t e n t of the p r e v i o u s l y Saxena and
(Al)-deoxidized
coworker's
'
previously deoxidized
con-
steel.
research
j e c t i o n of CaO-bearing s l a g s i n t o the was
to
(30 kg)
on i n melt which
with aluminum, have shown t h a t
by t h i s treatment alumina c l u s t e r s i n t o the melt changed to CaO-A^O^ i n c l u s i o n s and
that MnS
are
gradually
'disappears." I t i s a l s o i n d i c a t e d t h a t the i n c l u s i o n s , present a f t e r the p r e f u s e d
slag i s injected
are s p h e r i c a l
aluminates with p e r i p h e r a l s u l f i d e s . 1
4
8
J
Saxena e t a l .
have proposed t h a t as soon as the
s l a g i s i n c o n t a c t with the melt two place,
calcium (147,
CaO-bearing
primary r e a c t i o n s
take
namely:
mCaO, , . + (slag)
nAl_0 * t 2 3
mCaO-'n A1,0,(1) 2 3
(19)
and
3 C a 0
(slag)
+
2 [ A 1 ]
*
Al 0 *(s) 2
3
+ 3[Ca]
(20-a)
85 where the c o e f f i c i e n t s m and n i n r e a c t i o n (19) r e p r e s e n t s t o i c h i o m e t r i c f a c t o r s a c c o r d i n g t o the e q u i l i b r i u m pseudo * b i n a r y (CaO-A^O^) phase diagram. A l ^ O ^ r e p r e s e n t s the primary
(Al) d e o x i d a t i o n
Gatellier et a l .
products.
(19 7)
and Holappa
(210)
also
support
the d e o x i d a t i o n mechanism g i v e n by the r e a c t i o n (20). Holappa g i v e s an e q u i v a l e n t r e a c t i o n which comprises
both
e q u i l i b r i a ; namely A l - d e o x i d a t i o n and Ca-treatment: x[Ca]
+ y(Al 0 ). 2
3
n
c
l
u
s
Saxena and c o w o r k e r s ^ reactions
i
o
1 4 7
t
n
'
1 4 8
xCaO.[y-Kr]Al 0 2
^
+ |x.[Al]
3
(20-b)
have p o i n t e d out t h a t these
(19) and (20) o r (21) take p l a c e i n s o f a r as the
bath c o n t a i n s s u f f i c i e n t aluminum and hence low oxygen
acti-
vity. Since a simultaneous ation^
'
'
'
d e o x i d a t i o n and d e s u l f u r i z ;
i n C a - i n j e c t i o n processes
, . , _ (147,148) , ,^ has been observed then Saxena has proposed t o r e p r e s e n t t h i s e q u i l i b r i u m by the r e a c t i o n : (CaO)* + [S] = (CaS)* + [0]
(21)
I t i s a n t i c i p a t e d t h a t i f the CaO and CaS have u n i t a c t i v i t i e s then a ^ = 0.0266 a and hence Saxena and c o O s workers p r e d i c t the p r e c i p i t a t i o n o f CaS s o l e l y i f the oxygen l e v e l i n the melt
i s lower than or equal t o 10 ppm.
Thus, i f a strong d e o x i d a t i o n i s obtained oxygen l e v e l s
pure CaS would p r e c i p i t a t e .
t o reach
such
They propose
86 t h a t s i n c e the CaO has a l s o a very h i g h a f f i n i t y f o r A l 0 2
3
then a s e r i e s o f c a l c i u m aluminates would be formed, namely: CaO + 6A1_0_
Z
Ca0«6Al_0 2 3
(CA,) 6
(19-a)
CaO + 2 A 1 0
3
t
Ca0-2A1 0
(CA )
(19-b)
CaO +
3
t
CaO-Al 0
(CA)
(19-c)
12CaO + 7 A 1 0
3
t
12CaO-7Al 0
3CaO + 2 A 1 0
3
t
3Ca0*2Al 0
2 -i
2
A1 0 2
2
2
Although
o
2
2
3
3
2
(
3
2
2
3
C
A 1 2
7
)
(19-d)
(C^)
i n these l a b o r a t o r y s t u d i e s '
4 7
(19-e) '*
4 8
^
r i c h e d i n c a l c i u m were i d e n t i f i e d , r e a c t i o n which p r e c i p i t a t e the C ^ A 2
, c l e a r l y revealed. the
CaO-CaF
and the C A
7
3
2
oxides en(19d) and (19e)
phases were not
, (147,148) ^, ^ Saxena e t a l . propose t h a t
s l a g s do not c o n t r i b u t e to form CaS on i n -
2
c l u s i o n s u n l e s s the A 1 0 2
aluminates.
i s f i r * s t l y transformed i n t o Ca-
3
Hilty et a l .
Nashiwa e t a l . ' * ^ 5
(
1
6
8
)
,
Salter et a l .
(
1
4
0
)
and
have a l s o agreed w i t h Saxena' s p r o p o s a l .
Gatellier et a l .
(
1
9
7
)
,
Saxena e t a l .
(
1
4
7
,
1
4
8
)
and
Holappa( *°) h o have s t u d i e d the d e o x i d a t i o n i n l a d l e s w i t h 2
w
Ca-treatments have suggested t h a t the i n c l u s i o n morphology can
be r e t a i n e d i n the f i n a l i n g o t only i f sources o f oxy-
gen, which produce r e o x i d a t i o n
are r e s t r i c t e d .
(159) Church e t a l .
have proposed t h a t n u c l e a t i o n o f
Ca-bearing s u l f i d e s take p l a c e e x c l u s i v e l y on Ca-aluminates. • ^ - . - ^ • , ^ , (147,148) Experimental evidence g i v e n by Saxena and Engh shows t h a t as the i n j e c t i o n time o f CaO-slags i n t o the melt
87 increases., the amount o f s u l f u r i n the (Ca) s u l f i d e phase a l s o i n c r e a s e s g r a d u a l l y up to a l e v e l which i s thought t o be the maximum s u l f u r s o l u b i l i t y i n c a l c i u m a l u m i n a t e s . As a f u r t h e r c o r r o b o r a t i o n of these o b s e r v a t i o n s chemical a n a l y s e s o f samples
e x t r a c t e d d u r i n g the i n j e c t i o n
process show a g r a d u a l and continuous increment o f
Ca
which reaches a p l a t e a u a t approximately 20 ppm a t l a t e r i n j e c t i o n stages.
Saxena's and coworkers
previous lab-
o r a t o r y work on CaO-CaF2 i n j e c t i o n has been extended to industrial t r i a l s ^ oratory scale
2 1 4
have
).
Although the r e s u l t s on a l a b -
indicated a r e l a t i v e l y high y i e l d , i n
terms o f t r a n s f o r m a t i o n o f A l ° 3 2
to
t
o
Ca-aluminates and MnS I I
C a - s u l f i d e s , the i n d u s t r i a l s c a l e t r i a l s
d i d not show
such e f f i c i e n c y . The MnS I I was o n l y transformed t o duplex(Ca,
Mn)S- s u l f i d e In
and pure CaS by i t s e l f was not t r a c e d .
an apparent disagreement with a l l o f the p r e v i o u s l y
, , . (140, 147, 148, 159, 168) . .. described investigations with r e s p e c t to the r e q u i r e d c o n d i t i o n s t o change the A ^ O ^ and the MnS I I morphology, i t has been r e p o r t e d ^
2 1 !
^ that
"pure" CaS i s formed e x c l u s i v e l y a f t e r the "A^O^" c o n t e n t i n the Ca-aluminates
i s reduced by Ca t o l e s s than about
40.0%, i . e . when the CaO:Al C>2 r a t i o i s 3.0 or when the 2
3CaO«Al 0.j s t o i c h i o m e t r i c compound i s formed. 2
i n d i c a t e d t h a t once t h i s r a t i o i s reached
I t i s also
the CaS i s
sharply increased. (209) F a u l r i n g and H i l t y
have observed CaS i n the p r e -
88 sence of CaO-A^O^ and C a O ^ A ^ O ^ as the major and minor compounds r e s p e c t i v e l y .
According to the schematic
formation model proposed by T a h t i n e n e t a l .
(97)
trans-
and sup-
(94)
p o r t e d by Holappa
i t i s seen t h a t f a c e t e d
probably as the hexagonal
Ca-aluminate
inclusions,
which corresponds
to CaO'GA^O^, r e p r e s e n t the i n c i p i e n t t r a n s i t i o n o f the a-A^O-j to the Ca-aluminates
and the simultaneous
tran(94)
s i t i o n o f the MnS to (Ca, Mn) ,S. G u s t a f f s o n and Melberg (209 217) Faulring et a l . ' have observed these phases i n (15) Ca-treated ingots. phases
Mitchell
has a l s o r e p o r t e d these
i n ESR-ingots.
The most comprehensive
work which a n a l y z e s , on thermo-
dynamic p r i n c i p l e s , the p r e c i p i t a t i o n sequence o f A ^ O ^ and Ca-aluminates
i s t h a t developed by F a u l r i n g and
Ramalingam^ ^.
These r e s e a r c h e r s have developed a
21
t e r n a r y Al-O-Ca e q u i l i b r i u m , i s o t h e r m a l (1550°C, 1823°K) p r e c i p i t a t i o n diagram based on Henrian a c t i v i t i e s . have e s t a b l i s h e d t h a t although diagrams
They
o f t h i s k i n d (three
components, i s o t h e r m a l and Henrian behavior) are hypot h e t i c a l i n nature, these a r e very h e l p f u l
i n the
understanding and p r e d i c t i n g of the i d e n t i t y o f i n c l u s i o n s from the c h e m i s t r y o f the bath o f v i c e v e r s a . I t i s a l s o emphasized
by these r e s e a r c h e r s , t h a t
Henrian a c t i v i t y behavior was assumed due t o the i n c o n s i s t e n c y found i n the thermodynamic data a v a i l a b l e f o r
89 calcium. was
T h i s t h r e e dimensional diagram
developed
(h^, ^ c a ' ^ A l ^
by p r o j e c t i n g the i s o t h e r m a l Al-O,
and Ca-Al b i n a r y e q u i l i b r i a .
Ca-O
Thus, o r i g i n a t i n g the
sat-
u r a t e d and unsaturated s u r f a c e s which w i l l g i v e the volume of s t a b i l i t y ,
Figure (11).
Thermodynamic data used to
c o n s t r u c t t h i s diagram i s condensed i n t a b l e s (IV, V and VI) . F a u l r i n g ' s and Ramalingam's experimental and
theoreti-
c a l f i n d i n g s are condensed i n the f o l l o w i n g p o i n t s : 1)
The Ca:Al r a t i o determines
c l u s i o n phases.
2)
The
the i d e n t i t y o f the i n -
amount of c a l c i u m f o r a g i v e n
amount of aluminum v a r i e s over a narrow range f o r each aluminate phase.
3)
If h ^ A
> 0.01
i n s t e e l , c a l c i u m has
a n e g l i g i b l e e f f e c t as a d e o x i d i z e r but does a l t e r
the
composition and thus the morphology of the i n c l u s i o n s 4)
as the major phase
F i n a l l y , F a u l r i n g and Ramalingam have determined p i r i c a l l y s e v e r a l c o r r e c t i o n parameters based on C a
and
Close c o n t r o l of the Ca:Al r a t i o to o b t a i n a d e s i r e d
Ca-aluminate
h
Ca-
:
h l A
a n <
3
t
n
e
%Ca:%Al r a t i o s
h
i.e.
Ca "Al
2.3
Ca
_
Al
'
x 10~
6
from Ca
f
the
Al
f o r CA , C
• %Ca %
CA
0
A
1
and CA and when
em-
90
alumina
i s present as one of the phases
= 10 x 10 r
2.3.7.3
u
.
Al
Complex Oxides (92)
Pickering
i n h i s aim to c l a s s i f y the nature o f
n o n - m e t a l l i c i n c l u s i o n s i n complex s i l i c a t e systems d e f i n e d f i v e d i f f e r e n t c a t e g o r i e s-,namely: 2)
Olivines,
ierites.
3)
Garnets,
4)
has
1) Pyroxenes,
F e l d s p a r s and
5)
At the same time, these c a t e g o r i e s can be
Cordsub-
c l a s s i f i e d as f o l l o w s : 1)
Pyroxenes, these are compounds of the
MO«Si0 .
Where M can be Fe, Mn
2
grunerite
(FeO«Si0 ), 2
(MgO«Si0 ), 2
the d i o p s i d e
2
and MgO
and
enstatite
Since t h e r e i s e x t e n s i v e s o l u ^ i n the presence
of S i 0
2
then
be c o n s i d e r e d as a mix-
2
2
T h e i r names are
(MnO«Si0 ) and
(CaO«MgO•2Si0 ) may
t u r e of CaO*Si0 2)
rhodonite
respectively.
b i l i t y between CaO
and Mg.
type
MgO«Si0 2
O l i v i n e s , t h i s category comprises
the same e l e -
ments as the p r e v i o u s c l a s s i f i c a t i o n ; t h e i r s t o i c h i o m e t r y , however, i s g i v e n as: (2FeO-Si0 ), 2
2 MO«Si0 . 2
Thus,
t e p h r o i t e (2MnO«Si0 ) and 2
fayalite
forsterite
(2MgO«Si0 ) are the main phases of t h i s k i n d . 2
w i t h Ca i n this category i s not i n c l u d e d due ionic size.
A compound
to t h i s l a r g e
I t i s a n t i c i p a t e d , however, t h a t s i n c e the
main t h r e e phases have complete mutual s o l u b i l i t y d i s s o l v e up to 50%
CaO.
they
can
3) general
Garnets.
T h i s s e r i e s of compounds f o l l o w s the
stoichiometry
given by 3 M 0 « A 1 0 • 3SiC> 2
case can be Fe, Mn, Mg and Ca. A1 0 «3Si0 ), spessartite 2
3
2
(3MgO«Al 0 «3Si0 ) 2
3
3
Thus, almandine 2
(3FeO*
3
2
and g l o s s u l a r i t e (3CaO•A1 0 •3Si0 ) a r e
2
2
show v i r t u a l l y complete mutual
form:
M i n this
( 3 M n O « A 1 0 • 3 S i 0 ) , pyrope
the s u b c l a s s i f i e d phases i n t h i s group.
4)
.
2
3
2
A l l these phases
solubility.
The f e l d s p a r group i n c l u d e s phases o f the general
MO•A1 0 •2Si0 2
3
where M represents
2
Mn and Ca. These
phases a l s o show mutual s o l u b i l i t y and take i n t o s o l u t i o n c e r t a i n q u a n t i t i e s o f FeO or MgO r e p l a c i n g MnO o r CaO. 5)
Cordierites.
T h i s i s a group which
compounds o f the f o l l o w i n g g e n e r a l 5Si0 .
M there
2
represents
K i e s s l i n g and Lange
encompasses
chemistry:
2MO«2Al 0 « 2
3
Fe, Mn and Mg. (91)
(92) Pickering
i n agreement w i t h
have c l a s s i f i e d the most common compounds i n the C a O - A l 0 ~ 2
Si0
2
(C-A-S) system, i n the f o l l o w i n g manner:
anorthites.
2)
C A«S, gehlenite. 2
C o r d e r i t e and 4)
3)
2
2
Lange have e s t a b l i s h e d t h a t the C « A « S , C « A « S C
2* 2* 5 A
S
t v
P
e s
a
r
e
n
o
t
,
5
K i e s s l i n g and
3
2
2
C « A « S , Ca-
C «A«S , glossularite. 3
1) C « A « S
3
3
3
and the
common i n c l u s i o n phases. (9192)
I t i s g e n e r a l l y agreed
'
that to avoid
chemical a n a l y s i s by EPMA, due t o the extensive
misleadin
mutual s o l u -
92 bilities
and the wide v a r i a t i o n o f compositions
around the
s t o i c h i o m e t r i c v a l u e s , i t i s r e q u i r e d t o know not only the Ca, A l and S i but a l s o the amount o f Mn, Mg, Fe and T i . (91) A summary o f work performed
by K i e s s l i n g and Lange
i n the C-A-S system i s g r a p h i c a l l y shown i n F i g u r e (12). The L^ and
l i n e s r e p r e s e n t the maximum and the minimum
MeO:SiC>2 r a t i o s i n the phases o f the i n c l u s i o n s .
Although
the b i n a r y oxide MeO p r i n c i p a l l y r e p r e s e n t s CaO, i t can f r e q u e n t l y c o n t a i n v a r i o u s amounts o f FeO, MnO and MgO. I t has a l s o been p o i n t e d out t h a t the c e n t r a l between L^ and L
2
l a r g e l y corresponds
p a r t s o f the above systems.
t o the low-melting
The open c i r c l e s r e p r e s e n t
chemical composition o f indigeneous by K i e s s l i n g and Lange.
area
inclusions
determined
The major area, on the A l 0 2 - S i 0 2 2
s i d e are chemical a n a l y s i s o f e x t r a c t e d samples from a Ca-Si A • a. (207) d e o x i-Ad i z e dA ingots (91 92) I t i s suggested
'
the d e o x i d a t i o n products
t h a t t o t r a c e the o r i g i n o f a knowledge o f the furnace and
l a d l e s l a g and r e f r a c t o r y composition as w e l l as the deoxidation practice i s required.
S a l t e r and P i c k e r i n g ' ^ 4
have r e p o r t e d t h a t i n c l u s i o n phases i n the range of the C2*A'S-C2* * 2 types a r e commonly found i n Ca-Si de(208) M
S
o x i d i z e d melts.
Other
studies
on d e o x i d a t i o n o f s t e e l
w i t h complex d e o x i d i z e r s ( C a S i A l and MgSiAl) have r e p o r t e d i n c l u s i o n compositions
as f o l l o w s : A^O^/
5.0 - 82.7 %,
93
CaO,
6.6
- 37%;
FeO,
1.4
- 6.0%;
Lindon and B i l l i n g t o n ^ alumina
content i n the C-S-A
pure alumina
1 1 5
^
and S i 0 , 2
2.4
- 64.4%.
have a l s o found t h a t the
products i n c r e a s e s to approach
as the A pet. 0: pet. A l added decreases
l e s s than the s t o i c h i o m e t r i c r a t i o .
to
The c h e m i s t r y of the
d e o x i d a t i o n products i n d i c a t e t h a t the degree of u t i l i z a t i o n (181 of c a l c i u m i s maximum o n l y f o r a s h o r t p e r i o d of time 202 •'
'
20 5) .
Hence, i f there i s not s u f f i c i e n t r e s i d u a l
cium i n the melt
although CaO
cal-
i s present i n the d e o x i d a t i o n
p r o d u c t , i t w i l l mainly c o n t r i b u t e to reduce
the
activity
of s i l i c a and thus to achieve a lower oxygen content. (94) Holappa's r e s u l t s Experiments
also e x h i b i t s i m i l a r trends.
i n t h i s r e s e a r c h show t h a t the aluminum i n
s o l u t i o n c o n t r o l s the A l 0 : C a 0 r a t i o and a l s o the 2
3
content i n the d e o x i d a t i o n p r o d u c t s . s o l u t i o n i n c r e a s e s from 0.05
to 0.4%
a l s o i n c r e a s e s whereas the S i 0 the endogenous
Si0
2
I f the aluminum i n the A l 0 : C a O 2
3
ratio
g r a d u a l l y decreases i n
2
p r e c i p i t a t i o n products.
As d e p i c t e d i n the C a 0 - S i 0 ~ A l 0 2
2
3
ternary, t h i s (91)
h a v i o r agrees w i t h K i e s s l i n g ' s and Lange's i . e . i n c l u s i o n chemistry w i l l f o l l o w a tendency w i t h i n the area of low m e l t i n g p o i n t
be-
proposal, to
e n c l o s e d by
fall and
94 2.4
I n c l u s i o n s i n ESR-ingots In s p i t e of the improvement i n mechanical p r o p e r t i e s
mainly due to i n c l u s i o n s i z e and q u a n t i t y
o b t a i n e d by the
ESR-process/ l i t t l e work has been p u b l i s h e d with r e s p e c t to the i n c l u s i o n c h e m i s t r y .
One of the major drawbacks found
i n approaching the i n c l u s i o n chemistry m e t a l l o g r a p h i c o r microprobe t r a c t i o n methods
e i t h e r i n s i t u by
(EPMA) techniques
o r by
ex-
i s the s m a l l i n c l u s i o n s i z e .
While
en-
dogeneous (primary d e o x i d a t i o n products) i n c l u s i o n s i n conv e n t i o n a l steelmaking p r a c t i c e s are 15-40 products
manufactured
by
the
between 2 to 10 ym i n diameter.
ym i n diameter,
ESR-technology
;
they range
The second major d i f f i c u l t y
of t h e i r study i s the complexity of the r e a c t i o n scheme. The p r e c i p i t a t i o n of i n c l u s i o n s i n the ESR-process been s t u d i e d by B e l l
( 2 1 8 )
and M i t c h e l l
f e r e n t s l a g and d e o x i d a t i o n p r a c t i c e s . the Fe-O-Al system and CaF ~30% A^O^ 2
( 1 5
'
under
2 1 9 )
has
dif-
B e l l ' s f i n d i n g s on slag,
indicate
that
the f i n a l i n c l u s i o n composition cannot be e x p l a i n e d by the c l a s s i c a l n u c l e a t i o n theory a p p l i e d t o the l i q u i d i.e.
i n s u f f i c i e n t supersaturation for nucleation.
observed, however, t h a t t h i s requirement was e x c l u s i v e l y i n l a t t e r stages of
pool,
I t was
fulfilled
solidification.
(15) Mitchell
i n an attempt t o i n f l u e n c e the p r e c i p i t -
a t i o n s i t e i n l a b o r a t o r y ESR-ingots
has induced an i n s t a n t -
aneous s u p e r s a t u r a t i o n by adding f e r r o s i l i c o n i n t o the
95 metal p o o l through was
the s l a g .
Under these c o n d i t i o n s , i t
a n t i c i p a t e d t h a t the i n c l u s i o n s i z e d i s t r i b u t i o n i n the
i n g o t would show the e f f e c t of growth time and flotation. produced inclusion
possibly
His r e s u l t s i n agreement with B e l l ' s , however,
no d e t e c t a b l e change i n e i t h e r oxygen content or distribution.
Other s t u d i e s on F e - C u which e x h i b i t w e l l developed
( 1 5 )
and F e - N i
( 2 1 8 )
(ESR)-alloys
d e n d r i t e s , have shown e i t h e r
i n c l u s i o n s a l i g n e d along the i n t e r d e n d r i t i c r e g i o n or d e n d r i t e s f o l d e d around i n c l u s i o n s . enabled them to suggest
These o b s e r v a t i o n s have
that inclusions
i n the f i r s t
case
were formed a t e a r l y stages and i n the second case - they might be formed a t the beginning of s o l i d i f i c a t i o n . Hence, i t was
concluded
t h a t d e o x i d a t i o n i n the ESR process
occurs
by chemical e q u i l i b r a t i o n of oxygen and deoxidant with s l a g and
the
s i n c e almost a l l i n c l u s i o n s are n u c l e a t e d and
grown i n i n t e r d e n d r i t i c r e g i o n s d u r i n g s o l i d i f i c a t i o n , i n c l u s i o n f l o t a t i o n mechanism (15 Mitchell
was
the
discarded.
i
' has r e p o r t e d t h a t o n l y very few
inclusions
from the e l e c t r o d e p e n e t r a t e to the l i q u i d p o o l bulk
and
those which do so are s u b s t a n t i a l l y a l t e r e d i n composition. I t has been widely r e c o g n i z e d t h a t due area a v a i l a b l e f o r thermochemical a c t i o n s and temperature
to the s u r f a c e
and e l e c t r o c h e m i c a l r e -
d i f f e r e n c e s i n ESR-furnaces;
two
96 d i f f e r e n t behaviors a l s o observed.
i n terms o f i n c l u s i o n chemistry
are
Work on the Fe-O-Al and on the Ni-O-Al
(218 220) systems performed a t U.B.C. ' i n agreement with (38) Miska's and Wahlster's work i n l a b o r a t o r y ESR-furnaces has shown t h a t the A l - 0 behavior does not obey the s t o i c h i o (218) metric who
r a t i o expected from e q u i l i b r i u m c o n d i t i o n s .
has remelted e l e c t r o d e s i n CaF -25% A^O^
under an argon
2
atmosphere
has found t h a t i f an
t o t a l oxygen content of 30 ppm
(anodic) e l e c t r o d e
with a
i s remelted, a d r a s t i c i n -
crement of oxygen i s observed a t the d r o p l e t s and t h i s i s reduced down t o about 70 ppm passed through the c a t h o d i c
Bell
ppm)
a f t e r they have
ingot surface.
c o n d i t i o n s h e r c y n i t e or a mixture e n r i c h e d alumina as i n c l u s i o n s would be expected.
1600
Under the above i n hercynite
and
Miska e t a l . ' s
(38) work
on aluminum a l l o y e d s t e e l s remelted i n a l a b o r -
a t o r y ESR-furnace under alumina s a t u r a t e d C a F ~ s l a g s has 2
a l s o shown t h a t the oxygen content f a r exceeded brium,
2 3 [Al] [0] , product.
B e l l has a l s o performed
(ESR)
laboratory scale experi-
ments i n which aluminum d e o x i d a t i o n was trodes c o n t a i n i n g 700 and 30 ppm through a CaF ~25 wt% 2
levels
the e q u i l i -
(1.15, 10.3
A l 2
°3
s l a
and 44.0
d e o x i d i z e r i n the melt was
9~ ' s
c a r r i e d out.
Elec-
of oxygen were r e f i n e d deoxidized a t various
grams).
The i n t r o d u c t i o n of
c a r r i e d out by a t t a c h i n g aluminum
97 wires to the e l e c t r o d e s .
R e s u l t s o f these s e r i e s of ex-
periments showed an 'apparent e q u i l i b r i u m temperature' of 2000 to 2100°C
r a t h e r than 1700°C.
/
Thus, whereas the
metal was expected t o l o s e aluminum and oxygen as alumina to the s l a g
sometimes the opposite
was observed.
I t was
suggested t h a t t h i s d i f f e r e n c e i s due to the i n e f f i c i e n c y of the aluminum d e o x i d a t i o n i s required
and t h a t an excess of aluminum
to lower the oxygen content.
Since c a l c u l a t i o n s
have shown t h a t l o s s e s of aluminum to atmospheric o x i d a t i o n would be as important as the s l a g d e o x i d a t i o n
reaction
then i t was proposed that the r e a c t i o n s : 2A1
( 1 )
+ 3(FeO) t
2A1
( 1 )
+ |
F
e
(i)
+
Al 0 (s) 2
3
(12-iv)
and
take p l a c e .
(O)
t Al 0 (s) 2
3
(ll'-ii)
T h i s l a s t r e a c t i o n was the most probable,
since
the condensation s i t e would be the c o l d mold w a l l where the aluminum i s not r e f l u x e d but removed from the system. Miska e t a l . ' ^ 8
2 2 0
in
^
have
found
i n agreement w i t h B u r e l ' s findings'"'"'
. t h a t the amount o f alumina or h e r c y n i t e
(ESR) l a b o r a t o r y
s c a l e i n g o t s was s t r o n g l y
as compared t o the i n i t i a l q u a n t i t y
increased
t r a c e d i n the e l e c t r o d e .
(55) Kajioka achieved
et a l .
have r e p o r t e d
that better c l e a n l i n e s s i s
i n l a r g e r r a t h e r than i n smaller ESR-furnaces.
e r a l explanations
Sev-
have been proposed to account f o r the above
98
facts; than
i t i s , however, accepted t h a t e l e c t r o c h e m i c a l r a t h e r chemical
reactions
control
the
ingot
and
hence
(63)
the
inclusion
chemistry.
Boucher's
work
on e q u i v a l e n t s l a g compositions to the p r e v i o u s works have suggested t h a t i n i n d u s t r i a l ESR-ingots i s a l a r g e r s u r f a c e area exposed
where t h e r e
t o the s l a g , chemical
i n s t e a d o f e l e c t r o c h e m i c a l r e a c t i o n s govern the i n g o t and thus the i n c l u s i o n chemistry. w i t h some s c a t t e r
Boucher's
findings,
show t h a t there i s a l i n e a r
although
relationship
between the "FeO" content i n the s l a g and the aluminum i n the i n g o t .
T h i s behavior was an i n d i c a t i o n that thermo-
dynamic e q u i l i b r i u m was p r a c t i c a l l y achieved.
While
Bell's
f i n d i n g s suggest an "apparent e q u i l i b r i u m temperature" i n the 1900° t o 2000°C range f o r alumina i n s m a l l Boucher's an almost 1700°C.
i n d u s t r i a l s c a l e ESR-experiments
ESR i n g o t s ,
suggest t h a t
t r u e thermodynamic e q u i l i b r i a i s reached a t He a l s o c l a i m s t h a t almost pure alumina
were i d e n t i f i e d when the p r o t e c t i v e
inclusions
(Ar) atmosphere was
t i g h t l y maintained throughout the r e f i n i n g p e r i o d . R e t e l s d o r f and W i n t e r h a g e r ^ ^ 9
i n t h e i r aim t o produce
alumina f r e e h i g h carbon ferrochrome and metal chrome by ESR.
have found t h a t r e l a t i v e l y l a r g e diameter
about 200 mm,
ingots,
c o n t a i n e d e i t h e r a-A^O^ 'C^O^ or a-alumina
(corundum) and the aluminum and oxygen contents always c o r -
responded
to the A l - 0 e q u i l i b r i u m .
Their "unsuccessful"
f i n d i n g s were claimed to be due t o the high o x i d a t i o n p o t e n t i a l of the s l a g
(CaF -CaO-Al C> 2
2
3
w i t h 30%
Al 0 ) 2
3
and to the i n e f f i c i e n c y of the p r o t e c t i v e atmosphere. (15) Mitchell complex
who
has remelted e l e c t r o d e s c o n t a i n i n g
(calcium alumina s i l i c a t e ) i n c l u s i o n phases
r e p o r t e d t h a t i n g o t s remelted through CaF ~20 wt.%
A1 0
2
and h i g h aluminum d e o x i d a t i o n (0.5% A l ) t a i n calcium bearing i n c l u s i o n s .
has 2
3
are prone to con-
I t has a l s o been r e p o r t e d
i n t h i s study t h a t although l e s s than one p e r c e n t of these i n c l u s i o n s c o n t a i n e d s i l i c a , where i t was h i g h as
found i t was
as
50%. (74)
Holzgruber's work CaF ~CaO-Al 0 2
2
levels
3
on the e f f e c t of s i l i c a of the
s l a g system,
has found t h a t a t low
silica
(4.2%) i n the s l a g , c a l c i u m aluminates c o n t a i n i n g
84% Al C» , 12% CaO 2
3
and about
sulfide phase—probably Another 32% A l 0 ^ 2
1% s i l i c a w i t h a p e r i p h e r a l
( C a M n ) s — a r e commonly found.
p e c u l i a r i n c l u s i o n composition
and 56% CaO)
(14%
r e p o r t e d by Holzgruber
c o n t a i n e d a p e r i p h e r a l s u l f i d e phase
was
Si0 , 2
which a l s o
obtained under
the above experimental c o n d i t i o n s , the s i l i c a i n the however was t h a t about
about
12.0
wt.%.
12-15% s i l i c a
Holzgruber's f i n d i n g s
slag, indicate
i n the s l a g y i e l d s the h i g h e s t Ca
100
content i n i n c l u s i o n s . These r e s u l t s were l a t e r confirmed by A l l i b e r t e t (53 al.
54) '
.
I t should be mentioned t h a t Holzgruber's e x p e r i -
ments were performed though s i l i c o n was
under v a r i a b l e CaOrSiC^
used as d e o x i d i z e r
r a t i o s and a l -
the amount was
not
specified. (53 A l l i b e r t et a l . ' s studies
54) '
on the a c i d - b a s i c
r e a c t i o n s i n the CaF2-Al202-CaO-SiC>2 s l a g system i n agreement with Holzgruber's
f i n d i n g s have r e p o r t e d t h a t a t
low
s i l i c a content i n the s l a g , c a l c i u m aluminates a s s o c i a t e d with a s u l f i d e phase are c o i n c i d e n t a l l y Holzgruber's of
precipitated.
and A l l i b e r t ' s e t a l . ' s f i n d i n g s i n terms
s l a g and i n c l u s i o n chemical composition a r e shown i n (53 54)
Figures
(12) and
(13).
A l l i b e r t et a l .
'
have c l a s s i -
f i e d the i n c l u s i o n composition i n oxides p l u s s u l f i d e s sulfides.
The
and
f i r s t types are l o c a t e d i n the t e r n a r y where
a r e l a t i v e l y high a c t i v i t y of s i l i c a The s u l f i d e zone
i s found, Zone (1).
(2) i s l o c a t e d a t moderate s i l i c a
activities.
Holzgruber*s r e s u l t s , c i r c l e s e n c l o s i n g a s o l i d square,
also
r e f l e c t s i m i l a r trends. (74) I t has been r e p o r t e d the ESR-slag
t h a t i f th,j s i l i c a content i n
i s h i g h e r than 10%,
the percent of s i l i c a i n
i n c l u s i o n s w i l l be higher than the p e r c e n t i n the s l a g . Simu l t a n e o u s l y to t h i s s i l i c a increment
the s i z e of
inclusions
w i l l be l a r g e r and hence the t o t a l oxygen w i l l a l s o be i n creased. (92) Holzgruber i n agreement with P i c k e r i n g and Lange (91) has a l s o found t h a t higher s i l i c a
and K i e s s l i n g content
101 i n the s l a g , the alumina s i l i c a t e phase i n i n c l u s i o n s c o n t a i n s e i t h e r CaO or MnO, but n o t both compounds t o g e t h e r . Holzgruber has a l s o noted t h a t i f r e f i n i n g i s c a r r i e d out
i n alumina f r e e CaO-CaF
2
slags
manganese s i l i c a t e s which c o n t a i n
small alumina f r e e a maximum o f 10 wt %
CaO w i l l be the most common type o f i n c l u s i o n s
found.
(83) Rehak e t a l .
who have s t u d i e d
the e f f e c t of e l e c -
trode and s l a g chemistry on i n c l u s i o n s i n ESR-ingots remelted a s t e e l (CSN 19.426 used f o r c o l d r o l l i n g
have
rods)
produced v i a e l e c t r i c a r c furnace under e i t h e r CaSi or A l deoxidation
practices.
clusions i n electrodes
The chemical composition o f i n Al-deoxidized
2.23 wt% CaO and 5.43 wt % MgO. electrodes
i t was as f o l l o w s :
CaO, 5.36 wt. % S i 0
2
is:
92.25 wt% A^O^,
In the CaSi
deoxidized
58.48 wt.% A l 0 , 2
3
19.46 wt. %
and 16.7% MgO.
Three major s l a g types were s e l e c t e d t o r e f i n e these electrodes;
namely b a s i c , n e u t r a l and a c i d i c .
s e r i e s o f aluminum d e o x i d i z e d i n i n c l u s i o n s and only
ingots
While the
showed almost pure
Al 0
t r a c e s of Ca ( l e s s than 1%), s i l i c a
was d e t e c t e d e x c l u s i v e l y i n one case where the s i l i c a
con-
t e n t i n t h e s l a g was as h i g h as 25%. The
CaSi d e o x i d i z e d
after refining
s e r i e s of e l e c t r o d e s
a h i g h e r Ca-content
showed,
(2.41 t o 6.91%). The
e f f e c t o f the s i l i c a content i n the s l a g was s t r o n g l y
2
3
r e f l e c t e d i n the i n c l u s i o n chemistry.
The
s l a g and
chemistry are a l s o shown i n Figures (12 and t a i n i n g 50% C a F
2
30% CaO
and 20% S i 0
both c o n s i d e r e d as n e u t r a l duced S i 0
2
v a r i e d from 2.4 1.5
to The
(53.0
from 27.0
to 5.0%.
and a pure C a F
2
The MgO
t o 71.36% S i 0 ) . 2
t o 39.4%. ranged
The CaO
from
con-
slag,
Their
content
approximately
3.5%. CaSi s e r i e s of e l e c t r o d e s remelted through b a s i c
s l a g s showed a s l i g h t l y higher CaO-contents than i n the p r e v i o u s ESR s i o n s of about 0.3
ingots.
to 0.57%
were
on the other hand v a r i e d from 5.1 content
A slag
and the h i g h l y a c i d i c s l a g s p r o -
enriched inclusions
alumina content ranged
2
13).
inclusion
which was
(3.2 to 6.9 5%)
Traces of s i l i c a i n i n c l u f o u n d s
The MgO
t o 10.0%
the major component, was
contents,
and the
alumina
86-87%.
Rehak e t a l . have concluded t h a t oxide i n c l u s i o n s are s e q u e n t i a l l y formed as t h e i r thermochemical oxygen i s d i c t a t e d .
They have suggested
affinity for
t h a t the a-A^O^
(corundum) w i l l form f i r s t and as the a c t i v i t y of aluminum in for
the melt decreases other elements with lower
affinity
oxygen, such as c a l c i u m - a l u m i n u m - s i l i c a t e i n c l u s i o n s ,
w i l l subsequently be formed.
Thus, the parameters which i n f l u e n c e the f i n a l i n c l u s i o n chemical composition are the s l a g chemical composition trode
(49 51 53 54 74)
( 8 3 )
o f the e l e c -
.
Several obtained
and the d e o x i d a t i o n
s t u d i e s on mechanical p r o p e r t i e s o f ESR-ingots
under d i f f e r e n t p r a c t i c e s have been r e c e n t l y pub(133)
lished.
Work c a r r i e d out by Boldy e t a l .
w i t h the e f f e c t of s u l f i d e i n c l u s i o n s on the phenomenon.
has d e a l t "overheating"
Overheated m a t e r i a l s , as a r e s u l t of p r e c i p i -
t a t i o n o f manganese s u l f i d e s onto h i g h temperature 1400°C) a u s t e n i t i c g r a i n boundaries toughness.
These r e s e a r c h e r s
(1100°-
show a r e d u c t i o n i n
describe
t h a t a f a c e t e d ap-
pearance of the f r a c t u r e s u r f a c e i s c h a r a c t e r i s t i c of an "overheated" m a t e r i a l . I t has been found t h a t although r e f i n i n g processes such as ESR and VAR i n g o t s
a r e capable o f r e d u c i n g the
s u l f u r content i n i n g o t s down t o very
low l e v e l s and hence
promoting the p r e c i p i t a t i o n o f a f i n e d i s p e r s i o n o f s u l -
104
f i d e s , i t enhances the i n t e r g r a n u l a r ( a u s t e n i t i c ) p r e c i p i t a t i o n which causes o v e r h e a t i n g .
S e v e r a l c o u n t e r a c t i n g measures
have been proposed t o overcome such a problem, i . e . changes i n i n g o t chemistry o r d e o x i d a t i o n p r a c t i c e s o r c o o l i n g r a t e s other
than a i r c o o l i n g (^100°C/min).
Another communication
(221) which has e v a l u a t e d and compared mechanical p r o p e r t i e s between VAR and c a l c i u m - t r e a t e d ESR-ingots under s e v e r a l s l a g s and d e o x i d a t i o n r a t e s , has shown t h a t impact s t r e n g t h i s s t r o n g l y a f f e c t e d by these v a r i a b l e s . at h i g h c a l c i u m d e o x i d a t i o n r a t e s
T h i s work shows t h a t
(0.14% Ca) the aluminum
and oxygen and p a r t i c u l a r l y the s i l i c o n content are s h a r p l y increased during remelting.
The ESR i n g o t s e x h i b i t e d a
g r a d u a l increment i n the i n c l u s i o n s i z e as the Ca-deoxidation l e v e l was i n c r e a s e d
(0.032%, 0.047% and 0.14% Ca).
As a
r e s u l t o f the above parameters the lowest toughness was a t the h i g h e s t c a l c i u m d e o x i d a t i o n l e v e l s . studies
found
In these
n e i t h e r the i n c l u s i o n chemical composition
nor a
s e l f - c o n s i s t e n t e x p l a n a t i o n as t o why the mechanical prope r t i e s e x h i b i t e d such a behavior, Although
the Ca/CaF
2
have been c o n s i d e r e d .
s o l u t i o n has been used
industri-
(86) ally and
i n ESR f o r removing phosphorous from s t a i n l e s s (85) s u l f u r from r o t o r s t e e l s
and as a r e s u l t
improved
mechanical p r o p e r t i e s have been r e p o r t e d , the i n c l u s i o n chemical composition
has not been i n v e s t i g a t e d .
steels
105
Viswanatan
and Beck (222) have r e c o n f i r m e d f i n d i n g s from R a t l i f f
(223) and Brown
i n terms of determining the i n f l u e n c e o f
A l i n the mechanical p r o p e r t i e s o f a r o t o r Their results c l e a r l y (more than 230 ppm) trides,
(Cr-Mo-V) s t e e l .
show t h a t the presence o f aluminum
i n solid solution
without forming n i -
markedly reduces the r u p t u r e d u c t i l i t y and hence
leads to premature
failures.
106
CHAPTER I I I NATURE OF THE PROBLEM A comprehensive work on s e m i - i n d u s t r i a l o r f u l l - s c a l e ESR
experiments, which would account f o r a l l o f the s t e p s -
a t the e l e c t r o d e , e l e c t r o d e - s l a g , s l a g - l i q u i d p o o l and i n the process
of s o l i d i f i c a t i o n during r e f i n i n g and the e f -
f e c t s o f s l a g s and d e o x i d i z e r s on the f i n a l i n g o t and hence the i n c l u s i o n chemistry,
3.1
has y e t not been performed.
I n c l u s i o n s i n the E l e c t r o d e (2-5) Several studies
have attempted t o e l u c i d a t e the
nature o f the t r a n s f o r m a t i o n s to i n g o t s d u r i n g r e f i n i n g . have analysed
of i n c l u s i o n s from e l e c t r o d e s
Mathematical m o d e l s ^ ^ which 9
the thermal h i s t o r y o f e l e c t r o d e s
s t r a t e d that c r i t i c a l
have demon-
thermal g r a d i e n t s are developed a t
the e l e c t r o d e t i p . Regarding the mechanism by which i n c l u s i o n s i n the e l e c t r o d e a r e removed, c o n t r o v e r s i a l and i n c o n s i s t e n t models -,(1,5) have been proposed ' .
., . (1,12,13,15,16) While some r e s e a r c h e r s '
have r e p o r t e d t h a t i n c l u s i o n s are g r a d u a l l y d i s s o l v e d
as a
consequence o f the thermal g r a d i e n t s a t the e l e c t r o d e t i p , (17 19 20) others (?
ers
'
•' 35
have r e p o r t e d the o p p o s i t e .
Other
research-
i
have suggested t h a t the e l i m i n a t i o n o f i n c l u s i o n s
from e l e c t r o d e s i s by mechanical a c t i o n .
On the other hand,
107 (15) studies
performed on i n c l u s i o n s a t the l i q u i d f i l m have
demonstrated t h a t i n c l u s i o n s do not c h e m i c a l l y show any l a r i t y with i n c l u s i o n s i n areas where e l e c t r o d e s (22) low thermal g r a d i e n t s .
Other s t u d i e s
simi-
experience
i n f u l l scale
(ESR)
e l e c t r o d e s , i n agreement with t h i s p r o p o s a l , have a l s o suggested
t h a t there i s a c r i t i c a l l e n g t h above the l i q u i d
where c e r t a i n v o l u m e t r i c Russian
changes of i n c l u s i o n s take (19 20)
investigators
'
film
place.
have a l s o p o i n t e d
out
t h a t the c h a r a c t e r i s t i c
l i q u i d u s - s o l i d u s l e n g t h of
a l s o p l a y s an important
r o l e i n the removal of i n c l u s i o n s
from the e l e c t r o d e .
seen i n t h i s summarized review,
As
there i s a v a s t q u a n t i t y of q u a l i t a t i v e i n f o r m a t i o n
alloys
but
o n l y a l i m i t e d amount of q u a n t i t a t i v e i n f o r m a t i o n a v a i l a b l e . Since the chemical
nature of i n c l u s i o n s i s r e l a t e d to
t h e i r t r a n s f o r m a t i o n as a r e s u l t of the steep thermal g r a d i ents a t the e l e c t r o d e t i p i t has qualitative basis
only been approached on a
( i n terms of the chemical
composition
of
the e l e c t r o d e ) and q u a n t i t a t i v e a n a l y s i s ( i n terms of i n clusion size distributions),
i t was,
however, very c l e a r
t h a t a deeper study which c o u l d r a t i o n a l i z e the r e s e a r c h , would be very
valuable.
reported
108 3.2
The
Chemical I n f l u e n c e of the ESR
Components on
the
Composition of I n c l u s i o n s TT
•
(37,55,58,75-77,79) .
Various to o p t i m i z e by the ESR melting
-
,
have been performed
the chemical homogeneity of i n g o t s manufactured technology.
I t i s widely
accepted
that i f r e -
i s conducted under atmospheric c o n d i t i o n s , an
hanced and occurs.
studies
.
continuous
accumulation
of i r o n oxide
en-
i n the s l a g
I t i s a l s o known t h a t the o x i d a t i v e s t a t e of
the
s l a g with r e s p e c t to the l i q u i d p o o l i s r e l a t e d to the s l a g ^ (38,48,82) system ' ' On an a p r i o r i b a s i s , i t i s understood t h a t i f d e o x i d a t i o n i s not c a r r i e d out d u r i n g r e m e l t i n g then a
sacrifi-
c i a l o x i d a t i o n of r e a c t i v e a l l o y i n g elements takes
place.
S e v e r a l w o r k e r s ' ^ ' ^ ' ^ ' have p o i n t e d out t h a t the
chemical
composition
of the s l a g s t r o n g l y enhances or suppresses c e r -
t a i n reactions during r e f i n i n g . (28 29 58 71) oxides
and
The
net p r o d u c t i o n of
iron
the p r o d u c t i o n of c a l c i u m or alum-
inum a t the e l e c t r o - a c t i v e i n t e r f a c e s d i c t a t e s the o x i d a t i v e s t a t e of the molten p o o l and hence the f i n a l ESR-ingot and i n c l u s i o n chemical
composition.
I t has been proposed t h a t p o l a r i z a t i o n due p a s s i n g through the slag-^skin/mould
w a l l i n t e r f a c e , which
generates s m a l l arc c o n t a c t s , i n c r e a s e s the i n the A.C.
ESR
process
and hence
symetry of r e a c t i o n s (1-5).
to c u r r e n t
rectification
i t enhances the net
as-
This p o l a r i z a t i o n increases
the
109 Fe 2+ content
of the s l a g bulk
a t i o n r a t e s i n the system. p l a i n the chemical
and
thus, accentuates a l l o x i d -
T h i s p r o p o s a l has been used to
composition
of i n c l u s i o n s i n the
ex-
Fe-Al-0
. (219,220) system • ' . The b a s i c i t y index of the s l a g chemical
p o t e n t i a l ) and
(as a measure of i t s
i t s e f f e c t on the chemical
composition
(49-51) of i n g o t s
and
to a l i m i t e d extent on the chemical
t u r e of i n c l u s i o n s ' ' 8
7 4
the German l i t e r a t u r e .
na-
^ , has been s t r o n g l y supported i n These s t u d i e s , however, have not
c l u s i v e l y determined the r o l e of the d e o x i d i z e r , the of the s l a g and/or d e o x i d i z e r , and/or the chemistry
con-
chemistry of
the
e l e c t r o d e or the combined e f f e c t of these parameters on i n c l u s i o n chemical
composition
of ESR
the
ingots.
S e v e r a l d e o x i d a t i o n p r a c t i c e s have been suggested i n / ^ g 74 the l i t e r a t u r e ^
'
8 3)
'
.
Among the uneconomic
deoxidation
techniques,
to overcome l o s s e s of r e a c t i v e elements ( A l ,
Ti,
e t c . ) , i t has been proposed t o :
S i , Mn,
eliminate
the
hard s c a l e from r o l l e d e l e c t r o d e s , d e l i b e r a t e l y i n c r e a s e
the
r a t i o of these s p e c i e s i n the e l e c t r o d e , use p r o t e c t i v e p a i n t i n g s based on Mg or A l , to d e p o s i t o x i d a t i v e elements on electrode surface, etc. nique
The most f r e q u e n t d e o x i d a t i o n
developed e x c l u s i v e l y on an e m p i r i c a l b a s i s
the
tech-
has
been the e x t e r n a l a d d i t i o n of e i t h e r aluminum or s i l i c o n
as
wire, p e l l e t s , f e r r o a l l o y s , e t c . i n t o the s l a g to achieve
a
d e s i r e d i n g o t chemistry.
The
conventional
widespread
deoxi-
110
d a t i o n l e v e l i s about 0.2 wt. % A l o r S i .
I t has been p r o -
(74) posed
t h a t e f f i c i e n t d e o x i d a t i o n i s achieved when a de-
o x i d i z e r i s i n t r o d u c e d i n t o the s l a g which does not c o n t a i n i t s oxide.
On the other hand, other r e s e a r c h e r s have p r o -
(39 48) posed
'
t h a t i f an element i s prone t o o x i d a t i o n ( i . e .
r e a c t i v e elements as T i , S i , Z r , A l etc.) d u r i n g r e f i n i n g , then a d d i t i o n s o f i t s r e s p e c t i v e oxide i n t o the s l a g p r e vents i t s l o s s e s .
The p o t e n t i a l harm o f i n a p p r o p r i a t e de-
o x i d a t i o n w i l l m a n i f e s t i t s e l f i n an uneven d i s t r i b u t i o n (55 75 79) of c r i t i c a l a l l o y i n g elements i n i n g o t s ' ' and r e (221) s u i t i n d e l e t e r i o u s mechanical p r o p e r t i e s These s t u d i e s , however, have not approached the r e a c t i o n mechanisms and hence i n g o t and i n c l u s i o n composition has remained unexplored.
chemical
In summary, although
the need t o i n t r o d u c e a deoxidant i n t o the s l a g , has been i d e n t i f i e d , the net e f f e c t o f i t has not been e l u c i d a t e d . Thus, t o a l a r g e extent the e x p l a n a t i o n f o r the i n g o t chemi s t r y and hence the composition o f i n c l u s i o n s has remained obscure.
In a d d i t i o n , s i n c e the r e a c t i o n mechanisms which
c o n t r o l the chemistry of i n g o t s have not been completely understood,
the e x p l o r a t i o n o f o t h e r a l t e r n a t i v e means of
d e o x i d a t i o n — w i t h t h e i r p o t e n t i a l advantages and d i s a d v a n t a g e s — h a s never been p r o p e r l y i n v e s t i g a t e d .
Ill 3.3
The
P r e c i p i t a t i o n of I n c l u s i o n s from L i q u i d Pool
to
Ingot ,
. ,.
(1,33,36,48,58,61,64)
Several studies
'
' • '
'
'
proached the r e a c t i o n scheme i n the ESR
'
.. . , which have
process
have c l e a r l y
demonstrated the e x i s t e n c e of o x i d a t i o n - r e d u c t i o n a t the e l e c t r o a c t i v e ( e l e c t r o d e t i p - s l a g and
ap-
reactions
slag-liquid
pool) i n t e r f a c e s which l a r g e l y c o n t r i b u t e to c o n t r o l the (218—220) i n g o t and ried
the i n c l u s i o n chemistry.
out a t U.B.C.
has
Research
c l e a r l y r e v e a l e d the
carelectrochemical
nature of i n c l u s i o n p r e c i p i t a t i o n i n the Fe-O-Al system. Chemical a n a l y s i s ( i n s i t u by m e t a l l o g r a p h i c microscopic
techniques
and e l e c t r o -
and by e x t r a c t i n g i n c l u s i o n s and
an-
a l y z i n g them by X-ray techniques) have c o n c l u s i v e l y shown t h a t a s t a t e of thermochemical e q u i l i b r i u m i s only i v e l y obeyed. alumina was
qualitat-
From thermochemical c o n d i t i o n s i n s l a g s
where
expected as the o n l y type of i n c l u s i o n , a mix-
t u r e of i r o n oxide
and h e r c y n i t e , h e r c y n i t e and
found i n s t e a d of pure alumina. The m a j o r i t y of s t u d i e s on the chemical
alumina were
composition
i n c l u s i o n s have been performed on samples from the
of
liquid
(15) film
(at the e l e c t r o d e t i p ) , d r o p l e t s i n process
of form-
a t i o n which have been i n c o n t a c t with the s l a g ' ^ ' ^ " ^ ( a l s o at the e l e c t r o d e t i p ) and ingots.
from samples of a l r e a d y
solidified
112
I t should be p o i n t e d out t h a t these s t u d i e s have been performed i n i n g o t s r e f i n e d i n l a b o r a t o r y ESR-furnaces as p r e v i o u s l y c i t e d , the i s smaller
s u r f a c e area
than i n i n d u s t r i a l
and
available for reactions
s i z e furnaces.
p h y s i c a l l i m i t a t i o n s i n the s m a l l furnaces
In a d d i t i o n
( i . e . electrode
mould w a l l spacing) pose another drawback f o r e x t r a c t i n g samples from e i t h e r l i q u i d p o o l or s l a g . not allowed
researchers
These f a c t o r s have
to e l u c i d a t e the o r i g i n of i n c l u s i o n s .
Thus, the need to i n v e s t i g a t e the thermochemical or e l e c t r o chemical
i n f l u e n c e of the s l a g - l i q u i d p o o l i n t e r f a c e on
chemical
composition
of i n c l u s i o n s and
the
t h e r e f o r e t o unambigu-
ously i d e n t i f y t h e i r o r i g i n i s e s s e n t i a l .
113 3.4
D i s t r i b u t i o n of Inclusions during I t i s g e n e r a l l y accepted
b u t i o n s i n ESR-ingots a r e
Solidification
that i n c l u s i o n size
distri-
markedly s m a l l e r compared t o
i n g o t s produced under c o n v e n t i o n a l and most of the secondary ( r e f i n i n g ) steelmaking
processes.
While i n c o n v e n t i o n a l processes
localized
concen-
t r a t i o n o f i n c l u s i o n s have been widely r e p o r t e d
due to
t h e i r c h a r a c t e r i s t i c c r y s t a l l i z a t i o n mode, i n s e m i - i n d u s t r i a l or f u l l
s c a l e ESR-ingots t h i s phenomenon has almost never been
reported. ESR-ingots
Other i n t e r e s t i n g f e a t u r e s commonly observed i n o b t a i n e d under c o n v e n t i o n a l d e o x i d a t i o n p r a c t i c e s , (224)
are t h e i r i n c l u s i o n s i z e d i s t r i b u t i o n s
(about 2 t o 12ym) (225)
and t h e i r r a d i a l l o c a l s o l i d i f i c a t i o n times
, expressed
as a r e g u l a r d e c r e a s i n g v a r i a t i o n o f t h e i r primary
and second-
ary d e n d r i t e arm spacings along t h e i r r a d i a l d i r e c t i o n s from (65) the c e n t r e l i n e towards the mould w a l l . Several d e t a i l e d (218) s t u d i e s on i n c l u s i o n s i n ESR i n g o t s
where r e f i n i n g o f a
f e r r o u s N i e n r i c h e d a l l o y was performed through a CaF^^CaO s l a g , have found round i n c l u s i o n s a l i g n e d along d e n d r i t e arms.
primary
These o b s e r v a t i o n s l e d to the b e l i e f t h a t
p r e c i p i t a t i o n o f i n c l u s i o n s takes p l a c e homogeneously from the i n t e r d e n d r i t i c l i q u i d . (15 219) formed a t U.B.C. In t h i s study
'
Complementary s t u d i e s
also per-
have a l s o c o r r o b o r a t e d t h i s p r o p o s a l .
i t i s r e p o r t e d t h a t i n c l u s i o n s were l o c a t e d i n
i n t e r d e n d r i t i c spaces and very r a r e l y were d e n d r i t e arms seen
114 f o l d e d around i n c l u s i o n s . Since a t t e m p t s ^ ^ 15
t o generate a s i l i c o n
supersaturation
i n l a b o r a t o r y ESR melts d i d not produce any d e t e c t a b l e
change
i n the i n c l u s i o n s i z e or i n the t o t a l oxygen a n a l y s i s , i t was proposed t h a t n u c l e a t i o n and growth o f i n c l u s i o n s takes almost e x c l u s i v e l y as a r e s u l t of r e j e c t i o n of s o l u t e s solidification.
during
I t was t h e r e f o r e concluded t h a t under a con-
v e n t i o n a l degree o f d e o x i d a t i o n
the i n c l u s i o n f l o t a t i o n mech-
anism was not a p p l i c a b l e , i n disagreement with other ers
place
research-
(1,12,35) ' ' As p r e v i o u s l y s t a t e d
s i n c e there are p h y s i c a l
limit-
a t i o n s and d i f f e r e n t k i n e t i c s a t the e l e c t r o a c t i v e i n t e r f a c e s i n s m a l l ESR furnaces
researchers
have not been able t o ap-
p r o p r i a t e l y monitor a l l o f the r e a c t i o n s i n the v a r i o u s
com-
ponents and stages of r e f i n i n g , a more complete i n v e s t i g a t i o n is
required.
115
3.5
E s t a b l i s h m e n t of the P r o p o s a l and O b j e c t i v e s Sought Through t h i s
Research
A c l e a r n e c e s s i t y to understand
and thereby to c o n t r o l
the sequence of events to which i n c l u s i o n s and the
liquid
metal are s u b j e c t e d i n the v a r i o u s stages of r e f i n i n g i s r e q u i r e d , as seen from the p r e v i o u s review.
Thus, i n order t o
cover a l l the e x i s t i n g gaps and to extend our p r e s e n t unders t a n d i n g r e g a r d i n g the nature of i n c l u s i o n s i n t h i s f i e l d s e r i e s of f o u r q u e s t i o n s was
a
addressed:
1)
How
are e l e c t r o d e i n c l u s i o n s removed?
2)
Is the i n c l u s i o n composition c o n t r o l l e d
by
the chemistry of e l e c t r o d e s , s l a g s or d e o x i d i z e r s ? 3)
Are i n c l u s i o n s i n the l i q u i d p o o l the same as i n the i n g o t ? and
4)
Is the i n c l u s i o n s i z e d i s t r i b u t i o n r e l a t e d to r a d i a l d i s t a n c e s from the c e n t r e l i n e to the mold w a l l of ESR i n g o t s .
These q u e s t i o n s were s t a t e d i n such a way
t h a t a l l of the
phenomena i n v o l v e d i n the process of r e f i n i n g , i n terms of inclusions
were addressed.
the o r i g i n of i n c l u s i o n s
Once the mechanisms which
( r e a c t i o n s ) were determined
the deoxidant, d e o x i d a t i o n technique and the s l a g
govern
then
chemical
composition would be s e l e c t e d and a comparison between r e sults
as a f u n c t i o n of e l e c t r o d e and s l a g compositions
w e l l as deoxidants c o u l d be c a r r i e d out.
as
116 CHAPTER IV EXPERIMENTAL WORK AND TECHNIQUES 4.1
Experimental Procedure Ingots were r e f i n e d through s e v e r a l s l a g systems u s i n g
l a b o r a t o r y and s e m i - i n d u s t r i a l s c a l e ESR-furnaces cribed e l s e w h e r e ^ ^ ' 2 2
2 2 7
^.
des-
E l e c t r o d e s of s e v e r a l chemical
compositions and diameters were r e f i n e d u s i n g s e v e r a l systems and
(commercial grades) and deoxidants.
slag
Tables (VII)
(VIII) summarize t h i s i n f o r m a t i o n . E l e c t r o d e s 31.75 and 44.75 mm
i n the l a b o r a t o r y s i z e ESR-furnace from
1.2 t o 1.5 Kg m i n . - 1
i n diameter were melted at melting rates ranging
1020, 4340 and r o t o r (Ni-Cr-Mo)
s t e e l s which were 76.2, 88.9 and 114.3 mm remelted i n the s e m i - i n d u s t r i a l
(200 mm)
m e l t i n g r a t e s o f approximately 1 Kg min use l i n e frequency A.C. power.
i n diameter were ESR-furnace a t .
Refining
with and without a p r o t e c t i v e atmosphere.
Both furnaces
was c a r r i e d out In the f i r s t
case
the system e n c l o s e d an argon gas s h i e l d and deoxidant a d d i t i o n s c o u l d be made a t monitored r a t e s , F i g u r e (14). The d e o x i d i zers were g r a n u l a r aluminum 99.99% p u r i t y , c a l c i u m s i l i c i d e a l l o y s and aluminum 65 wt.% S i , i n the s i z e range o f 8-32 mesh-
S p e c i f i c compositions are g i v e n i n Table ( I X ) . S e v e r a l d e o x i d a t i o n p r a c t i c e s were f o l l o w e d , namely i)
Constant a d d i t i o n i n s m a l l ESR-ingots,
117 ii)
i n t e r m i t t e n t a d d i t i o n s and
iii) The
continuously
increasing.
l a s t two p r a c t i c e s were performed i n i n g o t s 200 mm i n
diameter.
Experiments t o determine the i n c l u s i o n removal
mechanisms i n e l e c t r o d e
t i p s were c a r r i e d out i n 1020 m i l d
s t e e l produced v i a a c i d e l e c t r i c furnace, 4340 C a - S i - A l steel pleted
t r e a t e d , and 114 mm diameter r o t o r
Ca-Si-Al
treated.
electrodes
Once r e f i n i n g
scopic
(Ni-Cr-Mo)
experiments were com-
were r a p i d l y withdrawn from s l a g s t o achieve
as f a s t a c o o l i n g r a t e as p o s s i b l e . sectioned
89 mm diameter
and m e t a l l o g r a p h i c
Electrode
t i p s were
( o p t i c a l ) and e l e c t r o - m i c r o -
(SEM and EPMA) a n a l y s i s were performed.
Qualitative
d i s p e r s i v e - X - r a y - s p e c t r u m a n a l y s i s by the SEM and backs c a t t e r e d and e l e c t r o n composition maps by the EPMA as w e l l as q u a n t i t a t i v e a n a l y s i s
(by EPMA) on i n c l u s i o n s were c a r r i e d
out. Samples from l i q u i d p o o l s and slags were taken as deoxidation
and r e f i n i n g was t a k i n g p l a c e .
samples were e x t r a c t e d
L i q u i d metal
by s u c t i o n from l i q u i d p o o l s and s l a g
samples by means of a s m a l l copper c h i l l .
Chemical a n a l y s i s
of i n c l u s i o n s i n samples d i s c r e t e l y e x t r a c t e d p o o l s as w e l l as from s o l i d i f i e d EPMA.
The
liquid
i n g o t s were c a r r i e d out by
Oxygen a n a l y s i s by vacuum f u s i o n
of samples
from
a l s o on both types
were performed. chemical composition o f s l a g samples
were analyzed
118 by standard spectrophotometric techniques.
The chemical
composition o f i n g o t s was c a r r i e d out by s p e c t r o g r a p h i c a n a l y s i s along the v e r t i c a l a x i s of i n g o t s . F i n a l l y , complementary experiments
to determine
where and when i n c l u s i o n s were n u c l e a t e d and grown were performed.
S i l i c a tubes which c o n t a i n e d e i t h e r r a r e e a r t h metals
(mischmetal) the s l a g
o r Zirconium wires were i n t r o d u c e d through
w h i l e helium was g e n t l y blown
i n t o the l i q u i d
p o o l to e x t r a c t l i q u i d metal by the s u c t i o n technique. wards
After-
samples were p o l i s h e d and q u a l i t a t i v e and q u a n t i t -
a t i v e a n a l y s i s o f i n c l u s i o n s were performed. s t u d i e s on i n c l u s i o n s t o determine
EPMA and SEM
t h e i r chemical
and the d i s t r i b u t i o n o f t h e i r phases
composition
(composition maps) were
c a r r i e d out.
4.2
Analysis of Inclusions A t r i p l e spectrometer
J e o l c o JXA-3A e l e c t r o n
probe and an E t e c "Autoscan"
scanning e l e c t r o n
micro-
microscope
w i t h a d i s p e r s i v e X-ray a n a l y s e r were used to determine the chemical nature o f i n c l u s i o n s . Since the diameter
o f the e l e c t r o n beam which e x c i t e s
the sample, the specimen c u r r e n t d e n s i t y and the a c c e l e r a t i n g v o l t a g e determine signals
the s t e a d i n e s s and the magnitude o f the
(X-rays, secondary
and b a c k s c a t t e r e d e l e c t r o n s , e t c . )
119
emitted they were c o n t i n u o u s l y c a l i b r a t e d t o g i v e a beam approximately
1.0 ym i n diameter when the e x c i t a t i o n
age was 25 kV and the specimen c u r r e n t d e n s i t y was 0.08 yA .
voltabout
Hence, the e l e c t r i c a l - o p t i c a l c o n d i t i o n s i n these
instruments were c a l i b r a t e d i n such a manner t h a t the maximum
p o s s i b l e c u r r e n t was o b t a i n e d i n the s m a l l e s t e l e c t r o n
probe. Aluminum, c a l c i u m , s i l i c o n ,
s u l f u r , manganese, chromium,
t i t a n i u m , and magnesium were determined f l u o r i n e were determined
a t 10 kV.
a t 25 kV.
Oxygen and
The i d e n t i f i c a t i o n o f
i n c l u s i o n phases was a l s o o b t a i n e d by the v i s i b l e l i g h t uced by the e l e c t r o n beam and photon r a d i a t i o n
prod-
(cathodo-
luminescence). Since compound standards are known t o produce
more a c -
(228229) c u r a t e and r e p r o d u c i b l e a n a l y s i s l i k e CaC0 , A^O^, 3
S l
0 ' 2
standards t o determine inclusion
M (
? ' 0
Z
n
S
a
' n
d
,
compounds
pure Mn were used as
the chemical composition
of the
phases.
Raw data
(specimen background, a c c e l e r a t i n g v o l t a g e ,
t a k e - o f f angle, specimen counts, compound standard i n f o r m a t i o n , background from standards, X-ray counting time, e t c ) were t r a n s l a t e d i n t o chemical composition, t a k i n g i n t o account c o r r e c t i o n f o r atomic number e f f e c t s , a b s o r p t i o n and secondary f l u o r e s e c e n c e , by Colby's MAGIC IV p r o g r a m ' * with U.B.C.'s 3 0
120 AMDAHL computer.
R e l a t i v e accuracy of ± 7-10%
was
obtained.
These v a l u e s are i n f a i r agreement with r e p o r t s a v a i l a b l e i n the l i t e r a t u r e '
0 6
'
2 2 8
'
2 2 9
!
(±5-7%).
to mention t h a t , as r e p o r t e d i n the
I t i s also
worthwhile
literature'
4 0
the c a l c i u m to aluminum r a t i o i n i n c l u s i o n s i n the
'
2 1 6
'
2 1 7
^
Ca-deoxidized
i n g o t s gave a c l o s e r i n d i c a t i o n of the d e o x i d a t i o n sequence. These r a t i o s et a l . • s
( 2 0 9
'
3 1 6 )
(Ca:Al)
i n agreement with F a u l r i n g ' s
and S a l t e r ' s and P i c k e r i n g • s '
4 0 }
findings
were found to approximate the corresponding s t o i c h i o m e t r i c of those phases given by the pseudo-binary
ratios
CaO-A^O^ diagram.
S p e c t r o g r a p h i c and oxygen a n a l y s i s of samples from i n gots and l i q u i d p o o l
and
spectrophotometric and
graphic a n a l y s i s of i n c l u s i o n s
crystallo-
(by Debye-Scherrer
and d i f -
f r a c t o m e t e r techniques) e x t r a c t e d from i n g o t s c o r r o b o r a t e d (207) these f i n d i n g s . aluminate
Based on a r e p o r t e d work
on c a l c i u m
i n c l u s i o n s a minimum o f twenty and a maximum of
50 s i n g l e assays were performed
to o b t a i n a r e p r e s e n t a t i v e
a n a l y s i s o f a sample, i . e . t h i s r e p r e s e n t s one p o i n t on
the
graphs. The
i n c l u s i o n s were grouped a c c o r d i n g to s i z e , chemi-
c a l composition, tities.
f l u o r e s c e n c e , shape and r e p r e s e n t a t i v e quan-
I n c l u s i o n s s m a l l e r than 3 ym i n diameter were chemi-
c a l l y analyzed; they were, however o n l y q u a l i t a t i v e l y
con-
s i d e r e d due t o the cumbersome i n t e r a c t i o n e f f e c t s o f the i n c l u s i o n chemical composition and
the metal m a t r i x .
Aluminum
121
d e o x i d i z e d i n g o t s c o n t a i n e d e i t h e r FeO-A^C^, pure or
c a l c i u m hexaluminate
as i n c l u s i o n s phases which were
very s m a l l s i n g l e or c l u s t e r e d . were l e s s than 6-8 pm
alumina,
Since i n c l u s i o n
diameters
i n c l u s i o n s s m a l l e r than 3.0 ym were
a l s o a n a l y s e d on a q u a l i t a t i v e b a s i s . Analyses were c a r r i e d out by scanning d i a g o n a l l y a c r o s s the sample and the i n c l u s i o n s so t h a t r e s u l t s s t a t i s t i c a l l y r e p r e s e n t e d the i n c l u s i o n chemistry of the sample. T y p i c a l i n c l u s i o n s o f a g i v e n sample were microphotographed, o p t i c a l , scanning and b a c k s c a t t e r e d (EPMA) analyses and composition maps were a l s o o b t a i n e d .
4.3
T o t a l Oxygen Analyses The
t o t a l oxygen content of samples e x t r a c t e d from
l i q u i d p o o l s and i n g o t s was determined
by the standard
inert
gas vacuum f u s i o n technique u s i n g a Leco 537 i n d u c t i o n f u r nace
(507-800) and a Leco oxygen analyzer
weighing
(509-600).
Samples
1.0 - 1.5 grams were c u t , ground, and washed, u l t r a -
s o n i c a l l y cleaned and r i n s e d with anhydrous 1,1,1, t h r e e chloroethane.
Since the accuracy and r e p r o d u c i b i l i t y of
t h i s a n a l y s i s was s t r o n g l y i n f l u e n c e d by the weight o f the sample and i t s p r e p a r a t i o n ,
a
meticulous procedure
was
f o l l o w e d to o b t a i n a minimum of t h r e e assays with a maximum o f 2-5% d e v i a t i o n amongst them.
I f the d e v i a t i o n i n analyses
were g r e a t e r than t h i s , a new s e t of t h r e e analyses was p e r -
122
formed. To o b t a i n an a p p r o p r i a t e
c a l i b r a t i o n of the
analy-
t i c a l equipment standards of known oxygen content were analyzed.
A n a l y s i s on samples c o n t a i n i n g
an upper and
l i m i t of oxygen as w e l l as a blank t e s t to check the a t i o n i n gas
(helium) flow r a t e were c o n t i n u o u s l y
to m a i n t a i n them c o n s t a n t l y Samples e x t r a c t e d
throughout any
lower
vari-
performed
s e r i e s of
analyses.
from l i q u i d p o o l s were c a r e f u l l y s e l e c t e d
because p o r o s i t i e s and
s l a g entrapment were o c c a s i o n a l l y
de-
tected .
4.4
Inclusion
E x t r a c t i o n Method
I t i s an accepted f a c t t h a t c h e m i c a l e x t r a c t i o n methods
of n o n - m e t a l l i c
i n c l u s i o n s followed
by a n a l y s i s p r e -
sent s e v e r a l advantages over chemical a n a l y s i s performed i n s i t u . ( b y microprobe or scanning E.M.). vantages are the 1.
The
major
ad-
following:
A n a l y t i c a l r e s u l t s are f a r more
representative
because a much l a r g e r sample i s taken f o r e x t r a c t i o n than f o r i n s i t u methods. 2.
Phases can be
specifically identified after
ex-
traction. 3.
The
t o t a l oxygen content and
the t o t a l amount
of most phases i n s t e e l can be estimated by chemical a n a l y s i s of the
residue.
123
There are, however, s e v e r a l disadvantages as w e l l . 1.
Some phases cannot be q u a n t i t a t i v e l y e x t r a c t e d .
T h i s f a c t i s due t o e i t h e r i n c l u s i o n s i z e (< 5ym i n d i a meter) o r t o the chemical nature o f i n c l u s i o n s and r e agents
(too a g r e s s i v e ) . 2.
Phases c o n t a i n i n g
common elements and amorphous
or/and isomorphic s t r u c t u r e s may i n t e r f e r e with c e r t a i n a n a l y sis . 3. small
Since i n c l u s i o n s i z e i n ESR-materials i s r e l a t i v e l y
(S 10ym i n diameter) a n a l y s i s by X-rays i s r a t h e r
dif-
ficult. S e v e r a l chemical methods o f i n c l u s i o n e x t r a c t i o n were performed.
Among them
bromine i n methanol,
a n o l , bromine-ester-methanol methanol.
i o d i n e i n meth-
and i o d i n e - m e t h y l a c e t a t e -
From a l l the above methods only the l a s t two were
s u i t a b l e t o t h i s purpose.
The iodine-methanol-methyl a c e t a t e
however, was found to be the most convenient because o f i t s accuracy and r e p r o d u c i b i l i t y . 4.4.1
Apparatus and Experimental Procedure The apparatus used was i n t e g r a t e d i n f o u r u n i t s .
f i r s t unit
(I) was used to pour i o d i n e c r y s t a l s and the
methyl acetate-methanol mixture sphere c o n s i s t i n g of) anhydrous
under a p r o t e c t i v e atmoargon.
T h i s p a r t o f the s y s -
tem was a l s o used as a d i s s o l u t i o n chamber. s o n i c c l e a n e r o r a magnetic erature
The
An u l t r a -
s t i r r e r w i t h c o n t r o l l a b l e temp-
served t o speed up the i o d i n e d i s s o l u t i o n .
The second u n i t
(II) c o n s i s t e d of a m i l l i p o r e
which c o n t a i n e d a whatman paper No. pore f i l t e r
(0.5 ym) .
u n i t . T h i s was served as
was
or a t e f l o n
a g l a s s c o n t a i n e r w i t h four o u t l e t s which
a) b r e a t h i n g system
b) r e a g e n t - l e v e l r e g u l a t o r ,
d) a r g o n - f l u x
valve.
T h i s cham-
i n s i d e the u l t r a s o n i c a g i t a t o r which was
speed up the d i s s o l u t i o n of the metal sample. unit
(IV) was
milli-
The r e a c t i o n chamber was the third (III)
c) vacuum c o n t r o l l e r and ber
50
filter
used to
The
fourth
a l s o equipped w i t h another m i l l i p o r e
filter
s i m i l a r t o the one used i n u n i t no. 2 but t h i s had a ym diameter porous s i z e f i l t e r
0.5
(made of teflon), F i g u r e
(15) .
Since humidity i s one of the major concerns i n any halogen-methanol-methyl a c e t a t e technique cedure was
followed.
Reagents used
methyl a c e t a t e were 99.99% i n p u r i t y
a c a r e f u l pro-
such as methanol
and
and i o d i n e c r y s t a l s
were p r e v i o u s l y d r i e d i n a d e s s i c a t o r which c o n t a i n e d gel
and
silica
drierite.
T h i s e x t r a c t i o n method was based on Rooney's and S t a p l e (231) ton's
, i t was,
however, improved i n terms of a v o i d i n g
c e r t a i n complexity In i t s d e s i g n and m i n i m i z i n g the r i s k of
contaminating the apparatus by moisture and o t h e r vapours
c a r r i e d away during e v a c u a t i o n and h e a t i n g .
Combustion
tube
c o n t a i n i n g s p i r a l s o f copper and n i c k e l as w e l l as s u l f u r i c a c i d and contaminated
i r o n t u r n i n g s were a l s o avoided.
125 Experimental Procedure 20-30 grams of an E S R - s t e e l sample cleaned
with 1,1,1-trichlorethane
were i n t r o d u c e d
and d r i e d w i t h h o t a i r
i n t o the r e a c t i o n chamber.
completely dehydrated by p a s s i n g taning d r i e r i t e ,
Argon was
i t through 3 U-tubes con-
s i l i c a - g e l - i n d i c a t i n g and a c t i v a t e d carbon
i n a U-tuhe immersed i n l i q u i d n i t r o g e n . functions:
f r e e o f oxide,
The argon had two
t o sweep out t h e a i r and humidity i n the f o u r
u n i t s and to pump the l i q u i d s from one u n i t t o another. t h i s l a s t purpose The
a vacuum was a l s o used.
whole d r y i n g o p e r a t i o n
was executed i n two hours.
Once the system was f r e e o f moisture and a i r the p r e d r i e d
For
dissolution of
i o d i n e c r y s t a l s was c a r r i e d out.
The next
step
i n t h i s technique was t o pump the i o d i n e s o l u t i o n e i t h e r by vacuum or by argon t o the f i r s t
f i l t e r i n g unit.
Then the
s o l u t i o n was pumped t o the r e a c t i o n chamber. When the s t e e l sample was completely d i s s o l v e d a f t e r 10-24 was
hours, the l i q u o r c o n t a i n i n g
sent t o the l a s t f i l t e r i n g u n i t .
r i n s i n g o f the f i l t e r e d was
inclusions
At t h i s l a s t u n i t ,
i n c l u s i o n s w i t h 99.99% methyl a l c o h o l
performed s e v e r a l times u n t i l the f i l t e r e d
completely c o l o r l e s s , i . e . was
the e x t r a c t e d
iodine free.
alcohol
This l a s t
was
operation
performed under an argon atmosphere. Extracted
i n c l u s i o n s were d r i e d and weighed
a f t e r s u l f i d e i n c l u s i o n s were e l i m i n a t e d .
b e f o r e and
Samples from sev-
126
e r a l ESR
i n g o t s were s u b j e c t e d under t h i s e x t r a c t i o n t e c h -
nique f o r v a r i o u s purposes, namely EPMA i n c l u s i o n chemistry
1) to c o r r o b o r a t e the
by q u a n t i t a t i v e
and q u a l i t a t i v e c r y s t a l l o g r a p h i c
(spectrophotometry)
(X-rays) a n a l y s i s
v e r i f y the v a l i d i t y of the t o t a l oxygen a n a l y s i s and determine how
4.5
2) to 3) to
i n c l u s i o n s were p r e s e n t i n the f i n a l product.
C r y s t a l l o g r a p h i c X-ray A n a l y s i s of E x t r a c t e d I n c l u s i o n s The e x t r a c t e d i n c l u s i o n s were c r y s t a l l o g r a p h i c a l l y
an-
a l y s e d by a P h i l i p s high angle d i f f r a c t o m e t e r and a DebyeS c h e r r e r camera was
114.83 mm
40 kV and 15 uA.
meter was
1° 26/min.
The
i n diameter.
The machine s e t t i n g
scanning r a t e used i n the d i f f r a c t o -
The camera i s designed such t h a t 2
measured on the f i l m corresponds to 1° 6.
mm
The d i s t a n c e along
the f i l m between the zero p o i n t and the r e f e r e n c e end i s 180mm. In both X-ray techniques the i r o n ka^ r a d i a t i o n was
(X = 1.9 36)
used. Although the amount of e x t r a c t e d i n c l u s i o n s ranged
from
10 t o 30 m i l l i g r a m s , p r i o r t o t h e i r X-ray a n a l y s i s , microphotographs
and q u a l i t a t i v e SEM
a p o r t i o n of the sample.
a n a l y s i s were performed
The c r y s t a l l o g r a p h i c X-ray
o f i n c l u s i o n s c l e a r l y showed a sequence of A ^ O ^ and 12 CaO*7Al C> 2
3
(as g i v e n by the C a O - A l 0 2
3
on
analysis
up t o C a O * A l 0 2
3
pseudo b i n a r y phase
127
diagram) as the Ca-Si d e o x i d a t i o n l e v e l was
increased.
It
i s worthwhile to mention t h a t i n the c a l c i u m aluminates riched i n calcium
(CaO•2Al 0 ~CaO•A1 0 2
3
2
3
and
CaO•Al 0^-12CaO• 2
7 A l 0 ) very wide d i f f r a c t i o n peaks and bands were 2
3
T h i s was
en-
observed.
a c l e a r i n d i c a t i o n of t h e i r lower degree of c r y -
stallinity.
The d i f f r a c t i o n bands corresponding
12CaO«7Al 0 2
3
to the
were very weakly t r a c e d .
G e n e r a l l y , the c r y s t a l p a t t e r n s showed from 6 to 16 p r i n c i p a l d i f f r a c t i o n bands with v a r i o u s i n t e n s i t i e s . t u r e s of at l e a s t two
i n c l u s i o n c r y s t a l s t r u c t u r e s and some
n i t r i d e s and c a r b i d e s were
4.6
observed.
Atomic A b s o r p t i o n A n a l y s i s A P e r k i n Elmer 306
model HGA-220 was
(Spectrophotometry)
spectrophotometer with a c o n t r o l l e r
used to analyze
c l u s i o n s from metal m a t r i c e s .
s l a g s and e x t r a c t e d i n -
The
l i t h i u m metaborate f u s i o n (232
procedure The
Mix-
a v a i l a b l e i n the l i t e r a t u r e
233) '
was
followed.
c o n c e n t r a t i o n of the elements of i n t e r e s t were determined
by u s i n g a p p r o p r i a t e l y matched standards
and blanks with
r o u t i n e procedure given i n the g e n e r a l i n f o r m a t i o n of Perkin-Elmer
manual.
s o l u t i o n a n a l y s i s was F + 0.2%,
Mg
G e n e r a l l y speaking Ca ± 0.2%,
the
the
the accuracy of the
A l ± 0.06%, S i ± 0.04%, .
± 0.002% and Fe ± 0.001
wt
%.
Stoichiometric
balances were c a r r i e d out on the bases t h a t Ca, A l , S i , Fe, and F were p r e s e n t as CaO, pectively.
Al 0 , 2
3
Under t h i s assumption
S i 0 , FeO, 2
MgO
and C a F
2
res-
the s t o i c h i o m e t r i c c a l c u -
l a t i o n s gave 10 0% with a minimum accuracy of +
1.0%.
Mg,
128 4.7
Metallographic
Analysis
Ingots were s e c t i o n e d l o n g i t u d i n a l l y i n such a manner t h a t a s l i c e 2.5 cm i n t h i c k n e s s across the diameter was obtained.
These p l a t e s were s u r f a c e ground and etched with a 50%
HCl-H^O s o l u t i o n a t 70-80°C f o r approximately
one hour.
l i q u i d p o o l marks made with m e t a l l i c tungsten
powder to
identify vealed.
deoxidation
Thus
l e v e l s and i n g o t s t r u c t u r e were r e -
L o n g i t u d i n a l d i s c r e t e sampling
(matching the pro-
g r e s s i v e sampling o f l i q u i d p o o l s and s l a g s ) t o perform spectrographic, were thus
i n c l u s i o n chemical
and t o t a l oxygen a n a l y s i s
obtained.
Samples o b t a i n e d
r a d i a l l y were used t o determine i n -
c l u s i o n s i z e d i s t r i b u t i o n s and d e n d r i t e arm s p a c i n g s .
The
o p t i c a l a n a l y s i s was performed u s i n g a Z e i s s u l t r a p h o t i n d i f f e r e n t i a l i n t e r f e r e n c e mode. tips,
Samples from e l e c t r o d e
l i q u i d pools and r a d i a l and l o n g i t u d i n a l specimens
from i n g o t s were ground on emery paper and diamond p o l i s h e d . P o l i s h i n g was c a r r i e d o u t t o determine i n c l u s i o n s i z e s and
t h e i r l o c a t i o n with r e s p e c t t o d e n d r i t e s i n samples ex-
t r a c t e d from l i q u i d p o o l and i n g o t s u s i n g : pastes met,
(Metadi
diamond compound
II) down t o 0.25 ym diamond p a r t i c l e s i z e , t e x -
m i c r o c l o t h and n y l o n p o l i s h i n g (Buehler)
cloth
( o i l and
water r e s i s t a n t and a l c o h o l and an o i l based l u b r i c a n t , (Geomet t h i n n e r M i c r o m e t a l l u r g i c a l MM218). By f o l l o w i n g the above sequence
removal o f i n c l u s i o n s
from metal m a t r i c e s i n any s i z e range was completely avoided. To determine the l o c a t i o n o f i n c l u s i o n s and d e n d r i t e arm spacings
standard O b e r h o f f e r ' s reagent was used t o l i g h t l y
e t c h these specimens.
Four and f i v e f a c e s of each
specimen
were p o l i s h e d , etched and microphotographs were taken a t a m a g n i f i c a t i o n such t h a t r e p r e s e n t a t i v e number of i n c l u s i o n s were i n each photograph.
The m a g n i f i c a t i o n used was very
dependent on the l e v e l o f d e o x i d a t i o n and the c h e m i s t r y o f the deoxidant.
130 CHAPTER V
RESULTS AND 5.1
DISCUSSION
Mechanism by Which E l e c t r o d e I n c l u s i o n s are In the l i t e r a t u r e review on i n c l u s i o n s
emphasis has
Eliminated
particular
been given to the p r e c i p i t a t i o n sequence.
has been e s t a b l i s h e d t h a t i n c l u s i o n s
according
It
to the
de-
o x i d a t i o n technique
e x h i b i t s e q u e n t i a l changes i n t h e i r
chemical
as s o l i d i f i c a t i o n takes p l a c e .
composition
t r a n s i t i o n s may
take p l a c e a t s u b s o l i d u s
These
temperatures;
parti-
c u l a r l y where s u l f i d e phases p r e c i p i t a t e . Thus, to f u l l y understand the mechanism by which i n c l u s i o n s are removed, e l e c t r o d e t i p s from 1020 and
rotor
(Ni-Cr-Mo) s t e e l s were s t u d i e d .
M.S.,
1020
4340
M.S.
ingots
were o r i g i n a l l y produced by a c i d e l e c t r i c furnace p r a c t i c e . The
4340 and
the r o t o r s t e e l were c a l c i u m aluminum t r e a t e d
in
the l a d l e .
Subsequently,
i n t o e l e c t r o d e s 76.2,
88.9
and
they 114.3
were mm
hot
rolled
i n diameters r e s -
pectively. 5.1.1
Behavior of O x i s u l f i d e I n c l u s i o n s i n 1020 Electrode The
and 1020
Tips
most complete p i c t u r e of the i n c l u s i o n d i s s o l u t i o n
the t r a n s f o r m a t i o n M.S.
M.S.
electrodes.
of the metal matrix
i s g i v e n by
the
Typical inclusions i n electrodes i n
t h i s s e r i e s of experiments, as r e c e i v e d , are shown i n Figures
(16)
and
(17).
T h e i r q u a l i t a t i v e (SEM)
chemical
131
composition are a l s o presented Two
(spectrum X-ray
w e l l - d e f i n e d phases are i d e n t i f i e d .
analysis).
The darker phase
i s e n r i c h e d i n S i and the l i g h t phase i s e n r i c h e d i n manganese s u l f i d e .
Iron was
a l s o found i n both phases.
M e t a l l o g r a p h i c s t u d i e s o f e l e c t r o d e t i p s which were subjected to c r i t i c a l
(ESR)
thermal g r a d i e n t s have c l e a r l y r e -
v e a l e d the e x i s t e n c e of s e v e r a l heat a f f e c t e d areas, F i g u r e s (18) t o
(21).
F i n d i n g s from t h i s r e s e a r c h
agreement w i t h p r e v i o u s t h e o r e t i c a l 19 20 '
(8)
in qualitative
and experimental work
(13
'
22) '
. show t h a t a u s t e n i t i c g r a i n growth and changes i n
the morphology of i n c l u s i o n s occurs between 0.5 the l i q u i d f i l m .
S u l f i d e i n c l u s i o n s are f i r s t
and subsequently
- 0.8
spherodized
d i s s o l v e d i n t h i s r e g i o n as w e l l .
i c a l composition of i n c l u s i o n s determine
cm above
The chem-
the c r i t i c a l l e n g t h
at which the above changes take p l a c e . The d r i v i n g f o r c e s t o produce these changes i n order of importance of
are:
the heat produced
by the h i g h r e s i s t i v i t y
the s l a g and hence the a u s t e n i t i c g r a i n growth of the e l e c -
trode t i p .
The deformation of i n c l u s i o n s and metal matrix which
produce sharp c o n c e n t r a t i o n g r a d i e n t s and the n o n - e q u i l i b r i u m nature of the i n c l u s i o n p r e c i p i t a t i o n — a s
indicated i n Figure
(5)
by the s i n g l e d o t t e d l i n e — c a n a l s o p r o v i d e a d r i v i n g f o r c e f o r this
sequence
'
6
4
~
1
6
6
\
The
Mn
depletion
around
i n c l u s i o n s i n the metal m a t r i x should another d r i v i n g f o r c e ' inclusions tory
according
166,199)^
6 4
a l s o be c o n s i d e r e d T h e
c n e m
i
c a
to t h e i r appearance and
( l o c a t i o n ) can be c l a s s i f i e d a s :
phase o x i - s u l f i d e s and
-]_
as
nature of
thermal h i s -
a) Deformed double
deformed s u l f i d e s , F i g u r e s
(16,17).
These i n c l u s i o n s were commonly found i n areas where i n c i p i e n t g r a i n growth was s u l f i d e s and
observed,
b)
Comparatively l a r g e
o x i s u l f i d e s which were l o c a t e d i n r e l a t i v e l y grown
a u s t e n i t i c grains, Figure
(22).
dark i n appearance, F i g u r e p r e c i p i t a t e d complex
c) S p h e r i c a l s i n g l e oxide phas
(23)
and d) R e l a t i v e l y small
(Ca, A l and
Si) o x i d e s .
of i n c l u s i o n s were l o c a t e d i n p a r t i a l l y and q u i d areas.
globular
The
l a s t type was
These two
rekinds
completely
li-
p r e f e r e n t i a l l y l o c a t e d i n the
l i q u i d f i l m and
i n droplets, Figures
As
shown i n
Figures
(20), areas at which p h y s i c a l and
chemical
(18)
to
(24,25).
changes take p l a c e e i t h e r i n i n c l u s i o n s or i n the metal t r i x are very w e l l d e f i n e d . previously of
time
described at
which
a l l y affected. conditions Figures ive
(SEM)
presence of the d r i v i n g f o r c e s
compensate the r e l a t i v e l y the
volume
of
(5).
the
Based on
and q u a n t i t a t i v e
e l e c t r o d e t i p and
predicted the
short
electrode
T h i s promotes q u a s i - e q u i l i b r i u m
approaching
(4) and
The
ma-
is
therm-
thermo-chemical
changes
given
experimental
(EPMA) i n f o r m a t i o n
periods
qualitat-
about how
i n c l u s i o n s are p h y s i c a l l y and
formed as a p r i n c i p a l consequence of the thermal
in
the
chemically gradients
tran
and
the chemical
describes
composition
of
inclusions,
a mechanism w h i c h
the removal of o x y s u l f i d e i n c l u s i o n s
is
proposed.
Once a g i v e n r e g i o n i n t h e e l e c t r o d e t i p i s a f f e c t e d by
the heat
metal
coming from
matrix
oidization
start
of
the l i q u i d
to experience
sulfides
and
slag
the
certain
oxisulfides
inclusions
changes.
takes place
simultaneously
t o the growth o f the a u s t e n i t i c
metal
Experimentally estimated
matrix.
positions
i n t h e e l e c t r o d e and
the
The
spher-
almost
grains of
temperatures
theoretical
and
the
along
axial
calculations
(8) indicate occur
that this
a t a b o u t 0.5
electrode 21).
transition
t o 0.8
cm
above t h e
i s a t a temperature
This finding
(a + p e a r l i t e -»• y) liquid
o f about
approximately
i r o n p l u s p e a r l i t e t o gamma i r o n
f i l m where
corresponds
t o the
transformation.
1350°C) s u l f i d e s
e n r i c h e d i n manganese a r e a l m o s t
the
(about
should
a l s o be
166)^
4
Figures
d e p e n d e n t on
literature'°"*' "'" * . 1
3
(4) and
t h e Mn:S
Oxisulfide
(5). ratio
(2,
zone
1000°C t o totally
dis-
a f a c t w h i c h i s i n a g r e e m e n t w i t h T u r k d o g a n ' s and
workers' f i n d i n g s ^ ^
in
the
alpha
In the
l a r g e g r a i n s were o b s e r v e d
sults
to
850-950°C, Figures
where r e l a t i v e l y
solved,
starts
co-
These r e as
indicated
inclusions containing
s i l i c o n , a c c o r d i n g t o Van V l a c k e t a l . ' * , Silverman'^ * * r, (129,163,168) ,. ., , . . and H i l t y and C r a f t s • a r e d i v i d e d i n two c a t e g o r i e s , 3
namely those
i n which the
Si:0 r a t i o
0
i n wt.
9
% i s either
smaller
or g r e a t e r than u n i t y . Low
S i phases, S i : 0 r a t i o s
obey T u r k d o g a n e t a l . ' s ' * *
4
less
than u n i t y
* equilibrium
qualitatively
stability
phase
diagram.
In the temperature
e q u i l i b r i u m phases
i n the Fe-Mn-S-0 system are r u l e d by the
u n i v a r i a n t h i n F i g u r e (5). by the gamma i r o n , "0"as oxisulfide. it
range of 900° t o 1225°C the
This univariant i s constituted
[Fe(Mn)0],
Under normal
"MnS"
and
%^ as
liquid
ESR-operating c o n d i t i o n s , however,
i s not expected t h a t the composition of i n c l u s i o n s
l y follows t h i s univariant
(h).
Instead
strict-
the b e h a v i o r given
by the " t r i p l e - d a s h e d " - l i n e s i n t h i s diagram i s expected, Figure
(5).
cumulated
Simultaneous w i t h the above changes
s o l u t e ac-
i n g r a i n boundaries, growth of some i n c l u s i o n s
and s u l f u r d e p l e t i o n from s u l f i d e i n c l u s i o n s are observed. These events f u l l y c o i n c i d e w i t h the formation o f oxisulfide,
i^, i n F i g u r e s (4,5).
that the s p e c i f i c temperature
I t i s important to note
a t which
%^ forms, i s s t r i c t l y
a f u n c t i o n o f the o r i g i n a l amount of Mn p r e s e n t and the degree which Mn(Fe)S' commercial content,
6 4
~
1 6 6
^.
(Mn:S
ratio)
the i r o n i s s a t u r a t e d w i t h Mn(Fe)0 and
I t a l s o has to be emphasized
s t e e l s i n these s e r i e s
that with
which have standard S
(0.02-0.05 wt % ) , t h e r e i s s u f f i c i e n t Mn and S i
p r e s e n t t h a t no l i q u i d o x i s u l f i d e e r a t u r e s lower than 1150°C.
u i d o x i s u l f i d e i s expected p e n e t r a t i n g the " o r i g i n a l "
(^)
i s p r e s e n t a t temp-
Above t h i s temperature
(131
was
liquid
*~'
the
liq-
132) to show up as m a t e r i a l
austenitic grainsi
a fact
which
indeed observed. In areas c l o s e r to the f u l l y transformed
(austenitic)
grains
the Mn content i n i n c l u s i o n s , due mainly t o the d i s s o l -
u t i o n o f s u l f u r i n the metal m a t r i x
i s i n c r e a s e d , F i g u r e (4).
Although the Mn content was not s i g n i f i c a n t l y g r e a t e r the i n c l u s i o n composition q u a l i t a t i v e l y obeyed the u n i v a r i a n t h. From approximately 1150° t o 1250°C the composition o f low S i o x i s u l f i d e i n c l u s i o n s changes and £^ i s expected t o f l u x the s o l i d s u l f i d e as S i l v e r m a n ' * ' * and Van V l a c k e t a l . ' 9
have i n d i c a t e d .
3
0
*
Mn w i l l c o n t i n u e i n c r e a s i n g a t slower r a t e s
than i n p r e v i o u s t r a n s f o r m a t i o n s as the temperature i s increased. Upon quenching f u l l y ytransformed
a sample taken from areas c l o s e r t o t h e region, duplex
( r e l a t i v e l y grown) o x i -
s u l f i d e s low i n S i should be p r e c i p i t a t e d ; a f a c t which i s c l e a r l y 'seen i n F i g u r e (22 a-b).
T h e i r major c o n s t i t u e n t s
were i d e n t i f i e d as a Mn r i c h s u l f i d e , Mn(Fe)S, and a Mn r i c h o x i d e , Mn(Fe)0.
At temperatures higher than 1250°C the
manganese s u l f i d e e n r i c h e d phase p r a c t i c a l l y d i s a p p e a r s ; a f a c t which was observed i n the q u a l i t a t i v e
(SEM X-ray
spectrum a n a l y s i s ) and s e m i q u a n t i t a t i v e (EPMA) a n a l y s i s , F i g ures
(23 and 25). A t temperatures
about
1370° t o 1420°C r e l a t -
i v e l y l a r g e a u s t e n i t i c g r a i n s a r e observed. i s exposed
t o t h i s temperature
to d e l t a i r o n t r a n s f o r m a t i o n .
The r e g i o n which
range experiences the gamma This t r a n s i t i o n i s i d e n t i f i e d
i n F i g u r e (5) as the i n t e r s e c t i o n o f the " t r i p l e - d a s h e d "
line
c r o s s i n g the u n i v a r i a n t g_ i n which d e l t a and gamma i r o n , 0
136 and
£^ are
i n equilibrium.
The major changes i n i n c l u s i o n
composition w i l l s t a r t j u s t a f t e r u n i v a r i a n t f i s a univariant i r o n , o, ^
equilibrium
and & , 2
where &
2
f i s reached,
which i s c o n s t i t u t e d i s the l i q u i d metal.
by d e l t a After
f_ i s reached the o n l y s o l i d compounds may be the Fe(Mn)0 and
a very s m a l l amount o f i r o n o x i d e .
I t i s important to
r e c a l l t h a t t h i s event takes p l a c e only i f S i content i s low 4-u i•n these li a tx-ot e r stages (130,169) ' Under t h i s c o n d i t i o n ,
between f_ and e u n i v a r i a n t s
d e l t a i r o n , o and £, are i n e q u i l i b r i u m 2
the remaining S from
i n c l u s i o n s goes i n s o l u t i o n i n d e l t a i r o n . the
Furthermore,
remaining i n c l u s i o n s w i l l be e x c l u s i v e l y c o n s t i t u t e d by
Mn(Fe)0.
This
l a s t step was p a r t i c u l a r l y c l e a r i n the range
a t which the l i q u i d f r a c t i o n was about the
where
l i q u i d f r a c t i o n was g r e a t e r than 0.5
completely d i s s o l v e d
and r e p r e c i p i t a t e d .
0.5.
In areas where
i n c l u s i o n s were Since t h i s
was i n c o n t a c t with the s l a g some r e p r e c i p i t a t e d clusions acter,
(very
few)
Figures
region
small i n -
(24, 25), show the s l a g char-
i . e . , some A l and Ca.
The
second category o f o x i s u l f i d e i n c l u s i o n s which S i : 0
r a t i o i s l a r g e r than u n i t y e x h i b i t an almost e q u i v a l e n t t e r n as the p r e v i o u s behavior l a s t stages. and
(i.e.
pat-
S i : 0 < 1 ) , except i n the
Instead of p r e c i p i t a t i n g Mn(Fe)0 and FeO, S i 0
MnO o r 2Mn0 w i l l p r e c i p i t a t e i n the f u l l y
austenitized
zone and when l i q u i d f r a c t i o n s a r e s m a l l e r than 0.5
2
These t r a n s f o r m a t i o n s as proposed and Van V l a c k e t a l . ^
1 3
^*
9
can be r e p r e s e n t e d by quaternary
diagrams, F i g u r e s (6) and (7). and
by S i l v e r m a n ' * * *
(7) as the temperature
As shown i n F i g u r e s (6)
i n c r e a s e s Mn ( and thus 'MnO')
and the p r o p o r t i o n o f o r t h o s i l i c a t e
i n c r e a s e s . As a r e s u l t
the l i q u i d u s f o r the "MnS" i s decreased, nificant sulfide if
range o f compositions i s increased.
thus over a s i g -
the amount of l i q u i d o x i -
Silverman'** * 9
has p o i n t e d o u t t h a t
the p r o p o r t i o n o f s i l i c a t e i s i n c r e a s e d , as observed i n
t h i s case
then a t temperatures
above 1300°C what i s l e f t
as a s o l i d
(from the p r e v i o u s Fe-O-S-Mn-system, FeO and
Mn(Fe)O) w i l l become almost completely l i q u i d . t r a n s f o r m a t i o n s as proposed from C t o B i n F i g u r e During t h i s
by Van V l a c k e t a l . '
(8a) and C
temperature
These
to B
3
0
*
occur
i n F i g u r e (8b).
i n c r e a s e "FeS", "MnS" and "FeO" a r e d i s -
s o l v e d , F i g u r e (25). Subsequent chemical r e a c t i o n s o f the i n c l u s i o n components which take p l a c e i n the f u l l y a u s t e n i t i z e d meta l and the p a r t i a l l y
l i q u i d zones a r e shown i n macrophotographs
(18a-b) and (21) and photographs
(23a) and 23b). These r e a c t i o n s
are r e p r e s e n t e d by:
2MnO + S i 0
2
Z
2MnO«Si0 «- M n S i 0
2
X
MnO«Si0
2
2
4
or 2MnO + S i 0
2
+ MnO
t Mn
0
+ MnSi0
3
138 I f a sample with t h i s composition and thermal h i s t o r y i s r a p i d l y c o o l e d then
. s i n g l e phase i n c l u s i o n s e n r i c h e d i n
manganese and s i l i c o n must be found, a f a c t which i s l a t e r c o r r o b o r a t e d w i t h the i n c l u s i o n chemical a n a l y s i s . f i n a l composition, a c c o r d i n g t o Van V l a c k e t a l . ' s
Their
work' °V 3
i s d i c t a t e d by the S i : 0 r a t i o and the amount of manganese p r e s e n t i n the e l e c t r o d e .
Thus, i f the S i content exceeds
the amount o f oxygen, as seen i n a n a l y s i s this series
from samples o f _3
(0.25 wt% S i and 90 ppm = 9.0 x 10
wt!)
then
a v i t r e o u s ( s i l i c e o u s ) type of i n c l u s i o n i s formed i n p l a c e of the monophasic t e p h r o i t e
(MnO'SiC^) o r rhodonite
(2MnO'SiO^) as the temperature i s i n c r e a s e d , Some e l e c t r o d e s the
Figures
(23a,b).
which were very r a p i d l y withdrawn from
s l a g showed s m a l l s i l i c e o u s and (iron) s u l f i d e s as r e -
precipitated inclusions exclusively Their q u a l i t a t i v e
(SEM) and s e m i q u a n t i t a t i v e (15)
as reported, i n the l i t e r a t u r e stoichiometric
i n the l i q u i d (EPMA)
film. analysis,
i d e n t i f i e d them as non-
f a y a l i t e ^ F e O S i C ^ ) compounds.
To c o n f i r m the p r e v i o u s l y
described
uence o f t y p i c a l a n a l y s i s
i s shown.
(spectrographic) analysis
i n wt. %
mechanism a seq-
The e l e c t r o d e as r e c e i v e d ,
follows: C
Mn
S
Si
0.19
0.71
0.026
0.025
P 0.01
chemical
i s as
The average i.e.
total
oxygen a n a l y s i s
as r e c e i v e d , was 90 ppm.,
a t c e n t r e l i n e 87 ppm., midradius
93 ppm.
The average
91 ppm.
i n c l u s i o n chemistry i n a t . %
and edges as r e -
c e i v e d , was S 35.0 The average
Si
Mn
Fe
27.0
37.0
balance
chemical composition o f i n c l u s i o n s l o c a t e d b e t -
ween the r e c r y s t a l l i z e d area and l i q u i d
f r a c t i o n s smaller
than 0.5,were ( i n at.%) as f o l l o w s Si
Mn
51.0 T h i s composition roite
( 1 3 0
S
46.0
2.0
immediately
Fe balance
suggest the formation o f teph-
>.
Due t o the number and s i z e of i n c l u s i o n s found i n the neighbourhood o f the l i q u i d
film
chemical a n a l y s i s
from
i n c l u s i o n s l o c a t e d i n l i q u i d f r a c t i o n s g r e a t e r than 0.6 were performed
o n l y on a q u a l i t a t i v e b a s i s .
aluminum i n these i n c l u s i o n s and
(25)
Calcium and
as shown i n F i g u r e s (24)
were t r a c e d .
T h i s p a r t i c u l a r e l e c t r o d e was remelted through a (50 wt% C a F , 30 wt% Al C> 2
2
Ca-Si d e o x i d i z e d . l i q u i d pool
3
and 20 wt% CaO) s l a g which was
The chemical a n a l y s i s o f i n c l u s i o n s
(a) and from the (ESR) i n g o t (b) i n a t . % .
from
140 are as f o l l o w s :
Al
Ca
S
a)
49.0
30.0
20.43
b)
46.0
30. 5
22.80
Thus, i n summary position
Mn
Fe
0.3
balance balance
the change i n i n c l u s i o n chemical com-
i n terms o f s u l f i d e s and low S i - o x y s u l f i d e s and the
m o r p h o l o g i c a l changes o f i n c l u s i o n s take p l a c e i n a u s t e n i t i c temperature
ranges
i n the metal matrix.
In i n t e r m e d i a t e stages
the d i s s o l u t i o n o f s u l f i d e s i n the metal matrix a l s o o c c u r s . These s e r i e s o f events r e p r e s e n t approximately total
10-30% o f the
" t r a n s f o r m a t i o n - d i s s o l u t i o n " mechanism and i t takes p l a c e
a t about
0.4 - 0.8 cm
above the l i q u i d f i l m .
The next 20-
40% o f the t r a n s f o r m a t i o n o f i n c l u s i o n phases occur
either
between the g_-f u n i v a r i a n t s , F i g u r e (5), i n the low S i cont e n t phases o r i n the C-B sequence o f t r a n s f o r m a t i o n s , F i g u r e (8a),
i n the h i g h S i c o n t e n t phases.
The next sequence o f
t r a n s f o r m a t i o n s takes p l a c e between f - e and B-A f o r low and h i g h S i c o n t e n t phases r e s p e c t i v e l y . f u l l y austenitized t i o n does not exceed remaining
I t occurs between the
r e g i o n and the p o i n t where the l i q u i d 0.5.
I t r e p r e s e n t s another 20-40%.
fracThe
" t r a n s f o r m a t i o n - d i s s o l u t i o n " takes p l a c e i n the
neighbourhood
of the l i q u i d f i l m where i n c l u s i o n
dissolution
i s the major mechanism and i n c l u s i o n s l a g r e a c t i o n s (forma t i o n o f lower m e l t i n g p o i n t i n c l u s i o n phases with s l a g chara c t e r ) a c t s as a very l i m i t e d mechanism (^1.0-3.0%).
141 5.1.2
Removal of Oxide and S u l f i d e I n c l u s i o n s i n 4340 and Rotor
Steels
Since the aim of t h i s r e s e a r c h i s t o g a i n an e x t e n s i v e understanding of the i n c l u s i o n - r e m o v a l mechanism; e l e c t r o d e s w i t h d i f f e r e n t m a t r i x - i n c l u s i o n compositions were a l s o a n a l yzed.
4 340-electrodes w i t h alumina type of i n c l u s i o n s and
t o o l s t e e l e l e c t r o d e s with c a l c i u m - a l u m i n u m - s i l i c a t e s were a l s o i n c l u d e d i n t h i s r e s e a r c h program. Macrophotographs
(19) and (20) show the sequence of t r a n s -
formations i n 4340 and r o t o r s t e e l s r e s p e c t i v e l y .
One of
the f i r s t d i f f e r e n c e s t o n o t i c e between these two types of s t e e l s i s t h a t i n the l a t t e r type a u s t e n i t i z a t i o n d i d not occur due t o t h e i r chemical composition the chemical composition of i n c l u s i o n s .
( e l e c t r o d e ) and t o Another
conse-
quence of t h i s i s t h a t s o l u t e p e n e t r a t i o n (between a u s t e n i t i c g r a i n s ) a t s u b s o l i d u s temperatures d i d not take p l a c e . molten
i n the r o t o r
steel
On the other hand i n the p a r t i a l l y
e l e c t r o d e much more"segregated
m a t e r i a l , " as a r e -
s u l t of the i n c l u s i o n d i s s o l u t i o n and the i n t e r a c t i o n o f the e l e c t r o d e with the s l a g , was observed a t l i q u i d
fractions
l a r g e r than 0.5. Once the d i f f e r e n t areas were i d e n t i f i e d
(incipiently
heat a f f e c t e d a r e a , semi or a u s t e n i t i z e d r e g i o n , l i q u i d f i l m i n o r out of the d r o p l e t ) i n each type o f e l e c t r o d e , m e t i c u l o u s c h e m i c a l a n a l y s i s of i n c l u s i o n s
(by EPMA) was
c a r r i e d out a t every 250-300 ym.
R e s u l t s o b t a i n e d from 4340
and r o t o r s t e e l e l e c t r o d e s are shown r e s p e c t i v e l y i n F i g u r e s (26) t o
(28).
Among the most important c o n c l u s i o n s from t h i s are the f o l l o w i n g :
study
a) s i n c e the a u s t e n i t i c t r a n s f o r m a t i o n
i n the r o t o r s t e e l was
almost absent
the i n c l u s i o n
transform-
a t i o n - d i s s o l u t i o n s t a r t e d t o take p l a c e p r i n c i p a l l y i n the partially liquid the s o l i d u s . electrodes
zone.
I t takes p l a c e about 0.3-0.5 cm above
b) A l and S i n i n c l u s i o n s i n both types of
(4340 and r o t o r s t e e l ) were g r a d u a l l y d i s s o l v e d
as the e l e c t r o d e experienced h i g h e r thermal g r a d i e n t s . changes, shown i n F i g u r e s
(26) t o
(28)
s t a r t t o take p l a c e
i n a very d i s c r e t e manner j u s t above the s o l i d u s f o r the r o t o r s t e e l and i n e a r l i e r ents) s u b s o l i d u s temperatures graph
(27), i t can be observed
isotherm
(lower temperature
i n the 4340 i n g o t s .
t h a t due t o a s t r o n g g r a i n
compositions were s h i f t e d i n 2500-4500 ym range. u
163
gradi-
c) In
growth and thus i n t e r g r a n u l a r s e g r e g a t i o n , the A l , Mn
suits
These
and
S
These r e -
. . ... . (1,17,18,129,131-133, i n agreement with p r e v i o u s r e s e a r c h ' ' ' ' '
169)
a
n
(
j^ w
t n
p
r
e
v
i
o
u
s
f i n d i n g s i n the
1020-series
show t h a t s u l f i d e s are the most t h e r m a l l y a f f e c t e d phases. Oxide i n c l u s i o n s i n deformed 4340 e l e c t r o d e s a l s o e x p e r i enced g r a d u a l m o r p h o l o g i c a l changes.
d)
The
largest
changes
i n the i n c l u s i o n chemical composition i n both e l e c t r o d e s a
manner
curred
in
equivalent the
to
partially
the
1020
liquid
M.S. region.
electrodes
in oc-
The presence
of
s t r o n g i n t e r g r a n u l a r and i n t e r d e n d r i t i c (segregated) m a t e r i a l which c o n t a i n e d
inclusion-formers
c l u s i o n s were completely l i q u i d Figure
c l e a r l y indicate that i n -
i n t h i s t r a n s i e n t zone.
(19a) from 4340-electrodes and (20) from the r o t o r
steel electrodes
strongly corroborate
these f i n d i n g s ,
e) Chemical a n a l y s i s i n 4340 e l e c t r o d e s , F i g u r e s
(26,27),
suggest t h a t S i and Mn i n i n c l u s i o n s , p a r t i c u l a r l y i n the liquid film
f o l l o w the same behavior as i n 1020 M.S., i . e .
i n c l u s i o n s get r i c h e r i n S i and Mn j u s t b e f o r e totally
dissolved.
they are
144 5.1.2.1
Removal of Oxides and S u l f i d e s i n 4340-electrodes
The sequence of changes i n the chemical
composition
of i n c l u s i o n s i n these e l e c t r o d e s i s summarized as f o l l o w s . The s p h e r o i d i z a t i o n and a subsequent fides
d i s s o l u t i o n of
sul-
j u s t as i n p r e v i o u s o b s e r v a t i o n s i n the 1 0 2 0
M.S.
e l e c t r o d e s i s the f i r s t
step i n the removal mechanism.
takes p l a c e i n s u b s o l i d u s temperature (26) and
It
ranges. F i g u r e s (19),
(27) i n d i c a t e t h a t these changes occur a t about
2000-
3000 ym above where the s o l i d u s of the a l l o y was m e t a l l o g r a p h i cally identified.
The most d r a s t i c changes, however, take p l a c e
i n areas where complete
a u s t e n i t i z a t i o n was
In f u l l y a u s t e n i t i z e d
observed.
areas and i n the r e g i o n
where the m e l t i n g s t a r t e d the A l and S i n i n c l u s i o n s
de-
crease w h i l e the S i , Mn and the Ca c o r r e s p o n d i n g l y i n c r e a s e . T h i s behavior i s accentuated as the l i q u i d f r a c t i o n i n creases.
A mixture of f e l d s p a r s
and garnets 2AI2O.J
(3M0«Al 0.j *3Si02) °
r
(9192) ' e
v
e
n
2
• 5Si02)
(MO "A^O^
cordierites
i n s t e a d of the o r i g i n a l aluminates
p r e c i p i t a t e as the l i q u i d f r a c t i o n approaches
«2Si02) (2M0* should
unity.
The
a c t u a l s t o i c h i o m e t r y of t h i s compound i s i r r e l e v a n t s i n c e M i n a l l of these compounds cart be e i t h e r Fe, Mn or Ca these s e r i e s of (91 solubility
compounds show v i r t u a l l y complete
and
mutual
92) '
.
The most important f i n d i n g , however,
i s t h a t oxides i n t h i s matrix are suddenly not so much i n s u b s o l i d u s temperature
transformed
ranges
as occurs i n
145 the 1020 M.S. as i n the s e m i - l i q u i d stage.
The presence
of i n c l u s i o n r e l i c s and " l i q u i d " e n r i c h e d i n i n c l u s i o n c o n s t i t u e n t s i s shown i n F i g u r e s (19c) and (2 0a) as i n t e r dendritic
segregates.
In the l i q u i d f i l m ,
about
50ym from the edge o f the
e l e c t r o d e t i p a s i m i l a r e f f e c t as t h a t seen i n the 1020 M.S. e l e c t r o d e s was observed.
Since t h i s volume of l i q u i d
e l e c t r o d e was s u b j e c t e d to a d i r e c t i n t e r a c t i o n with the s l a g a s h i f t i n the chemical composition o f i n c l u s i o n s was detected.
T h i s i n d i c a t e s t h a t the e l e c t r o d e
composition was completely transformed. of i n c l u s i o n s i n the l i q u i d f i l m it
4340 (I)
a) b)
4340 (II)
a) b)
inclusion
The chemical
analysis
(a) i n the d r o p l e t or
are ( i n at.%) as f o l l o w s : Al
Ca
S
19.0 7.0
2.78 3.90
_
8.27 6.30
9.30 11.00
1.5 _
-
Si
Mn
78.0 70 .20
0.22 17.40
56.0 56.0
26.46 27.60
F i n a l l y , the chemical composition o f i n c l u s i o n s i n e i t h e r (a') l i q u i d
434 0 (I)
4340 (II)
(pool) stage o r .(b')the i n g o t correspond t o : a')
Al„0_ and t r a c e s o f s i l i c a + MnS I I
b')
A1 0
a')
Ca«Al 0
b')
2
2
3
3
+ MnS I I
2
3
12CaO-7Al 0 2
3
146
I t i s important t o note t h a t 4340 (I) was A l - d e o x i d i z e d and 4340 (II) was CaSi t r e a t e d . deoxidized
Ingot 4340
(I) was
0.02 kg ton "'') and i n g o t 4340 (II) was h e a v i l y -
CaSi d e o x i d i z e d (10 Kg t o n ) - 1
both i n g o t s were r e f i n e d
through a 50wt % C a F , 30 wt% Al C> 2
2
3
and 20 wt% CaO.
I f the above chemical analyses are compared clearly
slightly
i t can
be seen t h a t i n c l u s i o n r e l i c s from the bulk o f the
e l e c t r o d e , i f any, are d i s s o l v e d and r e p r e c i p i t a t e d i o n s which show the s l a g c h a r a c t e r .
inclus-
I n c l u s i o n s i n the l i q u i d
f i l m are s m a l l and complex i n composition.
Therefore, i n -
c l u s i o n s l o c a t e d i n t h i s narrow f i l m do not r e p r e s e n t i n any way what happened i n the t r a n s f o r m a t i o n - d i s s o l u t i o n o f p r e v i o u s stages.
5.1.2.2
Calcium-Aluminum S i l i c a t e s
i n a Rotor
(Ni,Cr,Mo)
Steel The
i n c l u s i o n chemical composition was m e t i c u l o u s l y
determined
at discrete locations i n electrode tips.
These
a n a l y s i s were c a r r i e d out a t every 250-300 ym s t a r t i n g the l i q u i d f i l m . studies
as i n p r e v i o u s
(1020 and 4340), they were arranged a c c o r d i n g t o
the s p e c i f i c film
For the sake of c l a r i t y
from
area a t which they belonged
i.e., liquid
( i n and out o f d r o p l e t ) , p a r t i a l l y molten
s e v e r a l l i q u i d f r a c t i o n s and a t s u b s o l i d u s
area a t
temperatures.
147 A summary of the r e s u l t s o b t a i n e d by EPMA and t h e i r c l a s s i f i c a t i o n a c c o r d i n g t o the thermal h i s t o r y a t which these volumes were subjected
i s shown i n F i g u r e
Since these e l e c t r o d e s during
(28) *
experienced almost no g r a i n growth
a u s t e n i t i z a t i o n , the composition o f i n c l u s i o n s was
exclu-
s i v e l y changed i n r e g i o n s c l o s e t o the s o l i d u s temperature o f the alloy.
I t i s important t o n o t i c e t h a t the s i z e o f the mushy zone
i n the r o t o r s t e e l (> 2800 pm) i s l a r g e r than i n 1020 M.S. o r the 4340 s t e e l s .
The s l a g - i n c l u s i o n d i s s o l u t i o n ( i n only
remaining i n c l u s i o n s )
took p l a c e
of the o t h e r e l e c t r o d e s ,
i.e.
very few
i n a manner e q u i v a l e n t
liquid
to a l l
film.
T y p i c a l a n a l y s i s o f i n c l u s i o n s from these areas i n a t . %, are as f o l l o w s : Al
Ca
Si
i n g o t (1)
25.18
61.15
8.65
5.0
ingot
25.88
61.36
9.40
3.5
38.48
20.20
34. 85
6.50
61.16
21.63
16.38
0. 82
62.35
2.27
3.16
0.16 1.16
Partially Liquid
Liquid
( f ^ ^ 1)
(2)
S
Mn
Film out in
A f t e r ESR
of droplet droplet
148 These
i n g o t s were r e f i n e d through the 50% C a F , 2
30% A ^ O ^ and 20% CaO s l a g .
T h e i r d e o x i d a t i o n was c a r r i e d
out with the CaSi a l l o y a t approximately
5.1.3
0.1-0.2 Kg ton . 1
F i n a l Remarks About the Removal Mechanism I n c l u s i o n s i n e l e c t r o d e t i p s d u r i n g ESR are removed by
d i s s o l u t i o n i n the metal matrix
i n w e l l d e f i n e d steps a c -
c o r d i n g t o the e l e c t r o d e i n c l u s i o n composition i n the e l e c t r o d e t i p .
and l o c a t i o n
The thermal g r a d i e n t to which the
e l e c t r o d e and hence i n c l u s i o n s are s u b j e c t e d d r i v i n g f o r c e f o r t h e i r removal.
i s the main
T h i s mechanism, however,
does n o t correspond
t o t h a t p r e v i o u s l y d e s c r i b e d i n the
l i t e r a t u r e review.
Gradual d i s s o l u t i o n along the heat
a f f e c t e d zones or s t r i c t d i s s o l u t i o n of i n c l u s i o n s a t the l i q u i d film,
and the "washing o f f " or the mechanical r e -
moval o f i n c l u s i o n s are not o p e r a t i v e mechanisms. stead
In-
a mechanism based on s u b s t a n t i a l experimental
t h e o r e t i c a l evidence chemical
and
which suggests the quasi-thermo-
e q u i l i b r i u m of i n c l u s i o n s and t h e i r l o c a t i o n
is indicated. The
s e r i e s of a c t u a l chemical
transformations
and the
d i s s o l u t i o n of i n c l u s i o n s i n electrode t i p s are s t r i c t l y c o n f i n e d t o a d i s t a n c e no g r e a t e r than 0.5 - 0.8 cm above the l i q u i d f i l m .
S u l f i d e s i n the Fe-Mn-S-0 system and o x i -
s u l f i d e s i n the Fe-O-S-Mn-Si system a r e p a r t i a l l y d i s s o l v e d and p a r t i a l l y transformed
a t subsolidus
temperatures..
149 Reactions between i n c l u s i o n components and the metal matrix leads t o the s o l u t i o n o f c e r t a i n i n c l u s i o n components as
"FeS", "FeO", "MnS", e t c . , which i n i t i a t e
t i o n i n a u s t e n i t i c g r a i n boundaries.
such
solute penetra-
This f a c t implies
that
these i n c l u s i o n s are a mixture o f phases, namely "MnS", "FeO" and
a small amount o f "FeS".
i n c l u s i o n s are subjected
The chemical r e a c t i o n s t o which
and t h e i r d i s s o l u t i o n i n the metal
m a t r i x a r e q u a l i t a t i v e l y p r e d i c t e d by u s i n g diagrams a v a i l a b l e (164 —16 6) i n the l i t e r a t u r e S-0
.
S u l f i d e s belonging
t o the Fe-Mn-
system and o x i s u l f i d e s low i n s i l i c o n which belong t o the
general
Fe-O-S-Si-Mn system i n e l e c t r o d e t i p s f o l l o w a q u a s i -
thermochemical e q u i l i b r i u m d i c t a t e d by the F i g u r e e q u i l i b r i u m phase diagram workers
is
n
o
obtained
(5).
This
by Turkdogan and c o -
t completely obeyed and i n s t e a d a be-
h a v i o r g i v e n by the " t r i p l e dashed l i n e " Inclusions belonging
i s followed.
t o the Fe-Si-Mn-O-S system which
have a s i l i c o n content such t h a t the S i : 0 r a t i o i s g r e a t e r than 0.5, f o l l o w the FeO-MnS-MnO-Si0 quaternary system dev2
eloped ure
by S i l v e r m a n ' * * ^ 9
(9).
The b e h a v i o r o f these i n c l u s i o n s i s a l s o complemented
by the b i n a r y MnO-Si0 ernary (8a)
as i n d i c a t e d by the arrow i n F i g -
2
as p a r t o f the Si0 ~MnO-FeS-MnS quat-
diagram developed by Van V l a c k
and (8b).
This proposal
2
et a l .
, Figures
corresponds l a r g e l y t o t h a t a l (168) ready suggested by H i l t y and C r a f t s , i . e . the pseudo
150 t e r n a r y behavior
of the m e t a l - o x i d e - s u l f i d e phases.
Thermo-
d y n a m i c a l l y more s t a b l e phases such as Mn(Fe)0, MnO, MnO«Si02A
2 M n 0 « S i 0 2 / c a l c i u m aluminates,
uminates, e t c . , a r e transformed bourhood o f the l i q u i d
calcium s i l i c o n a l -
and d i s s o l v e d i n the n e i g h -
f i l m between the f u l l y a u s t e n i t i z e d
area and the f u l l y l i q u i d metal.
Electrode inclusion
( i f any) i n the l i q u i d
f i l m r e a c t , up t o a l i m i t e d
w i t h the s l a g producing
complex i n c l u s i o n phases.
Finally,
relics
extent
i n c l u s i o n s i n ESR i n g o t s which show the e l e c t -
rode i n c l u s i o n c h e m i c a l composition s t a b l e ESR c o n d i t i o n s , "hot t o p p i n g "
Si02^
stages.
a r e found o n l y under un-
i . e . a t the s t a r t i n g and d u r i n g the
151
5.2
The Chemical
I n f l u e n c e o f the E l e c t r o d e , Slag
and D e o x i d i z e r on the Chemical Composition o f Inclusions
5.2.1
D e s c r i p t i o n of Experimental F i n d i n g s
5.2.1.1
P r e l i m i n a r y S t u d i e s on the E f f e c t o f the S l a g and the D e o x i d a t i o n
4340-electrodes
31.75 and 44.75 mm
i n diameter and with
d i f f e r e n t i n c l u s i o n chemical compositions were r e f i n e d t o 75 mm i n diameter
i n g o t s a t m e l t i n g r a t e s o f about
1.3 Kg m i n
through d i f f e r e n t s l a g systems and under a p r o t e c t i v e
- 1
(argon)
atmosphere. The components o f the s l a g systems
(CaF , CaO, Al-^O^ 2
and S i 0 ) were p r e v i o u s l y d r i e d a t 650°C and the " c o l d 2
s t a r t i n g procedure" was f o l l o w e d . through s l a g s which had s e v e r a l S i 0 f e r e n t s l a g systems were chosen CaSi a l l o y and A l , Table form o f p e l l e t s
(99.9%).
E l e c t r o d e s were r e f i n e d 2
contents.
Two
dif-
t o be d e o x i d i z e d w i t h a
(X). The aluminum was i n the The CaSi a l l o y c o n t a i n e d 62.5
152
wt.
% S i , Table
(^ 2.3
(IX).
The d e o x i d a t i o n r a t e s were c o n s t a n t
Kg/ton) and they were performed
when steady r e m e l t i n g
c o n d i t i o n s were observed. The purpose
of these experiments
were:
i ) to
determine
the chemical composition of i n c l u s i o n s as an e x c l u s i v e e f f e c t of the s l a g composition
(and e l e c t r o d e ) .
i i ) to i n -
v e s t i g a t e what changes i n i n c l u s i o n compositions c o u l d be achieved by u s i n g the same s l a g system to compare r e s u l t s from
and d e o x i d i z e r s
( i ) a g a i n s t ( i i ) and
(iii)
and
to d e t -
ermine the most a p p r o p r i a t e s l a g systems to be used i n the 200 mm
i n diameter
ESR-furnace.
Experimental r e s u l t s are shown i n Table s l a g chemical composition i n wt.
%
#
(X)
where the
the i n c l u s i o n chemical
composition i n a t . %, the chemical composition of i n c l u s i o n s i n e l e c t r o d e s and the major i n c l u s i o n phases are g i v e n . i s important to note t h a t although c l u s i o n s was scatter
performed
(± 5.0
- 7.0%)
It
chemical a n a l y s i s of i n -
on a l a r g e number
(30-40) a wide
i n t h e i r a n a l y s i s was
found.
s c a t t e r i s p r i n c i p a l l y a t t r i b u t e d t o the i n c l u s i o n
The size
153
distributions
( l e s s than 5ym
i n diameter) and
steady r e f i n i n g c o n d i t i o n s due s l a g systems.
to the use
of
to the
inappropriate
As a consequence o f t h i s l a c k of
o c c a s i o n a l l y an uneven s u r f a c e of the ingot was and
l i q u i d enriched
un-
stability observed
i n d e o x i d i z e r s and oxygen p r e c i p i t a t e d
alumina type of i n c l u s i o n s i n a c o n f i n e d volume, F i g u r e The
first
oxidizer was
s e t of experiments
performed without a
than 10
wt
%.
Calcium-aluminum s i l i c a t e s i n
i n c l u s i o n s were found above t h i s l e v e l . more than two
i n c l u s i o n phases was
same sample. Table
was
composition
s p e c i f i c a l l y ingots as i n g o t
of i n c l u s i o n s i n i n g o t
showed almost e x c l u s i v e l y c a l c i u m (9)
presence of
commonly observed i n the
second s e r i e s of experiments
c a r r i e d out,
The
(X).
v i r t u a l l y the same behavior
and
de-
showed s i l i c o n i n i n c l u s i o n s where S i C ^ i n s l a g s
higher
The
(29).
i n which (7) and (1).
The
aluminates.
chemical
(1) and
whereas i n i n g o t
higher.
reference
Ingots
(7)
the Ca:Al r a t i o ,
cases.
t e n t of i n c l u s i o n s i n i n g o t s (9). i t was
(9), showed
(1), used as a
a l s o showed c a l c i u m aluminates,
however i s l a r g e r than i n p r e v i o u s
deoxidation
The
s i l i c o n con-
(7) were e q u i v a l e n t ,
I f the a n a l y s i s of i n c l u s i o n s from e l e c t r o d e s used i n ingots
(1) to
(7) are compared a g a i n s t
(9) and
(10)
then
154 i t can be i n f e r r e d t h a t the i n c r e a s e d S i content comes from the e l e c t r o d e , Table
(X).
c a l c i u m aluminates, was
The maximum c a l c i u m c o n t e n t , as
found i n i n g o t s remelted
through
r e l a t i v e l y high CaO
(15-22 wt %) and r e l a t i v e l y low
( l e s s than 10 wt %)
slags.
The and
i n c l u s i o n chemical a n a l y s i s performed
15/15/15) s l a g system, t h e i r composition with and
the
(2)
(55/
without
On the other hand,
f o r e l e c t r o d e s r e f i n e d under the same s l a g system and o x i d i z e d w i t h aluminum; lower
2
i n ingots
(10) shows t h a t by r e f i n i n g e l e c t r o d e s through
Ca-Si d e o x i d a t i o n remains u n a l t e r e d .
Si0
de-
s i l i c o n and r e l a t i v e l y higher
c a l c i u m and hence higher aluminum i n i n c l u s i o n phases i s found. R e s u l t s i n t h i s i n v e s t i g a t i o n c l e a r l y show t h a t the i n trinsic
s l a g e f f e c t i n the chemical composition of
f o l l o w s a very w e l l d e f i n e d p a t t e r n . the S i 0 (5),
2
S l a g systems i n which
content i s lower than 10 wt
(7), and
dominantly
2
2
3
%
as i n i n g o t s (1), (4),
(9) y i e l d e d i n c l u s i o n compositions which p r e -
l i e i n the C a O - A l 0
on the A l 0
inclusions
r i c h side, i . e .
3
pseudo b i n a r y phase diagram
alumina
types and low
CaO-
aluminates. To c o r r o b o r a t e these f i n d i n g s periments
i n the 200 mm
other s e r i e s of
ESR-furnace were performed.
exEx-
p e r i m e n t a l d e t a i l s and a summary of f i n d i n g s are g i v e n i n
155
Tables
(VIII) and
(XI).
The main p o i n t to be c o n s i d e r e d
i n t h i s s e t of experiments (0.02
kg ton
1
i s the low l e v e l of d e o x i d a t i o n
) to which the s l a g - l i q u i d p o o l was
j e c t e d and the e l e c t r o d e s u r f a c e p r e p a r a t i o n . Table
(XI)
sub-
As seen i n
c o n s i s t e n t q u a l i t a t i v e r e s u l t s are found
terms of the chemical composition of i n c l u s i o n s
in
i n both
ESR-furnaces. P a r t i c u l a r emphasis should be g i v e n to r e s u l t s t a i n e d from i n g o t (11).
A rotor steel electrode
ob-
with
chemical composition i s g i v e n i n Table
(VII)
average
( i n at%) as f o l l o w s :
was
i n c l u s i o n chemical composition Al
Ca
Si
S
28.5
24.1
42.0
2.2
Mn
2
12 wt
% Si0
2
and 6 wt
% MgO
Fe
2.5
remelted through a 49 wt % C a F , 16 wt
A^O-j,
slag.
balance % CaO,
(ESR)
chemical ingot,
i s as f o l l o w s :
Al 44.70
Ca 13.60
Si
S
Mn
24.5
7.4
9.2
Since the at.%Mn:at.%S r a t i o i s approximately it
17 wt %
The average
composition o b t a i n e d from 40 i n c l u s i o n s i n the in at.%
and with an
can be assumed t h a t a MnS
s u l f i d e phase was
phase was
Mg + Fe balance one
then
precipitated.
The
commonly found surrounding the oxide phase.
156 X-ray composition p r o f i l e s and maps as w e l l as d i s p e r s i v e X-ray
spectrum
a n a l y s i s confirmed these f i n d i n g s .
oxide phase was
not s p h e r i c a l
The
(as c a l c i u m aluminates-
c a l c i u m s u l f i d e i n c l u s i o n s ) , i n s t e a d angular oxides were observed. maining
I f the above v a l u e s are normalized
then the r e -
elements can be f u r t h e r analyzed; thus the o v e r a l l
composition i s Al
Ca
Si
^54
^16
^30
From these computed v a l u e s the r a t i o s f o r A l , Ca and S i r e s p e c t i v e l y are approximately
4:1:2.
Thus, the f e a s i b l e phase
p r e s e n t i n these type of i n c l u s i o n s c o u l d be: CaO«2Al 0 '2Si0 2
T h i s compound, as i n d i r e c t l y 9 2
^
3
2
s t a t e d i n the l i t e r a t u r e
review*
has not been r e p o r t e d as an i n c l u s i o n phase; i t can
i n s t e a d a f e l d s p a r of the type M 0 « A 1 0 « 2 S i 0 2
can be e i t h e r FeO,
MgO,
MnO
or CaO.
3
2
Based on
i n which
individual
a n a l y s i s of i n c l u s i o n s ; alumina r i c h phases and CaO-Al 0 2
3
MO
complex
s i l i c a t e s were indeed the major phases p r e s e n t .
Hence, the o n l y f e a s i b l e compounds i n t h i s i n g o t are the Al 0 «CaO•2Si0 2
3
Al_0_
2
( a n o r t h i t e ) phase i n c o n j u n c t i o n with
(corundum) e n r i c h e d phase.
an
be
157
5.2.1.2
I n t e r m i t t e n t CaSi A d d i t i o n s and the R e a c t i o n Scheme
Since no d i f f e r e n c e was
found between d e o x i d i z e r s
(Al and the Ca-Si a l l o y ) i n s m a l l ESR-furnace, the chemical composition of i n c l u s i o n s of
(i.e.
i n terms of precipitation
c a l c i u m aluminates and up t o a given e x t e n t c a l c i u m
s u l p h i d e s ) , an e x t e n s i o n of these experiments
i n the
i n d u s t r i a l s i z e ESR-furnace was
These e x p e r i -
ments are l i s t e d
i n Table
c a r r i e d out.
(VIII).
50 grams of
the Ca-Si a l l o y were a l t e r n a t e l y added a t two
FeO
semi-
and
discrete
time
i n t e r v a l s d u r i n g r e f i n i n g under two d i f f e r e n t s l a g systems; namely 50/30/20 and 70/30/0. C a F , A^O^, 2
and the CaO
These f i g u r e s r e p r e s e n t the
compositions
i n wt %.
1020
M.S.
e l e c t r o d e s whose chemical composition and i n c l u s i o n chemi s t r y have a l r e a d y been d e s c r i b e d , were r e f i n e d a t about 1 kg min
1
, with and without
(RIII-W and RII-W r e s p e c t i v e l y )
an argon atmosphere s h i e l d i n g . T o t a l oxygen content, s l a g chemical a n a l y s i s from
samples
taken d u r i n g r e f i n i n g , i n g o t chemical a n a l y s i s and
inclusion
chemical composition as w e l l as s i z e d i s t r i b u t i o n s
from
i n g o t s were determined.
These r e s u l t s are shown i n F i g u r e s
(30) to
(36).
S i , Mo,
Cr, A l and N i were analyzed i n the s l a g s and i n g o t s
respectively.
Ca, F, A l , S i , Mn
and Fe and Mn,
C, P,
S,
Elements with s i g n i f i c a n t changes i n t h e i r
composition are p l o t t e d . Figures
(32) and
(33a-b) from RII-W and RIII-W, show the
158 e f f e c t of the Ca-Si a l l o y
(intermittent) additions.
These
graphs show t h a t the d e o x i d i z e r produces a sharp decrement i n a l l of the s l a g c o n s t i t u e n t s .
Correspondingly,
the chem-
i c a l composition of i n g o t s show a sharp increment i n A l and
S i , Figures
considered
(34,35).
Mn,
Other important p o i n t s to
be
from these graphs are t h a t s u l f u r i s decreased
when the Ca a l l o y was
added and
i r o n oxide a d d i t i o n s i n the
s l a g d i d not produce as sharp changes i n the i n g o t composit i o n as d i d a d d i t i o n s o f the d e o x i d i z e r . comes from the e l e c t r o d e
gradually
as r e f i n i n g takes p l a c e ,
Figure
The
and
response time of the system was
The
i n the s l a g
(33b). a l s o observed.
RII-W
i n about 100-150 seconds
RIII-W w i t h i n 200-250 seconds. The
i n the s l a g and
s i l i c o n which
increased
(32) and
showed a response to the d e o x i d i z e r
The
e f f e c t of the
deoxidizer
i n g o t decrease i n a r e l a t i v e l y slow manner.
sudden changes i n FeO
content
(expressed
as wt
% of
Fe)
i n the s l a g as w e l l as the abrupt changes i n the t o t a l oxygen content and
the i n c l u s i o n chemical composition as a d i r e c t
e f f e c t o f these i n t e r m i t t e n t ( C a - S i )
a d d i t i o n s are the most
important responses i n the r e f i n e d i n g o t , F i g u r e s (33).
I t i s important t o n o t i c e t h a t there was
r e a c t i o n time t o show t h e • i n d i v i d u a l Ca or FeO o f oxygen i n (RIII-W), F i g u r e The
to
not enough e f f e c t s i n terms
(30).
d i f f e r e n c e between RII-W and
s t a r t i n g s l a g compositions and
(30)
RIII-W are
the
the presence o f an argon
s h i e l d i n g atmosphere i n the l a t t e r , T a b l e
(VIII).
Thus
a
159
lower oxygen content
(15-20 ppm)
and observed, F i g u r e s The
(30)
and
i n RIII-W was
expected
(31).
main c o n c l u s i o n from the above r e s u l t s i s t h a t
ESR-process i n terms of s l a g s and plex reactor.
The
s l a g do not occur
d e o x i d i z e r s i s a very com-
s e r i e s o f r e a c t i o n s t a k i n g p l a c e i n the independently
the l i q u i d p o o l and
of the ones t a k i n g p l a c e i n
i n the i n g o t , i . e .
p o s i t i o n i s not c o n t r o l l e d by one 5.2.1.3
the
R e f i n i n g of 1020 Deoxidized
M.S.,
Continuously
the
i n c l u s i o n com-
single factor. 200
mm
Diameter Ingots
with Aluminum
To g a i n a b e t t e r understanding of the above sequence of r e a c t i o n s , complementary and more d e t a i l e d experiments by which r e a c t i o n s i n the l i q u i d monitored were planned.
s l a g l i q u i d p o o l and The
purpose of these experiments was
s l a g compositions.
to d i s c r i m i n a t e the
to i d e n t i f y s e p a r a t e l y the e f -
f e c t of d e o x i d i z e r s on the s l a g d u r i n g the three the r e f i n i n g p r o c e s s . c l u s i o n chemistry a t i o n and / and
f o r other
stages
through an i n i t i a l
% CaO,
was
i n g o t s , CaSi and
of
intrinsic electrode-slag-in-
of a r e f i n e d (1020) i n g o t , without
remelted 20 wt
The
50 wt%
CaF^,
deoxid-
30 wt
%
used as the b a s i s of comparison Al-deoxidized.
the The
intrinsic
e f f e c t o f the e l e c t r o d e i t s e l f on the s l a g ( i . e .
without any d e o x i d i z e r ) . a n d
A^O^
be
next s e t o f experiments i n c l u d e d
r e f i n i n g of e l e c t r o d e s through e q u i v a l e n t
chemical
ingots could
160
The
i n g o t i d e n t i f i e d as R I - I l was
argon atmosphere and "FeO"
r e f i n e d under an
i n the absence of a deoxidant.
i n the s l a g and
the t o t a l oxygen content
approximately constant
i n the i n i t i a l
stages,
The
remained Figure
(37).
I n c l u s i o n s i n samples e x t r a c t e d from the l i q u i d p o o l and
from
the i n g o t were e s s e n t i a l l y i d e n t i f i e d as s p h e r i c a l s i n g l e p a r t i c l e s or as small c l u s t e r s of alumina type and
a-A^O-j) and
The
alumina type was
fides,
l e s s f r e q u e n t l y as f a y a l i t e type
i n the s l a g was
The
to 0.125
wt.%
MnS
II.
The
considerable. up to
s i l i c o n content
(2FeO«Si02) •
u s u a l l y a s s o c i a t e d with manganese s u l -
(Fe,Mn)S and
the bottom and
(FeQ'A^O^
gradual
i n c r e a s e of
I t ranged from 0.75
about 2.0
wt.%
a l y s i s i s shown i n F i g u r e
The
2
at
at the top of the
ingot. up
i n g o t chemical
an-
(38).
Experiments which are e q u i v a l e n t to the s m a l l
M.S.
wt.%
i n the i n g o t ranged from 0.095
from s t a r t to f i n i s h .
and A l ) d e o x i d i z e d
Si0
(Ca-Si
(4340) ingots were a l s o c a r r i e d out.
e l e c t r o d e s were r e f i n e d through e q u i v a l e n t
slags
1020
and
samples from l i q u i d s l a g s and pools were e x t r a c t e d while
continu-
o u s l y i n c r e a s i n g a d d i t i o n s of d e o x i d i z e r s to the s l a g were made.
Table
experiments.
(VIII) summarizes the d e t a i l s of t h i s s e t of Refined
i n g o t s r e f e r r e d to as R I I - I l and
RII-I2 were aluminum t r e a t e d by u s i n g two
different
deoxid-
a t i o n sequences.
Deoxidation
r a t e s were 3.63,
6.1,
6.8
and
7.6
1.21,
3.64,
and
12.12
kg
kg t o n
- 1
and
2.42,
4.85,
6.06
ton
- 1
161 f o r R I I - I l and RII-I2 r e s p e c t i v e l y .
RII-I2 was CaSi (50
grams) d e o x i d i z e d i n the i n i t i a l r e f i n i n g stage. .. The i r o n oxide content, g i v e n as wt- % i r o n i n F i g u r e s (39) and (40), slowly and c o n t i n u o u s l y decreased
from about
0.6 wt.% down t o about
0.4 wt-%
as the aluminum a d d i t i o n
r a t e s were i n c r e a s e d .
While h i g h d e o x i d a t i o n r a t e s
r e l a t i v e l y steady t o t a l oxygen content
( R I I - I l ) and hence
e q u i l i b r i u m behavior i n i n c l u s i o n compositions, o x i d a t i o n r a t e s produced parameters,
(RII-I2),
an o s c i l l a t i n g behavior
Figures
(41, 42) and
F i n d i n g s i n these experiments,
produced
the low dei n both
(43,44).
although not as drama-
t i c as the (Ca-Si) i n t e r m i t t e n t l y d e o x i d i z e d i n g o t s , show t h a t the aluminum as a d e o x i d i z e r a l s o produces s i m u l t aneous exchange r e a c t i o n s between two l i q u i d s o f the g e n e r a l type
(11) and r e a c t i o n s o f the type
.(12).
The elements i n -
v o l v e d i n these r e a c t i o n s , i n a manner e q u i v a l e n t t o the i n termittent itself,
Ca-Si a d d i t i o n s
F i g u r e s (37-40) and
are the S i , Mn and the A l by (43-46).
The most s e n s i t i v e p a r t s of the system t o the aluminum d e o x i d a t i o n were the t o t a l oxygen content and the chemical composition o f i n c l u s i o n s r e p r e s e n t e d by the a t . % C a : a t % A l i n Figures Figure
(43) and (44). (40) from RII-I2
shows t h a t the aluminum was
a b l e t o s l o w l y overcome the s i l i c o n e f f e c t from the e l e c t r o d e .
162 Hence, from the c a l c i u m
t o aluminum, r a t i o of i n c l u s i o n s ,
the chemical composition o f i n g o t s and s l a g , i t i s i n f e r r e d t h a t the major r e a c t i o n s which govern the chemical composition of i n c l u s i o n s d e f i n i t e l y slag.
On the other
i n v o l v e the CaO and A ^ O ^ from the
hand the s i l i c o n - from e l e c t r o d e s ,
although i t i s t r a n s p o r t e d
i n the i n g o t , F i g u r e s
not play a r o l e i n the d e o x i d a t i o n The
(45,46), does
scheme.
sequence o f i n c l u s i o n formation
was as f o l l o w s :
1) i n the bottom p a r t o f these i n g o t s , where r e f i n i n g was unstable
some i n c l u s i o n s (approximately 5%)
contained
silicon.
T h i s was almost i n v a r i a b l y l o c a t e d i n the i n -
c l u s i o n core and a s s o c i a t e d with manganese and c a l c i u m . This i s considered
as a c l e a r i n d i c a t i o n t h a t some i n c l u s i o n s ,
a t low r e f i n i n g e f f i c i e n c i e s , come from the e l e c t r o d e and i n subsequent stages they a r e t r a n s p o r t e d
d i r e c t l y i n t o the
i n g o t which i s a l s o s o l i d i f y i n g under unsteady s t a t e tions.
condi-
The b u l k of these i n c l u s i o n s are, however, mainly
represented
by s m a l l s i n g l e o r c l u s t e r e d type
galaxies) of i n c l u s i o n s , Figures degree o f d e o x i d a t i o n
(47) t o (48).
i s increased,
s i n g l e i n c l u s i o n s were observed
(alumina 2) As the
g l o b u l a r and f a c e t e d
(FeO-A^O^ and a-A^O^ r e s -
p e c t i v e l y ) , F i g u r e (49). These types were u s u a l l y a s s o c i a t e d with a s u l f i d e phase (MnS I I ) and
3) A t the h i g h e s t
deoxidation
rates,
163 a mixture of s p h e r i c a l and f a c e t e d alumina w i t h
hexagonal
aluminates were observed, F i g u r e (50). T h i s l a t t e r type had a p e r i p h e r a l double, are shown i n Graphs a g a i n s t the S:Mn
(Mn,Ca)S, s u l f i d e .
These f i n d i n g s
(51) and (52) where the Ca:Al r a t i o
i n a t . % are p l o t t e d .
These f i g u r e s were
o b t a i n e d from i n c l u s i o n s i n R I I - I l and RII-I2 RII-Il
respectively.
which was a h e a v i l y d e o x i d i z e d i n g o t
very h i g h l y segregated m a t e r i a l .
These segregates
under the e l e c t r o n beam produced
a red fluorescence
showed which occurred
i n the t h i r d d e o x i d a t i o n l e v e l , F i g u r e (53) and t h e i r
typical
composition i n a t %, was as f o l l o w s : Al
Ca
26.23
Si
45.67
17.19
Mn Balance
Composition maps shown i n F i g u r e s (53a-d) are t y p i c a l of these segregates.
T h e i r area ranged from 10ym
2
up t o 65-70ym . 2
T h i s f i n d i n g a l s o confirms the " m u l t i - e x c h a n g e - r e a c t i n g " nature of the d e o x i d a t i o n i n the ESR-process, r e a c t i o n s of the type were commonly
(12 a-b).
e.g.
exchange
These types of segregates
seen i n samples e x t r a c t e d from l i q u i d p o o l s .
In these types of samples
inclusions containing s i l i c o n
and o c c a s i o n a l l y f a y a l i t e type of i n c l u s i o n s were a l s o found. Based on mass balances the "FeO" content of the s l a g d u r i n g r e f i n i n g changed from 0.45 wt % down t o 0.27 wt %
164
i n R I I - I l and
from 0.6
wt % to 0.26
lowest "FeO" l e v e l i n s l a g s was
wt % i n RII-I2.
The
a l s o accompanied by a change
i n the A^O^tCaO r a t i o ; whereas the C a F ^ content was s l i g h t l y changed
(from 0.5
to 1.0
wt % ) .
Thus, the minimum
l e v e l of d e o x i d a t i o n reached without
s h i f t i n g the
composition
% FeO
i s about
0.28
- 0.30
wt
5.2.1.4
(54,
slag
f o r 1.3
C a O i A ^ O ^ r a t i o s i n s l a g s of R I I - I l and RII-I2 Figures
only
and
1.5
respectively,
55).
1020
M.S.
Ingots Deoxidized Continuously with a
CaSi A l l o y Since the e f f i c i e n c y
of the Ca-Si a l l o y i n the s m a l l
4340 i n g o t s and i n the l a r g e diameter intermittently deoxidized
was
(200 mm)
observed *
1020
to be h i g h e r
i n the aluminum d e o x i d i z e d i n g o t s , a s e r i e s of were conducted
than
experiments
u s i n g e q u i v a l e n t s l a g systems and
of d e o x i d a t i o n as w e l l as m e l t i n g r a t e s (1 kg min the CaSi a l l o y .
M.S.
Experimental techniques used t o
degrees *) w i t h determine
the t o t a l oxygen content from l i q u i d pool and i n g o t , the s l a g chemical a n a l y s i s , the i n c l u s i o n composition and
their
s i z e d i s t r i b u t i o n s and the chemical a n a l y s i s of i n g o t s were the same as those used to study the 1020 f i n e d through
the C a F - A l 0 - C a O system. 2
2
3
M.S.
ingots r e -
The Ca-Si a l l o y
was *
added to the s l a g i n R I I I - I l and RIII-I2 i n about e q u i v a l e n t
* N o t i c e t h a t 1 gram A l i s approximately of the CaSi a l l o y ; Table (IX).
e q u i v a l e n t t o 3.12
grams
165 aluminum r a t e s as i n R I I - I l and RII-I2 namely: 16.83, 22.24 and p a r t i a l l y 28.0 kg t o n 16.83, 22.44, 28.05, and 56.1 kg t o n
- 1
- 1
5.11, 11.23,
and 5.11, 11.23,
, Table
(VIII).
The p r i n c i p a l d i f f e r e n c e s between R I I I - I l and RIII-I2 are . t h e i r s l a g chemical composition and t h e i r d e o x i d a t i o n r a t e s . R I I I - I l and RIII-I2 were r e f i n e d through 60/36/4 and 50/30/20; lowest
(CaF , A 1 0 2
2
3
and CaO) r e s p e c t i v e l y .
The t h r e e
(CaSi) r a t e s were added i n s h o r t e r p e r i o d s o f time
a t the bottom o f the i n g o t i d e n t i f i e d as RIII-I2 and the f o u r t h l e v e l of a d d i t i o n s than i n R I I I - I l . analysis
(22.4 4 kg ton ^),was longer
Due to these d i f f e r e n c e s the t o t a l oxygen
shown i n F i g u r e s (56) and (57)
c l u s i o n chemical compositions,
and hence the i n -
F i g u r e s (58) and (59) from
R I I I - I l and RIII-I2 r e s p e c t i v e l y , were the most affected
critically
parameters.
T h e i r s l a g and i n g o t compositions f o l l o w e d e q u i v a l e n t b e h a v i o r , F i g u r e s (60) and (61) and F i g u r e (62) and (63). The S i and Ca contents i n s l a g s g r a d u a l l y i n c r e a s e d the "FeO"and the A l 0 2
3
given as Fe and A l i n wt %
whereas
gradually
decreased as the (Ca-Si) d e o x i d a t i o n r a t e s were i n c r e a s e d . An important p o i n t to note i s t h a t the i r o n oxide i n s l a g s from both i n g o t s was reduced t o about Figures
(64) and (65)
0.2 wt%
as shown i n
without producing s t r o n g changes i n
the composition o f the s l a g s .
These graphs c o n s i s t e n t l y show
166
t h a t the aluminum and
s i l i c o n g r a d u a l l y i n c r e a s e d as
the
l e v e l of d e o x i d a t i o n i s i n c r e a s e d . The
i n c l u s i o n chemical composition
principally
as the a t . % Ca: a t % A l r a t i o i n F i g u r e s R I I I - I l and pattern.
RIII-I2
(58) and
given
(59) f o r
r e s p e c t i v e l y , f o l l o w e d an e q u i v a l e n t
T h i s r a t i o , however, was
l a r g e r i n RIII-I2
to h e a v i e r d e o x i d a t i o n i n i t s f o u r t h l e v e l .
due
Another
import-
ant f i n d i n g i n regard to the i n c l u s i o n composition
was
p r o p o r t i o n a l changes of s u l f u r
Ca:Al
(as a CaS)
with the
r a t i o s and hence with the d e o x i d a t i o n r a t e s , F i g u r e s to
(68).
I n c l u s i o n s a t the bottom of i n g o t s
r a t e s of d e o x i d i z e r were used alumina types,
were mainly
( a - A ^ C ^ and F e O * A l 0 ) . 2
3
where
I I I and
At i n t e r m e d i a t e
de-
(rate) ranges
s p h e r i c a l aluminates
(CaO«2Al 0 , C a O « A l 0 2
3
3
(Mn,Ca)S) were found.
2
3
and
d i t i o n s , as i n RIII-I2 CaS
In the h i g h
aluminates, sulfides
deoxidation
enriched i n calcium,
12CaO•7A1 0 ) 2
p e r i p h e r a l CaS were i d e n t i f i e d .
low round
(a-A^O^ and C a O 6 A l 0 ) as c l u s t e r s , together with (MnS
(66)
f a c e t e d and
grees of d e o x i d a t i o n f a c e t e d alumina and hexagonal 2
the
a s s o c i a t e d with
3
Extreme d e o x i d a t i o n con-
and p a r t i a l l y i n R I I I - I l , produced a
phase w i t h i n c i p i e n t amounts o f aluminum ( u s u a l l y
l o c a t e d i n t h e i r core) and
the l a r g e s t segregated
e n r i c h e d i n d e o x i d i z e r s ( A l , S i , Ca and
sometimes
These r e s u l t s indeed c o r r o b o r a t e the
material Mn).
qualitative
f i n d i n g s p r e v i o u s l y d e s c r i b e d f o r RII-W and RIII-W as w e l l as f o r the small 4340-ingots which were Ca-Si
deoxidized.
167 The above f i n d i n g s RIII-I2) c l e a r l y
(RII-W, RIII W,
RIII-Il
and
i n d i c a t e t h a t the CaSi as a d e o x i d i z e r
p l a y s by f a r a more important r o l e i n the chemical composit i o n of i n g o t and of the
composition
slag.
The A^O^
i n c l u s i o n s than the chemical
low l e v e l of SiC>2 and the gradual decrement of
i n the s l a g , the amounts of S i and A l which are c o n t i n u -
o u s l y i n c r e a s i n g i n the i n g o t and the Ca:Al r a t i o i n i n c l u s i o n s immediately reacting
(ESR)
suggest t h a t the S i i s u t i l i z e d
system as a c a r r i e r .
t h a t simultaneous
I t i s also
i n the
observed
exchange r e a c t i o n s between the two
liquids
(slag and metal pool) d e f i n i t e l y c o n t r i b u t e t o the deoxida t i o n mechanism, F i g u r e s (60-68). t h i s mechanism, r e a c t i o n s of the type
Further evidence t h a t (11) and
(12 a-b) ,
r u l e s the chemistry of the melt, i s seen i n the S i content i n i n c l u s i o n s at h i g h d e o x i d a t i o n r a t e s i n RIII-I2, F i g u r e (68).
Excessive
(CaSi) d e o x i d a t i o n performed
i n t h i s ingot
induced the f o r m a t i o n of c a l c i u m aluminates with p e r i p h e r a l CaS
and some s i l i c o n as w e l l as the formation of
e n r i c h e d i n d e o x i d i z e r s , F i g u r e (69).
segregates
168 5.2.1.5
C o r r o b o r a t i o n and E x t e n s i o n of Previous F i n d i n g s t o a 4340 S t e e l CaSi (continuously) Deoxidized
Once the l i q u i d p o o l - s l a g d e o x i d a t i o n mechanism was unmistakenly
i d e n t i f i e d through the p r e v i o u s work, a f u r -
t h e r s e t o f experiments was c a r r i e d out t o r e c o n f i r m and extend
these r e s u l t s t o more complex d e o x i d i z e r s and a l l o y
systems such as 4340 and a r o t o r (Ni-Cr-Mo) s t e e l .
Re-
m e l t i n g of these e l e c t r o d e s was performed u s i n g the e q u i v a l e n t experimental remelted
c o n d i t i o n s as i n the 4 340 e l e c t r o d e s
by the s m a l l ESR-furnace and the 1020 M.S.
rodes remelted
by the s e m i - i n d u s t r i a l ESR-furnace.
m e l t i n g r a t e s were kept i n the 1 kg min The
1
electThe
range.
l a s t i n g o t i n c l u d e d i n the f u l l y monitored s e t o f
experiments
(through the three r e f i n i n g stages) was a
4 340-electrode
which was r e f i n e d through a 50 wt. % CaF /
30 wt. % A 1 0
and 20 wt. % CaO s l a g and CaSi
2
The
3
2
deoxidized.
degree o f d e o x i d a t i o n was c o n t i n u o u s l y i n c r e a s e d from
4.17 to 41.67 kg (CaSi) t o n
- 1
f o r almost e q u i v a l e n t p e r i o d s
of time as i n R I I I - I l .
The l a s t l e v e l o f d e o x i d a t i o n was
a l s o suddenly
from 41.67 down t o 20.83 kg ton
decreased
Chemical composition
of the s l a g and i n g o t f o l l o w e d
the same p a t t e r n as the 1020-ingots, a l l o y , Figures
d e o x i d i z e d with the CaSi
(70) and (71). The major d i f f e r e n c e found
i n t h i s i n g o t was i t s i r o n oxide and i t s oxygen Figure
(72). The i r o n oxide
given i n Figure
content,
(73)
changed
169 from 0.4
down to 0.15
creased.
The average
10-20
ppm.
deoxidized
as the r a t e of d e o x i d a t i o n was i n t o t a l oxygen content was about
Whereas i n the 1020 the l e v e l ranged
ingots
e i t h e r A l or CaSi
from 30 and up to 80
ppm.
This s u b s t a n t i a l d i f f e r e n c e i s e s s e n t i a l l y a t t r i b u t e d to the t i g h t Ar-atmosphere e n c l o s u r e of the f u r n a c e , the gree of
(Ca-Si) d e o x i d a t i o n of these
ingots
de-
(50-70
ppm
of oxygen) and the chemical composition of the e l e c t r o d e . The chemical composition of i n c l u s i o n s Figures
given i n
(74 a,b), f o l l o w e d the g e n e r a l t r e n d observed i n
the e q u i v a l e n t 10 20 M.S. of i n c l u s i o n s
ingots.
The chemical
composition
i n s i m i l a r manner to p r e v i o u s 1020
i n g o t s d e o x i d i z e d with the CaSi a l l o y
e x h i b i t e d the
a l t r a n s i t i o n from aluminate
to c a l c i u m aluminate
T h e i r p r o p o r t i o n a l increment
i n s u l f u r content
up to 25 a t . % was was
a l s o observed,
increased, Figure A very important
M.S. gradu-
phases.
(as
CaS)
as the d e o x i d a t i o n r a t e
(75). f a c t to address
i s the r a t i o of the S i
in
i n these
the C a S i - a l l o y
i s c o n s t i t u t e d by approximately
62.0
wt.
even
experiments though i t
% S i , i t has
not
p l a y e d a r o l e i n the d e o x i d a t i o n scheme p r e v i o u s l y presented, i.e.
i n v o l v i n g the CaO
and A^O^
of the s l a g and the Ca
and A l i n i n c l u s i o n s and d e o x i d i z e r s .
It i s also
important
to emphasize t h a t the S i from e i t h e r the e l e c t r o d e ( i n
170 the 1020 ported
e l e c t r o d e s ) or the CaSi a l l o y i s v i r t u a l l y c o n j o i n t l y to the A l and
Ca
trans-
i n t o the i n g o t
and
i t does not appear i n i n c l u s i o n s . At t h i s p o i n t i n t h i s d e s c r i p t i o n , i t becomes e s s e n t i a l to r e c a l l t h a t although the A l as a d e o x i d i z e r seems to be o p e r a t i n g w i t h i n the same frame of r e a c t i o n s as the ( s l a g - d e o x i d i z e r and
l i q u i d pool), i t
t o r s , does not d e o x i d i z e CaSi a l l o y .
due
to k i n e t i c
to c o r r o b o r a t e
fac-
the ESR-melt as e f f i c i e n t l y as
In the l i g h t of these f i n d i n g s a new
three experiments was
CaSi
planned.
s e t of
The major purpose
was
the c o n c l u s i o n t h a t the s i l i c o n i n the
de-
o x i d i z e r works e x c l u s i v e l y as a c a r r i e r , to r e c o n f i r m v a l i d i t y of the proposed mechanism
the
( r e a c t i o n scheme) and
to compare the degrees of d e o x i d a t i o n
reached through
d i f f e r e n t d e o x i d i z e r s , Table
Three r o t o r
(VIII).
s t e e l e l e c t r o d e s were r e f i n e d i n the 200 furnace
using e q u i v a l e n t m e l t i n g
deoxidation
r a t e s , Table
were C a S i , SiAlCaBa chemical
(XII).
mm
The and
diameter
ESRand
(Si-based) d e o x i d i z e r s an A l S i a l l o y .
compositions are given i n Tables
Despite
three
(Cr-Mo-V)
r a t e s , s l a g system
("hypercal")
the
the f a c t t h a t the chemical
Their
(XII a - c ) .
composition
of
the
d e o x i d i z e r s i s q u i t e d i f f e r e n t c a l c i u m aluminate phases with p e r i p h e r a l c a l c i u m
s u l p h i d e are p r e c i p i t a t e d .
Ca:Al r a t i o vs. the s u l f u r content
The
are p l o t t e d i n F i g u r e
(76).
171 Again
i t i s shown t h a t exchange r e a c t i o n s of the
(12 a-b)
type
p l a y the most important r o l e i n the d e o x i d a t i o n
( r e a c t i o n ) scheme and s i n c e the S i appears
i n the i n g o t
but i t does not i n i n c l u s i o n s i t s r o l e i s p r i n c i p a l l y
as
a c a r r i e r of Ca and A l i n t o the l i q u i d p o o l and i n g o t . These r e s u l t s support the three p r e v i o u s p r o p o s a l s . The chemical composition of i n c l u s i o n s i n d i c a t e t h a t s i l i c o n free, c a l c i u m aluminates with p e r i p h e r a l c a l c i u m s u l f i d e ( i . e . o t h e r s than C a O 6 A l 0 2
c i p i t a t i n g phases.
The
3
and
(Mn,Ca)S) were the p r e -
s i l i c o n content i n the s l a g
c o n s i d e r a b l y i n c r e a s e d and the "FeO"content was i n the ranges p r e v i o u s l y d e s c r i b e d , Table Furthermore,
was
also held
(XII).
segregates which were found i n the
ex-
c e s s i v e l y and a b r u p t l y A l and CaSi d e o x i d i z e d i n g o t s were the same as observed
i n ( s i z e , f l u o r e s c e n c e under the
ron beam and t h e i r chemical composition) ingot.
elect-
the A l S i d e o x i d i z e d
The d i s t r i b u t i o n of elements i n a segregate e n r i c h e d
i n s t r o n g oxide formers, namely aluminum, s i l i c o n and c u l a r l y c a l c i u m , i s shown i n F i g u r e s composition was
(77a-d).
parti-
Their t y p i c a l
( i n at.%) as f o l l o w s : Ca 40.6
Al 41.5
Si
Mn + Fe
19.7
balance
T h i s f i n d i n g i s c o n s i d e r e d as another evidence t h a t the p r o posed mechanism i s indeed o p e r a t i n g .
172 5.3
D i s c u s s i o n of R e s u l t s
i n Terms of E l e c t r o d e
Slag Composition, Related 5.3.1
The
and
to the Second Question
E f f e c t of the E l e c t r o d e on the I n c l u s i o n Comp-
o s i t i o n of ESR-ingots The
experimental
f i n d i n g s p r e v i o u s l y d e s c r i b e d have
been used to address the second q u e s t i o n III, i . e . chemical
i s the i n c l u s i o n composition
composition
This question
s t a t e d i n Chapter c o n t r o l l e d by
of e l e c t r o d e s , s l a g or
deoxidizers?
as envisaged i n the l i t e r a t u r e review ( i n
terms o f the complexity
of the r e a c t i o n scheme and
c l u s i o n chemical
composition
and
the p r e v i o u s l y d e s c r i b e d r e s u l t s
as shown i n
of r e f i n i n g and
the i n -
of i n g o t s i n the ESR-process) cannot
be answered u n l e s s the r e a c t i o n s between the three f e r e n t stages
the
i t s components
dif-
(electrode,
slag, s l a g - l i q u i d film, deoxidizer, l i q u i d pool-slag
and
ingot) are c a r e f u l l y monitored. Through the f i r s t p a r t of t h i s r e s e a r c h concluded t h a t i n c l u s i o n s from e l e c t r o d e s r e f i n i n g conditions rode t i p . The and
are completely
i t has
under s t a b l e
d i s s o l v e d i n the
Thus, f u r t h e r d i s c u s s i o n assumes t h i s
e l u c i d a t i o n of the r o l e p l a y e d by the
the s l a g on the chemical
composition
been
elect-
fact.
electrode
of i n c l u s i o n s i n
the ESR-ingot have been shown through s e v e r a l experiments: 1)
The
small 4340 i n g o t
.(6), Table
(X), r e f i n e d through
173
an alumina
f r e e s l a g and
a t i v e and deoxidant
(external) sources, i . e .
and without deoxidant. 1020
M.S.
i n the absence of gaseous o x i d -
2) A l a r g e diameter
e l e c t r o d e r e f i n e d through
under (200
M.S.
mm)
a CaF -CaO-Al 0 2
2
s l a g under the above c o n d i t i o n s , ( R I - I l ) , Table and 3) A s e r i e s o f 1020
argon
3
(VIII)
e l e c t r o d e s r e f i n e d i n the 200
mm
i n diameter ESR-furnace which were i n t e r m i t t e n t l y d e o x i d i z e d with CaSi and o t h e r s c o n t i n u o u s l y d e o x i d i z e d with A l and a CaSi
alloy.
1. 31 wt.%
The
i n g o t (6)
C a F , 46 wt. 2
which was
% CaO,
remelted through
and 23.0
wt.
% Si0
a dominant r o l e i n the f i n a l i n c l u s i o n chemical of the r e f i n e d i n g o t .
The
r e p r e s e n t e d as A l i n Table g i v e n as s i l i c o n ,
alumina
has
2
c l u s i v e l y shown t h a t the e l e c t r o d e composition
the con-
indeed p l a y s composition
content i n i n c l u s i o n s
(VIII) with r e s p e c t t o
silica,
shows t h a t the aluminum which came ex-
c l u s i v e l y from the e l e c t r o d e ( i n s o l u t i o n ) has the i n c l u s i o n chemical composition.
controlled
This finding
i n agree-
(83) ment with Rehak s e t a l . ' s 1
i n A l and CaSi t r e a t e d e l e c t r o d e s
c l e a r l y demonstrates t h a t the chemical composition of e l e c t rodes s p e c i f i c a l l y due
to the presence of d e o x i d i z e r s i n
s o l u t i o n , under a g i v e n s l a g system can p l a y an
important
r o l e i n the f i n a l i n c l u s i o n composition of r e f i n e d i n g o t s , i.e.
self-deoxidation.
174 2.
Results
found from a 1020-ingot remelted under a
p r o t e c t i v e atmosphere without the i n f l u e n c e of a are shown i n F i g u r e s illustrate 200
mm
t h a t as the r e m e l t i n g
mould takes p l a c e
s l a g and
a gradual
occurs.
The
and
(37,38). These graphs
from R I - I l
of the e l e c t r o d e
clearly
i n the
an accumulation of s i l i c a
change i n the alumina and
i n the
calcium
oxide
S i C ^ i n the s l a g a c t s e x c l u s i v e l y as a d i l u e n t
only c o n t r i b u t e s
to a g r a d u a l
s h i f t i n the II
r a t i o s and
deoxidizer
CaOiA^O^ (38
II
to c o n t r o l the i n t r i n s i c "FeO"content i n the
slag
I t does not,
however, i n f l u e n c e the chemical composition of
inclusions
A deeper d i s c u s s i o n r e l a t e d to t h i s matter w i l l
r
be pursued i n a subsequent s e c t i o n . clarify
t h a t the change i n the CaOrA^O^ r a t i o was
f l u e n c e d by or HFl)
the formation
s i n c e the f l u o r i n e a n a l y s i s was
The
i n the
as the t o t a l A l and d e p l e t i o n i n the p o i n t out (0.65
i n the
% and
0.09
i n g o t , o n l y aluminates
sulfides
and "FeO"in the
2
Ca content i n F i g u r e
ingot, Figure
wt.
((Fe,Mn)S and
changed only
CaOtA^O^ r a t i o i n the
t h a t i n s p i t e of the to 0.72
MnS
not i n -
(38).
i n the
slag
slag—given
(37)--and an A l
I t i s worthwhile to
(gradual) to 0.13 (A^O^
2
(± 0.2%).
continuous increment of S i 0
produces a s h i f t
to
of v o l a t i l e f l u o r i d e s (AlF^, S i F
measure of the experimental e r r o r ,
Si
It i s pertinent
i n c r e a s e i n Mn wt.
and
% respectively)
and A^O^'FeO)
II) were p r e c i p i t a t e d .
and
3.
A t y p i c a l a l t e r a t i o n o f the otherwise
o u s l y i n c r e a s i n g content
of s i l i c a
S i i n the i n g o t i s shown i n F i g u r e f i e d as RIII-W
was remelted
v a l e n t s l a g to R I - I l . contents
continu-
i n the s l a g and hence (32). T h i s i n g o t
identi-
under argon and under an e q u i -
The abrupt changes i n the S i and Mn
i n the s l a g and i n g o t
and'the Ca:Al r a t i o i n i n -
c l u s i o n s are a r e s u l t from the i n t e r m i t t e n t a d d i t i o n s of the (CaSi) d e o x i d i z e r .
Since the s i l i c o n comes from the e l e c t -
rode and the d e o x i d i z e r a more a p p r o p r i a t e
analysis
should
be performed on the Mn s i n c e i t comes e x c l u s i v e l y from the electrode.
The Mn content
changes from about 0.65 down t o
0.45 wt. % i n the s l a g , F i g u r e (32). The
behavior
o f the S i from the e l e c t r o d e becomes more
important when the 1020 M.S. e l e c t r o d e s are A l d e o x i d i z e d . The
i n g o t i d e n t i f i e d as R I I - I l c l e a r l y shows t h a t as the
degree o f d e o x i d a t i o n
i s increased
i n the s l a g and i n g o t — F i g u r e s a constant
level.
the l e v e l o f S i and Mn
(39) and ( 4 5 ) — a r e
held to
T h i s suggests t h a t the chemical
composition
of the e l e c t r o d e no longer p l a y s a r o l e i n the r e f i n i n g cess.
T h i s i n g o t was r e f i n e d , as shown i n Table
pro-
(VIII),
through a S i and Mn f r e e s l a g under an argon atmosphere. Thus, the o n l y source o f S i (0.25 wt. %) and Mn
(0.6 - 0.7
wt. %) e i t h e r i n s o l u t i o n o r as i n c l u s i o n s i s the e l e c t r o d e . The
above r e s u l t s c l e a r l y i n d i c a t e t h a t i f an e l e c t r o d e
176 c o n t a i n s oxide forming elements i n s o l u t i o n or as i n c l u s i o n s , which are not present as oxides d e o x i d i z e r s than those present d e o x i d a t i o n takes p l a c e .
i n the s l a g and are stronger i n the s l a g , a c o o p e r a t i v e
The mechanism by which these r e -
a c t i o n s take p l a c e i s w i t h i n the g e n e r a l scheme given by reactions
(11) and (12 a-b). The most important
conclusion
from these experiments i s t h a t these r e a c t i o n s predominate s o l e l y i n the absence of or under i n e f f i c i e n t A conventional Al-deoxidation
deoxidation.
(0.05 - 0.2 wt. %) i s able
to overcome the e f f e c t of the S i from the e l e c t r o d e i f the r e f i n i n g s l a g i s low (< 10 wt, %) i n SiO,,.
5.3.2
E l u c i d a t i o n of the E f f e c t of Slag and D e o x i d i z e r s (Preliminary The
Studies)
e l u c i d a t i o n of the e f f e c t of s l a g s and d e o x i d i z e r s
was approached through the s m a l l 4340 i n g o t s . to
(6)
slags,
Ingots
(1)
which were r e f i n e d through d i f f e r e n t S i 0 - c o n t a i n i n g 2
y i e l d e d c a l c i u m aluminate
c a t e phases.
and calcium-aluminum
sili-
The former type of i n c l u s i o n s d i d not exceed
3.75 a t . % Ca and they were i d e n t i f i e d o n l y where the S i 0 ~ 2
content
i n the s l a g was l e s s than
10 wt. %.
Above t h i s
c e n t the l a t t e r type of phases were i d e n t i f i e d . summarizes the main f e a t u r e s of these
Table
experiments.
per(X)
177 I f the above a n a l y s i s i s extended to both s l a g s and i n c l u s i o n compositions
and they are p l o t t e d i n t e r n -
ary diagrams
by A l l i b e r t e t a l . (207)
f o r ESR
as suggested
i n g o t s and
s l a g s and Bruch
(14 53 54) ' '
and K i e s s l i n g
and
(91) Lange
f o r CaSi d e o x i d i z e d i n g o t s i n c o n v e n t i o n a l
making processes c l u s i o n s and Figures
then the chemical compositions
t h e i r probable o r i g i n i s e a s i l y
(12) and
(13) .
of i n -
followed.
S e v e r a l important p o i n t s should
c o n s i d e r e d i n these diagrams:
i ) the s l a g chemical
t i o n i s p l o t t e d under the assumption t h a t the C a F an i n e r t d i l u e n t
( 3 3
'
3 8
steel-
'
4 5
'
5 3
'
8 8
'
8 9 }
.
composia c t s as
i i ) r e g a r d i n g the
nary diagram which d e s c r i b e s the i n c l u s i o n (91) K i e s s l i n g ' s and Lange*s
2
be
ter-
composition,
s t u d i e s as an e x t e n s i o n of
(207) Bruch's have c o n s i d e r e d a replacement of e i t h e r Mn, Mg or Fe by Ca as oxides i n the CaO c o r n e r . The replacement (34) of Mn by Ca as oxides has a l s o been r e p o r t e d by i n ESR
ingots.
the A^O-j
And
the two
Holzgruber
d i v e r g e n t l i n e s which emerge from
corner to the CaO-Si0
2
b i n a r y are l i n e s which r e p -
r e s e n t the maximum and minimum MeO:Si0 respectively, in inclusions.
2
i i i ) The
r a t i o s , L^ and
f i n d i n g s from C a - t r e a t e d
3
(conventional) i n g o t s
al.'s' and
data o b t a i n e d by other r e s e a r c h e r s i n c o n v e n t i o n a l '
'
diagram.
and
i n ESR-research
1 0
^
iv) 4 0
'
15115783) '
2
t r i p l e l i n e which
a l s o emerges from the A l 0 ~ c o r n e r are Holappa e t 2
L
i s also included i n t h i s
1 4 4
'
178
Slags c o n t a i n i n g l e s s than 10 wt.
% Si0
2
c l u s i o n s l y i n g along the A^O^-CaO b i n a r y and l o c a t e d c l o s e r to the A l 0_-corner. 2 3 u s u a l l y a s s o c i a t e d with s u l f i d e s (Ca, Mn)S).
The
produce i n specifically
These types were J
(MnS
c
I I , MnS
I I I or
type and composition of these
sulfides (34)
depended on the Ca:Al r a t i o i n the oxide phase. (14 53 54) and A l l i b e r t e t a l . (12 v i i i ) , Figures
have
also
'
'
who
reported
Holzgruber
have s t u d i e d the r e a c t i o n these
inclusion
phases,
(12,13).
The chemical composition of i n c l u s i o n s which were obt a i n e d from s l a g s c o n t a i n i n g more than 10 wt. l o c a t e d along the S i C ^ - A ^ O ^ a x i s . (8),
(10) and
20 t o 85 wt. about
30 wt.
Bruch's
Ingots
% Si0
2
were
(2), (3),
(11) were l o c a t e d i n an area c o n f i n e d i n the %.
Al 02 2
% CaO.
range along the S i C ^ - A ^ O ^ a x i s
and
These r e s u l t s are i n agreement with
and K i e s s l i n g ' s and L a n g e ' s ^ ^ ' and
with A l l i b e r t ' s et a l . ' s
( 5 3 )
,
Rehak's
( 8 3 )
qualitatively
and Holzgruber ' s
( 3 4 )
F i n d i n g s from the l a t t e r two r e s e a r c h e r s were o b t a i n e d from ESR experiments
where experimental c o n d i t i o n s were not
dir-
e c t l y concerned with the s l a g chemical composition. Thus, i f C a F
2
i s s t r i c t l y c o n s i d e r e d as an i n e r t (234 )
and Rein's and Chipman's data
diluent
are used t o s u b s t a n t i a t e
the thermodynamic behavior of s i l i c a
i n ESR-slags
then i f
.
a_.__ Si0
2
£ 0.01, a , , . AlO^
S 0.5 and a„ . 5 0.1 , aluminates CaO
5
w i l l precipitate.
On the other hand i f the S i 0
of s l a g s exceeds 10 wt. % with some c a l c i u m
then a l u m i n u m - s i l i c a t e i n c l u s i o n s
(up to about 30 wt. % CaO) w i l l
The a c t i v i t y r e l a t i o n s a r e as f o l l o w s : a
C
a
0
< 0.10 and a
content
2
A
1
^ 0.5.
Q
a„.^
precipitate.
^0.01,
SiO„
'
Holappa's r e s u l t s
'
v
1. 5 from C a - t r e a t e d i n g o t s suggest i n the melt i s reduced
t h a t as the a c t i v i t y of A l
and the a c t i v i t i e s o f S i and Ca are i n -
creased, a g r a d u a l change i n composition of the i n c l u s i o n phase as i n d i c a t e d by the ' t r i p l e - d o t t e d ' l i n e i n F i g u r e be observed.
(12) should
T h i s behavior i n ESR i n g o t s (1) t o (6) was not
completely f o l l o w e d and i n s t e a d a mixture o f c a l c i u m -
silicon-
aluminate and aluminate phases were found, Table (X). The b e s t d e o x i d a t i o n in inclusions* * ^ 2 1
3
measured as the C a O : A l 0 2
was found i n the C a F - C a O - A l 0 2
s p e c i f i c a l l y where the C a F
2
2
3
ratio
3
system,
and CaO contents were 50 wt. %
and 20 wt. % r e s p e c t i v e l y i n the s l a g .
Polish researcher's
work ^ ^ ' o n s l a g s b e l o n g i n g to t h i s system have r e p o r t e d a maximum of 71.0% r e d u c t i o n o f n o n - m e t a l l i c i n c l u s i o n s i n r e l a t i o n t o the s t a r t i n g s t e e l e l e c t r o d e i n e x a c t l y the same s l a g composition
(50/30/20) a t which the l a r g e s t
Ca:Al
r a t i o i n i n c l u s i o n s was found i n t h i s r e s e a r c h , Table (X). Thus, through
the p r e v i o u s d e s c r i p t i o n
i t has been
found t h a t the s l a g d e f i n i t e l y p l a y s a r o l e i n the r e f i n i n g process.
What has not been answered y e t i s how l a r g e the
180 s l a g e f f e c t i s i n comparison with
the d e o x i d i z e r .
q u e s t i o n can be answered i n a t r i v i a l manner by r e s u l t s i n Table composition
(X).
of i n g o t
This
analyzing
By comparing the i n c l u s i o n chemical (1) a g a i n s t
(7) and
(9),
can
ob-
serve t h a t the Ca-content i n i n c l u s i o n s i n the l a t t e r
two
i n g o t s i s double that i n the former. b a s i s , one
one
Thus, on an
apriori
could e s t a b l i s h that since deoxidation
s l a g were e q u i v a l e n t
rates
(2.3 kg ton ^, 50/30/20) and
ratios in
i n c l u s i o n s i s twofold
deoxidized
ingots
(7) and
i n the A l and
(9) r e s p e c t i v e l y
the
the
l a r g e r than 1.15
kg ton
And
deoxidation
molten i r o n then a r e l a t i v e l y
ex-
higher
r a t e c o u l d generate aluminates r i c h e r i n c a l c i u m
however, do not r e s t on any do not e x p l a i n why
mechanism and
the A l and
compositions.
62.5
i n c l u s i o n chemical
(2.3 kg ton
wt.%
Si.
The
composition,
r e f i n e d through the 55 wt.% 15 wt.
consequently they produce
i n terms o f i n c l u s i o n
I t i s important to c l a r i f y t h a t although
amounts of d e o x i d i z e r s a l l o y contains
These premises,
the CaSi d e o x i d a t i o n
an almost e q u i v a l e n t t r e n d i n r e s u l t s
and
rates
t h a t s i n c e the Ca i s
and hence much lower t o t a l oxygen c o n t e n t s .
CaO
de-
i f these f i n d i n g s are
t r a p o l a t e d , i t c o u l d be estimated almost i n s o l u b l e i n
Ca:Al
CaSi
then the
o x i d i z e r overcomes the s l a g e f f e c t at d e o x i d a t i o n
and
% Si0
0
1
) were e q u i v a l e n t
the
e f f e c t of d e o x i d i z e r s
i n the s m a l l 4 340
C a F , 15 wt.% 2
the
Al 0 ,
s l a g i s shown i n Table
2
3
(X).
ESR
CaSi
on
ingots
15 wt.
%
the
181
If
ingots
oxidized the
a r e compared
against ingot
The S i C ^ e f f e c t
e v e r , was a l m o s t (Al).
from
completely
( 2 ) , one c a n s e e t h a t
i n diameter
This p a r t i c u l a r
findings
was r e m e l t e d
ingot
a constant rate
i n ingot
by t h e d e o x i d i z e r , a
1020-electrode
under e q u i v a l e n t c o n d i t i o n s .
Kg/ton
).
The e f f e c t o f
(X) and i n c l u s i o n
composition
was n o t enough t o c o u n t e r b a l a n c e
the slag.
( 8 ) , how-
( 1 1 ) , however, was A l - d e o x i d i z e d
(0.02
the d e o x i d i z e r , T a b l e ously c i t e d ,
the s l a g
suppressed
To c o r r o b o r a t e t h e s e
76.2 mm
of
(10) w h i c h were A l and C a S i d e -
C a S i d e o x i d i z e d i n g o t d i d show t h e i n f l u e n c e o f t h e
silica.
at
(8) and
The i n c l u s i o n p h a s e s were
previ-
the SiC^ e f f e c t
" a n o r t h i t e " and
alumina. It
i s worthwhile
t o p o i n t out that the s i l i c o n
in
the i n c l u s i o n phases of i n g o t s
of
magnitude
And
although
sition of
there
silicon
deoxidant
slag
the aluminum-deoxidized
ingots.
i n the chemical
(1) t o ( 8 ) and (9) and (10) (SiC^ i n i n c l u s i o n s ) ,
to the large q u a n t i t i e s
and t h e c h e m i c a l
than
(2) and (8) a r e one o r d e r
i s a difference
content
i s attributed
larger
than
of electrodes
their
fect
the
larger
10 wt. %.
composition
treatment,
contents
s m a l l e r than
10 wt. %.
i n terms
t h e main e f -
of the slag, i . e . ,
Thus, t h e c h e m i c a l
s h o u l d be c a r r i e d
compo-
i n t h e (CaSi)
composition of
a t w h i c h an a p p r o p r i a t e d e o x i d a t i o n
the CaSi
content
i n terms o f
out i s at s i l i c a
182 Hence, the most important
c o n c l u s i o n from p r e v i o u s
f i n d i n g s i s t h a t the d e o x i d a t i o n phenomenon i s a n e t r e s u l t o f c o o p e r a t i v e r e a c t i o n s between d e o x i d i z e r s and s l a g s . Thus, t o o b t a i n an e f f i c i e n t d e o x i d a t i o n
an a p p r o p r i a t e
s e l e c t i o n o f these parameters i s e s s e n t i a l . of these statements
A f u r t h e r proof
w i l l be approached i n the next s e c t i o n .
I t i s a l s o worthwhile to c l a r i f y
t h a t although there i s
a common t r e n d o f r e s u l t s i n both ESR-furnaces the v a l i d i t y of p r e v i o u s f i n d i n g s i s q u a l i t a t i v e .
The
lower
sur-
f a c e area a v a i l a b l e f o r r e a c t i o n s , the higher thermal
gradi-
ents and the unsteadiness o f the s o l i d i f i c a t i o n c o n d i t i o n s i n the small ESR-furnace
a r e f a c t o r s t h a t must be con-
sidered.
5.3.3
P r e l i m i n a r y D i s c u s s i o n on the Deoxidation Mechanism In the l i g h t of p r e v i o u s d i s c u s s i o n o f f i n d i n g s , the
e v a l u a t i o n of the o r i g i n a l q u e s t i o n — I s the i n c l u s i o n compo s i t i o n c o n t r o l l e d by the chemical composition slag or deoxidizers?—becomes
of electrodes,
i r r e l e v a n t and i n s t e a d o t h e r
q u e s t i o n s emerge, i . e . what i s the mechanism by which the deoxidation
( i n i n d u s t r i a l s l a g s and deoxidants)
What i s the r o l e p l a y e d by the s l a g ?
takes p l a c e ?
and What a r e the c o n d i -
t i o n s which an a p p r o p r i a t e d e o x i d a t i o n i s c a r r i e d out under? To s a t i s f a c t o r i l y answer t h i s s e t o f q u e s t i o n s
a summary
183 of experimental i s presented
r e s u l t s c o r r e l a t e d to the g e n e r a l
i n advance.
The
theory
f o l l o w i n g s e c t i o n emphasizes
the r e s u l t s obtained w i t h the 20 0 mm
ESR
ingots continu-
o u s l y or c o n s t a n t l y d e o x i d i z e d . F i n d i n g s from the small suggest
t h a t the chemical
clusions A^O^
(4340) ESR
composition
i n g o t s , Table
of i n g o t s and i n -
(Ca:Al r a t i o s ) i s determined s o l e l y by the
r a t i o i n the s l a g when the Si02 content
10 wt.
% and d e o x i d a t i o n i s absent.
through the 200 mm
(X)
The
i s lower
results
ESR-furnace have confirmed
ings and they have a l s o c o n t r i b u t e d to the
CaO: than
obtained
these
find-
formulation
of a more s e l f - c o n s i s t e n t d e o x i d a t i o n model. The
i n h e r e n t r e a c t i o n scheme (1-5)
a t the e l e c t r o a c t i v e
• ^ * • v „r.T, (27,28,30, 33,34) i n t e r f a c e s i n the ESR-process • ' ' / atmos• (1,34,38) , . . phere-slag-liquid pool i n t e r a c t i o n ( i n terms of t
t
h
e
n
the oxygen t r a n s p o r t ) . and the amount of s c a l e (as a r e s u l t o f the thermal i n the s l a g
h i s t o r y of the e l e c t r o d e )
introduced
are the main f a c t o r s which determine the
oxi-
d a t i v e s t a t e of the s l a g and hence the oxygen p o t e n t i a l i n the l i q u i d
pool.
Thus, the deoxidant,
the sequence and degree of
de-
o x i d a t i o n as w e l l as the s l a g system are parameters which should be adequately without The
s e l e c t e d to optimize
s a c r i f i c i n g the chemical
deoxidation
i n t e g r i t y of
a p p r o p r i a t e c o n t r o l of the '^ed i n the s l a g 1
ESR-ingots. by the
de-
184 oxidation p o o l and The "FeO"
w i l l i n f l u e n c e the l e v e l of oxygen i n the molten consequently the p r e c i p i t a t i o n of i n c l u s i o n s . importance of the e l e c t r o c h e m i c a l r e a c t i o n s on
l e v e l of a melt and
composition Table
(XI).
t h e i r i n f l u e n c e on the
of i n c l u s i o n s i s seen through i n g o t This rotor
the
chemical (14) i n
(Cr-V-Mo) s t e e l e l e c t r o d e was
sur-
face ground, thus s c a l i n g formed during mechanical working was
removed from i t s s u r f a c e
was
a l s o coated
with
The
(ESR)-ingot
vious surface preparation,
c l u s t e r s o f aluminates
i r o n oxides
and
This
chemical
a n a l y s i s of i n -
the argon atmosphere (0.02
kg ton ^ ) , round, s i n g l e
(mostly
s u l f i d e s (FeO,
FeS)
FeO-A^O^ and A^O^) and
(Mn,Fe)S) were
(218) metal i n thermodynamic e q u i l i b r i u m , i.e. (234) Chu
saturated. rates
Kun ' s phase diagram
- 1
s l a g which can be achieved The
i s a minimum "FeO"
"FeO"
de-
according A^O^-
deoxidation l e v e l i n the
for a given deoxidation p r a c t i c e .
e f f e c t of the atmosphere as w e l l as the
introduced
and
slag-liquid
this slag i s
On the other hand, d e s p i t e l a r g e
(10 kg t o n ) there
pre-
enclosure
t e c t e d i n s t e a d of the a-A^O^ expected from the
to Kuo
electrode
show t h a t d e s p i t e the
and a s l i g h t A l - d e o x i d a t i o n and
1 mm).
an Al-Mg s p i n e l p a i n t i n g t o prevent i t s
oxidation during r e f i n i n g . clusions in this
(about
artificially
i n the s l a g and hence i n the l i q u i d
are c l e a r l y shown i n F i g u r e s
(32,33) and
to the i n g o t s i d e n t i f i e d as RII W and
RIII
pool
(34,35) which belong W.
185 The
i n i t i a l stages
s l a g composition "FeO
( 1 , 3 8
mitted
'
8 2 )
.
of r e f i n i n g are c o n t r o l l e d by
which i n i t s e l f allows a g i v e n amount of I f the
"FeO"
content
i n the s l a g i s p e r -
to r i s e above t h i s l e v e l by any of the
mechanisms
the
described
the r e s u l t i s an i n c r e a s e d r a t e of o x i d a t i o n
of the r e a c t i v e s p e c i e s from the e l e c t r o d e or the s l a g , hence moving the system towards unacceptable r e f i n i n g i n terms of s l a g or i n g o t composition. 2[A1] which has
+ 3 (FeO)
t
The
(Al^)
reaction
+ 3Fe
d e p l e t i o n of
A l i n the i n g o t ; i d e n t i f i e d as R I - I l , F i g u r e s
the slag) has gradual
slag
(37,38),
(change i n the C a O i A ^ O ^ r a t i o i n
a l s o been i n f l u e n c e d by the presence of
i n t r o d u c t i o n of "FeO"
(mostly
s l a g as the r e f i n i n g took p l a c e . controlled
(12-iv) (12-iv)
c o n t r i b u t e d to produce the gradual
a t expense of the
conditions,
The
the
as s c a l e ) i n t o the CaOtA^O^ r a t i o i s
by 2[A1]
+ 3(CaO)
J
( A 1 0 ) + 3[Ca] 2
(20-C)
3
Although the extent t o which t h i s r e a c t i o n o c c u r r e d was limited,
i t s r e s u l t s were d e t e c t e d ,
Figures
(37) and
very
(38).
These r e a c t i o n s can take p l a c e only when there i s not enough d e o x i d i z e r to suppress the c o n t i n u o u s l y "FeO"
i n the s l a g .
i n c r e a s i n g amount of
Under these c o n d i t i o n s the major pre-
c i p i t a t i o n r e a c t i o n s are governed by the oxygen p o t e n t i a l as follows:
186 Fe + 2[A1]
t
+ 4[0]
(22)
(FeO«Al„0 ) 2 3 inclusion
or 2[A1]
+ 3[0]
t
(11-i)
(Al 0_) 2 3 inclusion o
These p r e c i p i t a t i o n r e a c t i o n s are c o n t r o l l e d by r e a c t i o n (12-iv) i n the A l d e o x i d i z e d i n g o t . e n t i a l has been decreased finite
"FeO"
content
p l a y s a very Figures
(45) and
RII-I2).
the r e a c t i o n
(46) which r e p r e s e n t the
deoxid-
(RII-Il
and
I t can a l s o be seen t h a t the"FeO"content i n the to about 0.3
i n c l u s i o n composition, FeO«Al 0 2
to a - A l 0
3
CaO«6Al 0 2
2
3
3
wt.
%.
7
Figures
(54,55).
and at. v e r y h i g h d e o x i d a t i o n r a t e s
i n c l u s i o n phase i s p r e c i p i t a t e d , F i g u r e s
(41,42).
of Mn
it
This
the p r e c i p i t a t i o n of the C a O - e A ^ O ^ phase
(up to the same degree) the p a r t i a l s u b s t i t u t i o n
by Ca i n the s u l f i d e phases,. F i g u r e s
consequence of these according
trend,
"deoxidation
Phenomenon" i s a l s o a t t r i b u t e d to the r e a c t i o n (20).
also
the
(47-50).
From a c o n s i d e r a t i o n of these r e s u l t s
i s i n f e r r e d t h a t to a l i m i t e d extent the
r e a c t i o n induces
The
however,•changes g r a d u a l l y from
t o t a l oxygen a n a l y s i s a l s o r e f l e c t s the d e o x i d a t i o n
Figures
and
(20)
behavior
show t h a t the A l as a
i n t r o d u c e d i n t o the i n g o t s
s l a g i s decreased
The
then
but
role.
of the A l - d e o x i d i z e d i n g o t s izer is virtually
as a r e s u l t of the low
i n the s l a g
important
Once the oxygen p o t -
(50,52).
As a
r e a c t i o n s i n c l u s i o n s are p r e c i p i t a t e d
(140,144,147,148,216)
to:
187 m CaO + n A l 0 2
J
3
[m(CaO) « n ( A 1 0 ) ] i n c l u s i o n 2
(19)
3
or i n a more s p e c i f i c f o r m u l a t i o n : CaO
+ 6(A1 0 ) t 2
CaO-6Al 0
3
2
(19-a)
3
Since these r e a c t i o n products are i n e q u i l i b r i u m w i t h oxygen and s u l f u r according
then a s u l f i d e phase can be p r e c i p i t a t e d
(147, 148,197,210,215),. ' ' ' ' to: CaO
ic
+ [S] t
For low CaO content phases
ic
CaS
+ [0]
such as the C a O « 6 A l 0 , a 2
s u l f i d e phase such as the double s u l f i d e be
expected
3
(Mn, Ca)S should
t o (heterogeneously) p r e c i p i t a t e on o x i d e s .
Although very r a r e Ca,
(21)
when the s u l f i d e phase d i d not c o n t a i n
i t was f a c e t e d and c o n t a i n e d o n l y Mn and S.
Hence, i t
was c l e a r l y i d e n t i f i e d as MnS I I I . The
1020-M.S. i n g o t s i n t e r m i t t e n t l y d e o x i d i z e d with
the CaSi a l l o y have c l e a r l y r e c o n f i r m e d t h a t the d e o x i d a t i o n r e a c t i o n s are n o t e x c l u s i v e o f each o t h e r .
Instead a
c o o p e r a t i v e process between the d e o x i d i z e r , s l a g and l i q u i d metal takes p l a c e .
At a g i v e n d i s c r e t e
addition
of CaSi i n t o the s l a g i t s "FeO" content decreases, F i g u r e s (32) and (33).
Simultaneously t o t h i s change an increment
of A l i n the i n g o t and a decrement o f A l 0 ^ in. the s l a g 2
i s a l s o observed. reactions
As a r e s u l t of the above c o i n c i d e n t a l
a net change i n t o t a l oxygen content
which i s
a consequence of the i n c l u s i o n q u a n t i t i e s and compositions i s expected.
A r e d u c t i o n from 75 down t o 30 ppm was ob-
it r e p r e s e n t s a p e r i p h e r a l phase on i n c l u s i o n s
188 served. Another i n t e r e s t i n g f i n d i n g i s t h a t the r e d u c t i o n of t o t a l oxygen content was very dependent on the m e l t i n g conditions.
RII-W was melted under a i r w h i l s t RIII-W
was under an argon b l a n k e t .
The i n c l u s i o n phases
identified
i n t h i s experiment (RII-W and RIII-W) were e s s e n t i a l l y a-A^O^ and FeO-A^O^ as c l u s t e r s of s m a l l s p h e r i c a l p r e cipitates.
The samples c r i t i c a l l y
of d e o x i d i z e r — F i g u r e
a f f e c t e d by the a d d i t i o n s
(36)—showed Ca:Al r a t i o s
(at. %)
which c l o s e l y correspond to the f o r m a t i o n of the C a O « 6 A l 0 2
phase.
T h i s phase was m e t a l l o g r a p h i c a l l y i d e n t i f i e d
3
be-
cause of i t s f a c e t e d hexagonal appearance and i t s p e r i p h e r a l envelope of ( C a , M n ) S
( 1 5
'
9 4
'
1 4 5
'
2 0 3
'
2 1 0 )
.
The a - A l 0 2
the F e O A ^ O ^ were observed c l o s e r t o the and they were a s s o c i a t e d with
FeO
3
and
additions
(Mn,Fe)S or MnS I I .
The s e r i e s of f i n d i n g s from the c o n t i n u o u s l y CaSi deo x i d i z e d i n g o t s remelted through the CaF -Al 0.j-CaO s l a g 2
i n the 200 mm
2
diameter moulds can be condensed as f o l l o w s .
The s l a g chemical a n a l y s i s have s h o w n — F i g u r e s
(60) and
(61)-^that as the degree o f d e o x i d a t i o n i s i n c r e a s e d
the
CaO content of the s l a g i s i n c r e a s e d w h i l e the A l i s decreased. decrement
Although the f l u o r i n e a n a l y s i s showed a s l i g h t suggesting the formation o f v o l a t i l e
by r e a c t i o n s
fluorides
(8 to 10), the major changes, however, were
189 due to the r e a c t i o n between the d e o x i d i z e r and the s l a g . The "FeO' Content of the s l a g was g r a d u a l l y reduced
as the
1
d e o x i d a t i o n r a t e s were i n c r e a s e d . changes are adequately (FeO) t
[Ca] +
The i n i t i a l
d e s c r i b e d by the f o l l o w i n g r e a c t i o n s :
Fe(1) + (CaO)
2[A1] + 3(FeO) t
(12-v)
3Fe(l) + ( A l 0 ) 2
(12-iv)
3
At t h i s degree of d e o x i d a t i o n of the s l a g i n c l u s i o n s and MnS cipitated. increased observed,
deoxidation
alumina type of
I I were v i r t u a l l y the only phases p r e -
As the l e v e l of d e o x i d a t i o n i n the s l a g
was
Ca-aluminates with i n c r e a s i n g CaO-content were Figures
(58,59) and
(66 ,67). The i n c l u s i o n chem-
i c a l a n a l y s i s r e v e a l e d the f o l l o w i n g p r e c i p i t a t i o n s e quence:
a-Al 0 , 2
3
CaO«6Al 0 , CaO«2Al 0 , CaO«Al 0 2
traces of 12Ca0«7Al 0 2
(^0.2
wt
"FeO").
a t i o n o f segregates
3
3
2
3
2
3
and
a t extreme degrees o f d e o x i d a t i o n
Beyond t h i s d e o x i d a t i o n l e v e l the forme n r i c h e d i n Ca, A l , S i (and Mn)
formation o f ( A l , Ca)S were seen.
These s u l f i d e s showed
(EPMA a n a l y s i s ) t h a t the A l ( A l 0 ) although 2
and the
3
i n very
amounts was p r e f e r e n t i a l l y l o c a t e d i n the i n c l u s i o n
low core.
C o i n c i d e n t a l to the p r e c i p i t a t i o n o f the oxide phases a s u l f i d e phase, which was e n r i c h e d i n c a l c i u m p r o p o r t i o n a l to the amount o f CaO i n the Ca-aluminate phase served.
was
ob-
These a n a l y s i s l e a d to the c o n c l u s i o n t h a t the
mechanism by which the d e o x i d a t i o n - p r e c i p i t a t i o n occurs
is
190 as f o l l o w s : reached
once the l e v e l of the "FeO"
i t s minimum
the t r a n s p o r t of aluminum and
i n t o the l i q u i d p o o l 3[Ca] takes p l a c e .
2
3
2[A1]
+
calcium
(CaO)
(20-c)
Thus, the l e v e l s of d e o x i d a t i o n are
t i o n a l to the amount of A l and to the amount of CaO ratios).
has
by:
(A1 0 ) t
+
i n the s l a g
propor-
S i i n the i n g o t and
i n the i n c l u s i o n phases
also
(i.e.
Ca:Al
Hence the p r e c i p i t a t i o n sequence, i n terms of
the degree of d e o x i d a t i o n
i s as f o l l o w s :
i n the absence
of or a t very low d e o x i d a t i o n r a t e s i n a c o n v e n t i o n a l ( i n dustrial)
C a F - A l 0 - C a O s l a g , the p r e c i p i t a t i o n i s gov2
2
erned
by:
2[A1]
+ 4[0] + Fe
2[A1]
+ 3[0] =
The
3
(24)
(A1 0 ) i n c l u s i o n
(11-ii)
former oxide
(Mn,Fe)S or MnS or MnS
3
=
2
(FeO«Al 0 ) i n c l u s i o n 2
3
(Fe0*Al 0 ) 2
II.
3
i s u s u a l l y a s s o c i a t e d wi th
With the l a t t e r oxide
I I I are u s u a l l y observed.
(a-Al 0 )
The degree of
2
3
MnS
II
(Al) de-
o x i d a t i o n d i c t a t e s the f o r m a t i o n of a s p e c i f i c s u l f i d e .
At
i n t e r m e d i a t e d e o x i d a t i o n l e v e l s the r e a c t i o n (20-c) s t a r t s to operate
a c c o r d i n g to r e a c t i o n (19) or
(19a).
191 T h i s p a r t i c u l a r oxide phase w i t h e i t h e r MnS
I I I or
a d d i t i o n to r e a c t i o n
2
(Ca,Mn)S.
(20-c)
[Ca] + MnS was
(CaO«6Al 0 ) was
commonly
3
observed
Hence suggesting t h a t i n
the f o l l o w i n g r e a c t i o n CaS
t
+
[Mn]
(25)
also taking place. At r e l a t i v e l y h i g h d e o x i d a t i o n l e v e l s , where the r e -
action
(20-c) e n t i r e l y c o n t r o l s the t r a n s p o r t of d e o x i d i z e r s
i n the melt and when very low reached
"FeO"
content i n the s l a g i s
the p r e c i p i t a t i n g phases are C a O « 2 A l 0 2
(CaMn)S or CaS
and C a O « A l 0 2
These l a t t e r two envelope
of CaS.
f i d e s ) suggests aluminates
and
3
3
with
either
12CaO«7Al 0 . 3
3
oxide phases were surrounded
T h i s mixture of phases (oxide and
by
an
sul-
t h a t the c a l c i u m oxide from the c a l c i u m
s t r o n g l y i n t e r a c t s w i t h the s u l f u r and oxygen
i n s o l u t i o n according to: (CaO)* +
[S] =
T h i s r e a c t i o n generated
(CaS)* + a CaS
minimum oxygen content was F i n a l l y , a t extremely CaO:Al 0 2
shifted,
3
[0]
(21)
e n r i c h e d phase wherever the
reached
(^20-30
ppm).
h i g h d e o x i d a t i o n r a t e s where the
r a t i o i n the s l a g i s d r a s t i c a l l y and
suddenly
the f o r m a t i o n of s m a l l segregates e n r i c h e d i n Ca,
A l and S i can o c c u r .
Under these d e o x i d a t i o n c o n d i t i o n s
192 the f o r m a t i o n of Si-phase
(Al,Ca)S and
around the CaS
a p e r i p h e r a l envelope of
(which surrounds the
aluminate) were a l s o observed. w i t h 4 340
and
rotor
calcium
S i m i l a r r e s u l t s were obtained
(Cr-Mo-V) s t e e l s .
This allows
the
f o r m u l a t i o n of a comprehensive mechanism d i s c u s s e d i n the next s e c t i o n . I t i s worthwhile t o mention t h a t while t h e r e are some , . (151,153, 157,214,221,235,236) . . .^ . . advantages • ' • ' • ' ' ' to p r e c i p i t a t i n g aluminates shape and and
e n r i c h e d on c a l c i u m oxide t h e i r CaS
(because of t h e i r
round
envelope) i n s t e a d of the alumina g a l a x i e s
the manganese s u l f i d e s
the c o i n c i d e n t a l t r a n s p o r t of
aluminum i n t o the r e f i n e d i n g o t c o n s t i t u t e s a p o t e n t i a l problem.
T h i s behavior
j e c t i o n processes X[Ca]
+ Y(Al 0 ) 2
This r e a c t i o n
3
can be r e p r e s e n t e d
(210)
i n c l u s
, by: .
o n
ixCaO(Y-f)
as H o l a p p a *
ent to r e a c t i o n (20-c). i s used
as i n the c a l c i u m i n -
2 1 0
^
A l ^ + § X(A1)
has p o i n t e d out
(20-b)
i s equival-
Thus, i f an excess of d e o x i d i z e r
(CaSi)
A l i s i n t r o d u c e d i n the melt and hence the p o t e n t i a l • (221-223)
to reduce the mechanical p r o p e r t i e s i s enhanced
5.3.4
Comprehensive D i s c u s s i o n on the D e o x i d a t i o n When A l or Ca i s added to the ESR-slag as a
i t becomes p a r t of a r e a c t i o n scheme r e p r e s e n t e d
Mechanism deoxidant,
by:
193 [Ca] + 2[A1]
(FeO)
%
Fe(l) +
(CaO)
+ 3(FeO) + F e ( l ) + A l 0 2
3[Ca] +
( A 1 0 ) % 2[Al] 2
3
(12-v) (12-iv)
3
+ 3(CaO)
(20-C)
At high l e v e l s of "FeO", r e a c t i o n s (12-v) and dominate
l e a d i n g to a simple d e o x i d a t i o n scheme
the deoxidant a d d i t i o n appears component. over
(12-iv) w i l l prewhich
as the a p p r o p r i a t e s l a g oxide
At low l e v e l s of "FeO"
(12-v) and
in
reaction
(20-c) w i l l
(12-iv) and i t w i l l be observed
take
t h a t an
ex-
(46 47 change r e a c t i o n
( s i m i l a r to those a l r e a d y r e p o r t e d
'
52 '
'
54) for
S i / A l and T i / A l ) i n which the a l l o y Ca:Al r a t i o i n
the i n g o t w i l l be determined by the CaO:Al20 s l a g low i n s i l i c a ,
( l e s s than 10 wt.
% S i 0 ) , not by the 2
r a t e , form or composition o f the deoxidant. the p o i n t a t which r e a c t i o n s (12-v) and way
r a t i o i n the
3
In determining
(12-iv) w i l l g i v e
t o (20-c) i n the sense of producing i n g o t composition,
the l e v e l of s l a g F e O - a c t i v i t y i s e v i d e n t l y of prime ance.
I t i s more important than the i n t r i n s i c
e l e c t r o d e chemical composition. slag
import-
s l a g and
the
At low F e O - a c t i v i t y i n the
i f l a r g e q u a n t i t i e s of Ca are added as a d e o x i d i z e r ,
the r e s u l t
i n a c o n v e n t i o n a l ESR-slag composition
be a c o r r e s p o n d i n g i n c r e a s e i n the a l l o y A l l e v e l , reaction
(20-c).
will through
194 In order to i l l u s t r a t e the r o l e o f r e a c t i o n s (12-v) to
(12-iv) the r e s u l t s o b t a i n e d from the 4 340
selected
i n g o t were
as the p r o t o t y p e o f the g e n e r a l behavior
approach t h i s d i s c u s s i o n .
to
The d e o x i d a t i o n sequence
in
terms o f the chemical composition of the i n g o t and the s l a g are shown i n F i g u r e s (70) and (71). A p p l y i n g a mass balance to t h i s i n g o t and the s l a g , i t i s apparent addition
(from the d e o x i d i z e r ) , appears
t h a t the s i l i c o n
almost q u a n t i t a t -
i v e l y i n the i n g o t
with very l i t t l e
I t i s a l s o observed
t h a t the c o n c e n t r a t i o n o f A ^ O ^ i n
the s l a g decreases
w h i l e the CaO content
p a r t o f the t o t a l Ca content) data
o f S i C ^ t o the s l a g .
increases.
(represented as a Utilizing
this
i n c o n j u n c t i o n with the i n c r e a s e d A l assay o f the
i n g o t l e a d s to an e x c e l l e n t c l o s u r e o f a mass balance drawn on the system u s i n g equation
(20-c).
In consequence, i f
the f o l l o w i n g s t o i c h i o m e t r i c r e l a t i o n s h i p *
^
2 1 0
which r e -
l a t e s the r e d u c t i o n o f alumina by Ca i n the chemical
comp-
o s i t i o n o f the i n c l u s i o n s , X[Ca]
+ Y(Al 0,). , t z J inclusion o
XCaO-(Y - *-) A l 0 , + \ X[A1] J z 6 s o
(20-b) is u t i l i z e d
t o perform the balance, e q u i v a l e n t r e s u l t s and
a very c l o s e p r e d i c t i o n o f the i n c l u s i o n chemical i s obtained.
composition
These r e s u l t s are taken as a s t r o n g evidence
t h a t the c a l c i u m component o f the CaSi a l l o y a d d i t i o n has r e duced A ^ O ^
from
s l a g , f o l l o w i n g (20C) producing A l i n the
195 i n g o t and l e a d i n g to a CaO
i n c r e a s e i n the s l a g .
d u c t i o n i s s t o i c h i o m e t r i c , as would be 210
expected'
4 7
'
1 4 8 ,
216) '
from an e q u i l i b r i u m a n a l y s i s of
process of r e f i n i n g , as expected ' ' l e v e l i n the s l a g remained 0.1
This re-
- 0.2
wt.
2 7
'
3 8
(20) .
'^ ' 7
8 2
During
^
a t low but f i n i t e
the
the
"FeO"
l e v e l of
%, F i g u r e (73).
These r e s u l t s l e a d to the c o n c l u s i o n t h a t a t an 'FeO" a c t i v i t y c o r r e s p o n d i n g to approximately 0.1 in t h i s slag
(50/30/20),
- 0.2
the r e a c t i o n of A l 0 2
wt.
%
to g i v e an
3
i n c r e a s e i n the i n g o t w i l l take p l a c e i f c a l c i u m i s used as a deoxidant.
When e i t h e r A l or aluminum s i l i c o n
used as deoxidant at e q u i v a l e n t r a t e s , i t was the s l a g "FeO"concentration was Figures
(39, 40) and
was
observed
again h e l d a t low
that
levels—
(45,46) and Tables XII and X I I I
(a-c)
— a n d t h a t both A l and S i were q u a n t i t a t i v e l y t r a n s f e r r e d to ... . . . , . ,(147, 148,210,216) the i n g o t .
T h i s r e s u l t i s to be expected
from r e a c t i o n
'
'
(20-C) as o n l y a very s l i g h t degree of alum-
inum r e d u c t i o n of Ca from CaO would a r i s e from
reaction
(20-C), producing composition changes not d e t e c t a b l e w i t h i n the accuracy o f t h i s mass balance. c l u s i o n compositions
The behavior of the i n -
i s a more s e n s i t i v e guide than the
mass balance i n r e l a t i o n to the Ca/Al exchange r e a c t i o n i n the s l a g .
The Ca:Al r a t i o i n the oxide phase and
the
p a r t i a l s u b s t i t u t i o n of Mn by Ca i n the s u l f i d e phase i n i n c l u s i o n s i n A l - d e o x i d i z e d i n g o t s — F i g u r e s (43,44) and 52)--as w e l l as the Ca:Al r a t i o i n the oxide
(51,
(inclusion)
196 phases and t h e i r p r o p o r t i o n a l amounts of CaS
i n the CaSi
and i n the A l - S i based d e o x i d i z e d i n g o t s — F i g u r e s (66,67),
(71,75) and F i g u r e
( 7 6 ) — i n d e e d monitor
(58,59),
the magni-
tude and d i r e c t i o n of the e q u i l i b r i u m d i c t a t e d by r e a c t i o n s (20-b,c). F i g u r e 4340 i n g o t
(74)
which shows the behavior of the
shows t h a t the Ca:Al r a t i o i n the oxide i n -
c l u s i o n s r i s e s r a p i d l y to a c o n s t a n t value which i s a p p r o x i mately may
equal t o a composition CaD'A^O^.
These r e s u l t s
be compared to those r e p o r t e d f o r c a l c i u m i n j e c t i o n
processes
(144
'
148
'
154
'
steelmaking p r o c e s s '
157) 4 0 , 2 0 6
and f o r the b a s i c e l e c t r i c arc ^
p a r t i c u l a r l y those shown i n
(178) Figure
(78)
where an e q u i v a l e n t l y l o w - s u l f u r s t e e l shows
the same b e h a v i o r .
F a u l r i n g and R a m a l i n g a m * ^ 21
s t u d i e d the r e l a t i o n s beween CaO oxide i n c l u s i o n s i n t h i s system. r e p r e s e n t e d by the p r e c i p i t a t i o n shown i n F i g u r e (11).
and A^O^
have
i n generating
T h e i r c o n c l u s i o n s are ( e q u i l i b r i u m ) phase diagram
When the Ca a c t i v i t y i s estimated
i n the ESR s l a g / m e t a l system f o l l o w i n g r e a c t i o n (20-c), (234 ) (19 8) u s i n g the data of Rein e t a l . and S p o n s e l l e r and F l i n n and assuming t h a t C a F v i t y of h
(_a
= 6.7
2
x 10
a c t s as an i n e r t d i l u e n t , an —8
a t 0.1
wt.%
acti-
A l i s obtained.
This
c o n c l u s i o n would i n d i c a t e from F a u l r i n g ' s data, F i g u r e (11), t h a t one
should observe an i n c l u s i o n composition c l o s e t o
CaO-A^O^/ which i s indeed the case.
I t i s c l e a r , there-
f o r e , t h a t i n s p i t e of an e x c e s s i v e l y h i g h a d d i t i o n of
197
calcium
('vlO kg/ton)
, the i n c l u s i o n composition i s
c o n t r o l l e d e n t i r e l y by r e a c t i o n
(20-c) and t h a t i n c l u s i o n
c a l c i u m contents w i l l not r i s e above those p e r m i t t e d by reaction
( 2 0 - c ) , d e s p i t e the c a l c i u m a d d i t i o n .
teresting dition,
It i s i n -
to note a l s o t h a t a t t h i s l e v e l o f c a l c i u m ad-
the s u l f i d e i n c l u s i o n
surrounding the c a l c i u m a l -
uminates were e x c l u s i v e l y composed of CaS not MnS.
This
f i n d i n g can a l s o be compared t o those r e p o r t e d i n (Ca,CaO) i n j e c t i o n p r o c e s s e s i n A l d e o x i d i z e d melts of r e l a t i v e l y low oxygen a c t i v i t y , where the p r e c i p i t a t i o n
o f e i t h e r MnS
c i p i t a t i o n o f aluminates ls
, ,
ui
p h e r a l double 19 7
i n c i p i e n t amounts o f Ca induce o
4-
r
n e
pre-
(low i n CaO content) with a p e r i -
/„
sulfide,
m ' ^ " ' ^ ^
„ ^ ( 1 4 0 , 144, 146,153, 159, 160,
(Mn,Ca)S
'
212)
'
'.
T h i s t r a n s i t i o n i s o b v i o u s l y d i c t a t e d by: MnS
and i t i s expected
+ [Ca]
.
•
(25)
t o occur when the Ca i n the melt i s ap-
p r o x i m a t e l y 5-10 ppm. N
CaS + [Mn]
t
At h i g h e r l e v e l s of Ca, the s u l -
. ,(140, 144, 146,147, 153,157,211,216)
f i d e phase i s expected
•
'
•
'
'
'
•
.
to
be r u l e d by: * CaO
* + [S]
and hence p r e c i p i t a t i n g or pure CaS. the observed
t
CaS
+ [0]
a p e r i p h e r a l s u l f i d e , namely
(21)
(Mn,Ca)S
In the case o f d e o x i d a t i o n with the A l S i
alloy,
changes i n s l a g composition were almost e q u i -
198
v a l e n t t o the C a S i , the o n l y change being a s l i g h t i n c r e a s e i n both S i C ^ and Al^O^ a t low "FeO" Table
(XII).
The observed
of Ca-aluminates about 5-7%
l e v e l s i n the
i n c l u s i o n composition was
c o n t a i n i n g approximately
S as CaS
slag, that
20-30% CaO
and
i n t h e i r p e r i p h e r y , F i g u r e (76).
These
f i n d i n g s i n d i c a t e t h a t s i n c e the e q u i l i b r i u m p o s i t i o n of reaction
(20-c) r e s u l t s i n r e d u c t i o n of CaO
by A l , the
t o t a l mass of Ca c a r r i e d i n t o the metal by t h i s means w i t h the A I S i a l l o y i s s i m i l a r t o t h a t i n the CaSi and " h y p e r c a l " case, F i g u r e (76).
the
The e q u i l i b r i u m r a t i o s of
Ca:Al r e p o r t e d by F a u l r i n g and R a m a l i n g a m ^ ^
hence are
2 l
r
a t t a i n e d by the C a S i , " h y p e r c a l " and the A I S i a l l o y .
The
chemical r e s u l t of d e o x i d a t i o n by A I S i and the " h y p e r c a l " a l l o y i n r e s p e c t of i n g o t composition i s t h e r e f o r e v i r t u a l l y i d e n t i c a l w i t h t h a t o b t a i n e d by c o n v e n t i o n a l CaSi d e o x i d a t i o n a t about the same r a t e .
It i s interest-
i n g t o note t h a t aluminum d e o x i d a t i o n f o l l o w s a p a t t e r n f a m i l i a r from e l e c t r i c furnace p r a c t i c e . aluminum d e o x i d a t i o n a t the p r e s e n t l e v e l s
In the case of (10 k g / t o n ) , a
range of A l content i s achieved i n the i n g o t as shown i n Figure
(71).
The
corresponding l i q u i d and s o l i d i n g o t
oxygen a n a l y s i s are shown i n F i g u r e (72 a-b)
where i t can
be seen t h a t the minimum oxygen content i s a t 0.1 wt% A l .
T h i s minimum i s a t the composition (175
Figure 2
(10) J
expected,
177) '
, from a c o n s i d e r a t i o n of
[Al] + 3 [0] t
1
approximately
1
J
(Al 0-,) . i . ' 2 3 inclusion o
(11-ii)
199 u s i n g the compiled
i n f o r m a t i o n by G u s t a f f s o n and
Melberg
(175)
Al Figure
(10), f o r e
proximately
a t an e q u i l i b r i u m temperature of
Q
ap-
1600°C.
I t can t h e r e f o r e , be assumed t h a t the d e o x i d a t i o n p r e c i p i t a t i o n of i n c l u s i o n s are c l o s e l y e q u i v a l e n t to e s t a b l i s h e d i n the e l e c t r i c 5.3.5
furnace'
4 0 , 2 0 6
and
those
^.
F i n a l Remarks I t i s important
to emphasize t h a t an inadequate
o x i d a t i o n o f a ESR-melt w i t h A l or Ca-bearing becomes very important properly adjusted.
de-
deoxidants
where ever the aluminate-CaS i s not
The A l d e o x i d a t i o n or the l a c k of
CaSi d e o x i d a t i o n seen as generators
of alumina g a l a x i e s or as
(133) i n d u c e r s of "burning"
or the excess
a l l o y s , because of the excess through r e a c t i o n (15 a-b)
of A l , A l S i or CaSi
of A l i n i n g o t s i n t r o d u c e d
c o n s t i t u t e a p o t e n t i a l source of
sul-
f i d e s and n i t r i d e s and hence to a d e g r a d a t i o n of mechanical (221-223) properties
of the r e f i n e d i n g o t s .
Hence, the f i n a l remarks, the l a t t e r s e t of q u e s t i o n s i)
ESR-deoxidation
which at the same time answer
to be drawn a r e :
w i t h Ca w i l l f o l l o w the r e a c t i o n
(20-c) a t low oxygen p o t e n t i a l s , i . e . below 0.2 ii)
s l a g "FeO"
contents
wt.%; At i n t e r m e d i a t e oxygen p o t e n t i a l s
( s l a g "FeO"
ranging between 0.4-0.6 wt,%), the d e o x i d a t i o n process e i t h e r A l or Ca i s e q u i v a l e n t and
content using
serves o n l y to c o n t r o l
the s l a g composition.
This l a t t e r
f a c t o r w i l l t h e r e f o r e de-
termine the c h o i c e o f deoxidant; iii)
Deoxidation
w i t h A l w i l l a l s o f o l l o w the r e a c t i o n
(20-c) but w i l l not reach the p r e d i c t e d i n g o t Ca:Al due
t o unfavorable
a carrier
k i n e t i c f a c t o r s , unless
ratio
S i i s added as
f o r Ca;
i v ) The maximum S i C ^ content
i n the s l a g f o r e f f i c i e n t
d e o x i d a t i o n through r e a c t i o n ( 1 2 - v ) , ( 1 2 - i v ) , and ( 2 0 - c ) ; i s l e s s than
10 wt. %;
v) The chemistry r o l e i n the d e o x i d a t i o n (low)
o f the e l e c t r o d e does not p l a y a ( r e a c t i o n ) scheme u n l e s s
d e o x i d a t i o n r a t e s a r e used, i . e .
inappropriate
sacrificial
elect-
rode d e o x i d a t i o n which leads t o change the ESR s l a g or i n g o t composition; v i ) E x c e s s i v e and/or abrupt
d e o x i d a t i o n can l e a d t o
d e l e t e r i o u s mechanical p r o p e r t i e s , i . e . h i g h l e v e l s o f A l or d e o x i d i z e r s
i n i n t r o d u c t i o n of
(as s m a l l segregates) i n
the ESR i n g o t ; and v i i ) The shape o f i n c l u s i o n s depends upon the type and degree o f d e o x i d a t i o n :
1) i n A l d e o x i d i z e d i n g o t s s p h e r i c a l
s i n g l e o r c l u s t e r s o f alumina phases
( a - A l ^ ^ and FeO'A^O^)
a s s o c i a t e d w i t h manganese s u l f i d e s are found a t r e l a t i v e l y low deoxidation inates
l e v e l s and f a c e t e d aluminates
and low c a l c i u m alum-
(CaO-eA^O-j) as s i n g l e o r c l u s t e r s a t r e l a t i v e l y
deoxidation rates.
2) i n C a S i ,
high
"hypercal" or AISi deoxidized
201 ingots, faceted calcium
(a-Al 0 2
3
and C a O 6 A l 0 ) and s i n g l e s p h e r i c a l 2
3
aluminates ( C a O * 2 A l 0 , C a O « A l 0 2
3
2
3
and
12CaO«7Al 0 )
w i t h p e r i p h e r a l s u l f i d e s are found at r e l a t i v e l y low and deoxidation
rates respectively.
2
3
high
202 5.4
F i n d i n g s and D i s c u s s i o n Related t o the T h i r d Question
5.4.1
D e s c r i p t i o n of Experimental
5.4.1.1
The I n c l u s i o n Mean Diameter Tables
Results
(XIV a-b) show the standard i n f o r m a t i o n drawn
from the i n c l u s i o n
(EPMA) a n a l y s i s .
As p r e v i o u s l y d e s c r i b e d ,
a minimum o f twenty and a maximum o f 40 s i n g l e analyses were performed i n each sample.
S o l i d i n g o t samples 2.5 x 2.5 cm
i n area and l i q u i d p o o l samples approximately
2
75% o f t h i s
area were s y s t e m a t i c a l l y analyzed. Analyses were performed i n l o n g i t u d i n a l and t r a n s v e r s a l d i r e c t i o n s i n both
types
of samples. The mean i n c l u s i o n diameter Figures The
was s t a t i s t i c a l l y
obtained.
(79 a,b) show an example o f each type of sample.
linearity
shown i n these graphs c l e a r l y i n d i c a t e s t h a t
the s i z e o f i n c l u s i o n s i s r e p r e s e n t e d by a normal d i s t r i b u t i o n . The
c o r r e l a t i o n c o e f f i c i e n t s ranged from 0.97 t o 0.99 which
are e x c e l l e n t f o r the p a r t i c l e s i z e found. information
Based on t h i s
p l o t s o f mean i n c l u s i o n diameter,
50% o f the cumulative
frequency,
given as the
a g a i n s t i n g o t h e i g h t (or
d e o x i d a t i o n l e v e l s ) were o b t a i n e d .
To c o r r e l a t e t h i s
inform-
a t i o n to the d e o x i d a t i o n b e h a v i o r , these f i n d i n g s are a l s o p l o t t e d along w i t h the t o t a l oxygen a n a l y s i s from both of
samples.
types
203 5.4.1.2
F i n d i n g s from I n d i v i d u a l Experiments The
as RII-W
Figure
( 36 ) which corresponds t o i n g o t
labelled
i n which the CaSi was d i s c r e t e l y added, shows t h a t
the i n c l u s i o n average s i z e depends s t r o n g l y on the d e o x i d a t i o n practice.
T h i s p l o t c l e a r l y shows t h a t c o i n c i d e n t a l to the
l a r g e s t Ca:Al r a t i o s i n i n c l u s i o n s
the s m a l l e s t mean i n -
c l u s i o n s i z e i s found. The Figure with
behavior
corresponding
t o R I I - I l i s shown i n
(41). T h i s shows t h a t the mean i n c l u s i o n s i z e v a r i e s
the t o t a l oxygen content.
a t low d e o x i d a t i o n
T h i s graph a l s o shows t h a t
r a t e s (3.60 and 6.1 kg ton ^ ) , the i n -
c l u s i o n s i z e of samples from the l i q u i d p o o l are s m a l l e r the ones from the i n g o t .
At moderate and high
l e v e l s , however, the opposite
behavior
deoxidation
i s observed.
ference i n average s i z e i s approximately 1 pm.
(43)—also
behavior.
Findings
from
RII-I2 a r e shown i n F i g u r e (42).
Since t h i s i n g o t was d e o x i d i z e d than R I I - I l
The d i f -
Vari-
a t i o n s i n the Ca:Al r a t i o s i n i n c l u s i o n s — F i g u r e reflect this
than
by lower A l - a d d i t i o n r a t e s
the mean i n c l u s i o n diameter i n samples from
i n g o t and l i q u i d p o o l were almost e q u i v a l e n t .
The average
Ca:Al r a t i o s o f i n c l u s i o n s i n t h i s i n g o t a l s o changed i n an e q u i v a l e n t manner, F i g u r e (44). The
i n g o t i d e n t i f i e d as R I I I - I l , which was CaSi de-
oxidized,
i n some r e s p e c t behaved as RII-I2.
Variations in
the Ca:Al r a t i o s i n i n c l u s i o n s and oxygen contents are a l s o r e f l e c t e d i n the mean s i z e o f i n c l u s i o n s .
It i s
important t o note t h a t the CaSi a d d i t i o n r a t e s were almost e q u i v a l e n t from one t o the other and g r a d u a l l y i n c r e a s e d during r e f i n i n g , Figures
(56 a-b) and
(58).
RIII-I2 used an e q u i v a l e n t d e o x i d a t i o n procedure to RIII-Il.
R I I I - I 2 , however, was r e f i n e d under d i f f e r e n t de-
o x i d a t i o n regimes.
The three lowest CaSi a d d i t i o n s were
added i n s h o r t e r p e r i o d s o f time a t the bottom o f RIII-I2, w h i l e the f o u r t h l e v e l of a d d i t i o n s (22.4 4 kg t o n ^) was much longer than i n R I I I - I l . unmistakenly
In t h i s experiment,
i t is
shown t h a t i n c l u s i o n s from l i q u i d p o o l , a t
moderate and h i g h e r CaSi a d d i t i o n s , a r e l a r g e r i n s i z e the ones from the i n g o t .
The Ca:Al r a t i o s , the t o t a l oxygen
content as w e l l as the mean i n c l u s i o n
diameters behaved i n
e x a c t l y the same way as R I I - I l , F i g u r e s 57(a-b) and Finally,
than
(59).
Ingot 4340 which was CaSi d e o x i d i z e d shows
the same p a t t e r n , i n terms o f t o t a l oxygen a n a l y s i s , r a t i o s and p a r t i c l e s i z e s , as RII-I2 (72 a,b) and (74a,b).
Ca:Al
and R I I I - I l , F i g u r e s
205 5.4.1.3
Complementary S t u d i e s To gain a b e t t e r understanding about i n c l u s i o n
a t i o n and growth and
to e l u c i d a t e whether the
mechanism operates
under the ESR-conditions
of experiments was
performed.
form-
flotation one more s e t
Samples were sucked
from
the l i q u i d p o o l i n t o s i l i c a tubes which contained e i t h e r a mishmetal or Zr w i r e .
R e f i n i n g was
and at a constant d e o x i d a t i o n r a t e A I S i or C a S i ) . of i n c l u s i o n s
c a r r i e d out under argon (10 kg/ton of e i t h e r
Three major areas, i n terms of the were i d e n t i f i e d
i n these samples.
composition Regions
where i n c l u s i o n s were mainly c o n s t i t u t e d by e i t h e r r a r e e a r t h or z i r c o n i u m e n r i c h e d phases.
A r e g i o n where the Zr o r the
r a r e e a r t h phases were mixed w i t h complex C a - A l - s i l i c a t e s and a r e g i o n where a mixture few
of pure Ca-aluminates and
very
i n c l u s i o n s with p e r i p h e r a l r a r e e a r t h or z i r c o n i u m
s u l f i d e phases were i d e n t i f i e d . c l u s i o n s i s shown i n F i g u r e s
T h i s l a t t e r type of i n -
(80,81) and
(82,83) where
the composition maps f o r A l , Ca,Ce, La, S and i s very important as much as 7-10%
Zr are g i v e n .
to emphasize t h a t t h i s type accounted of the t o t a l amount of i n c l u s i o n s
for
analyzed
(40-50) i n each sample. M e t a l l o g r a p h i c a n a l y s i s on specimens o b t a i n e d from l i q u i d pools
(1020
and 4340)show t h a t a c o n s i d e r a b l e amount
It
of i n c l u s i o n s was found c l o s e t o the w a l l of the s i l i c a
206 tube.
Most of them, however, were l o c a t e d i n i n t e r d e n d r i t i c r e g i o n s and o n l y approximately 5-7% were trapped by primary d e n d r i t e s , Figures
(85) and (86).
207 5.4.1.4
Summary of Experimental F i n d i n g s
In o r d e r to approach
the answer
q u e s t i o n a summary of f i n d i n g s , size,
( d i s c u s s i o n ) to t h i s
i n terms of 1) i n c l u s i o n mean
2) i n c l u s i o n composition and 3) t o t a l oxygen a n a l y s i s ,
i s presented. 1)
-
I n c l u s i o n s i z e d i s t r i b u t i o n s obey the normal bution 0.96
(the c o r r e l a t i o n c o e f f i c i e n t ranged
distri-
from
- 0.99) .
The mean i n c l u s i o n diameter was The average
approximately 6-8
ym.
i n c l u s i o n s i z e i n c r e a s e s approximately
1 ym i n diameter i n both types of samples
(ingot
and l i q u i d pool) as the d e o x i d a t i o n r a t e i s i n creased. In i n g o t heads (CaSi d e o x i d i z e d ) some i n c l u s i o n s were seen as l a r g e as 30 ym i n samples e x t r a c t e d from l i q u i d p o o l s and t h i s s i z e was
very r a r e l y seen i n
the i n g o t . The
i n c l u s i o n d e n s i t y , number of i n c l u s i o n s per a r e a ,
i s g r a d u a l l y i n c r e a s e d from the c e n t e r t o the mould wall.
T h i s f a c t was
accentuated i n CaSi d e o x i d i z e d
ingots. 2)
-
Calcium aluminates were almost always observed to c o n t a i n a core e n r i c h e d i n alumina
( i . e . A l by EPMA).
208 The
Ca:Al r a t i o s i n i n c l u s i o n s i s almost always smaller
i n samples e x t r a c t e d from l i q u i d p o o l s than from i n g o t s The p e r i p h e r a l S content
as CaS
i s p r o p o r t i o n a l to
the Ca:Al r a t i o s i n the c a l c i u m e n r i c h e d
aluminate
phases. At r e l a t i v e l y l a r g e d e o x i d a t i o n r a t e s the formation of segregates ( A l , Ca and
Si) was
enriched i n deoxidizers
observed.
r e c a l l t h a t these segregates
(^10-12 kg/ton)
I t i s important
to
were commonly seen i n
samples e x t r a c t e d from the l i q u i d p o o l and very in ingots.
3)
-
The
They a l s o contained
some
mately 20
5.4.2
Mn.
average d i f f e r e n c e i n t o t a l oxygen content
samples e x t r a c t e d from l i q u i d p o o l and
rarely
between
ingot i s approxi-
ppm.
P r e c i p i t a t i o n of I n c l u s i o n s i n the Fe-Al-Ca-O-S(Mn) System By using F a u l r i n g ' s and
Tables
(IV) to
Ramalingham's d a t a ^
2 1
^
given i n
f
(VI), to c o n s t r u c t the Fe-Al-Ca-0 p r e c i p i -
t a t i o n diagram, c o n j o i n t l y with o b s e r v a t i o n s
of other
investi-
g a t o r s , p r e v i o u s l y d e s c r i b e d i n s e c t i o n s 2.3.5, 2.3.7.2 and 5.3.4, the p r e d i c t i o n of the p r e c i p i t a t i o n of the Ca-aluminate/ C a - s u l f i d e phases can be pursued a l i t t l e Fe-Al-Ca-0 system i s now
approached by
further.
I f the
superimposing
the
(CaS)
[0]
+
CaO
t
e q u i l i b r i u m to the Fe-Al-Ca-0 system,
+
(21)
[S]
system, as the Fe-Al-Ca-O-S
and care i s taken to c o n s i d e r the phase r u l e , a
diagram r e p r e s e n t i n g the p r e c i p i t a t i o n of
Ca-aluminates
and t h e i r corresponding s u l f i d e phases was c o n s t r u c t e d . The procedure used et a l . (
239
^
was
e q u i v a l e n t to t h a t used by Wilson
and F a u l r i n g e t a l .
efficients
.
The a c t i v i t y
[CaO-Al 0
f o r CaS i n e q u i l i b r i u m w i t h l i q u i d
( l i q u i d ) - C a S ( l i q u i d ) ] and
2
[CaO-CaS]solid were estimated N
(240
from Sharma's and R i c h a r d s o n s s i n v e s t i g a t i o n s (XV).
T h i s diagram based on Henrian a c t i v i t i e s i s
= 0.001,
A l
,
(1550° C) and was developed f o r l e v e l s of A l
isothermal (h
241) '
1
Table
co-
0.01 and 0.1)
i n the range of major i n t e r e s t .
The data generated from these e q u i l i b r i a i s summarized i n Table
(XV). The major r e a c t i o n s are g i v e n i n Appendix ( I ) .
Although the Fe-Al-Ca-O-S system was
exclusively
veloped as a four f o l d component e q u i l i b r i a , the MnS e q u i l i b r i u m with A^O^
• 4- •
•
n
-A
and the double ••'
u t i o n of Mn by Ca i n the MnS
in
[(Ca,Mn)S] s u l f i d e i s
-,(140,146,210)
i n t r i n s i c a l l y considered
de-
, .
,
.
The g r a d u a l s u b s t i t -
phase i s governed by the
fol-
lowing e q u i l i b r i u m : (MnS)*+ [Ca] t
(CaS)*+
[Mn ]
(25)
The presence of Ca i n s o l u t i o n i n the melt generates s e v e r a l transitions.
I n c i p i e n t amounts of Ca
o r i g i n a t e the
210 t r a n s i t i o n of MnS
I I to
(91
MnS
92
R e l a t i v e l y h i g h e r Ca contents double s u l f i d e s , e.g.
(Ca,Mn)S.
duced i n the melt i s i n c r e a s e d CaS
and MnS
appears' * ^. 4
between the f o r m a t i o n The
144)
i n the melt induce
I f the amount of Ca a m i s c i b i l i t y gap
This t r a n s i t i o n occurs
5
of the C a O ' e A ^ O ^ and
the
the
intro-
between the somewhere
CaO^A^O^.
s u l f i d e phase, as r e p o r t e d by s e v e r a l r e s e a r c h e r s
heterogeneously described)
and
Ca(Al)
is
p r e c i p i t a t e d on the oxide phases ( p r e v i o u s l y i t i s very dependent on the a c t i v i t y of the A l .
In p r e v i o u s d i s c u s s i o n s i t was
CaO
140
acknowledged t h a t as
d e o x i d a t i o n l e v e l i s i n c r e a s e d , the amount of Ca
i n the Ca-aluminate phase i s i n c r e a s e d by r e a c t i o n
and hence the amount of CaS and/or
(26).
The
produce pure CaS
phase i n c r e a s e s by
f a c t t h a t the i n j e c t i o n of CaO i s also considered.
the
as (20)
reactions
(25)
s l a g s do
As Saxena and
not
cowork-
(147 148 214) •' ' have r e p o r t e d , t h i s t r a n s i t i o n w i l l take p l a c e (144 153 a f t e r Ca-aluminates have formed. As s e v e r a l r e s e a r c h e r s ' ' 154,156 .185,197.211) . _ . . . .. . _ _ • • • ' work suggest, the p r e c i p i t a t i o n of pure CaS
ers
i s expected to occur once the Ca-content i n the melt oxygen l e v e l i s approximately
10-40
o s i t i o n i n the double s u l f i d e , to 50.0
wt.
(or the
ppm)
i s such t h a t a comp-
(Mn,Ca)S
i s g r e a t e r than 4 3.0
% (140,146)^
T h i s t r a n s i t i o n i s reached once the (202) CaO-A^O^ s t o i c h i o m e t r i c phase i s formed . O t o t a n i ' s and Kataura's r e s u l t s * ^ c o n f i r m K i e s s l i n g s and Westman s* ^^ 2 1 5
S a l t e r and
1
(140) Pickering's
r e p o r t a "pure" CaS
v /
and
Church's
phase a f t e r the
(159) ' findings.
" A l 0 " content 2
3
14
They
i n the
Ca-aluminates i s reduced by Ca to approximately i s also r e p o r t e d ' ^
t h a t once t h i s p e r c e n t
1
i s reached a sharp increment i n the CaS
40.0%.
of CaO
It
(40.0%)
i s noted.
A schematic r e p r e s e n t a t i o n of the above d e s c r i p t i o n i s shown i n F i g u r e thermal
(87).
(1823K) and
This Figure
prehensive h ^ A
(h
g
= h
A l
manner the h ^ t h ^
= 0.001, 0.01
and
I I - I I I , the Ca-aluminates 2
3
and
0.1)
(88) and
(89). A^O^/ and
5.4.3.1
N u c l e a t i o n , Growth and
Results F l o t a t i o n of
d i f f e r e n c e i n the mean diameter
from l i q u i d p o o l and
(1-3
Inclusions ym)
of i n c l u s i o n s
from i n g o t s i n d i c a t e s t h a t the
mechanism i n the ESR-conditions under which t h i s behavior was
operate.
The
d i s p l a y e d were:
flotation
conditions a) when the
d i f f e r e n c e i n t o t a l oxygen content between the l i q u i d i n g o t s i s g r e a t e r than 20 ppm
g r a d u a l and c l u s i o n s and
the
CaO/CaS e q u i l i b r i a .
D i s c u s s i o n of
and
the
i n a com-
of the
(C•6A,C•2A)/(Mn,Ca)S
5.4.3
The
To
r a t i o s are p l o t t e d a g a i n s t e i t h e r
(88,89) summarize the behavior
CaO-Al 0 (liq)
= 0.1.
f t l
composite phases over
or hg i n l o g a r i t h m i c s c a l e s i n F i g u r e s
These F i g u r e s MnS
i s necessarily iso-
at a f i x e d A l a c t i v i t y , h
r e p r e s e n t the s t a b i l i t y of these ranges of i n t e r e s t
(87)
and
pool
b) Where smooth,
e q u i v a l e n t changes i n the Ca:Al r a t i o s of i n i n the t o t a l oxygen content
l i q u i d p o o l and
i n g o t were observed.
i n samples from
Case (a) was
speci-
212 f i c a l l y observed i n the A l - d e o x i d i z e d and
p a r t i a l l y i n RII-I2.
ference
i n oxygen content
r a t e with A l
was
These two
ingots, i . e .
ingots e x h i b i t t h i s
when the h i g h e s t
applied.
RII-Il dif-
deoxidation
I t i s important to note t h a t
because of the changes i n oxygen a n a l y s i s i n the l i q u i d and
ingot
(RII-I2), a d i f f e r e n c e g r e a t e r than 20
i s observed i n t o t a l oxygen.
T h i s behavior
i n the Ca:Al r a t i o s i n i n c l u s i o n s .
Case
ppm
i s also reflected
(b) i s found i n R I I I -
12 and p a r t i a l l y i n R I I - I l where the d e o x i d a t i o n given by the behavior
sequence,
of the t o t a l oxygen content
A l r a t i o s i n i n c l u s i o n s , Figures
pool
(57,59) and
and
the
Ca:
(43,44), shows
smooth and p a r a l l e l changes. The
s o l i d i f i c a t i o n c o n d i t i o n s i n samples from i n g o t s
(center p a r t )
are l e s s d r a s t i c than i n samples e x t r a c t e d from
l i q u i d pool.
The
secondary d e n d r i t e arm
i n g o t s where the samples were o b t a i n e d
spacing
was
(DAS
about
1 1
, as acknowledged i n the l i t e r a t u r e " '
provides
(
In s p i t e o f . t h i s
ym
A larger '
1 0 3 - 1 0 6
>
more advantageous c o n d i t i o n s f o r the n u c l e a t i o n
growth o f i n c l u s i o n s . extracted
1 0 1
) in
250-300
w h i l s t i n samples from the l i q u i d p o o l 30-50 ym. DAS
1 1
the
and
i n c l u s i o n s i n samples
from the l i q u i d p o o l , under the d e s c r i b e d
conditions,
showed a l a r g e r mean diameter. I t i s a l s o important to note t h a t the d i f f e r e n c e i n i n c l u s i o n mean s i z e was
1 ym,
above
where
the
faceted
(a-A^O^)
al-
213
umina
was
observed.
i r o n aluminates
At lower c o n c e n t r a t i o n s o f aluminum round
(FeO'A^O^) were i d e n t i f i e d whereas at
higher d e o x i d a t i o n r a t e s the aluminates and
some angular
with some c a l c i u m
alumina were i d e n t i f i e d .
These f i n d i n g s (99
s t r o n g l y agree with T u r p i n ' s and E l l i o t ' s and o t h e r s 184) (99) observations.
These r e s e a r c h e r s
who
the n u c l e a t i o n phenomenon under sub-cooled suggested
t h a t the angular
sub^-liquidus temperatures.
'
have s t u d i e d
c o n d i t i o n s , have
alumina phase was
the melt a t e q u i l i b r i u m temperature and
183 '
nucleated i n
i t simply grew at
C o i n c i d e n t a l l y to t h i s
ob-
(99) servation
, i t was
a l s o r e p o r t e d t h a t i n very e a r l y stages
o f s u b - c o o l i n g a scum was Thus,
formed on the s u r f a c e of t h e i r
i n d i c a t i n g t h a t a t the beginning
i n c l u s i o n s simply
melts.
of s u b - c o o l i n g some
f l o a t e d to the s u r f a c e .
To determine the e x t e n t a t which the f l o t a t i o n mechanism i s allowed
i n the E S R - l i q u i d p o o l a more e l a b o r a t e
(SEM
and
EPMA) study, through the e x t r a c t e d samples c o n t a i n i n g e i t h e r RE o r Zr, was
c a r r i e d out.
The p e r i p h e r a l RE and
Zr as o x i -
s u l f i d e s e n c l o s i n g the Ca-aluminates have c l e a r l y r e v e a l e d t h a t the l a t t e r phases were a l r e a d y p r e s e n t i n the pool.
These experiments a l s o suggest
a liquid-solid
state
( 9 2
'
9 4
'
l 2 l )
liquid
t h a t i n c l u s i o n s are i n
, Figures
(80) to
r e s u l t s which are a l s o i n agreement with the
(84).
These
metallography
o b s e r v a t i o n s , show t h a t the f l o t a t i o n of i n c l u s i o n s can
occur
214
i n as much as 7-10% i n the i n g o t . resent
of
the
total
These r e s u l t s , however,
inclusion do
not
content
rep-
the amount o f i n c l u s i o n s removed from the s o l i d i f y i n g
ingot. one
out
I f an a n a l y s i s o f F i g u r e s
(79a) and (79b) i s made
can see t h a t i n o r d e r t o account f o r the d i f f e r e n c e i n
size
(1.0 - 1.5 ym i n diameter) a d i s p l a c e m e n t i n t h e cumul-
a t i v e frequency from 50 t o 70% produces the expected ence.
This
differ-
i n d i c a t e s t h a t an e l i m i n a t i o n o f i n c l u s i o n s o f
a p p r o x i m a t e l y 20% i s c a r r i e d o u t by f l o t a t i o n . A l t h o u g h these experiments do not c l e a r l y r e v e a l the nature of s a t u r a t i o n , the
i t i s believed
three mechanisms' ^ 00
o x i d i z e r s and d u r i n g of d e o x i d a t i o n
t h a t i t i s r e a c h e d by
namely by c o o l i n g ,
solidification.
additions
The h i g h e s t
o f de-
degrees
which r e s u l t from the i n t r o d u c t i o n o f l a r g e
amounts o f A l i n t h e melt e i t h e r from the d e o x i d i z e r o r through r e a c t i o n
(20a-c)
and the h i g h c r y s t a l l i n e c h a r a c t e r
o f the alumina phase l e a d t o the b e l i e f t h a t t h i s phase is uniformly the
n u c l e a t e d i n e a r l y stages o f u n d e r c o o l i n g a t
beginning of s o l i d i f i c a t i o n .
enriched ingot
i n deoxidizers
a l s o suggest t h a t
The presence o f s e g r e g a t e s
i n some samples from l i q u i d p o o l and " l o c a l supersaturation"
(by a d d i t i o n s )
can be a c h i e v e d . It i s i n f e r r e d that
i f growth o f i n c l u s i o n s r e s u l t s from
a mechanism o t h e r than d i f f u s i o n and p r e c i p i t a t i o n , s p e c i f i c a l l y growth due t o c o l l i s i o n c o a l e s c e n c e between i n c l u s i o n s o f d i f f e r e n t s i z e s and t h e r e i s
s u b s t a n t i a l con-
215 v e c t i v e mixing
i n the i n g o t p o o l then t h i s phenomena should
be r e f l e c t e d i n i n c l u s i o n s i n the ESR-ingot.
The
and arrangement of i n c l u s i o n s e x t r a c t e d by the acetate-methanol i n Figures
(91)
s i z e , shape
iodine-methyl
method from A l d e o x i d i z e d i n g o t s i s shown and
(92).
These
that the growth by c o l l i s i o n and
(SEM)
photographs r e v e a l
coalescence
of A^O^
and
CaC"6Al2C>2 i n the l i q u i d p o o l indeed has taken p l a c e . As
4. A u
suggested
i
u
by s e v e r a l r e s e a r c h e r s
(38, 121,242,243) '
,
s i n c e there i s not a complete a s s i m i l a t i o n of i n c l u s i o n s by the s l a g some i n c l u s i o n s are c a r r i e d back i n t o the ingot.
The
type of i n c l u s i o n s , c l u s t e r s of
solidifying
aluminates,
i d e n t i f i e d i n t h i s r e s e a r c h very much resemble those i n conventional mechanically,
,,
cally
..
,
s t i r r e d melts
t h e r m a l l y , or
(38,120,183, 189,193-195) ' ' ' ' .
reported
electromagnetiThus,
. ..
.
although
the growth o f i n c l u s i o n s i n ESR-ingots can be accounted f o r by the simultaneous
d i f f u s i o n - p r e c i p i t a t i o n mechanism, the
d i f f e r e n c e i n s i z e found
i n l i q u i d p o o l and
i n g o t cannot be
e x p l a i n e d by a mechanism other than the f l o t a t i o n . also r e a l i s t i c
to suggest
It i s
t h a t the i n c l u s i o n s i z e d i s t r i b u t i o n
seen by the s o l i d i f y i n g i n t e r f a c e i s not s t r i c t l y simply by buoyance c o n s i d e r a t i o n s but i n s t e a d by
controlled overall
(244 ) bath hydrodynamics as suggested
by Engh and
Lmskog
(245) and L i n d e r
.
From t h i s d i s c u s s i o n , i t i s e v i d e n t t h a t
the i n c l u s i o n f l o t a t i o n mechanism cannot be approached by
216 s t r a i g h t Stokes t h i s equation The that 0.1
1
Law
u n l e s s the a p p r o p r i a t e c o r r e c t i o n s to
(13) are c o n s i d e r e d , Table ( I ) .
second important
c o n c l u s i o n from these r e s u l t s i s
at d e o x i d a t i o n r a t e s which produce an A l content - 0.15
wt.
% i n (ESR)
i n g o t s , i n c l u s i o n s are e x c l u s i v e l y
n u c l e a t e d and grown i n i n t e r d e n d r i t i c spaces d u r i n g fication.
of
solidi-
These f i n d i n g s i n agreement with A l d e o x i d i z e d
4. • 4 . - n 4. i , • (90, 172,183-187) ingots i n conventional steelmakmg p r a c t i c e indicate levels
t h a t the n u c l e a t i o n phenomenon at these
deoxidation
i s c o n t r o l l e d by the formation of the F e O « A l 0 2
c l u s i o n phase, e.g. fication.
l o c a l supersaturation during
Recent s t u d i e s *
i n g o t s d e o x i d i z e d w i t h 0.1
2 4 6
2.0
% Al
in-
solidi-
^ in unidirectionally
and
3
solidified
which c l o s e l y r e -
semble the Al(ESR) d e o x i d i z e d i n g o t s , have shown t h a t the FeO«Al 0 2
3
phase i s p r e c i p i t a t e d at a s o l i d f r a c t i o n of
i n the low A l (0.1%) content and a t 0.89 r e s u l t s suggest
t h a t the F e O « A l 0
phase p r e c i p i t a t e d and searchers
2
3
i n the o t h e r .
i s the i n c l u s i o n
t h e r e f o r e as suggested
( 1 8 3 , 1 8 4 , 1 8 6 _ 1 8 8 )
umina as the s o l i d i f i c a t i o n
These
first
by other r e -
t h i s phase i s transformed proceeds.
0.65
to a l -
217 5.4.3.2
Comparison Between T h e o r e t i c a l and
Experimental
Results The and
t o t a l oxygen content of samples from the l i q u i d
ingot
Figures
pool
under an a p p r o p r i a t e d e o x i d a t i o n sequence,
(41) and
(57), have c l e a r l y shown t h a t there i s a
d i f f e r e n c e between the samples of approximately
20 ppm.
This
(63)
behavior Figure both
i s expected
(10).
The
from an e q u i l i b r i u m s i t u a t i o n i n
average Ca:Al r a t i o s i n i n c l u s i o n s from
types of samples
( l i q u i d p o o l and
ingot) a l s o i n d i c a t e
t h a t under a g r a d u a l d e o x i d a t i o n sequence with e i t h e r
an
A l S i , CaSi o r h y p e r c a l a l l o y the c a l c i u m which remains i n s o l u t i o n p r e c i p i t a t e s on c a l c i u m aluminates fication.
during
solidi-
T h i s , a c t s to r a i s e the Ca:Al r a t i o s by a l l o w i n g
the r e a c t i o n (CaO)*+ [S] X ,
,
(CaS)*+ [0] , ,.
to take p l a c e i n the forward
^.
(18)
(147,148)
direction
'
o r t a n t to emphasize t h a t d e s p i t e the 20 ppm
^ .
.
I t i s imp-
of oxygen i n
s o l u t i o n i n the l i q u i d p o o l , the e q u i l i b r i u m i s achieved i n the d i r e c t i o n i n d i c a t e d by the r e a c t i o n (18). temperature decreases
a-c)
sulfide, i.e.
t r a n s i t i o n of these phases i s presented * where the CaS/CaO
T h i s behavior
the
the c a l c i u m , oxygen and s u l f u r . p r e -
c i p i t a t e as p e r i p h e r a l oxide and The
As
CaS. (92
revealed.
when the l e v e l of "FeO"
i s such t h a t the c a l c i u m aluminates
and
i n Figures
interphase i s c l e a r l y
i s observed
CaO
i n the
are e i t h e r CaO«2Al O_ n
slag
218 or
12CaO«7Al 0_. 2 3
At higher l e v e l s of "FeO"
where the A l 0 _ 2 3
3
o
i s transformed to CaO-GA^O^, the r e a c t i o n which c o n t r o l s the p r e c i p i t a t i o n of s u l f i d e i s : MnS
+
[Ca] t
CaS +
[Mn]
(19)
T h i s r e a c t i o n enables the p r e c i p i t a t i o n of double i.e.
(Ca,Mn)S, F i g u r e s (51) and
sulfides,
(52).
The most important f a c t to p o i n t out i s t h a t the secondary p r e c i p i t a t i o n strictly
which i s heterogeneous
i n nature
c o n t r o l l e d by the Ca:Al r a t i o i n the i n c l u s i o n
The e f f e c t o f the temperature on the p r e c i p i t a t i o n particularly CaO
is phases.
sequence,
i n the Ca:Al r a t i o s where aluminates e n r i c h e d i n
are i n e q u i l i b r i u m
i s e q u i v a l e n t to an increment i n the
aluminum c o n t e n t i n the melt i n the Ca-Al-0 system, F i g u r e
(11)
T h i s b e h a v i o r i s a l s o expected from the Ca0-Al 0.j pseudo 2
b i n a r y e q u i l i b r i u m diagram.
T h i s i n d i c a t e s t h a t as the
CaO
c o n t e n t i n c r e a s e s i n the aluminates t h e i r s t a b i l i t y i n terms of
temperature
decreases and a more s t a b l e compound i s formed.
The completion of the s u l f i d e p r e c i p i t a t i o n r e a c t i o n s and
(19) i s e x p e c t e d ' ^ 4
(18)
to occur a t approximately 1000°C
where the m i s c i b i l i t y gap i n the MnS-CaS b i n a r y diagram appears.
I t i s a l s o important to mention
f i c a t i o n some i r o n or Cr
can
be
in
dis-
that during s o l i d i -
solution
with
the
. (92, 140,159) s u l f i d e phase ' ' Another p o i n t to be c o n s i d e r e d i n t h i s a n a l y s i s i s t h a t where the aluminate phase
(A^O^
or CaO'GA^O^) i s s t a b l e
the s u l f i d e phase i n e q u i l i b r i u m with i t i s o n l y the MnS
in
219 any
of i t s shapes, i . e .
MnS
I, I I or I I I which are
dependent on the chemistry of the melt. h a v i o r of the a l u m i n a t e - s u l f i d e ures
Figure
of "pure" CaS
(87)
also
The o v e r a l l be-
t r a n s i t i o n i s condensed i n F i g -
(88,89) which are an e x t e n s i o n
(87).
also
of r e s u l t s shown i n F i g u r e
indicates
cannot occur unless
that
the
precipitation
lower oxygen p o t e n t i a l s ,
than those r e q u i r e d to p r e c i p i t a t e C a O i A ^ O ^ and
12CaO • 7AI2O.J
are reached. If
these f i n d i n g s are compared a g a i n s t s t u d i e s on
i n j e c t i o n p r o c e s s e s then i t can be ous
seen that the
simultane-
d e o x i d a t i o n - d e s u l f u r i z a t i o n mechanism i s a l s o r e f l e c t e d
• 4.1. ^ 4.i n the d e o x i d a t i o n
J 4. (140,147,148,153,197, 211,214) products ' ' ' ' ' . (14 7
T h i s diagram i n agreement w i t h Saxena et a l . ' s work 148
in
'
214) '
CaO
Ca-
c l e a r l y r e v e a l s t h a t Ca does not d i r e c t l y
i n c l u s i o n s unless
e i t h e r as a C a S i or
as
c o n t r i b u t e to the CaS p r e c i p i t a t e
the alumina i s f i r s t transformed i n t o
Ca-aluminates. While c a l c i u m
aluminates w i t h p e r i p h e r a l Zr or
oxides s u l f i d e s , i n the samples e x t r a c t e d
from the
RE liquid
p o o l by the s i l i c a tube c o n t a i n i n g e i t h e r Zr or mischmetal, were not commonly found, a l l of the i n c l u s i o n s which cont a i n e d these elements
(Zr o r Ce and
La) homogeneously d i s -
t r i b u t e d were p r e f e r e n t i a l l y composed of phases e n r i c h e d calcium.
I n c l u s i o n s g e n e r a l l y show t h a t among the
in
elements
220 t r a c e d by the X-ray spectrum and
S i as o x i d e - s u l f i d e and
of the main c o n s t i t u e n t s taken as one
in iron
contributes reaction
analysis
of these phases.
'
. i s gradually
and
3
hence i t by
(20-C).
Reaction
to 12CaO«7Al 0 . 2
(20-C) and
The
3
sulfide transition, i.e. Figures
(87)
g i v e n i n Tables
and
(XVI)
MnS
(88) and
t h a t the p r e c i p i -
the r e a c t i o n scheme (19)
(21)
above ones
II
MnS
dictate
and
the
(25),
determine
III
the
(Ca,Mn)S
r e v e a l t h i s behavior.
(XVII)
(12-iv),
the gradual t r a n s i t i o n
reactions
which occur s i m u l t a n e o u s l y t o the
CaS.
solu-
( s e c t i o n 5.4.1.4,
established
chemistry o f the oxide phase, i . e . 2
to i t s low
as the s o l i d i f i c a t i o n p r o g r e s s e s .
t a t i o n o f i n c l u s i o n s i s r u l e d by
of A 1 0
one
This f i n d i n g i s
the Ca:Al r a t i o i n i n c l u s i o n s ,
5.4.3.1), i t was
(12-v), and
calcium i s
r e j e c t e d and
In p r e v i o u s d i s c u s s i o n of r e s u l t s 5.4.2
Ca
199)
to i n c r e a s e
(18)
( A l , Zr,
almost pure CaS)
more evidence that c a l c i u m , due (198
bility
(SEM)
-»-
Results
t o a c e r t a i n e x t e n t des-
c r i b e these r e s u l t s . The (XVI)
equilibrium,
isothermal
c a l c u l a t i o n s shown i n
were performed by assuming constant
i n t e r a c t i o n c o e f f i c i e n t s f o r Al-O, used were - 5 . 2 5
( 1 7 5 )
, -62.0
l a s t value f o r the Ca-S the
was
f r e e energy of the CaO
( 1 7 5 )
Ca-0
and
-40
Table
( f i r s t order)
and
Ca-S.
The
respectively.
assumed on the b a s i s t h a t i s approximately 1 1/3
values The since
l a r g e r than
t h a t f o r CaS,
Table
(XV), then the r a t i o of t h e i r
first
order i n t e r a c t i o n parameters c o u l d be e q u i v a l e n t . if
S-analyses
from the 1020
M.S.
the s t a r t i n g p o i n t i n e a r l y
Hence,
e l e c t r o d e are taken
(low) d e o x i d a t i o n stages
and they are compared a g a i n s t those g i v e n i n Table for in
as
(XVI)
the A l 0 - C a O « 6 A l 0 - C a S e q u i l i b r i u m , i t i s noted t h a t 2
3
2
3
terms of s u l f u r , very good agreement i s observed.
these v a l u e s are compared
i n terms of Ca- and S-
and t h e i r r e s p e c t i v e oxide phases
If
contents
a g a i n s t those r e p o r t e d
(144) by H i l t y and Popp
given
agreement i s found.
in
F i g u r e (78),
good
On the o t h e r hand, p r e d i c t e d values f o r
oxygen are overestimated, F i g u r e (72). Since, Gustafsson and M e l b e r g ' ^ ?
suggest the use of
7
v a r i a b l e f i r s t order i n t e r a c t i o n c o e f f i c i e n t s then a set
of c a l c u l a t i o n s was
performed.
r e s u l t s shown i n Table
second
Under these c o n d i t i o n s ,
(XVII) were computed.
The
first
order i n t e r a c t i o n c o e f f i c i e n t s w e r e ; - 5 3 5 " ^ , -400, -350 for
and -200 Ca-S,
CaS,
f o r the Ca-O,
-62.0
( 1 7 5 )
-300,
f o r A l - 0 and -110
( 2 1 1 )
f o r the A l 0 - C a O • 6 A l 0 ~ C a S , C a O • 6 A l 0 ~ C a 0 • 2 A l 0 2
3
2
3
2
3
2
CaO«2Al 0 -CaO«Al 0 -CaS, CaO'Al^-CaO + A l ^ - C a S 2
3
and Ca0^ y - CaO s
Table
(XV).
2
3
+ A l 0 ~ C a S e q u i l i b r i a , Figure
While
2
3
Regarding
and
the Ca, A l and 0 are p r e d i c t a b l e by
lowing t h i s approach the s u l f u r i s underestimated
(87)
(10
6
i s not.
The
sulfur
fol-
content
- 10 ^ wt.%).
the independence of r e a c t i o n
(20-C) on
the
3
222 oxygen p o t e n t i a l
t h i s i s c l e a r l y r e v e a l e d through these
c a l c u l a t i o n s . Table (XVII). ranges between 10-40
ppm
The oxygen content i n the melt
r e g a r d l e s s of the amount of A l
and Ca i n s o l u t i o n . I t i s a l s o important to note t h a t the p r e d i c t i o n s in section ition are
5.3.4
i n terms of the expected i n c l u s i o n compos-
which were based on F a u l r i n g s
also
stated
et a l . ' s ^
2 l 6
^
findings
i n agreement with the r e s u l t s presented i n F i g u r e
(88) . F i n a l l y , two important f a c t s are worthwhile t o mention: First,
the Ca-0
i n t e r a c t i o n parameters are very important i n
the Al-Ca-O-S p r e c i p i t a t i o n and second a c o n f i d e n t
prediction
of the p r e c i p i t a t i o n sequence cannot be f u l l y r e l i a b l e u n l e s s the
interaction
appropriately
( f i r s t and second order) c o e f f i c i e n t s are
determined.
223
CHAPTER VI THE
RADIAL DISTRIBUTION OF
INCLUSIONS IN CaSi AND
Al
DE-
OXIDIZED INGOTS
6.1
Experimental D e t a i l s and The
Techniques
l a s t p a r t of t h i s i n v e s t i g a t i o n was
e l u c i d a t e how
i n c l u s i o n s are d i s t r i b u t e d , i n terms of
t i c a l l y determined s i z e s , i n i n g o t s . s e r i e s of samples from s e v e r a l 1020 ESR
ingots
radially
undertaken to
deoxidized
w i t h A l and
For t h i s purpose a M. S.
and
l e v e l s and
s l i g h t l y etched on four and
f i v e of t h e i r f a c e s .
one
4340
the CaSi a l l o y , were
s l i c e d at known d e o x i d a t i o n
were p o l i s h e d and
statis-
samples
sometimes
P r i o r to performing measurements,
microprobe a n a l y s i s and
X-ray spectrum a n a l y s i s were c a r -
r i e d out to i d e n t i f y the major i n c l u s i o n phases. Measurements of mean diameter ary d e n d r i t e
arm
spacing
of i n c l u s i o n s or second-
were performed almost i n v a r i a b l y
a t every h a l f centimeter on each f a c e . A l deoxidized
i n g o t s were very
small and
Since
inclusions in
complex i n shape
(alumina g a l a x i e s a s s o c i a t e d w i t h manganese s u l f i d e s ) , s e v e r a l approaches to determine the mean s i z e o f i n c l u s i o n s were f o l l o w e d ,
i.e.
normal d i s t r i b u t i o n s and
l a r g e s t i n c l u s i o n s technique."
"the
five
224
6.2
Experimental
Findings
R e s u l t s of t h i s r e s e a r c h are shown i n F i g u r e s
(9 3) t o
(95) and (96) t o (99) f o r secondary d e n d r i t e arm spacing and i n c l u s i o n mean s i z e s r e s p e c t i v e l y . i n g o t s , as p r e v i o u s l y d e s c r i b e d and manganese s u l f i d e .
The A l d e o x i d i z e d
showed alumina g a l a x i e s
Only t r a c e s o f c a l c i u m were found.
The morphology o f i n c l u s i o n s i n the 1020 M.S. A l d e o x i d i z e d i n g o t s v a r i e d from g l o b u l a r s i n g l e and double phase
( s p h e r i c a l aluminates
and manganese s u l f i d e ) a t the
i n g o t core, t o elongated with double phase manganese s u l f i d e ) a t midradius
(aluminates and
and almost e x c l u s i v e l y
s m a l l alumina g a l a x i e s a s s o c i a t e d with manganese
sulfide
at the mould w a l l . The
1020 M.S. CaSi d e o x i d i z e d i n g o t s showed c a l c i u m a l -
uminates and s i n g l e and double c a l c i u m s u l f i d e s , i . e . , CaS and
(Ca,Mn)S.
aluminates
The d e o x i d a t i o n l e v e l was such t h a t c a l c i u m
o f the type C a O « 6 A l 0 2
3
as the p r i n c i p a l i n c l u s i o n phases. c l o s e d the oxide phase. showed v i r t u a l l y
and C a O • 2 A l 0 2
3
were
found
The s u l f i d e phase en-
The 4340 CaSi d e o x i d i z e d i n g o t
the same types o f i n c l u s i o n phases as the
1020 M.S. i n g o t s d e o x i d i z e d with the CaSi a l l o y .
I t i s im-
p o r t a n t t o mention t h a t the amount o f the p e r i p h e r a l CaS phase was p r o p o r t i o n a l t o the Ca:Al r a t i o i n the oxide phase and
i t was not n e c e s s a r i l y dependent on the s i z e of the i n -
clusions.
F i n a l l y , the i n c l u s i o n d e n s i t y
(number o f i n -
e l u s i o n s / p e r u n i t area) i n a l l of the i n g o t s was c o n s i d e r a b l y with
6.3
increased
the r a d i u s .
D i s c u s s i o n of
Results
In the d i s c u s s i o n of the p r e v i o u s
r e s u l t s , i t has
been
emphasized t h a t some f l o t a t i o n of i n c l u s i o n s (about 10-20%) w i l l take p l a c e .
T h i s was
determined to o r i g i n a t e during
s o l i d i f i c a t i o n i n e a r l y stages
of c o o l i n g .
T h i s statement, however, i s t r u e only when the
required
s u p e r s a t u r a t i o n r a t i o f o r the p r e c i p i t a t i o n o f aluminates i s achieved,
i.e.
The
d i s c u s s i o n has
previous
above 0.1
to 0.15
wt.
% A l i n the i n g o t .
also established that i n -
c l u s i o n s i n samples from l i q u i d p o o l were l a r g e r i n d i a meter ingots
(under an a p p r o p r i a t e
deoxidation
sequence) than i n
although the s o l i d i f i c a t i o n c o n d i t i o n s
t h e i r corresponding former samples.
secondary DAS)
by
were more d r a s t i c i n the
Consequently, i t was
i n c l u s i o n growth was
(given
concluded t h a t
the
almost e n t i r e l y c o n t r o l l e d by the
f u s i o n - p r e c i p i t a t i o n of s o l u t e s on p r e n u c l e a t e d On the other hand, r e s u l t s obtained
dif-
phases.
from the r a d i a l i n -
c l u s i o n s i z e d i s t r i b u t i o n s show that- the p r e c i p i t a t i o n i n i n g o t s i s e s s e n t i a l l y c a r r i e d out d u r i n g
solidification.
Hence, i t i s very dependent on the l o c a l thermodynamic ,... (99,100,101,104,10 5,10 6,121,143,184,186,189) conditions ' ' ' ' ' ' • ' ' •
Since the i n c l u s i o n mean s i z e ranges r a d i a l l y from 6.0 5.0
ym i n the i n g o t c e n t r e l i n e t o 3.0
w a l l and the secondary DAS
- 2.0
ym i n the mould
e q u i v a l e n t l y v a r i e s from 20 0-250
to 60-100 ym then the p r e c i p i t a t i o n of i n c l u s i o n s , c u l a r l y i n i n g o t s d e o x i d i z e d w i t h the CaSi a l l o y e n t i r e l y c o n t r o l l e d by the r e j e c t i o n of 121
-
partii s almost
solutes'
0
1
,
1
0
2
-
1
0
6
'
243) '
, e.g.
by the l o c a l thermodynamic
c o n d i t i o n s o f the
i n t e r d e n d r i t i c m i c r o p o o l s formed as the s o l i d i f i c a t i o n p r o ceeds . Thus, although the l o c a l s o l i d i f i c a t i o n time g i v e n DAS
X 1
*
= a t£
= b(GR)"
n
= 707.946 ( G R ) " ' 0
(65 i s very s h o r t , about (1-1.5 cm)
5-30
seconds
1
=
i n locations
close
1 0 0
'
1 0 6
'
up to even
1 1 5
^,
by the
larger
secondary d e n d r i t e arm spacing, i n ym
a and b =
constants
n
=
exponent which ranges from 1/2
t^
=
l o c a l s o l i d i f i c a t i o n time, i n seconds
GR
=
product o f qrowth r a t e by the thermal g r a d i e n t , in
°C/min.
^:
(26)
3 8 2 5
to the ESR-mould w a l l ; t h i s i s s u f f i c i e n t to grow
d i f f u s i o n - p r e c i p i t a t i o n mechanism 1
4 7
225) '
i n c l u s i o n s on p r e n u c l e a t e d p h a s e s ^ " '
* DAS
by'
to
1/3
sizes'
^.
2 1
Thus, the c o n t r o l l i n g steps are e i t h e r the
n u c l e a t i o n of i n c l u s i o n s where the s u p e r s a t u r a t i o n .
-
.
,
-
, .
i s not reached i n e a r l y stages of c o o l i n g the r e j e c t i o n o f s o l u t e s o
^
(oxygen and
ratio
(99,100,101)
d e o x i d i z e r s ) which are
-i • ^ • •
o.u
or
(102-106,
g r a d u a l l y b u i l d i n g up as the s o l i d i f i c a t i o n
progresses
121,185,121,227,243)
I t i s a l s o important
to emphasize t h a t the growth of i n -
c l u s i o n s d u r i n g c o o l i n g i s very dependent on the d e n s i t y andJ
• i, s i•z e of* ^the o r i•g i•n a l-i phases p r e s e n t 4- ( 9 1 , 1 0 1 , 1 2 1 ) . I f
T + T
5
these parameters are 1 0
7
-
10
inclusions/cm
2
i n r a d i u s , as expected i n ESR-melts, o n l y a very should be e x p e c t e d
( 1 0 1
'
1 2 1 , 2 4 3 )
,
Table
1 - 1 0 um
and
s l i g h t growth
(XVIII).
I t can a l s o be e l u c i d a t e d t h a t s i n c e "oxygen
segregation"
does not take p l a c e along r a d i a l d i r e c t i o n s i n i n d u s t r i a l ingots'
4 8
2 5
°)
f
i t i s expected to observe a gradual change i n
the i n c l u s i o n d e n s i t y , a f a c t which agrees with the in t h i s research. should be
size
Hence the i n c l u s i o n r a d i a l s i z e
observations distribution
i n v e r s e l y p r o p o r t i o n a l to the i n c l u s i o n d e n s i t y .
228 CHAPTER V I I * 7.0 7.1
Conclusions I n c l u s i o n s from the e l e c t r o d e a r e p h y s i c a l l y and chemic a l l y transformed i n the e l e c t r o d e t i p by the thermal gradients.
I n c l u s i o n s are c h e m i c a l l y
a l t e r e d by the
presence o f the l i q u i d s l a g a t the l i q u i d f i l m and they are almost e n t i r e l y removed
(by d i s s o l u t i o n -
r e a c t i o n s ) when the d r o p l e t i s completely
formed.
Thus, e l e c t r o d e i n c l u s i o n s only p l a y a r o l e i n the f i n a l ESR i n g o t i n s o f a r as t h e i r s o l u t i o n product e n t e r s i n t o the slag-metal during 7.2
reactions
experienced
processing.
I n c l u s i o n s i n ESR-ingots are more s t r o n g l y i n f l u e n c e d by the d e o x i d a t i o n p r a c t i c e than by the e l e c t r o d e composition SiC^ slags.
and/or the s l a g system used i n low I t i s important t o comment, however,
t h a t under low d e o x i d a t i o n chemistry
r a t e s the i n t r i n s i c
o f the s l a g predominates, i . e .
a t high
s l a g oxygen p o t e n t i a l s . 7.3
As a consequence of the above c o n c l u s i o n , i t has been confirmed t h a t the p r e c i p i t a t i o n o f complex silicate
i n c l u s i o n s i s p r e d i c t a b l e i n high
Al-Casilica
s l a g s where t h e i r o r i g i n i s s t r i c t l y given by the s l a g chemistry,
i.e.
i f wt. % SiO„ > 10.0.
For ease of r e f e r e n c e , the nomenclature o f r e a c t i o n s i n p r e v i o u s t e x t s a r e r e w r i t t e n i n t h i s chapter.
229 7.4
The most a p p r o p r i a t e s l a g system i n which t o perform an e f f i c i e n t d e o x i d a t i o n i s the CaF2~CaO-Al20
3
system a t 50, 30 and 20 wt. % r e s p e c t i v e l y , i . e . the h i g h e s t Ca:Al r a t i o i n i n c l u s i o n s i n the absence of d e o x i d a t i o n . 7.5
The i n c l u s i o n c h e m i s t r y s l a g system
expected, from the most common
(CaF -CaO-Al 0 ) 2
2
used i n the ESR-process,
3
i s c o n t r o l l e d by the f o l l o w i n g 2[A1] + 3(FeO) [Ca] + (FeO) t
t
3
(CaO) + Fe
(7.5.i)
( A ^ O ^ + 3Fe
( A 1 0 ) + 3[Ca] t 2
equilibria:
(7.5.ii)
3(CaO) + 2 [ A l ]
(7.5.iii)
T h i s r e a c t i o n scheme depends on the type and degree of deoxidation.
Hence the p r e c i p i t a t i o n o f i n -
c l u s i o n s i s d i c t a t e d by: mCaO + n ( A l 0 ) J mCaO-nA^O.^ 2
(7.5.iv)
3
or more a p p r o p r i a t e l y by: X[Ca] + Y(Al 0-.) *• i n c l u s i o n o
J
?
'XCaO'(Y - *-) A l 0 _ J
A
J
o
J
+ \ X[A1]
(7.5.v) 7.6
From the above e q u i l i b r i a ,
i t can be seen t h a t i f
an excess o f d e o x i d i z e r i s added t o the s l a g ( i n the forward d i r e c t i o n o f r e a c t i o n s 7 . 5 . i i i or 7.5.v)
230
u n d e s i r a b l e composition high A l c o n t e n t s ,
w i l l r e s u l t i n the i n g o t , i . e .
i n which case
there e x i s t s a
p o t e n t i a l problem of p r e c i p i t a t i n g A l n i t r i d e s or sulfides. 7.7
D e o x i d a t i o n of s l a g s d u r i n g r e f i n i n g by u s i n g C a S i , C a A l S i and CaSiBaAl
a l l o y s i s more e f f i c i e n t
than by u s i n g A l p e l l e t s alone. of the above a l l o y s system
The
silicon in a l l
under the a p p r o p r i a t e
slag
(7.3), a c t s e x c l u s i v e l y as a c a r r i e r of
deoxidant 7.8
AlSi,
the
i n t o the metal l i q u i d p o o l .
A l and A l S i a l l o y are e f f i c i e n t d e o x i d i z e r s , however, they do not c o n t r o l the shape of the d e o x i d a t i o n ucts, i . e . Although aluminate
A l generates
alumina g a l a x i e s and MnS
II.
the A l S i a l l o y does produce s p h e r i c a l Cai n c l u s i o n s i t does not so s t r o n g l y
the p r e c i p i t a t i o n of CaS The
prod-
induce
at the p e r i p h e r y of the
C a S i , C a A l S i and CaSiBaAl
i n c l u s i o n shape c o n t r o l l e r s .
a l l o y s are very
oxides.
strong
At low CaSi or h i g h
A l or A l S i d e o x i d a t i o n r a t e s MnS
I I - I I I or
(Ca,Mn)S
are formed. 7.9
I n c l u s i o n p r e c i p i t a t i o n can be e x p l a i n e d by a d e t a i l e d H e n r i a n - p r e c i p i t a t i o n diagram i n which the r e a c t i o n :
superimposing
231
(CaO)* + [S] t on
the p r e v i o u s l y
reported
(CaS)* + [0]
(7.5.vi)
(Ca-Al-0) diagram and
u s i n g i n t e r a c t i o n c o e f f i c i e n t s from the l i t e r a t u r e a realistic prediction
can be made.
intrinsically
the t r a n s i t i o n s o f s u l f i d e s ,
includes
T h i s diagram
r u l e d by: [Ca] 7.10
+ (MnS)
F l o t a t i o n of inclusions
*
[Mn]
+ (CaS)
to some e x t e n t
o c c u r s i n moderate or h i g h l y
*
(10-20%)
d e o x i d i z e d melts.
At low d e o x i d a t i o n r a t e s , as expected from 7 . 5 . i i and
7.5.v
dendritic 7.11
uniform n u c l e a t i o n
spaces d u r i n g s o l i d i f i c a t i o n takes p l a c e .
I f electrode inclusions, and
of inclusions i n
deoxidation rates
s l a g system, deoxidant
are known, by u s i n g a
s i m p l i f i e d t e r n a r y - Si02, (Ca,M)0
and A^O^-
diagram, the f i n a l i n c l u s i o n composition can be estimated. 7.12
Inclusion function
s i z e , as expected from
(7.10)
o f the l o c a l s o l i d i f i c a t i o n time
hence on the l o c a l ( i n t e r d e n d r i t i c ) conditions.
isa and
thermochemical
232 SUGGESTIONS FOR FUTURE WORK
Based on r e s e a r c h c a r r i e d out i n the p a s t , i n terms of i n c l u s i o n s i n c o n v e n t i o n a l steelmaking and i n ESR and the type o f r e a c t i o n s s t u d i e d i n t h i s r e s e a r c h , s e v e r a l immediate r e s e a r c h p r o p o s a l s a r e suggested: 1.
To determine
with a higher degree o f accuracy the
t r a n s i t i o n p o i n t between r e a c t i o n s which i n v o l v e the oxygen p o t e n t i a l i n the s l a g - l i q u i d metal 2[A1]
+ 3 (FeO) t
such a s :
( A l ^ ) + Fe
and [Ca] + (FeO) 1 (CaO) + Fe and the exchange r e a c t i o n s (between two l i q u i d s ) , 3[Ca] 2. termine
such a s :
+ ( A 1 0 ) X 3(CaO) + 2[A1] 2
3
With e x a c t l y the same purpose as above, t o dethe s e r i e s o f t r a n s i t i o n s i n the s u l f i d e
inclusion
phases: MnS I I
-y
MnS I I I
by d e s i g n i n g s p e c i f i c experiments ials
(Ca,Mn)S
CaS
where v a r i o u s oxygen p o t e n t -
( s e v e r a l amounts o f A l and Ca) i n the melt should be
involved.
233 3.
As an e x t e n s i o n o f the r e s u l t s found through
this
r e s e a r c h , i t i s suggested t o perform experiments w i t h exa c t l y the same techniques and purposes i.e.
t o determine
as i n t h i s work
the p o s s i b l e d e o x i d a t i o n and s l a g b e s t
combination i n terms o f the f o l l o w i n g r e a c t i o n schemes t ( S i 0 ) + Fe
[Si] + 2 (FeO) [Ca] + FeO t
2
(CaO) + Fe
and [Si] + 2(CaO) Z
s
i
0
t
+ 2
C a
l
and [Mn] + (FeO) % MnO + Fe and [Si] + 2(FeO) J S i 0
+ Fe
2
or [Ca] + (FeO) J CaO + Fe and
either [Si] + 2(MnO) t
s
i
0
2
+
2
[
M
n
J
or [Ca] + (MnO) t
2(CaO) + [Mn]
These r e a c t i o n s can be compared t o those a l r e a d y r e p o r t e d for A l 0 / A l / S i / S i 0 2
2
2
and f o r T i 0 / T i 2
.
I t i s worthwhile
to study these r e a c t i o n s s i n c e the excess o f A l i n i n g o t s can cause d e l e t e r i o u s mechanical
properties.
234 4. in point
I t becomes obvious t h a t the t r a n s i t i o n s s p e c i f i e d (1) w i l l be a l s o necessary f o r any other
s e t of
e q u i l i b r i a i n p r o p o s a l (3). 5.
I t a l s o becomes apparent t h a t once these c o n d i t i o n s
are f u l l y c o n t r o l l e d the best s l a g / d e o x i d a t i o n the most a p p r o p r i a t e
mechanical p r o p e r t i e s ,
of the i n g o t and i n c l u s i o n c h e m i s t r i e s
and hence as a r e s u l t
can be s e l e c t e d .
Thus, t h e i r e v a l u a t i o n i n terms o f mechanical and
chemical
r e s i s t a n c e as a f u n c t i o n o f these parameters should be evaluated. 6.
I t i s a l s o very
i n t e r e s t i n g t o note t h a t s i n c e the
Ca and the A l a c t i v i t i e s are c o n t r o l l i n g parameters, i n a Al and eo which have
8
been r e p o r t e d with a g r e a t d e a l o f s c a t t e r should be once and
f o r a l l a p p r o p r i a t e l y determined. 7.
Experimental and t h e o r e t i c a l work along
l i n e s as those proposed i n p o i n t s formed; i n t h i s case,
(1) and (2) c o u l d be per-
i t i s suggested t o use Ce as (RE)
d e o x i d i z e r i n the presence o f a CaO-CaF enriched
slag.
the same
2
(A^O^) o r a RE-
The r e a c t i o n scheme might be as f o l l o w s :
[RE] + (FeO) t
RE-O + Fe
and/or Ca + (FeO) t
(CaO) + Fe
235 L I S T OF REFERENCES
1.
Kay, D.A.R.: Proc. o f the F i r s t I n t e r n a t i o n a l Symposium on ESR and C a s t i n g Technology. P i t t s b u r g h , Pa, 1967, P a r t I I .
2.
Myzetsky, V . L . , e t a l . : Proc. I n t . Symp. on E l e c t r o m e t a l l u r g y , Kiev , 1972, 119.
3.
Klyueb, M.M. and Mironov, June, 1967, 6, 480-483.
4.
K u s l i t s k y , A.B., e t a l . : i b i d . , 85.
5.
Volkov, S.E.: i b i d . , 12.
6.
M i t c h e l l , A., J o s h i S. and Cameron J . : 2, February 1971, 561-567.
7.
E l l i o t , J . F . , and Maulvault, M.A.: P r o c , AIME, 1970, 2%_, 13.
8.
Mendrykowski, J . e t a l . , Met. Trans., ASM-AIME, 1972, 3, 1761.
9.
Tacke, K.H., and Schwerdtfeger, 1981, 52^, 4, 137-142.
M. Yu:
Stal i n English,
Met. Trans.
E l e c t . Furn. Conf.
K.: Arch.
Eisenhuttenwes,
10.
M i t c h e l l , A., and J o s h i J . ; Met. Trans. 1973, 4_, 631.
11.
F r e d r i k s s o n , H. and J a r l e b o r g , 0.: 2_3, 9, 32-40.
12.
Kay, D.A.R. and Pomfret, 962-964.
13.
Chan, J.C.F., e t a l . : IB, 135-141.
Met. Trans. B., March 1976,
14.
Wadier, J.F., e t a l . : 127-136.
T o o l A l l o y S t e e l s , A p r i l 1978,
15.
M i t c h e l l , A.: Ironmaking 1974, 3, 172-179.
16.
H a j r a , J.P. and Ratnam, U.: Trans o f the Indian I n s t , of M e t a l s . 31_, 1, Feb. 1978, 20-23.
J . M e t a l s , 1971,
R.J.: J . I . S . I . , 1971, 209
and Steelmaking
(Quarterly)
236 17.
Medovar, B . I . e t a l . : P r o c . o f t h e 5 t h S o v i e t - J a p a n e s e Symp. o n P h y s i c a l - C h e m i c a l B a s i s o f M e t a l l u r g i c a l P r o c e s s e s , 1975.
18.
M i t c h e l l , A.: P r o c . o f t h e 1 s t I n t . Symp. on ESR, P a r t I I I , M e l l o n I n s t . , P i t t s . , P a . , A u g u s t 1967.
19.
Roshchin, 679-681.
E. e t a l . :
Steel
20.
Roshchin,
E. e t a l . :
ibid.,
21.
B u r e l , B. a n d M i t c h e l l , 2253.
22.
P a t o n , B.E. e t a l . : P r o c . 5 t h I n t . Symp. o n ESR and O t h e r S p e c i a l M e l t i n g T e c h n o l o g i e s , P i t t s b u r g h , Pa., 1974, P a r t I , 433-448.
23.
Z h e n g b a n g , L i , Wenhiu, Z. a n d Y i d a L i ; V o l . 15, No. 1, J a n u a r y 1980, 20-26.
24.
J i e , Fu: Acta M e t a l l u r g i c a S i n i c a , Dec. 1979, 526-539.
25.
Wadier, J . F . , e t a l . : 127-136.
26.
M i t c h e l l , A. and Beynon B.: 3333-3345.
27.
Mitchell, Bulletin
28.
Schwerdtfeger, K.: Proc. M u n i c h , 1976, 133-141.
29.
Beynon, B., Ph.D. t h e s i s , D e p t .
30.
M i t c h e l l , A.: "Electroslag P r o c e s s e s , " t o be p u b l i s h e d m a k i n g , AIME p u b l i c a t i o n .
31.
P e o v e r , M.;
32.
Maximovitch,
i n t h e USSR, D e c . 1978,
F e b . 1980, 80-81.
A.: Met. T r a n s .
Tool Alloy
1970, 3^,
I r o n and S t e e l
V o l . 15, No. 4,
Steels,
Met. T r a n s .
A p r i l 1978,
2L, 1971,
A.: "The E l e c t r o s l a g R e m e l t i n c Process," 669, U.S. B u r e a u o f M i n e s , 1976, 15-19. 5th I n t l .
C o n f . V a c . Met.,
o f M e t . , U.B.C., 1973.
and Vacuum A r c R e m e l t i n g i n E l e c t r i c Furnace S t e e l -
J . I n s t . Met. 1972, 100, 97-106. B.I.;
Avtom.
Svarka,
19 61,
8, 86-88.
237 33.
Hawkins, R.J. e t a l . : Proc. Conf. i n E l e c t r o s l a g R e f i n i n g , S h e f f i e l d , Jan. 1973, 21-34.
34.
Holzgruber, W.: Proc. o f the 1st I n t l . Symp. on ESR M e l l o n I n s t . P i t t s , Pa., August 1967, P a r t I I .
35.
Klyguev, M.M. e t a l . : 168-171.
36.
M i t c h e l l , A.: Proc. 1st I n t l . Symp. on ESR, M e l l o n I n s t . , P i t t s , Pa., Aug. 1967, P a r t I I .
37.
Buzek, Z. and Hlineny, A.: Prob. S p e c i a l E l e c t r o m e t a l l u r g y . Naukova Dumak, Kiev 1972, P a r t I. (Sbornik Vedeck. Prac. Vys. Skol b.v.s. V o l . 11, 3, 1965, 483-487) .
38.
Miska, H. and Wahlster, M.: 44, (1), 1973, 19-25.
39.
T o b i a s , J.B., and Bhat, G.K.: Proc. o f the 1 s t I n t l . Symp. on ESR., M e l l o n I n s t . , P i t t s . , Pa., August, 19 76.
40.
Schwerdtfeger, K. and K l e i n , K.: Proc. o f the 4th I n t l . Symp. on ESR, Tokyo, Iron and S t e e l I n s t i t u t e of Japan, June, 1973, 81-90.
41.
M i t c h e l l , A.: 112.
42.
P o v o l o t s k i i , D.Y., e t a l . : Izv. Vyssh. Zared Chem. M e t a l l . 1977, 2, 40-42.
43.
Zhmoidin, G.I.: 1971, 6, 46-52.
44.
Choudhury, A.: 1012-1018.
45.
M i t c h e l l , A.: 1418.
46.
P a t e i s k y , G.: Prob. S p e c i a l E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 19 72, P a r t I I .
S t a l i n E n g l i s h , Feb.
1969,
Archiv. f u r Eissen,
Can. Met. Quart.,
1981, V o l . 20, 101Ucheban.
Izv. Abad. Nauk. CCCP M e t a l l y , S t a h l und E i s e n , 1980, 100, No. 17,
Trans. Farad. S o c , 1967, 6_3, 1408-
238 47.
P a t e i s k y , G. e t a l . : 1972, 9, 1318-1326.
J o u r n a l of Va. S c i . Technol.
48.
Kay, D.A.R.: Prob. Spec. E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 1972. P a r t I I .
49.
Kopoywuy, B.: Problemy S p e t s i a l ' n a i E l e c t r o m e t a l l u r g y , V o l . 13, 1980, 12-23.
50.
Korousiv, B. Berg-und Htlttenmannische Monatshefte 122, Jahrgang, J u l y 1977, Heft 7, 287-291.
51.
Ko ro usid, B. and Holzgruber, W.: i b i d . , January 1978, Heft 1, 17-22.
52.
K r u c i n s k i , M.:
53.
A l l i b e r t , M. e t a l . : Iron Making and Steelmaking, 1978, No. 5, 211-216.
54.
Wadier, J.F. e t a l . : Mem. S c i . M e t a l l . , Feb. 61-78.
55.
K a j i o k a , H., e t a l . : Proc. o f the 4th I n t . Symp. on ESR, Tokyo, Iron and S t e e l I n s t i t u t e o f Japan, June 1973, 102-114.
56.
F r a s e r , M.E.:
57.
Wei, Chi-ho and M i t c h e l l , A.: Proc. I n t l . Conf. on Process M o d e l l i n g , AIME, P i t t s b u r g h , 1982, t o be published.
58.
Knights, C.F., and P e r k i n s R.: Proc. of a Conference on ESR, S h e f f i e l d , The Iron and S t e e l I n s t . , Jan. 1973, 35-40.
59.
Kusamichi, H. e t a l . : Proc. o f the 1st I n t l . Symp. on ESR, P a r t I I I , M e l l o n I n s t . , P i t t s b u r g h , August, 1967.
60.
K r i c h e v e c , M.I. e t a l . : Prob. S p e c i a l E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev 1972, P a r t I, 61-72. (Neue Hdtt. Sept.-Oct. 1971, 16, (9-10), 614-618).
61.
P a t c h e t t , B.M. and M i l n e r , D.R.: Welding Research Supplement, (Paper presented a t the AWS 53rd Annual Meeting i n D e t r o i t , A p r i l , 1972), 491-505(s).
123, Jahrgang,
Hutnik, Rok 1974, Nr. 11, 539-548.
1978,
Ph.D. t h e s i s , Dept. o f Met. , U.B.C., 1970.
239
62.
M i t c h e l l , A.: Ironmaking 1974, 3, 172-179.
and Steelmaking
(quarterly)
63.
Boucher, A.: Prob. Spec. E l e c t r o m e t a l . Naukova Dumka, Kiev 1972, P a r t I I , 47-62.
64.
Cooper, C K . e t a l . : Trans. AIME, E l e c t . Furn. Conf. Proceedings, 1970, 26_, 8.
65.
B a l l a n t y n e , A.S.:
66.
M i t c h e l l , A. e t a l . : Proc. o f a Conference i n ESR. S h e f f i e l d , Iron and S t e e l I n s t . , 1973, 3-15.
67.
B a l l a n t y n e , A.S. and M i t c h e l l , A.: Steelmaking, 1977, 4_, 222-239.
68.
Wahlster, M.: Proc. o f the 5th I n t l . Conf. on ESR and Other S p e c i a l M e l t i n g T e c h n o l o g i e s , M e l l o n I n s t . , P i t t s b u r g h , Pa., P a r t I, October 1974, 40-61.
69.
R e t e l s d o r f , J.H., and Winterhager, H.: Prob. Spec. E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 1972, P a r t I I , 122-135.
70.
Pho, P. and E c k s t e i n , F. H.-J.: Sept. 1980, 342-244.
71.
M i t c h e l l , A.: Prob. Spec. E l e c t r o m e t a l l . , Naukova Dumka, K i e v , 1972, P a r t I I , 95-109.
72.
Holzgruber, W. and Peterson, K.: Prob. Spec. E l e c t o m e t a l l . , 1970, Naukova Dumka, Kiev, 4_, 90.
73.
Hozgruber., 6, 190.
74.
Holzgruber, W. : Proc. o f the 1st I n t l . Symp. on ESR and C a s t i n g Technology, M e l l o n I n s t . P i t t s b u r g h , Pa., P a r t I I , 1967.
75.
Rohde, L.E., Choudhury, A.U., Wahlster: 42, 1971, 165-174.
76.
Holzgruber, W. and P l o c k i n g e r , E.: 88, 1968, Nr. 12, 13 J u n i .
Steel
Ph.D. t h e s i s , Dept. o f Met., U.B.C., 1977.
W. and Peterson, K. :
Ironmaking and
Neue Hutte., H e f t 9.
i b i d . , 1973,
Arch.Eisen.
S t a h l und E i s e n ,
240
77.
Kusamichi, H. e t a l . : Proc. of the 1st. I n t l . Symp. on ESR and C a s t i n g Technology, Mellon I n s t . , Aug. 10, 1967, P a r t I I .
78.
Choudhury, A., Jauch, R. und V O l k l i n g e n , F.T.: S t a h l und E i s e n , 100, 1980, Nr. 17, 25 August.
79.
Jager, H. and Kdhnelt, G. : Berg und Htlttenmannische, Monatsheft, V o l . 190, Nr. 9, 1975, 423-429.
80.
Kamardin, V.A. e t a l . : 4, 1974, 59-63.
81.
O p r a v i l , 0.: Proc. Conf. "Metal-Slag-Gas-Reactions," E l e c t r o c h e m i c a l Soc. Toronto, 1975, 923-931.
82.
Kay, D.A.R., M i t c h e l l , A., and Ram, M.: S t e e l I n s t i t u t e , Feb. 1970, 141-146.
83.
Rehak, B. e t a l . : Proc. o f the 5th I n t l . Conf. on Vacuum M e t a l l u r g y and ESR Processes, Munich, Oct. 19 76, 147-152.
84.
Iodkovskiy, S.A. and Panin, V.V.: I z v e s t , Akad. Nauk. SSSR, M e t a l l y , Marz-Apr., (2), 1968, 115-121.
85.
Nakamura, Y. e t a l . : 623-627.
86.
M a r a k h o r s k i i , I.S. e t a l . : S t a l , 1968, 1, 277-279.
87.
Tokumitsu, N., Nakamura, Y., e t a l . : ' Proc. 6th I n t l . Vac. Met. Conf.) on S p e c i a l M e l t i n g , San Diego, Ca. A p r i l 19 79.
88.
S o m e r v i l l e , J . and Kay, D.A.R.: 2, 1727.
89.
C h a i , C.S. and Eagar, T.W.: W i l d i n g Research Supplement of the AWS, 1982, 229-S. (Paper presented a t the 62nd Annual Meeting i n C l e v e l a n d , Ohio, A p r i l 1981.)
90.
Sims, C.E.: The 1959 Howe Memorial l e c t u r e : "The Non-Metallic Constituents of S t e e l , " Trans, o f the Met. Soc. o f AIME, 215, June 1959, 367-393.
Russian M e t a l l u r g y (Metally)
J . Iron and
Trans. I S I J . , V o l . 16,
1976,
F i z . Khim. Osn. P r o i s v o d .
M e t a l l , Trans., 1971,
241
91.
K i e s s l i n g , R. and Lange, N. "Non-Metallic I n c l u s i o n s i n S t e e l , " , 2nd E d i t i o n . P u b l i s h e d by the Metals SocietyLondon, 1978.
92.
P i c k e r i n g , F.B.: " I n c l u s i o n s " , the I n s t i t u t i o n of M e t a l l u r g i s t s , Monograph No. 3, 1979.
93.
" S u l f i d e I n c l u s i o n s i n S t e e l , " Proc. of an I n t l . Symp. Nov. 1974. Port Chester, N.Y. Ed. J . B a r b a d i l l o and E. Snape, ASM, N.6.
94.
"Swedish Symposium on N o n - M e t a l l i c I n c l u s i o n s i n S t e e l " , arranged by Uddeholm Research Found. Swedish I n s t , f o r Met. Research, Apr. 1981.
95.
Van Vlack, L.H.: 1977, 187-228.
96.
S c a n i n j e c t . , I n t l . Conf. on I n j e c t i o n M e t a l l u r g y , Lule.a Sweden. June 9-10, 1977.
97.
S c a n i n j e c t I I . , Second. I n t l . Conf. on I n j e c t i o n M e t a l l u r g y , L u l e a , Sweden, June 12-13, 1980.
98.
Holappa, L.E.K.: "Ladle I n j e c t i o n M e t a l l u r g y , " Metals Reviews, 1982, V o l . 27, No. 2, 53-76.
99.
T u r p i n , M.L.
100.
Forward, G. 1967.
101.
Turkdogan, E.T.:
102.
Sigworth, G.K. and 1973, 105-113.
103.
Malm, S.: 137.
Scand. J o u r n a l of M e t a l l u r g y
5_, 1976,
104.
Malm, S.:
Scand. J o u r n a l of M e t a l l u r g y ,
5, 1976,
105.
Yarwood, J.C., Fleming, M.C. and E l l i o t , Trans., V o l . 2, Sept. 1971, 2573-2581.
106.
E l l i o t , J.F. and J.K. Wright.: 1972, V o l . 11, 574-584.
107.
F r e d r i k s s o n , H. and Hammar, 0.: Sept. 1980, 383-408.
:
and and
I n t e r n a t i o n a l Metals Reviews, Sept.
Elliot, Elliot,
J.F.: J.F.:
J I S I , 204, Elliot,
J I S I , 204,
1966,
J o u r n a l of Metals, 1966,
J.F.:
Intl. 217-225. 54,
914-919. Met.
Can. Met.
Trans 4_,
J.F.:
Jan. 134248-257. Met.
M e t a l l . Quart. Trans. B.,
Vol.
11B,
242 108.
Volmer, N. and Weber, A.: 1926, 277.
Z. Physik Chem. 119,
109.
Becker, R., Doring W.:
110.
Popel, S.I.:
Izv. VUZ Chem. Met 4, 1962, 5-13.
111.
Chipman, J . :
Trans. AIME, 224, 1962, 1288.
112.
McLean, A. and Ward, R.G.: 526.
113.
Kim, C M . and McLean, A.: Proc. Conf. "Metal-Slag-Gas Reactions," E l e c t r o c h e m i c a l S o c , Toronto, 19 75, 284-299.
114.
Von Bodgandy, L. e t a l . : Nr. 7. 1961, 451-460.
115.
Lindon, P.H. and B i l l i n g t o n , J . C : 340-347.
116.
Shewmon, P.G.: Diffusion i n Solids, New York. 1963, 19.
117.
Lindborg, U. and T o r s e l l , K.: 94-102.
118.
Wert, C. and Zener, C. :
119.
M i y a s h i t a , Y. :
120.
T o r s e l l , K. and O l e t t e , M.: 814-822.
121.
Iyengar, R.K.: D. of Ph., Department o f M e t a l l u r g y , C.M.U., P i t t s b u r g h , Pa., 1970.
122.
Mathew, M.P. e t a l . : Arch. Eisenhtlt. , 4_6, J u n i 1975, Nr. 6 ( i b i d . 45_, Sept. 1974 , Nr. 9, 569-573.)
123.
Jacobs, J . E . : Open Heart S t e e l Conf., AIME, Proc. 40, 1957, 315-318.
124.
Hartman, F. :
125.
Kawawa, T. e t a l . :
Ann. Physik., 2£, 1935, 719.
J . o f Metals, 2/7/ 1965,
A r c h i v . E i s s e n h u t . , 32,
J I S I , 207, 1969, McGraw-Hill
Co.,
Trans-TMS, AIME, 1968,
J . Appl. Phys. 21_ , 1950, 5.
Trans. I S I J , 1_, 1967, 1-8. Rev. de Met., Dec. 1969,
S t a h l und E i s e n , 65_, Nr. 3-4, 1945, 29-36. Trans. I S I J , 8, 1968, 203-219.
243 126.
Fuchs, N.A.: N.Y., 1964.
The Mechanics o f A e r o s o l s .
127.
Korber, F. : 1349-1355.
128.
Urban, S.F. and Chipman,J.: 1935, 645-671.
129.
C r a f t s , W. and H i l t y , D.C.: E l e c t r i c Furnace S t e e l Conf. P r o c , AIME, V o l . 11, 1953, 121-145.
130.
Van V l a c k , L.H., e t a l . : Trans o f the Met. Soc. o f AIME, V o l . 221, A p r i l 1961, 220-228.
131.
Weinberg, F.: 219-227.
Met. Trans B,, V o l . 10B, June 1979,
132.
Weinberg, F.:
i b i d . , Dec. 1979, 513-522.
133.
Boldy, N.D., e t a l . : MIT, t e c h n i c a l r e p o r t , Jan. DAAG-46-78-C-32; AMMRC-TR^-81-4.
134.
Sims, C E . and Dahle, F.B.: Ass. 46, 1938, 65-132.
135.
Dahl, W. e t a l . :
136.
F r e d r i k s s o n , H. and H i l l e r t , M.: l u r g y 2, 1973, 125-145.
137.
Mohla, P.P. and Beech, J . : J o u r n a l o f the Iron and S t e e l I n s t i t u t e , Feb. 1969, 177-180.
138.
Takada, H. e t a l . : 573.
139.
I t o , Y. e t a l . :
140.
S a l t e r , W.J.M. and P i c k e r i n g , F.B.: 992-1002.
141.
Wilson, G.W. and McLean A.: " D e s u l f u r i z a t i o n o f Iron and S t e e l and S u l f i d e Shape c o n t r o l , " ISS of AIME, pub. 1980, 1-40.
142.
Baker, T . J . and C h a r l e s , 706.
S t a h l und E i s e n ,
Pergamon
Press.
19 37, V o l . 57, 19 37, Trans, ASM. V o l .
27,
1981.
Trans. Am. Foundrymen s
S t a h l und E i s e n ,
1
1966, 86_, 796. Scand. J . o f M e t a l -
Trans. I S I J , V o l , 18, 1978, 564-
i b i d . , V o l . 21, 1981, 477-573. J I S I , J u l y 1969,
J.A.: J I S I , Sept. 1972, 702-
244 143.
Steinmetz, E. e t a l . : Arch. E i s e n h t l t t . 4_7, Feb. 1976, 71-76 ( i b i d . 47, Sept. 1976, 521-524).
144.
H i l t y , D.C. and Popp, V.T.: AIME E l e c t . Furn. Conf. Proc. 1969, V o l . 7, 1952, 56-66.
145.
T a h t i n e n , K. e t a l . : S c a n i n j e c t Conf. June 1980, paper 24. L u l e a , Sweden, ( r e f . 97).
146.
K i e s s l i n g , R. and Westman, C.: 669-670.
147.
Saxena, S.K. and coworkers: Scand. J . o f M e t a l s , V o l . 5, 1976, 105-112. ( i b i d . , V o l . 4, 1975, 42-48).
148.
Saxena, S.K. e t a l . : Proc. o f a Conf. i n Steelmaking, Chicago, 1978, V o l . 61, 561-573.
149.
Wilson, A.D.:
150.
Kobayashi, 260-269.
151.
Uemura, T. e t a l . : V o l . 59, 457-478.
152.
F O r s t e r , E. e t a l . : S t a h l und E i s e n , 23 Mai, 474-485.
153.
Nashiwa, H. e t a l . : S p e c i a l Rep. I S I J . , 1977, (6th Japan-USSR-Joint Symp. Phys. Chem. M e t a l l . Processes, 81-94.
154.
Takenouchi, T. and Suzuki, K.: 1978, 344-351.
155.
O e l s c h l a g e l , D. e t a l . : Dec. 1981, 332-330.
156.
Folmo, G. e t a l . : 99-104.
Scand. J . o f M e t a l l . , 9, 1980,
157.
Haida, O. e t a l . :
Tsetsu-to-Hagane,
158.
Haida, 0. e t a l . : Proc. o f the 8th, Japan-USSR J o i n t Symp. on Phys. Chem. of M e t a l l u r g i c a l Processes., June 19 81, Tokyo, 56-6 7.
J I S I , J u l y 1970,
Metal P r o g r e s s , A p r i l
S. e t a l . :
Steel
1982, 41-46.
Trans. I S I J . , V o l . 11, 1971,
AIME, Proc. Open Heart Comm., 1976 94, 1974, Nr. 11
Trans. I S I J . V o l . 18,
Iron and S t e e l
International,
1980, 6_6, 3, 48-56.
245 159.
Church, C P . e t a l . : 62-78.
J o u r n a l o f Metals., Jan.
1966,
160.
Eklund, G. : Jerkont A n n a l i , V o l . 154 , 1970, 321-325.
161.
Rosenqvist, T., and Dunicz, B.L.: V o l . 194, 604-608.
162.
Turkdogan, E.T.: 546-563.
163.
H i l t y , D.C and C r a f t s , W.: 1307-1312.
164.
Turkdogan, E.T. e t a l . : 1561-1570.
165.
Kor, G.J.W. and Turkdogan, E.K.: i b i d . , V o l . 2, June 1971, 1571-1578.
166.
Kor, G.J.W. and Turkdogan, E.K.: i b i d . , V o l . 3, May 1972, 1269-1278.
167.
H i l t y , D.C. and C r a f t , W.: 1954, 959-967.
168.
H i l t y , D.C. and F a r r e l l , 17-27.
169.
Silverman, E.N.: Trans, o f the Met. Soc. o f AIME, V o l . 221, June 1961, 512-517.
170.
Hilty, 414 .
17.1.
D'Entremont, J.C. e t a l . : ( i b i d . , 1967, 239^, 123) .
172.
Wentrap, H. e t a l . :
Arch. E i s e n , 13_, 1939, 15.
173.
Gokcen, N.A. e t a l . :
J . o f Metals, 1953, 173.
174.
McLean, H. and B e l l , H.B.:
175.
G u s t a f s s o n , S. and Melberg, P-O.: Scand. J . o f M e t a l l u r g y , V o l . 9, 1980, N. 3, 111-116.
176.
Janke, D. and F i s h e r , W.A. : 195-197.
177.
Fruehan, R.I.:
Trans AIME, 1952,
Trans. TMS-AIME, 1961, V o l .
221,
J . o f M e t a l s , Dec.
1952,
Met. Trans., V o l . 2, June 1971,
Journal o f Metals,
J.W.:
D.C. and C r a f t s , W.:
Sept.
I . and S.M., May 1975,
Trans. AIME, 188,
1950,
Trans. AIME, 1963, 227,
14
J I S I , 203, 123.
Arch. E i s e n 4_7, 1976,
Met. Trans. 1, 1970, 3403-3410.
246
178.
Rohde, L.W. p. 1966.
et a l . :
179.
Ototani,
180.
M i y a s h i t a , Y. e t a l . : 1969-1975.
181.
Kobayashi, S. e t a l :
182.
Kusakawa, R. e t a l : 1976, paper 21.
183.
Watanabe, S. e t a l . : 683-688.
184.
Steinmetz, E. e t a l . : Arch. E i s e n . 4_7, 1976, Nr. 4, A p r i l , ( i b i d . , Arch. E i s e n 4_8, 1977, Nr. 11, November 569-574.
185.
H i l t y , D.C. and F a r r e l , J.W.: 13th Annual Conf. of M e t a l l u r g y , Toronto. Aug. 27, 19 74.
186.
Hammar, 0.: "Progress Through Research Sandvik." S t e e l Research Centre Lab. Sandviken-Sweden.
187.
Waudby, P.E. and S a l t e r , W.J.M.: 518-522.
188.
Morgan, E.L. e t a l :
189.
Cremer, P. and D r i o l e , J . : Met. Trans. B., 13B., March 1982, 45-51.
190.
P l o c k i n g e r , E.: S t a h l E i s e n , 1956, 76, 810 1957, 7 7 / 701, i b i d . , 1960, 8_0, 656).
191.
Straube, H. e t a l . : Arch. Eisenhtlt. J u l y 1967, 509 ( i b i d . , 1967/ 38, 607).
192.
Sloman, H.A.
193.
Braun, T.B., E l l i o t , J.F. and Flemings, M.C.: Trans. B.,1979, V o l . 10B., 171-184.
194.
Okohira, K. e t a l . : 102-109.
195.
O o i , H. e t a l . :
T. e t a l . :
A f d . E i s e n h i i t t . , £2, 1971, Trans. I S I J . 16, 1976, 275-282. Tetsu-to-Hagane',
5_7, 1971,
Trans. I S I J . , 11, 1971, 260-269. Japan S c i . Assn. 19th Committee, Trans I S I J . , V o l . 19_, 1979,
J I S I , J u l y 1971,
J I S I , 1968, 206, 987.
and Evans, E.L.:
(ibid.,
J I S I , 165, 1950, 81. Metall..
Trans. I S I J . , V o l . 14, 1974,
Trans. I S I J . , V o l . 15, 1975, 371-379.
247
19 6.
Waudby, P.E. a n d W i l s o n , F.G.: P r o c . I n t l . Symp. C h e m i c a l M e t a l l u r g y o f I r o n and S t e e l , S h e f f i e l d , J u l y 1971, 195-197.
197.
Gatellier, 275-283.
198.
S p o n s e l l e r , D.L. 1964, 876.
199.
Shurmann, E.B. e t a l . : J u l i 1974, 433-436.
C. e t a l . :
ABM.
3_3 , No.
and F l i n n , R . A . :
Arch.
ibid.,
46, N r .
10, O k t o b e r
ibid.,
46, N r .
8, A u g u s t
ibid.,
4_5, N r . 6, J u n i
ibid.,
46, N r .
Trans.
Eisenhtltt.
1975,
1975,
1974 ,
234 , M a i o ,
AIME,
1977,
230,
45_, N r .
7,
619-622.
473-476.
336-371.
12, D e z . 1975,
767-771.
200.
K e p k a , M. : 645-652,
Neue H t l t t e , V o l . 2 1 ( 1 1 ) ,
201.
L i n d o n , P.H. 340-347.
202.
J a e g e r , H. and H o l z g r u b e r , W. : P r o c . I n t l . Symp. C h e m i c a l M e t a l l u r g y o f I r o n and S t e e l , S h e f f i e l d , J u l y 1971, 195-197.
203.
Boris, M.J. : 28, 89.
204.
Dunn,
205.
K o c h , W.:
206.
P i c k e r i n g , F.B.: P r o d u c t i o n and A p p l i c a t i o n C l e a n S t e e l , 1972, L o n d o n , 75-95.
207.
B r u c h , J..: M i k r o c h i m . A c t a , S u p l . 5., J a n . 1974, S p r i n g e r V e r l a g , 137-146. ( B r u c h , J . e t a l . : A r c h i v . E i s e n h t l t t , H e l f t 11, Nov. 1965, 799-807) .
208.
L i n d o n , P.H. 340-347.
E.J.:
and B i l l i n g t o n ,
AIME, E l e c .
ibid.,
Stahl
1971,
J.C
Furn.
29,
1976,
JISI,
March
Steel
Conf.
1969,
Proc,
1970,
117.
und E i s e n , 8 1 ,
and B i l l i n g t o n ,
:
Nov.
1961,
J.C:
1592.
JISI,
of
March
1969,
248
209.
F a u l r i n g , G.M. e t a l . : 14-20.
210.
Holappa, L.E.K.
211.
Sanbongi, K.:
Iron and S t e e l Maker, 1980,
( r e f . 94), 19-34. Trans. I S I J . , V o l . 19, 1979, 1-10.
(Emi, T., Sanbongi, K., e t a l . : 1978, 64 (10), 1538-1547) .
Tetsu-to-Hagane,
(Kobayashi, S., Sanbongi, K., e t a l . : 1961, 198, 260-269.)
Trans.
ISIJ.
212.
R i k a t a l l i o , P.:
Paper 13, Ref. 97, S c a n i n j e c t I .
213.
U s u i , T.:
214.
Saxena, S.K.: Ironmaking and Steelmaking, 1982, V o l . 9, No. 2, 50-57.
215.
O t o t a n i , T. and Kataura, Y.: 1972, 334-342.
216.
F a u l r i n g , G.M. and Ramalingam, S.: 11B, March 1980, 125-130.
Met. Trans. B.
217.
F a u l r i n g , G.M. and Ramalingam, S.: 10A, Nov. 1979, 1781-1787.
Met. Trans. A.
218.
B e l l , M.M.: M.A. Sc. t h e s i s , Department o f M e t a l l u r g y , U.B.C., 1971.
219.
M i t c h e l l , A. and B e l l , M.M. : 1972, 363-369.
220.
B u r e l , B.: M.A. Sc. t h e s i s , Department o f M e t a l l u r g y , U.B.C., 1969.
221.
V a c c a r i , J.A.:
222.
Viswanathan, R. and Beck, G.: Nov. 1975, 1997-2003.
Met. Trans. A., 6A,
223.
R a t l i f f , J . L . and Brown, R.M.: V. 60, 176.
Trans. ASM. 1967,
224.
K e l l y , T.N. e t a l . , Proc. o f the 3rd I n t l . Conf. on ESR and o t h e r Spec. M e l t i n g , Techs., M e l l o n I n s t . P i t t s burgh, Pa., June 1971* 125-140.
Paper 12, Ref. 98, S c a n i n j e c t I I .
Trans. I S I J , V o l . 12,
Can. Met. Quart.
2,
Design Engineer, May 1980, 57-60.
249
225.
B a l l a n t y n e , A.S. and M i t c h e l l , A.: Proc. of an I n t l . Conf. on S o l i d i f i c a t i o n . S h e f f i e l d M e t a l l , and E g. Assn. and U. of S h e f f i e l d . J u l y 1977, 363-370.
226.
E t i e n n e , M.: Ph.D. t h e s i s , Dept. of M e t a l l u r g y , U.B.C., 1971.
227.
S i d l a , G. and M i t c h e l l , A.: "The Design, C o n s t r u c t i o n and O p e r a t i o n of an ESR Furnace I n s t a l l a t i o n , " Special Report to DREP/DSS, June 1980.
228.
R i d a l , K.A. e t a l . :
229.
Malm, S.:
230.
Colby, J.W.: Company r e p o r t , B e l l Telephone Inc., Allentown, Penn. 1971.
231.
Rooney, T.E. and S t a p l e t o n , A.G.: 1935, 249-254.
232.
Y u l e , J.W. and Swanson, G.A.: l e t t e r , 8, 1969, 30.
233.
Ingamels, C O . :
234.
Rein, R.H. and Chipman, J . : Trans, o f the Met. Soc. of AIME, V o l . 233, Feb. 19 65, 418.
235.
K l i s i e w i c s , Z.. e t a l . :
Hutnik 1980, 47 (2), 56-60.
236 .
Kuo C-K. and Yen T-S. : 381.
A c t a Chim. S i n i c a ,
237.
Nakai, Y. e t a l . : 410.
238.
B e r c i k , P., Hutnicke, L i s t y , : 867-872.
239.
Wilson, W.G., Kay, D.A.R. and Va hed A.; J . of Metals, 1974, 26, 14-23.
240.
Sharma, R.A. and Richardson, F.D.: 386-390.
241.
Sharma, R.A. and Richardson, F.D.: Trans, of the Met. Soc. of AIME, Aug. 1965, V o l . 233, 1586-1592.
J I S I , Oct. 1965, 995-1003.
Scand. J . o f M e t a l l u r g y , 4_, 1975, 231-237. Labs.
J I S I , V o l . 131.
A t . A b s o r p t i o n News-
A n a l . Chim. Acta' 5_2, 1970, 323.
30_, 1964,
Trans. I S I J . , V o l . 19, 1979, 401V o l . 31, No. 12, 1976,
J I S I , Aug. 1961,
250
242.
Iyengar, R.K. and P h i l b r o o k , W.O.: J u l y 1972, 1823-1830.
243.
Lindskog, L. and Sanberg, H.: 1973, 2, 71-78.
244.
Engh, T.A.
245.
L i n d e r , S.:
246.
A r i t o m i , N. and Gungi, K.: Trans of the Japan I n s t , of M e t a l s , V o l . 22, No. 1, 1981, 43-56.
247.
Suzuki, A. e t a l . : Nippon Kinzoku Gakkai Shuho, 32, 1968. (see Brutcher T r a n s l . 7804 (1969).
248.
Choudhury A. e t a l . : S t a h l u. E i s e n 96, 946-951.
249.
Mochizuki, T. e t a l . : 4th I n t l . Symp. on ESR, I S I J , Tokyo, Japan, 260.
250.
Kadose, M. e t a l . : i b i d .
and Lindskog, N.: ibid.,
1974,
Met.
Trans. V o l . 3
Scand. J . M e t a l l u r g y , ibid.
1975,
4, 49-58.
5, 137-150.
246.
1976,
Nr. June
20, 1973
251
F i g u r e ( 1 ) - S c h e m a t i c i l l u s t r a t i o n o f an ESR
system.
252
Axial length (cm)
Figure
(2) - P r e d i c t e d and measured temperature p r o f i l e s f o r a 1018 M.S. e l e c t r o d e , 25 mm i n diameter.
253
Figure
(3) - Manganese content of the metal f o r u n i v a r i a n t e q u i l i b r i u m gamma i r o n + "MnO" + "MnS" + l i q u i d (1) f o r the Fe-Mn-S-0 system and u n i v a r i a n t e q u i l i b r i u m gamma iron + "MnS" + l i q u i d s u l f i d e f o r Fe-Mn-S system.
800
1000
1200
Temperature
Figure
(4)
1400
1600
(°C)
U n i v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 system the presence o f gamma i r o n and Mn(Fe) 0 (164) phases
255
>i
•P > •H
4 > O
<
—
CD CO
|Fe-Mn-0
CD (0 CO .£ CD ft
c
C i—I (0 O S co
ToFe-5-0'S> 1100
1300
1500
1700
Temperature (°C) —•>•
actual conditions
(cooling)
equilibrium conditions starting ~ —
(cooling)
composition
heating conditions f 16 6> )
F i g u r e (5) - U n i v a r i a n t e q u i l i b r i a i n v o l v i n g s o l i d metal and Mn(Fe)0 i n Fe-Mn-S-0 system bonded w i t h t e r n a r y Fe-Mn-0 and Fe-S-0 terminal-phase f i e l d s ; (e) 6, 'O', 1 ; (p) f S , l , 1 ; (f) 6, 'o', ; (n) 6, ' o \ 1 , 1 ; (g) 6, y, 'o'; 1 ^ 2
1
2
(h) # Y
1
'o'; 'MnS', 1
1
.
2
2
256
MiS
.MO-&0,
(a) MiS
MnO
Figure
(7)*
1 6 6
)-
E q u i l i b r i u m phases i n three planes o f the FeO-MnO-MnS-Si0 s y s t e m , a) MnS-FeO-2MnSiOj 2
b)
MnS-2FeO'Si0 -2MnO«Si0 2
2
and c)
MnS-FeO-MnO,
257
(95) Figure
(8)
a) MnO-Si0 b i n a r y phase d i a g r (T-Mn_SiO. and R-MnSiO-.) 2
b) Schematic i l l u s t r a t i o n of l i q u i d versus Mn/Si/O r a t i o s .
compositions
(b) i s a s e c t i o n of the Fe-Mn-Si-S-0 system. ABC are s i m p l i f i e d l i q u i d compositions. A'B'C* are l i q u i d compositions s a t u r a t e d with s o l i d s u l f i d e a t 1315°C.
258
gure
(9) - Schematic i l l u s t r a t i o n o f changes i n i n c l u s i o n composition (enriched i n S i and Mn) i n a 1020 MS electrode.
260
Figure
(11) - I s o t h e r m a l . activities)
Fe-Al-Ca-0 p r e c i p i t a t i o n diagram' *^. 1
(Henrian
to
263
Figure
(14) - Schematic i l l u s t r a t i o n of the ESR used i n t h i s i n v e s t i g a t i o n .
arrangement
I
II & 01
IV
Figure (15) - Schematic illustration of the "inclusion extractor".
265
Figure
(16) -
I n c l u s i o n s from 1 0 2 0 - s t e e l used as l i g h t microscope. 4 30 X. Spectrum X-ray a n a l y s i s are a i v e n 17 (a-b) .
electrode i n Figure
X-ray energy
Figure
(17)
Deformed i n c l u s i o n (a) S p e c t r u m X - r a y (b) S p e c t r u m X - r a y
(KeV)
i n a 1020 M.S. a n a l y s e s of dark phase. a n a l y s e s o f l i g h t phase.
267
Figure
(18) - M a c r o s t r u c t u r e o f a 1 0 2 0 - e l e c t r o d e t i p . (a) u n e t c h e d s u r f a c e (125X). (b) m a c r o s t r u c t u r e where l i q u i d f i l m , s e m i l i q u i d r e g i o n and y - g r a i n g r o w t h , a r e a s a r e shown.
268
(c) Figure
(d)
(19) - M a c r o s t r u c t u r e s from a 4340-electrode t i p . (a), ( c ) , and (d) show the l i q u i d f i l m , p a r t i a l l y l i q u i d r e g i o n and the f u l l y and p a r t i a l l y a u s t e n i t i z e d zones( b ) , (c) and (e) 30X. (a) shows a d r o p l e t i n process o f forming (b) 6.6 X.
269
270
Figure
(21)
S c h e m a t i c i l l u s t r a t i o n o f a 1020 e l e c t r o d e t i p s u b j e c t e d t o ESR t h e r m a l g r a d i e n t s .
271
Figure
(22)
- M u l t i p h a s e ( r e l a t i v e l y grown) i n c l u s i o n s i n a 1 0 2 0 e l e c t r o d e . 400 X.
272
Figure
( 2 3 ) - S i n g l e phase i n c l u s i o n s i n p a r t i a l l y and f u l l y molten r e g i o n s i n a 10 20 e l e c t r o d e t i p . (a) 45 X and (b) 400 X.
Figure
(24)
-
C o m p l e x ( C a , A l , S i , Mn) i n c l u s i o n s f o u n d in t h e l i q u i d f i l m a n d d r o p l e t s o f 1020 e l e c t r o d e s (a), (c), ( d ) - 1 . 8 x 1 0 X a n d (b) 3 . 6 x 1 0 X. 2
2
274
X-ray energy (KeV)
Figure
(25) -
(a) T y p i c a l in
complex
the l i q u i d
film
(2.4 x 1 0 X ) (b) S p e c t r u m X - r a y
(Ca, A l , S i , Mn) and d r o p l e t
3
analysis.
inclusion
o f 1020
electrodes
275
Composition i n a t . %
Figure
(26) - Changes i n i n c l u s i o n chemical composition i n a 4340(1) e l e c t r o d e t i p s u b j e c t e d to (ESR) thermal g r a d i e n t s .
276
Figure
(27)
- Changes i n i n c l u s i o n chemical composition i n a 4340 e l e c t r o d e t i p with strong r e c r y s t a l l i z a t i o n .
277
• A! ACa
E
o & • Mn
12000 •H
fr,
spherodization of sulfide inclusions
•a
cr •rl
8000
£ O 4-1
CD U
•f 4000
C
solidus
fO
w
•H
— i 20
40
Composition
Figure
" -|- 285Cym
Liquid-solid region
4J
Q
5500iim
Incipient heat affected zone
60
$- 350Mm
80
liqiidus
( a t . % x)
(28) - B e h a v i o r o f o x i d e i n c l u s i o n s i n an e l e c t r o d e t i p of a r o t o r s t e e l s u b j e c t e d t o ESR-thermal g r a d i ents.
Figure
(29) - A l - s i l i c a t e i n c l u s i o n s i n a 4340 ESR i n g o t , 75 mm i n d i a m e t e r . Deep e t c h e d sample by i o d i n e m e t h y l a c e t a t e m e t h a n o l ( I n g o t 3) (a) 1000 X and (b) 2000 X.
279
RIII-W
20
40
60
T o t a l Oxygen Content
Figure
80 (ppm)
(30) - I n f l u e n c e o f C a S i and FeO i n t e r m i t t e n t a d d i t i o n s on the oxygen c o n t e n t i n a 1020 M.S.
100
280
RII-W
25
Ca,
20
g
3
15
FeO, 2 nd add. 'Ca', 1st add.
4->
2
2ndaddJ
io
o Ul c
FeO,
1st add.
40
60 Total
Figure
Oxygen C o n t e n t
80
100
(ppm)
(31) - Changes i n t o t a l o x y g e n c o n t e n t r e s u l t i n g i n C a S i and FeO i n t e r m i t t e n t a d d i t i o n s d u r i n g r e f i n i n g o f a 1020 M s t e e l .
281
Figure
(32) - Changes i n s l a g chemical composition i n a 1020 (RIII-W) s t e e l r e s u l t i n g from CaSi and FeO i n t e r m i t t e n t a d d i t i o n s .
282
RII-W
01 0
1
1 0.2
(wt.% Mn)
Figure
1
U 0.4
I 2
| 3
(wt.% Fe X 10
| 4
)
(33a) - Changes i n s l a g chemical composition as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s of CaSi and FeO i n s l a g d u r i n g r e f i n i n g .
L 5
283
RII-W
Slag Chemical Composition
Figure
(wt.%)
(33 b) - Changes i n S i , A l and Ca as a r e s u l t of d i s c r e t e a d d i t i o n s of CaSi and FeO i n the s l a g during r e f i n i n g .
284
RIII-W
1
i—i—i—i—I
06
I—i—i—i—I
0 . 7 5 0 B 5 0.1 02 Ingot
Figure
i—I—I
Chemical
I—I—i—i—I—r
I
i
i
i
i
i
|
I
•
.
.
001 0.03 0 0 5 0 0 7 0 2 0 0 2 4 Composition
.
I
0.28
(wt.%)
( 3 4 ) - Changes i n i n g o t c h e m i c a l c o m p o s i t i o n a s a r e s u l t o f C a S i and FeO a d d i t i o n s i n s l a g .
285
Figure
(35) - E f f e c t of CaSi and FeO a d d i t i o n s i n the s l a g on the chemical composition of a 1020 MS ESR-ingot.
286
RIII-W
~i
i
1
r
1
o inclusion size x 10>m
251
power off
20 15
2nd Ca-addition 2nd FeO addition
+J
x:
Cn •H
10
(1)
BC JJ O Cn C
5h
20
40
60
80
a t . % Ca at.% A l
Figure
(36) a,b
100
1 n X
1
120
140
160
4
0
- Changes i n i n c l u s i o n c o m p o s i t i o n (a) and mean s i z e (b) i n a 1020 MS i n g o t as a r e s u l t o f i n t e r m i t t e n t o x i d a t i o n and d e o x i d a t i o n o f t h e s l a g .
287
Figure
(37)
- Chemical a n a l y s i s of s l a g samples i n
RI-H
288
0.1
0.2
0.1
Ingot Composition
Figure
0.6
0.2
(wt.
0.7
0.8
%)
(38) - Ingot chemical a n a l y s i s i n R l - I l . as a r e f e r e n c e ) .
(Ingot used
289
RII-Il
Slag Composition
Figure
(39) - Slag chemical a n a l y s i s
(wt. %)
(wt.%) i n R I I - I l .
290
4-> tn •H cu
K 4-1
o Cn c
H
0.2
0.6
1.0
28
30
Slag Composition
Figure
(40) - Slag chemical a n a l y s i s
(wt. % X)
(wt.%) i n RII-I2.
291
RII-Il
i—I—r
i—r
30h
\
V
25h
o i l i I i o
1 —
•
Solid
O
Liquid
20
o I t
15
o
V
10
A J
P
2 3 4 5 6 7 8 9
I n c l u s i o n Mean (ym)
(41) -
Diameter
60 Total
st add. i I00
80 Oxygen C o n t e n t
I n c l u s i o n mean d i a m e t e r and t o t a l content i n R I I - I l .
3rd add. 2nd add.J
L
I
Figure
1
4th add.
(ppm)
oxygen
292
30
1
T
r
T
r
()
25
5 th odd
-i 20 x: tn
•H
4th add
oi:
4-»
15
~o—-~
0)
3rd odd
K
4->
o
tn CJ
10 r
V
o Liquid pool •Solid / ingot I
2Qd.Qq!d
\ Ca
addition
*
\
o
r
2
j
/
4 6 8
30
I n c l u s i o n Mean Diameter (ym)
Figure
(4 2)
1 *A
40
L
50
\
° Liquid pool
1
• Solid ingot 1st add. * Calculated total oxygen content from extracted inclusions 70 80 90 100 t
60
T o t a l Oxygen Content (ppm)
- T o t a l oxygen content and i n c l u s i o n mean d i a meter i n RII-I2.
293
T
,* 10
1
1
20 20
1
40 30
40
1
1
, 6 0 50
60
,at.% Ca, 'at.% A1
1
1
,89 70
1
r
liguidpod, 80
ingot
1 Q 2
J
Figure
(4 3) - I n c l u s i o n chemical composition (at.%) as a f u n c t i o n of c o n t i n u o u s l y i n c r e a s i n g deoxida t i o n r a t e s (ingot height) i n i n g o t R I I - I l .
294
30
—3»0
25
o-=^-~
r-
/
20 o e
£ 15
/
o'
4-1
Cn
i
10
4-1
o in H
5
^
Ca addition
^
/
o u
g j_ ^ /
«/
.
, 50
Figure
(44)
•
solid ingot
°
liquid pool
, 100
I n c l u s i o n chemical composition as a f u n c t i o n of the i n g o t h e i g h t (or c o n t i n u o u s l y i n c r e a s i n g d e o x i d a t i o n r a t e s ) i n RII-I2.
295
RII-Il
Ingot Chemical Composition
Figure
(wt.%)
(45) - Ingot chemical composition a g a i n s t i n g o t h e i g h t (or d e o x i d a t i o n r a t e ) .
296
Ingot Composition
Figure
(46)
(wt.%)
- Ingot chemical composition v s . i n g o t h e i g h t (or d e o x i d a t i o n r a t e ) i n R I I - I 2 .
2 9 7
298
(c)
Figure
(d)
(4 8) - "Alumina g a l a x i e s * a s s o c i a t e d w i t h MnS I I i n an A l d e o x i d i z e d i n g o t , ( R I I - I l ) . 2000 X. (a) BE photograph, (b) A l (c) Mn and (d) S maps.
299
X-ray
Figure
(49)
- a-Al^O^
(corundum)
Energy
inclusions
in
(KeV)
Al
deoxidized
ingots. (a) u n e t c h e d s u r f a c e , ^ 1 0 0 0 X; (b) a n d ( c ) a r e d e e p ( i o d i n e m e t h y l a c e t a t e ) e t c h e d s a m p l e s , * 3 0 0 0 X; (d) s p e c t r u m a n a l y s i s o f (a) a n d (b) r e s p e c t i v e l y ; •v 2 0 0 0 counts.
300
(c) Figure
(d)
(50) - Calcium-aluminate i n c l u s i o n from a h e a v i l y A l deoxidized ingot. (a) b a c k s c a t t e r e d e l e c t r o n photograph taken a t 4000 X. Reverse p o l a r i t y . (b) , ( c ) , and (d) are A l , Ca and S maps. RIIII2-S8-SLD.
301 RII-Il
1-••
1
—"1
1
o o
S - Stoichiometry Ratio
8
6h
X
to u < 0\° 0\°
• -p
f0
/ /
•/
s
•
/
/
/
/
// —
4
c
+J
/
/
'
/
/
/
/«»
•
•
/ /
/
/
r
/*! ' 0.4
i
0.6
i
i i
i
0.8
1.0
1.2
.at. at.
Mn"
L
Figure
(51) - C o m p o s i t i o n dependence Ca-aluminate i n c l u s i o n
1.4
1.6
o f s u l f i d e p h a s e s on t h e phases i n R I I - I l .
Figure
(52) - Composition dependence o f s u l f i d e phases the Ca-aluminate i n c l u s i o n phases i n RII
'igure
(a)
(b)
(c)
(d)
(53)
- Segregated m a t e r i a l i n an A l - d e o x i d i z e d ingot, (a), (b) , (c) and (d) are A l , Ca, S i and Mn maps. -v 1 0 0 0 X.
3 0 4
Figure
(54) - Dependence of "FeO"
content
on the
r a t i o i n slag i n a continuously mgot, (RII-H). y
(—^3, CaO Al-deoxidized ueoxiaizea
305
u
1.3
1.2 A
Figure
(55)
1
1.1
2°3
Al 0 - Dependence of the "FeO" on the ( — - ) ratio , CsO i n s l a g i n a c o n t i n u o u s l y A l - d e o x i d i z e d incrot. (RII-I2).
y
'
306
RIII-Il
Figure
(56) - T o t a l oxygen content and i n c l u s i o n mean diameter i n a CaSi-deoxidized ingot (RIII-Il) .
307
RIII-I2
T—i—i—i—I
0
4
8
|
1
30
40
Inclusion Mean Diameter (ym)
Figure
'
1
60
1
1
80
T o t a l Oxygen Content
(57) - I n c l u s i o n mean diameter content i n RIII-I2.
r
(ppm)
and t o t a l oxygen
308
025
0.5
r a.t • L
Figure
(58)
at.
0.75
% Ca i % A1 J
- I n c l u s i o n chemical composition (at. % ) , as a f u n c t i o n o f d e o x i d a t i o n r a t e s i n RIII-Il.
309
Figure
(59) - I n c l u s i o n chemical composition as a f u n c t i o n of d e o x i d a t i o n r a t e s i n R I I I - I 2 .
310 RIII-Il
Figure
(60)
- Changes i n t h e s l a g c o m p o s i t i o n i n a c o n t i n u ously Ca-Si deoxidized ingot ( R I I I - I l ) .
RIII-I2
r
1
T
1
r
1
30 ^ 25 •
J
6 th addition
r
\ "
t t
20
-P
si
tn
•H
CD
15
-P O
tn
C
H
10
\
c/3rd
add..
/ \
2nd
add. Fe J
•
/
0.2
^
\
<
J
I
0.6
o Si \ 1st add.
I
'
I
1.0
A
Al\
L
1.4
II
13 15
Slag Composition
Figure
(wt. %)
(61) - Changes i n s l a g composition i n a c o n t i n u o u s l y (CaSi) d e o x i d i z e d i n g o t , (RIII-I2)
312
Figure
(62)
- Changes i n A l and S i i n ingot deoxidation i s increased.
( R I I I - I l ) as CaSi
313
RIII-I2
r~o—i
T
o Si
r
1
7 I _i/
r
6th addition 5 th addition
4th
add.
3rd
add.
2nd
add.
1st
add.
_o
1
6 0.2
0.6
0.7
0.8
)
i 1
i
i
i
2
3
4
Wt.% X (Al,Mn,Si) i n i n g o t
Figure
(63) - Changes i n chemical composition i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t , ( R I I I - I 2 ) .
314
RIII-Il
Figure
(64) - Dependence of "FeO" contents i n the s l a g on deoxidation rates i n R I I I - I l .
the
315
R HI 0.8
I
2.5
1 2
,
3.0
3.5
Wt. % Co ] . s l a g Wt. % Al
Figure
(65) - Dependence of "FeO" contents i n the the d e o x i d a t i o n r a t e i n RIII-I2.
slag
316
RIII-Il
Figure
(66) - S u l f u r content i n i n c l u s i o n s as a f u n c t i o n of the Ca:Al r a t i o i n the Ca-aluminate phases (RIII-Il).
317
R1I-I2 (Ca-Si ~i
deoxidized ingot) r-
r~w
1
( A t % S ).
,
.
inclusion
Figure
(67) - I n c l u s i o n composition i n samples from liquid p o o l and i n g o t as d e o x i d a t i o n r a t e i s i n c r e a s e d .
0
Ingot
Height
(cm)
ro
ro cn
o
o -I—
cn ro O H
C
P-
3
\
o
3 rt
n
0) I
0 3
01
O
OJ
ro
o
ao i- g c t> go H-
'
cn
*
o
OD
zr
a.
a a.
a.
a
o a. a.
o a. a.
Q.
a. a.
o.
•
V
2
_1_
O
01
~~ 01
Q
o
• 1 —
cr
— 3
01
At. At.
m Ul
» c H (-• M M I M
% Ca % Al
1
0
0
i
n
s
a
m
p i e s
from
liquid
pool
oo
cn
ro
rr
ort\
1
>>.
& (t O X H"
01
>
r
r
*\ \
a
a
—
01 3
a
0
^
\ *s
o
R
\
— \ \
\
\
cn x
0)
ro
o
8T£
1
1
J
\ X
\
-v. —1
319
Figure
(69)
- Segregate enriched (c) S i and (d) Mn.
i n (a) A l , * 5000 X.
(b)
Ca,
320 R-4340(1)
35
30 25
~
20
^7t
F
T—r
5. L
/
I.. ...
/
...
4J
15
fI
10
M 5h o
Fe Mn J
0
Si
A
L
01 02 03
-I
I
1
I
u
0.7 OS 11 13 15 17
%
Slag Composition
Figure
(70)
16
(wt.
38
AO
%)
- Slag chemical a n a l y s i s of a 4340 i n g o t c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y ([R-4340 ( 1 ) ] .
321
Figure
(71) - Ingot chemical composition of a 4340-ingot c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y . [R-4340 ( 1 ) ] .
322
Figure
(72) a - V a r i a t i o n i n mean i n c l u s i o n
size.
b - Oxygen a n a l y s i s i n a 4340-ingot c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y , [R-4340(1)].
323
0.1
25
26 (
Figure
2.7
2.8
wt.
% Al
29 }
S l a
3.0
3.1
^
(73) - Changes i n s l a g composition as a r e s u l t of c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s , R-4340 (1).
324
Figure
(74)
- I n c l u s i o n chemical composition, i n (a) i n g o t and (b) l i q u i d p o o l , as a r e s u l t of c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n a 4340 ingot R-4340(1).
325
R-4340 liquid pool
140
120
100
|At.%Caxl00 At.% Al
80
ingot
1-700 600
h500 /
400 /
60
(I)
300
40
/ / / 200 /
20
.00//
/
/
/
/
o'
,o
/
/
p
/
/
/
/
/
/
/ /
10
o
LIQUID POOL
•
SOLID
20
(At. % S )
Figure
(75) - I n c l u s i o n composition i n terms o f the Ca:Al r a t i o and s u l f u r content (as CaS) i n R-4340(1).
326
0.8 10
c o
CO r—I
u c
0.6
•H CO
U
-P cd
0.4
0.2
•
(§)
Ca-Si, solid and liquid
*
®
Hypercal,
(§)
Al-Si,
2.0
4.0
6.0
'»
»»
80
»«
10.0
12.0
S u l f u r Composition i n I n c l u s i o n s
Figure
(76)
(at.
S)
- I n c l u s i o n chemical composition (oxide and s u l f i d e phases) i n a r o t o r s t e e l d e o x i d i z e d with three d e o x i d i z e r s ; R-RS-I, R-RS-II and R-RS-III.
327
(c)
Figure
(77)
-
(d)
S e g r e g a t e e n r i c h e d i n A l (40 a t . % ) , C a (41 a t . %), S i (17 a t . % ) a n d Mn ( b a l a n c e ) i n t h e r o t o r steel deoxidized w i t h Al-65 wt. % S i . (a) A l , (b) C a , ( c ) S i a n d (d) M n , 250 X. t
328
401—i—i—i—i—i—i—i—i—r—r
Calcium conlent of steel ppm
Figure
(78)
- I n c l u s i o n " p r e c i p i t a t i o n sequence"in a s t e e l c o n t a i n i n g two l e v e l s of s u l f u r .
329
Figure
(79)
S t a t i s t i c a l determination of the mean i n c l u s i o n diameter (ym). (a) sample from an i n g o t , (b) sample from l i q u i d p o o l .
330
Ca
Al
Ce
Figure
(80) - A l , Ca and Ce d i s t r i b u t i o n i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l by a q u a r t z tube c o n t a i n i n g a RE-wire. (a) BE photograph, 4000 X (b) A l , Ca and Ce d i s t r i b u t i o n a c r o s s the inclusion.
331
Figure
(81) - (a) - BE photograph = 6COO X, and A l , Ca, Ce and La d i s t r i b u t i o n s i n a l i q u i d p o o l CaSi d e o x i d i z e d . La and Ce come from a RE-wire p r e v i o u s l y l o c a t e d i n the s i l i c a t e tube.
332
Figure
(82)
-
(a) - BE photograph, 4000 X and A l Ca and Zr d i s t r i b u t i o n s i n an i n c l u s i o n of a sample e x t r a c t e d from a l i q u i d p o o l d e o x i d i z e d with "hypercal". The Zr was p r e v i o u s l y l o c a t e d i n the s i l i c a tube.
333
Figure
(83)
- Composition p r o f i l e s and maps of an
inclusion
i n a sample e x t r a c t e d from a
(ESR)
d e o x i d i z e d with
"hypercal".
(b), ( c ) , (d)
(e) are A l , Ca,
S, and
Zr.
liquid
pool and
334
(e) Figure
(84)
(f)
- BE photograph (a) * 4000 X and composition maps from an i n c l u s i o n e x t r a c t e d from a l i q u i d p o o l d e o x i d i z e d with " h y p e r c a l " ; (b) Ca, (c) A l , (d) S, (e) S i and (f) Zr.
335
Figure
(85) - I n c l u s i o n d i s t r i b u t i o n i n a d e n d r i t i c s t r u c t u r e o f 1 0 2 0 - s t e e l samples t a k e n from l i q u i d p o o l during r e f i n i n g . ( a ) , (b) and (c) show commonly f o u n d i n c l u s i o n s i n a n A l - d e o x i d i z e d ingot. (a) 50 X, (b) and (c) 170 X.
336
337
Figure
(87) - Isothermal (1823°K) p r e c i p i t a t i o n (Fe-Al-Ca-O-S) diagram at 0.1 a c t i v i t y of aluminum.
338
Figure
(88, - E f f e c t o f the a c t i v i t y o f A l (h
=
0.001
Symbols: A
- A1 0
S C-6A
- MnS (11,111) - CaO-6Al 0
C-2A
I ?a"2A? 0 ^ " ' "2 3
C-A
- CaO.Al 0
C
- CaO
A
(l)
2
3
2
2
-
A 1
2°
( 1 3
)
3
3
(
C
a
'
M
n
)
S
°
r
C
a
S
339
Figure
(89)
- E f f e c t of the a c t i v i t y of S (h
= 0.1,
0.01
0.001) on the " p r e c i p i t a t i o n sequence" of c a l c i u m aluminates. Symbols are d e f i n e d i n F i g u r e
(88).
and
340
(b) Figure
(90) - I n c l u s i o n s e x t r a c t e d from a C a - S i - d e o x i d i z e d i n g o t by the Iodine-Methyl Acetate-methyl a l c o h o l method. (RIII-Il-Sl-SLD). Photographs were taken a t : (a) 3000; ( a ) and (b) 8000 X. 1
341
(a)
(b)
(c) Figure
(91) - I n c l u s i o n s e x t r a c t e d from a C a - S i - d e o x i d i z e d i n g o t by the Iodine-methyl a c e t a t e - m e t h y l alcohol"method. (RIII-I1-S3-SLD). (a) and (b) 4000 X and (c) ^ 1000 X. (calcium aluminates)
342
Figure
(92a)
- Calcium aluminate/calcium s u l f i d e i n t e r f a c e s of inclusions i n CaSi deoxidized ingots, (a) and (b) a r e SEM and EPMA p h o t o g r a p h s 1.2 x 1 0 and 6.0 x 1 0 X. (b) a l s o includes Ca and S a n a l y s i s . (c) a r e t y p i c a l compo s i t i o n s o f c o r e and p e r i p h e r y o f i n c l u s i o n s , respectively. 3
3
343
Figure
(92b) :
S p h e r i c a l c a l c i u m aluminate (core) v/ith ( p e r i p h e r a l ) s u l f i d e phases i n CaSi d e o x i d i z e d i n g o t s (a) and (b) EPMA photographs. ( c ) , (d) and (e) are A l , Ca and S maps, r e s p e c t i v e l y .
344
RII-I2
Figure ( 9 3 )
- Secondary d e n d r i t e arm spacing i n a round 1 0 2 0 MS — ESR i n g o t .
345
RIII-Il
ingot
Figure
(94) - S e c o n d a r y in
radius
dendrite
d i a m e t e r ) ESR
arm
ingot.
(cm)
spacing 1020
m
°
U
l
d
W
a
l
1
i n a round MS.
(200
346
R-4340 (1)
wall
Ingot Radius (cm)'
(95) - Secondary d e n d r i t e arm spacing i n a round i n diameter) ESR-ingot (4340)'.
(200mm
347
RII-I2
8 Ingot r a d i u s
Figure
9
mold wall
(cm)
(96) - R a d i a l s i z e d i s t r i b u t i o n of i n c l u s i o n s i n an A l deoxidized ingot.
348
RIII-Il
u
cn
-u
0)
e
3
o o R
(0 •H Q C O
•H tfi i H CJ
c
o o
o o
o
o
o o
o
o o
8 §
o o
8
A 3 measurements same points • average large dia. inclusions measurements o average value from one picture 1
I
i
i
i
4
i
'
5
6
Ingot Radius
Figure (97) - Radial i n c l u s i o n deoxidized ingot
(cm)
-I
8
I
9 mould w a l l
s i z e d i s t r i b u t i o n i n a low Ca(1020 MS).
349
RIII-Il
Figure
(98)
- Radial inclusion size distribution ESR i n g o t . ('5-biggest i n c l u s i o n s
i n a 200 mm technique')
350
R 4340
->
(1)
r
5.0
CD
4.0
+J
CD
E nJ
•H
Q
3.0
C O -H
CO
H U C
CD tn rd S-i CD >
2.0
1.0
8 Ingot
Figure
Radius
mold wall
(cm)
(99) - R a d i a l i n c l u s i o n s i z e d i s t r i b u t i o n i n a 4340 i n g o t (200 mm i n d i a m e t e r ) d e o x i d i z e d w i t h Ca-65% S i A l l o y .
351
TABLE Modification
Ideal
to Stokes'
condition
Correction wall
due
Law
I for Deviation
U
to
crucible
=
2
no
9
—
u = u
Ideality
2
9
(1
s t
from
=
r
U
s t
bJL)
+
distance of p a r t i c l e from w a l l b
Presence
of
other
particles
s 0. 5 t o
U = U
2
. / (1 + st
K*
/,) 3
* = concentration by v o l u m e K =
Inertial
effect
U = U Re
Liquid
particle
Presence agents
of on
1.3
s t
to
/(1
surface active liquid particle
^ st
+
I
particle-fluid
3
number
+
2-j
v
+
u'
st
2u
+
3p
Br + of
particle
3p'
of
coeff.
E
of
viscosity
. st
D
particles
Re)
= retardation
S l i p at the interface
of
1.9
= Reynolds
U = 0
center
liquid
particle
+ 1
Y +
n
3y.
coefficient
2L
;
sliding
friction
• st<li-H' U
= =
6 ' ( e x p ' a ' S (W slip
factor
k
- K
)/kT)-l)
Non-spherical
particles
9 r ^
X
v
= equivalent
g
X = dynamic
R
eq
r
=
, 7
X
radius
shape
factor
J sed
R
, = sedimentation sea
radius
x = f(x ) B
X
Slightly
deformed
inclusion
v
= coef.
S
=
of
2 Ap_ 3 u
sphericity
g r g
;
1 3
( 3 + | Re + j i -
We)
2rp Re = R e y n o l d s number 2rp,U We = Weber number * o r
= inclusion
radius
= density
of l i q u i d
o = surface
tension
U
J
metal
TABLE I I - A Data f o r I n v a r i a n t
Equilibria
i n Fe-S-0 System
-RT Invariant
Equilibria
pO^i
atm
P S 2 / atm
I.
560°C
Iron, wustite magnetite, p y r r h o t i t e , gas
4.8
X 10~
2 7
II.
915°C
Iron, wustite pyrrhotite, l i q u i d ( 1 ) , gas
3.2 X 1 0 ~
1 7
III.
942°C
Wustite, magnetite, pyrrhotite, l i q u i d (1), gas
1.1 X l o " " *
Composition of
a t 915°C:
C o m p o s i t i o n of l j a t 942°C:
5.5
N^ N
e
F e
-
1
2.2 X l o "
8
5.4
1
X lO
"
X 10~ * 6
in p0 kcal
2
-RT i n p kcal 2 g
100.3
50.5
89.6
41.6
77.6
29.3
= 0.50,
N
Q
= 0.19,
N
g
=
0.31.
= 0.49,
N
Q
= 0.19,
N
g
=
0.32.
a
Fe =
0.09.
LO
354
TABLE I I - B Estimated
Data
f o r Invariant Equilibria
Fe-Mn-S
a n d Mn-S-0 T e r n a r y
Fe-Mn-0 t e r n a r y
1527°C
Solid Liquid
system
800
iron:
a
oxide: oxide:
a
=0.65
FeO
FeO
- ° -
ternary
= 0.35
o
3
0.27 MnO
Solid
(Fe) s u l f i d e :
a
FeS
Solid
(Mn) s u l f i d e :
a
MnS
sulfide:
Solid
oxide:
Solid
sulfide:
Liquid
oxysulfide:
ppm S
1
°'
3
7
= 30 w t . p e t . S
= 1.0 X 10~ atm 7
system
Traces *MnO
o f S and 0 ° -
S
>MnS ~'
9
8
° '
9
8
3 0 % Mn, s 3 5 % S , s 351 0
E
p„
Gas:
£
2 1 w t . p e t . Mn p„
manganese:
83
15 ppm Mn
Mn-S-0 t e r n a r y
1230°C
MnO
system
iron:
Gas :
B
7
a
9
Gamma
Liquid
ppm 0
1130
1.2 X 10 ~ atm
Fe-Mn-S
Liquid
52 ppm 0
ppm Mn
Gas :
980°C
Systems
5 80 ppm Mn
6-iron: Liquid
i n Fe-Mn-0,
= 7.6 X
10
_ 2 0
atm
p_ b
"2
= 1.5 X 10" 2
atm Solid Liquid 1225°C
manganese: manganese:
Traces
o f S and O
Traces
o f S and 0
Solid
oxide:
MnO
Solid
sulfide:
MnS
s 0.98 = 0.98
= 5.8 X 1 0
Gas: w
2
atm
_ 2 0
atm,
p
= 1.2 X 10
_i
2
TABLE I I I E s t i m a t e d Data f o r I n v a r i a n t E q u i l i b r i a i n Fe-Mn-S-0 Q u a t e r n a r y System y-iron Solid =900°C
Solid
= 10 ppm. (Mn) s u l f i d e :
a
(Fe) s u l f i d e :
MnS FeS
= 0.4
M
s
1
g 0.5
a
a ^
Liquid
s 26 p e t . FeO, 54 p e t . FeS, 15 p e t . MnS and 5 p e t . MnO by w e i g h t
Solid
(1) o x y s u l f i d e :
p0
Fe/Mn:
"MnS" =1225°C
> 1 ppm. 0
Fe(Mn)0 o x i d e :
Gas:
II.
a
Mn
"MnO" Liquid (1): Liquid (2):
2
s 3.8 X 1 0
F
_ 1 8
atm,
pS
2
= 1.4 X 1 0 "
8
g
0
= 0.5
atm
90 p e t . Mn MnS MnO
s 1 = 1
s 0.1 p e t . FeO, 0.3 p e t . FeS, 65.2 p e t . Mns and 34.4 p e t . MnO by w e i g h t (pet.
O/pct. S) f o r 1
2
(metallic)
< ( p e t . O/pct. S) f o r l j ( o x y s u l f i d e )
Ul
356
TABLE Calculated for
and
Fe-O-Ca-Al
Published Free
Energy
System
K
Equation
Ca(g)
=
Al(l)
1/2
2 Al + C a +
372
1/2
2 Al + Ca
%)
0 , ( g ) = 0 ( 1 wt.
0
0
2
=
%)
-1
2°3
2°3
CaO = CaO-Al 0
CaO
+ Al °
3
CaO
+
2
M
2
CaO
+
6
A1 0
2
2
0 2
3
3
Data
(1550°c/
2 1 6
Atom
'
Ref.
50 (-39
574 .68 481 . 52 +
49.4T)
-114 (-63
137 . 1 220 .68
27.93T)
-122 (- 1 1 7
= CaO
2
3 0 = Al
+ 0 =
A 1
a t 1823
J/kg
C a ( l w t . %)
= A l (1 w t .
IV
Sigworth"''
Sigworth''' -
498 .9 230 .4 -•
Elliott
085
230 . 1
JANAF
3
-437
996, .22
JANAF
3
-489
480. .46
-366
081. .65
-45
845 ..46
3
= Ca0'2
A1 0
3
-50
869 .,62
Kireev^
3
= CaO-6
A1 0
3
-60
708. ,60
Taylor
CaO-Al 0
3
-901
407 .,57
-1
395
9 1 2 . 20
-3
363
6 7 3 . 03
Ca
+ 2 Al + 4 0 =
Ca
+ 4 Al +
Ca
+
12 A l + :19 0
Ca
+
S =
2
2
2
7 0 = CaO-2
A1 0 2
= CaO-6
3
A1 0 2
3
CaS
-257
1.
G.K.
Sigworth
and J . F . E l l i o t t :
2.
J . F . E l l i o t t a n d M. A d d i s o n - W e s l e y Pub.
3.
JANAF T h e r m o c h e m i c a l E d i t i o n , 1971.
4.
V.A. K i r e e v : p p 3-18.
5.
J . Taylor:
Sb. T r . Mosk.
Proc.
Brit.
Met•
S c i . , 1 9 7 4 , v o l . 8, p p .
Inzh-Stroit,
Soc,
298-310.
f o r Steelmaking,
2nd e d . , N a t i o n a l S t a n d a r d
Ceram.
5
659 . 0
Gleiser: Thermochemistry Co., 1960. Tables,
2
2.89T)
Inst.,
Ref.
1971, v o l . 69,
1 9 6 7 , v o l . 8, p p .
115-23.
TABLE V E q u i l i b r i u m Constants
Compound
A c t i v i t y Product
CaO
1
2
l / ( h 3
CaO-2 A 1 0
3
CaO-6 A 1 0
3
2
2
2
(
h C
CaO-Al 0
A1 0
/
1
1
h
/(
h
1 / ( h 3
Ca
/(
X
h
0
X
h
Al
a
C
a
C
a
Al
(216) Reactions
f o r Deoxidation
)
X
X
h
Al
X
X
h
Al
X
X
h
0
K (1823 K)
)
X
h
0
h
0
)
^
>
}
6
,
3
-
0 5
X
4
6
X
1
l o l
q
2
°
5
9.46 X 1 0 )
2
'
1 3
1
'
X
0 4
1
X
q
1
9
q
3 9
6
1
4
TABLE Equations
of Lines
Al 0 -CaO-6Al 0 2
3
2
C
X h
a
A l
3
X
2
/ h
3
2
h
C
h
2
3
3
X
C
=
O
h
=
3
X h
a
h• , { Al
2 / 3
2
3
a
X
h„
Q
Y h X h„ 0 h
/h { 2
3
CaO-Al 0 (solid)^030(42 3
h
h
h
CaO
10~
X
10"
1 3
5
8
2
1.59
,
0
1
X
X
1
0
10"
"
1 2
5
=
7.90
X
10"
=
2.24
X
10"
=
1.90
X
10
=
1.18
X
10"
8
-OaO-Al^ h
2
2.13
X
= 2.82 X l O "
Q
/h {
a
6.01
3
2
C
=
3
X h
a
A l
h
CaO-2Al 0
O
h
CaO-6Al 0 -CaO-2Al 0
=
Q
Ca l(
h
the I n d i c a t e d Phases
3
h
h
Between
VI
C
A l
h
h
3
X
/h {
a
A l
3
X
h
/h { 2
c
a
=
pet.) + A 1 0 2
0 3
1.89
=
=
7
X
10 10"
(liquid)
1 2
5
X lO"
7
(42.6 p e t . )
3
5
X
1.20
=
Q
5
(58 p e t . )
3
2.27
=
3
X h
a
=
Q
(57.4
C
2
0
h
2
C
( s o l i d ) -CaO h
X h
a
pet.) + A 1 0
1 2
3.29
-
7
7
X
5.70
X
1
0
10
~
-
1
6
X lO"
6
(liquid) 1
TABLE
VII
Chemical A n a l y s i s of E l e c t r o d e s Electrode 1020 M S t e e l (1)
Used i n t h i s
Research:
Chemical Composition i n wt.% Rotor S t e e l
4340 -
Steels
(1)
(2)
(1)
(2)
c
0 . 19
0 . 415
0.422
0.213
0 . 202
p
0 . 099
0 . 014
0.014
0 . 007
0.007
s
0.026
0.016
0.015
0.005
0 .006
Mn
0 . 709
0.697
0.696
0.673
0 . 673
Cu
-
0.094
0.091
0 .049
0.048
Ni
-
1.882
0 . 184
0 .357
0.0362
Cr
-
0 . 873
0. 867
1. 151
1.1150
Si
0 . 25
0.357
0.353
0 . 246
0 . 244
V
-
0. 005
0 .005
0 . 246
0 . 244
Mo
-
0. 189
0.188
0.940*
0.940*
Al
-
0 . 029
0.029
0.006
0 .006
0.005
0 .005
0.005**
0.005*
Sn
where and
(*) stands f o r more than 0.940 wt.%
(**) i n d i c a t e s l e s s than 0.005 wt.%.
TABLE V I I I
Run No.
1
Type o f Electrode
4340(I)
2
•'
3
••
Electrode D i a m e t e r (mm)
5
••
8
••
3
2
30
20
-
55
15
15
15
40
20
20
20
40
22
23
5
55
15
22
8
31
0
46
23
50
30
20
-
"
55
15
15
15
50
30
20
-
55
15
15
114.3
49
16
17
76. 2
70
0
30
114 ,3
70
15
15
"
70
0
30
••
50
20
30
76 . 2
50
30
20
9
4340(II)
44 .75
10
4340 ( I I )
"
11
rotor
steel
2
50
6 7
2
"
»
List
I n i t i a l Slag Composition CaF /Al O /CaO/SiO /Mg0
31.75
4
-
of
Type o f Deoxidizer
-
Nil
-
Al
-
Experiments
No.
of Additions Rates
-
-
Al
along
remelting
Type o f A d d i t i o n (deox.)
Deoxidation (kg t o n
-
- 1
rates )
2.3
constant
kg t o n
_i
"
-
Ca-Si
15
-
Ca-Si
12
6
Al
"
-
Al
"
-
Al
-
Al
Ca-Si
2
-
Ca-Si
2
Nil
-
Al
4
Al
5
constant
^
0.0 2 k g t o n
M.S.
76.2
70
30
-
M.S.
76.2
50
30
20
-
50
30
20
-
-
»
50
30
20
-
-
••
60
36
4
-
-
Ca-Si
4. 5
'•
50
30
20
-
-
Ca-Si
6
5.61,11.23,16.83,2; 28.05 and 56.10 .
88.9
50
30
20
-
-
Ca-Si
6
4.17,8.35,12.5,16. 20.85,41.7, and 20
114 . 3
50
30
20
R-RSII
50
30
20
-
R-RSI 11
50
30
20
-
12
1020
13
rotor
M.S. steel
14 15 RII-W RIII-W RI-Il
" 1020 1020 1020
M.S.
RII-Il RII-I2 RIII-Il
"
RIII-I2 R-4340
4340
R-RSI
rotor
steel
-
Al
Ca-Si Al-Si Hyperca1
" "
II
II
"
"
a long remelting
intermittent
continuously increasing
50 g r a m s
(each)
50 g r a m s
(each)
-
3.63, 6.1 a n d 3 7.6 k g t o n 1.21, 2.42, 3.6' 4.85,6.06 and 12.1/
"
constant
5.61,11.23,16.83,2; and p a r t i a l l y 28.0J
36.0 kg t o n
constant
33.0
constant
36.0
- 1
oo
o
361
TABLE Chemical
IX
Composition
of Deoxidizers
Calcium-Silicon
Hypercal
Al-Si
Calcium
29 .. 50
10,.50
-
Silicon
6 2 . . 50
39,.00
65
Iron
4 ,. 50
18,.00
-
Barium
0. . 50
1 0 , . 30
-
Aluminum
1.. 20
20 ,. 00
35
Manganese
0 ,. 2 5
0 .. 30
Carbon
0 .. 55
0 ,. 50
Chromium
0 .. 10
0 ,. 0 3
Copper
0 ,. 0 1
0 .. 03
Nitrogen
0 .. 0 3
0 ,. 0 5
Nickel
0 .. 0 1
0 ,. 0 2
Oxygen
0 .. 50
0 ,. 7 0
Phosphorous
0 .. 0 1
0 ,. 0 2
Sulfur
o ,. 0 5 5
0 ,. 12
Titanium
0 ,. 0 8
0 ,. 06
Bulk
Density
110 l b . / c u .
f t . 95 l b . / c u . f t .
TABLE X Inclusion
Chemical
Deoxidizer
a
No.
)
Inclusion
Nominal
CaF
2
Slag
A1 0 2
3
i n 4340
Chemical
System
CaO
Composition
1
50
30
20
-
2
55
15
15
3-
40
20
4
40
5
6
Atom
Al
2
diameter)
Composition
(wt.%)
Si0
(small
as a F u n c t i o n o f S l a g and ESR
Ingots
as a F u n c t i o n of Slag
Percent
Ca
Types
System
of Inclusions
Si
96.1
3.733
15
75.86
1.8470
22.28
20
20
85.33
2.470
13.160
22
33
5
99.20
0.19
0.60
"Alumina", sulfides
55
15
22
8
96.27
3.462
0.265
"Alumina" and Caaluminates, "Fayalite"
31
0
46
23
84.88
4.38
b)
Slag-Deoxidant
wt. %
Effect
(X)
0.170
10.74
on F i n a l
at. %
Calcium aluminates, Manganese s u l f i d e s Alumino-Silicates, Manganese s u l f i d e s , and "Fayalite."* Calcium, Aluminums i l i c a t e s , Manganese s u l f i d e s and " F a y a l i t e " * Manganese
Calcium-alumino silicates. Manganese s u l f i d e s and "fayalite".*
Inclusion
Chemistry
(X)
+ No.
CaF
CaO
Si0
7
50
30
20
-
Al
92.42
7.11
0.170
Calcium Calcium
8
55
15
15
15
Al
89.20
7.85
2.940
Aluminates, Calcium Aluminum s i l i c a t e s and "Fayalite".*
9
50
30
20
- Ca-Si (*)
91.00
7.20
1-80
Calcium aluminates, Manganese s u l f i d e s
10
55
15
15
15 C a - S i (*)
2
A1 0 2
3
2
Deox.
Al
Ca
76.217 2.143
Si
21.64
aluminatessulfides
Aluminum c a l c i u m s i l i c a t e s , f a y a l i t e * and Manganese sulfides
c)
Inclusion
Chemistry
E l e c t r o d e s f o r 1 t o 8 (31.75 im)
Al 89.00
E l e c t r o d e s ! * ) f o r 9 and 10 (44.75 nm)
81.08
of Electrodes
Ca Si 10.00 balance 5.237
Calcium Aluminates calcium sulfides 13.685 A l u m i n u m C a l c i u m silicates and
Remarks:
1. 3.
Manganese
sulfides
Melting rates 1.2 - 1.5 Kg m i n . , 2. d e o x i d a t i o n r a t e " ^ 2 . 3 Kg t o n F a y a l i t e * was not always observed t o f o l l o w the t h e o r e t i c a l s t o i c h i o m e t r y . - 1
- 1
TABLE Chemical
Effect
of
(Extension
Slag of
and
R e s u l t s Found 1020
Ingot
Electrode
Type
Nominal
CaF
2
CaO
Electrode
A 1
Steels
Slag
2°3
XI
S u r f a c e P r e p a r a t i o n on
i n 4340
to a
Small
Cr-V-Mo
Rotor
Composition
s
i
0
2
M
g
and
Large
Inclusion
Composition
ESR-ingots,
and
Steel*
Inclusion
Type
and
Shape
0
* 11
rotor
steel
49
16
17
12
12
rotor
steel
70
15
15
-
6
A l - C a s i l i c a t e s and a l u m i n a t e s . Semiround types; they were o c c a s i o n a l l y seen w i t h p e r i p h e r a l MnS. Mg t r a c e s w e r e a l s o d e tected . -
Aluminates A1 0 . 2
and
3
of
the
Round,
clusters
type
Fe0-Al 0
elongated
and
angular
2
and
3
(FeO-Al 0 ) 2
3
A1 0 . 2
3
* 13
rotor
steel
14
rotor
steel
70
30
-
-
A l u m i n a t e s , s i n g l e r o u n d and c l u s t e r s . I r o n o x i d e s a n d some i r o n s u l f i d e s w e r e also observed.
*
15
1020
50
20
30
-
70
-
30
-
-
A l u m i n a t e s , s i n g l e r o u n d and c l u s t e r s a minor amount o f r o u n d C a - a l u m i n a t e s MnS I I . -
Aluminates
generally
as
clusters
and
and and
MnS
II.
Remarks 1. 2. 3.
T h e s e E S R - i n g o t s w e r e s l i g h t l y d e o x i d i z e d w i t h A l a t a c o n s t a n t r a t e , 0.02 Kg t o n ^. E l e c t r o d e s 11, 12, 13 a n d 14 w e r e s u r f a c e g r o u n d a n d c o a t e d w i t h a n A l - M g s p i n e l p a i n t i n g p r e v e n t s c a l e ("FeO") o x i d e f o r m a t i o n d u r i n g r e m e l t i n g . E l e c t r o d e and E S R - i n g o t c o m p o s i t i o n a r e g i v e n i n T a b l e s ( V I I ) and (VIII).
4.
Refining 1 Kg
min
conditions
were
equivalent
f o r a l l experiment,
Ar-atmosphere
and
melting rates
to
about
TABLE Slag
Chemical
Analysis
from
XII
(Ni-Cr-Mo) R o t o r
Deoxidized with CaSi, A l S i
and CaF
Nominal
(initial)
Hypercal*
slag
CaO
A1 0 2
3
Si0
"FeO"
2
20
30
CaSi**
47.33
20.15
32.2
0.175
AlSi
43.32
18.27
38.11
0.141
43.51
18.19
37.88
0.25
Si alloy)
(wt.%)
2
50
(Ca, A l , Ba,
composition
ESR-ingots * Ca-Al-Ba-Si Alloys
0.14 .
0.147 0.165
* * Remarks:
D e o x i d a t i o n r a t e u s e d i n t h i s e x p e r i m e n t was s l i g h t l y l o w e r t h a n i n t h e o t h e r two e x p e r i m e n t s , i . e . ^ 33 grams/min and ^ 36 grams/min respectively. R e m e l t i n g c o n d i t i o n s were a p p r o x i m a t e l y c o n s t a n t f o r t h e a b o v e r u n s , i . e . , m e l t i n g r a t e s were ^ Kg/min. E x p e r i m e n t s were c a r r i e d o u t u n d e r a p r o t e c t i v e atmosphere (argon).
cn
TABLE XIII - A Chemical
A n a l y s i s (wt.%) o f a Cr-Mo-Mn-Ni-V-Steel Deoxidized
w i t h Al-65.0 wt. % S i
C
P
s
1
0, . 261
0 .008 .
0 .003
0 .707 .
0.,050
0 ., 353
1. 176
0 ,594 .
2
0 . 252
0 .007 .
0.,003
0., 700
0..051
0,. 369
1. 165
3
0 . 255
0..007
0..003
0 .695 .
0 .050 .
0 . 350
4
0.. 253
0..007
0..003
0..695
0.,050
5
0.. 251 '
0 .007 .
0..003
.0.,689
6
0 .249
0..007
0..003
7
0 . 255
0,.007
8
0 . 250
9 10
Mn
Cu
Ni
Cr
Si
V
Mo
Al
0 .239
.94 +0 ,
+ 0 .250
-0 .005
0., 536
0 .246
+ 0,.94
+ 0,.250
-0 .005
1., 160
0., 532
0 .242
+ 0 .94
+ 0 .250
-0.005
0 . 348
1. 160
0.. 536
0. 242
+0 .94
+ 0 .250
-0.005
0..051
0 . 362
1.. 147
0 . 536
0 .245
+ 0 .94
+ 0 .250
-0 .005
0,.691
0..049
0 . 355
1.. 155
0 .534 ,
0 .241
+ 0 .94
+ 0 .250
-0.005
0,.003
0 .693
0,.051
0 . 354
1.. 155
1 0 ., 538
0 .243
+ 0 .94
+ 0 .250
-0.005
0 .007
0 .003
0 .695
0,.051
0 . 359
1.. 160
0 . 538
0 .243
+ 0 .94
+ 0 .250
-.0.05
0 . 260
0 .008
0 .003
0 .701
0,.052
0 . 361
1,. 161
0 . 539
0. 245
+ 0 .94
+ 0 .250
-0 .005
0 .254
0 .007
0 .003
0 . 694
0 .052
0 .361
1 . 154
• 0 . 543
0 .246
+ 0 .94
+ 0 .250
-0 .005
Sn
TABLE Chemical
Analysis
(wt.%)
Deoxidized C
P
c
1
0 . 262
0 .007
0..002
2
0 .271
0..007
3
0 .242
4
pie
No.
Mn
XIII
- B
o f a Cr-Mo-Mn-Hi-V
with
a Ca-Si
Steel
Alloy
Cu
Ni
Cr
Si
0,.691
0 .049
0 .337
1.103
0 .627
0 . 247
+0 .94
0.. 157
-0 .005
0 .002
0 .696
0 .048
0 . 334
1. 116
0 .674
0 . 236
+ 0,.94
0.. 150
-0 .005
0 .007
0 .002
0,. 673
0 .046
0 . 321
1.091
0 .646
0 . 235
+ 0..94
0.. 147
-0 .005
0 . 258
0,.007
0,.002
0,.688
0 .045
0 . 324
1.118
0 .650
0 .235
+0,.94
0 .117 .
-0 .005
5
0 .266
0..007
0..002
0..691
0 .04 8
0 . 343
1.115
0 .648
0 .244
+ 0..94
0 . .126
-0 .005
6
0 . 226
0,.007
0..002
0..690
0 .047
0 . 340
1. 119
0 .654
0 . 242
+0..94
0 . 126
-0 .005
7
0 . 273
0..007
0..002
0 . 687
0 .047
0 .341
1. 116
0 .652
0 .652
+ 0..94
0 . .125
-0 .005
8
0 .264
0..007
0..002
0.. 680
0 .046
0 . 337
1. 1031
0 . 645
0 . 240
+ 0..94
, 121 0 .
-0 .005
9
0 . 273
0.,007
0 .002 .
0.. 685
0 .048
0 .351
1. 114
0 .660
0 . 246
+ 0 .94 .
0., 121
-0 .005
10
0 . 276
0..007
0..002
0., 687
0 .047
0 .332
1. 118
0 . 652
0 . 241
+ 0..94
0 ., 119
-0 .005
11
0 . 228
0..007
0..002
0., 700
0 .049
0 . 355
1. 125
0 . 665
0 . 245
+ 0..94
, 122 0 .
-0 .005
(+) - m o r e
than
a certain
calibration
(-)
than
a certain
calibration
- less
V
Mo
Al
Sn
cn
TABLE
XIII-C
Chemical A n a l y s i s of a
Cr-Mo-Mn-Ni-V-Steel
Deoxidized with a Ca-Si-Al-Ba
%C
9
p
%s
%Mn
%Cu
? Ni
%Cr
Alloy
Si
V
%Mo
%Al
Sn
1
0 . 253 0 008
0. 004
0.706
0.056
0 366
1. 126
0 815
0 229
+0 .94
+ 0 .250
-0 005
2
0. 255
0 007
0. 003
0.702
0.053
0 366
1. 146
0 772
0 241
+ 0 94
+ 0 250
-0 005
3
0. 253
0 008
0. 004
0. 704
0.051
0 34 7
1. 160
0 757
0 234
+ 0 94
+ 0 250
-0 005
4
0. 267
0 008
0. 004
0.718
0.052
0 356
1. 174
0 774
0 236
+ 0 25
+ 0 250
-0 005
5
0.263
0 008
0. 003
0.714
0. 056
0 382
1. 164
0 793
0. 248
+ 0 94
+ 0 250
-0 005
Ul CTi
TABLE
Example
Sample No.
of inclusion
Inclusion No.
size
XIV-A
distribution
Shape
i n Rlll-Il-LQD-Sample
Florescence under the e l e c t r o n beam
1.
Diameter i n pm
1
round
blue
4. 5
2
elongated
blue
5.0
3
semiround
blue
6.0
4
elongated
blue
7.0
5
round
blue
4.5
6
S-shape
blue
6.0
7
round
blue-green
6.0
8
angular
blue
4. 5
9
duplex-round
2-blue
5.0
10
round
blue
4.0
11
triangle
blue
5.5
12
duplex
blue
8.5
13
elongated
blue
5.5
14
elongated
blue
5.5
15
triangle
blue
5.5
16
angular
blue
4.5
17
elongated
blue
6.5
18
round
light-blue
8.0
19
duplex
2-blue
8.0
20
irregular
blue
6 . 0
21
round
blue
8.0
22
round
blue
6.0
369
TABLE Example
Sample No.
of
Inclusion
Lusion No.
Size
XIV-B
Distribution
Shape
i n RIII-Il-SLD-Sl
Fluorescence
Diameter i n ym
1
semi-round
blue
4.0
2
elongated
blue
6.0
3
round
violet
5.5
4
elongated
blue
4 . 5
5
round
blue
4. 5
6
irregular
blue
5.5
7
elongated
blue
5.5
8
round
blue^
8.0
9
irregular
blue
6.0
10
elongated
blue
5.0
11
round
blue
6.0
12
in a clusterround
blue-green
5.5
13
in a clusterround
blue
6.5
14
elongated
blue
5.0
15
round
blue
5.0
16
half-moon shape
blue
7.5
17
elongatedirregular
blue
5 .0
18
elongated
blue
5.0
19
elongated
blue
4 .0
20
elongated
blue
5 .0
TABLE Data
of Plot
Equilibria
V
Al 0 /CaO-6Al 0 /CaS 2
3
2
1.4155
3
6Al 0 -CaO/CaO-2Al 0 /CaS 2
3
2
1.995
3
CaO-2Al O /Ca0-Al 0 /CaS 2
3
2
3
+ CaO-Al 0 /(CaO)* 2
+
+
C
*
s o l i d
0
t +
+
a
+
Slag 3
a
CaS CaS
CaS
+
3
/
(
C
a
0
)
t
( A l ^ W C a S
(Al 0 ) /Cas
+
compositions = ° =
0
3
" ,
*
°- *8 9
~
3
according A
l
2
-1.0,
o
a
A
l
Ca
x 10'
x 10~
0.758 x 10 -3
3.360
x 10
4 x 10~
6.87
3
1.35 x 10"
a, CaO
^
suggest
a
0.8
CaO
(238,239) f r o m Sharma a n d R i c h a r d s o n @
Y
This
i s also
/ J
an average v a l u e
=
Y
x
1.4228
7.85
- !
2.5 -8
^
h
x 10
x 10~
1.2457
9
1.35 x 10
4
x 10
x 10"
-4
-3
K
h
x
10
!-567
x
10"
1-0
-3
@ 1650°C
X
CaS
0
568 '
Y
x
9-61
%
X = 1 x 6.3
x
10 10
3
x
(1550°C)
- 2 x 10~ . 3
and
a
v r
CaS(1650°C)
=
'
l
x lo"
65
CaS(solid)
-5
2-014
1.2156
3
3.84 x 10
Al O
- 0.9 = 0
a
and
C a S ( l ii q u i d )
since
x 10~
9
S
0.0625
0.1,
v /< CaS(solid)
Al
p s e u d o - b i n a r y d i a g r a m a t 1827°
C
They
S
x 10 -10
2.3155
x 10"
U
a
(87 - 8 9 )
S
to the C a O - A l ^ 2 3
0.7,
3
Figures
1.83
^
+
2
h
XV
l^fifl i
b
6
B
0
-
5
5
5
10~
6
371
TABLE
and
e
e^
=-5.25,
A 1
a
XVI
= -62,
%Ca Equilibrium (invariant)
«? = -
%0
(1)
1 x
10"
(2)
2.5
(3)
.5 x
(4)
8 x
10"
(5)
1 x
10"
x
and
2.65
3
10~ 10~
3
2.6
x x
%A1 10~ 10~
2
2
%S
2.35
x
5 x
10~
2
5.35
x
10
10~
2
3.95
x
10
2.75
x
10
1.56
x
10'
2.35
x
10~
2
1 x
3
2.27
x
10"
2
1.2
2
2.15
x
10"
2
1.89
3
4 0
x
10"
10~ x
3
2
10"
2
7.4
x
10" 2 2 -2 2
TABLE XVII Computed Compositions by Using Data i n Table XV
Interaction Parameter e£ Equilibrium (invariant)
Composition
a
Ca
Al
(ppm) 0
(i)
-535
10
15
20
(2)
-400
25
38
32
(3)
-300
65
97
34
ti
(4)
-250
80
120
36
ii
(5)
-200
100
150
42
II
The i n t e r a c t i o n parameter f o r the C a - 0 was assumed v a r i a b l e and the A l - 0 and Ca-S were: e = -62 A l
and -110
TABLE
Effect
of Initial
Growth
During
XVIII
Number
Cooling
of Inclusions of Liquid
on
Metal
Number o f Inclusions Initially
Initial Radius
Final Radius
10 /cc
1 ym
40
72
2
40
72
268. 0
5
40
75
238 . 9
9
40
87
208 . 3
10
40
92
201. 7
1
18
90
5 7 . 37
2
18
91
5 2 . 79
5
19
02
4 2 . 40
"
9
19
56
32. 87
"
10
19
79
30. 98
1
8 78
1 1 . 23
2
8 81
9 .58
5
9 28
6 .38
3
»
10 /cc 4
10 /cc 5
10 /cc 6
"
Growth Time (Lowe r Limi
um
279. 5
9
11
2
4 .15
10
11
88
3. 79
1
4 09
2. 02
2
4 23
1. 5
5
5 77
0. 76
9
9 27
0 .44
22
0. 39
10
10
10 /cc
1
1 98
0. 31
It
2
2 45
0. 19
9
9 03
0. 04
7
"
10
10
02
sees
0. 0 3 9 7
374
APPENDIX Thermodynamic faces
relationships
of s t a b i l i t y
1(1):
(I):
2°3
6 A 1
AG°
l f
2
2
1
4
7
'
1
4
'
8
2
2
C
a
3
0
1
'
6
2
+
o
G
^
[
+
6Al 0 -CaO
a
(
2
3
2
'
2
3
8
'
2
3
9
data
>.
S
]
3
6 A l 0 - C a O + CaS + [0]
=
2
A
the sur-
Al 0 /CaO/6Al 0 -CaO/CaS
+
=
to generate
f o r t h e Fe-Ca-Al-O-S system, u s i n g
from the l i t e r a t u r e
Equilibria
developed
G
O
A
B
=
S
~ "CaS"
3
A
G
-
~ Al 0
a
3
7.082 X 10
A
3
a
~ CaO
a
2
2 A G °
-
^
~
a
3
= RTlnK
Q
I ( 1 )
1
0 = -RT l n [ ^ ] S h
h
l
n
h
1(2):
I(l)
K
1
-
9
5
5
= 1.4155 X 1 0
Q
6 A 1
"
=
2°3
+
2
f
C
a
^
K
h
_ 1
+
i ( l )
h
=
4
-
6
3
2
7
x
h
Ca O S
=
7
'
5
9
4
2
x
h
h
C a
h
h
s
1
0
iO"
= 2.316 X 1 0 "
t
h
2 1
/
1 0
h
O
S
= 6 A l 0 - C a O + CaS 2
]
3
= -1.6781 X 1 0
5
Ca O S h
h
1
I(2)
-1 = —•
10
A - I (1)
[S]
+
x
g
= -RT l n [ - 5 - ^
-RT InK
l n K
i^iss
=
u
s
b
Y
K
i(2)
=
1
-
?n 3
1
substituting
6
8
x
1
0
A-I(l)
A-I(2)
375
1(3):
12 [ A l ] + 18[0] + CaO +
-7.8183 X 1 0
5
[S] = 6 A l 0 « C a O 2
= -RT l n K
-> l n K
l ( 3 )
+ CaS
3
I ( 3 )
= 2.158 X 1 0
2
93 K
I(3)
=
h
Al O
=
h
Equilibria
11(1):
5.46657 X 10
2
'
0
(II):
1
4
X
1
0
and by
AG°
=
6Al 0 •CaO/CaO/2Al 0 «CaO/CaS 2
3
2
3
AG°
AG°
+
[S] = 2 A l 0 « C a O 2
- |(AG°
A S
3
)
A 0
±
f
a
CaS
- |(AG
D
a
CA
"
0
a
CaO
"
a
CA
2
K
0 yh s
I I
II(D
^ j
= 1.4257 X 1 0
1
=
1
'
c
"
1
O
9
5
3
h
thus
) =
I I ( 1 )
"
-RTlnK
+ CaS + [0]
3
2 -RTknK
A-I(2)
A-I(3)
5
| ( 6 A 1 0 - C a O ) + y(CaO) + 2
substituting
= 1.953 X 10
X
-2
1
0
~
4
+ l n K ^ ^ j
=
- 3.9359
3
A-II(I)
11(2):
j(6Al 0 -CaO) 2
2A1 0 2
+ |[Ca] + |[0] +
3
[S] =
«CaO + CaS
3
-RTlnK
3.629
= 1. 3146 X 1 0
I l ( 2 )
X
10
-»• l n K
5
by
II(2)
=
substituting
h
11(3):
Ca S h
£
1
,
1
1
6
0
8
2
x
X
h
Equilbria
2
Al O h
1
q
1
*
5
2
)
2
ca O S h
h
=
-
2
3
1
9
5
x
iO"
1
6
1
0
=
8
~
A-IK2)
9
[Ca] +
[S] = 2Al <D -CaO 2
'
6
0
8
X
l
o
1
5
•* n ( 3 ) K
3
+ CaS
-+
=
2
- 324 4
X
10
3 7
A-II(1)
=
1
(III):
-
7
0
4
X
1
0
~
3
A-IK3)
5
2Al 0 -CaO/CaO/Al 0 •CaO/CaS 2
3
1 3 ( 2 A 1 0 - C a O ) + j CaO + 2
h
= - 3.11824 X 1 0
( l I ( 3 )
II(3)
substituting
III(l):
3
4[A1] + 6 [ 0 ] +
l n K
(
A-II(l)
-RTlnK
by
-
4
l
1
5 K
I
2
3
[S] = A l ^ - C a O
+ CaS +
[O]
377 AG°
=
AG°
-RTlnK
l
f
a
=
S
| ( A G °
~~ C A
a
A
2
~
a
= 1.67697
I I l ( 1 )
= 9.758
-
)
§(AG°
a 0
)
=
X 1 0 " h
2
X 1 0
a
4
CaO
+
L
N
"
1
= -4.63
K I
I
I
(
1
)
A-III(l)
3
g
y ( 2 A l 0 - C a O ) + |(CaO) + [Ca] + [S] = A l ^ - C a O + CaS 2
3
-RTlnK
by s u b s t i t u t i n g
h
Ca S h
=
= 7.0675 X 1 0
I I l ( 2 )
1.95111 X 1 0
111(3):
a
" CaS
3
Q
C
I I I ( 1 )
= RTlnK
h
AG
+
Al 0 .CaO 2
111(2):
A
-»• K
1
I I I ( 2
)
lnK
4
=
I I l ( 2 )
= 2.97546 X 1 0
8
A-III(l)
3
,
3
6
X
1 0
~
A-IIK2)
9
2[A1] + 3[0] + [Ca] +
[ s ] + CaO = A l ^ - C a O + CaS 5
-RTlnK
I I I ( 3 )
5.346 X 1 0
1
= -1.9366 X 10
K I I I (
3)
^
lnK
= 1-6568 X 1 0
I I l ( 3 )
2 3
=
378
by s u b s t i t u t i n g
A-III
(2)
2 h
Al O h
i -
=
Equilibria (IV)
2
1
5
6
!0~
x
A-III
5
:
A 1 0 - C a O / C a O ( 4 2 .0 wt.%) + A1 C> 2
(3)
3
2
58.0 wt. %
3
(liquid)/CaS
IV(1):
2CaO + A l 0 2
-RTlnK
l n K
u
a
0
CaO
=
a
CaO
a.
then
h
2
9
5
8
+
6
K I V
->
4
(1)
=
"5.18915 X 1 0 ~
2
a
S
f
" -
+ CaS + [0]
2
h~
l
=
[S] = C a O - A l ^
= 1.06873 x 1 0
I V ( 1 )
IV(l)
+
3
Q
C a S
CaS
a
A
1
X 5.18915 X l O
0
2
0.0355
= 4.0 X 1 0 ~
2
3
- 0.0625(
=
-
3
2 1 6
'
( 2 3 8
h
2 3 2
'
g
),
2 3 3
a
5
- 0.7
( 2 3 2 )
and
>
A - I V (1)
IV(2):
2 [ C a ] + 2[A1] + 4 [0] +
-RTlnK
K
by
IV(2)
[S] = C a O - A l ^
= -2.8111 X 1 0
=
5
'
0
5
3
3
a
substituting
4
x
1
q
3
+ CaS
->
5
3
= 0.0355
(
2
3
8
'
2 3 9
^
and
A - I V (1)
(-3 O
h
IV(3):
Al O h
f
1
X
1
0
5
A
CaO + 2 [ A l ] + 3 [ 0 ] +
AG
i
=
a
t° =
CaO
=
A G
A l
K ,,>
CA
+
2°3
A G
=
CaS
"
A G
[Ca] +
CaO
-
= 1.65287 X 1 0 —
substituting
-
a
, a L3b
h
Ca S h
=
6
,
8
7
R T l n K
( )
V
[S] = C a O - A l ^
2 3
=
C
X
a
2
+ CaS
IV(3)
[
S
-
a
by
I
1
"
IV(3)
TT7
=
_
CaO
i
.3. T~Al O Ca S 2
h
h
h
h
and A - I V (2) (_,civj
1
0
_
9
A
-
I
V
(
3
)
E q u i l i b r i a (V): CaO
/
C
a
S
( s )
/CaO(57.4
(s)
wt.%)
+ A
l
^ (42.6 wt.%)
(liquid)
380
±
f
a
CaS
0.988 - 1 . 0
B
and a _ s 0.8 CaO n
h
C a
h
s
h
Al O
h
Ca O
h
h
h
S
0
( 2 3 8
.9
s
1.35 X 10
=
9.6 X 10
3.29 X 10
= 2.35 X 10" h
s
2 3 9 )
( 2 1 6
'
,
a
A l O ,
,
=
0.1
( 2 3 2 )
2 3 2 )
A-V (1)
A-V (2)
6
3
Q
8
'
1
1
A-V (3)
A-V (4)
INCLUSIONS
ELECTROSLAG REFINED
IN
INGOTS
by FIDEL Ing.
Quim. Met., U n i v e r s i d a d
M.Sc,
REYES-CARMONA Nacional
The U n i v e r s i t y o f I l l i n o i s
A THESIS SUBMITTED
Autdnoma de M d x i c o ,
a t U r b a n a - C h a m p a i g n , 1978
IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE
STUDIES
Department o f M e t a l l u r g i c a l E n g i n e e r i n g
We
accept
this
t h e s i s as c o n f o r m i n g
to the r e q u i r e d
standard
THE UNIVERSITY OF BRITISH COLUMBIA January
©
Fidel
1976
19 83
Reyes-Carmona, 1983
In p r e s e n t i n g
t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the
requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it
f r e e l y a v a i l a b l e f o r reference
and study.
I further
agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s
thesis
f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . understood t h a t copying o r p u b l i c a t i o n o f t h i s f o r f i n a n c i a l gain
It is thesis
s h a l l n o t be allowed without my
permission.
F i d e l Reyes-Carmona
Department o f M e t a l l u r g i c a l E n g i n e e r i n g
The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date
E-6
(3/81)
March 21, 1983
written
ABSTRACT
The
o b j e c t i v e of
non-metallic chemically to the
this
inclusions
transformed,
final
1020,
were r e f i n e d by
e l e c t r o d e s was
removed and
4340 and
two
electrode
when t h e
are
t i p by
and
by
the
the
how
and electrodes
and
200
the
deoxidation
practices,
transformed
Inclusions
liquid
No
origin
in
the
are
slag at
d i s s o l v e d i n the
formed.
i n c l u s i o n s are
these
found t h a t i n c l u s i o n s i n
presence of
of e l e c t r o d e
i n mould
alloys.
chemically
entirely
mm
R e f i n i n g of
AISi
i t was
droplet i s completely as
and
electrodes
the
matrix
ingot inclusions
and
i t is
concluded
e i t h e r d i s s o l v e d or
removed
slag. The
on
mm
thermal gradients.
they are
a l l electrode
the
CaSiAlBa
p h y s i c a l l y and
were i d e n t i f i a b l e that
(7.5
s l a g systems.
research
a l t e r e d by
film
(Ni-Mo-V) s t e e l
done u n d e r d i f f e r e n t
Through t h i s
liquid
physically
c o n t r o l l e d from
rotor
ESR-units
namely p u r e A l , C a S i ,
chemically
to investigate
( i n c l u s i o n s ) are
diameter) under d i f f e r e n t
electrode
was
ESR-product.
Several
the
research
e f f e c t s o f the
chemical
composition
were t r a c e d d u r i n g i n c l u s i o n s was
refining
d e t e r m i n e d by
m e t a l samples d u r i n g m e a s u r e d by
the
slag with of the and
and
without
liquid
hence the
pool
deoxidizers and
chemistry
e x t r a c t i n g s l a g and
refining.
The
total
vacuum f u s i o n t e c h n i q u e ,
ingot of
liquid
oxygen c o n t e n t chemical
was
analyses
ii
of
s l a g by
spectrophotometric
a n a l y s i s by analysis. the
SEM
and
The
The
EPMA and
assays
deoxidation
and
chemical
techniques,
by
were u s e d t o f o r m u l a t e
precipitation
composition
slags.
inclusions and
The
The
i s the
of cooperative
2
+
3
[Ca]
+
(A1 0 )
+
3
The potential
composition
i n low
o f complex
Al-Ca-Si
silica
30 wt%
2
i n ESR
deoxidation practice
slags
Al 0 2
ingots takes
r e a c t i o n s between s l a g
3
an
and
2
wt%)
efficient
20 wt%
p l a c e by
and
Si0
(>10.0
system t o perform
CaF ,
ingots
the
CaO. process
deoxidizers i n
the
sequences:
[Al]
2
slag
slag
50 wt%
deoxidation
following
the
i s predictable i n high
deoxidation
corroborate
mechanisms.
precipitation
t h e most a p p r o p r i a t e
and
of inclusions i n refined
the e l e c t r o d e or the
content
micro-
x-ray ( c r y s t a l l o g r a p h i c )
a r e more s t r o n g l y i n f l u e n c e d by than
electron
(FeO)
t
( A l ^ )
+
(FeO)
t
(CaO)
Fe
[Ca]
t
3
+
(CaO
Fe
+ 2
[Al]
p r e c i p i t a t i o n r e a c t i o n s a r e c o n t r o l l e d by i n the melt,
thus
the
transitions
t o be
the
oxygen
expected
are : Al 0 «FeO 2
3
+ MnS An
+ MnS
I I I or
I I -»• c t - A l 0 2
(Ca, Mn)
excessive
+ Y
3
I I o r I I I -»• x C a 0 « y
Ca
+
* X CaO* (y - ^)
r a i s e s the A l content
Al 0 2
3
A l ^
CaS
to:
(A1 0 )* 2
+ MnS
S -*• x C a 0 « y A l ^
deoxidation with
ingot according X Ca
3
+ | X
[Al]
in
the
iii
R a d i a l i n c l u s i o n s i z e d i s t r i b u t i o n as w e l l as arm
spacings i n samples e x t r a c t e d
i n g o t s were determined.
I t was
from l i q u i d p o o l
found t h a t the
s i z e obeys the normal d i s t r i b u t i o n and v a r i a t i o n of the i n c l u s i o n Hence the i n c l u s i o n
s i z e along
composition and
l o c a l s o l i d i f i c a t i o n c o n d i t i o n s and thermochemical c o n d i t i o n s .
dendrite and
inclusion
there
i s a normal
radial
distances.
s i z e i s a f u n c t i o n of a l s o of the
local
iv TABLE OF CONTENTS Page Abstract
i
Table of Contents
iv
L i s t of F i g u r e s
ix
L i s t of Tables
xvii
L i s t of Symbols
xix
Chapter I II
INTRODUCTION
1
LITERATURE REVIEW
4
2.1 2.2
L i t e r a t u r e Survey on E l e c t r o d e Inclusions L i t e r a t u r e Survey on S l a g - L i q u i d Metal R e a c t i o n s and t h e i r I n f l u e n c e on the ESR Ingot Chemistry 2.2.1 2.2.2 2.2.3 2.2.4
2.3
P r i n c i p l e s of the Reaction Scheme i n the ESR Process On the Nature of the ESR R e a c t i o n Scheme Thermodynamic Approach of the ESR S l a g Systems O v e r a l l View on the M o d e l l i n g of ESR Reactions
General N u c l e a t i o n and Growth of I n clusions 2.3.2.1 2.3.2*2
2.3.3
Homogeneous Nucleation Heterogeneous Nucleation
Growth of I n c l u s i o n s
12 12 18 32 34
P r e c i p i t a t i o n of I n c l u s i o n s 2.3.1 2.3.2
4
36 * ....
36 39 39 42 43
V
Chapter
Page 2.3.4 2.3.5 2.3.6
Sulfides . . . Specific Sulfides Oxisulfides 2.3.6.1 2.3.6.2 2.3.6.3
2.3.7
III
The Fe-O-S System The Fe-O-S-Mn E q u i l i brium The Fe-O-S-Si-Mn Equilibrium
53 55 62 66
Aluminates Calcium Aluminates Complex Oxides
66 76 90
I n c l u s i o n s i n ESR-Ingots
94
NATURE OF THE PROBLEM
106
3.1 3.2
106
3.3 3.4 3.5
IV
47 51 53
Oxides 2.3.7.1 2.3.7.2 2.3.7.3
2.4
„
I n c l u s i o n s i n the E l e c t r o d e The Chemical I n f l u e n c e o f the ESR components on the Composition of Inclusions The P r e c i p i t a t i o n o f I n c l u s i o n s from L i q u i d Pool to Ingot D i s t r i b u t i o n o f I n c l u s i o n s During Solidification E s t a b l i s h m e n t of the Proposal and O b j e c t i v e s Sought Through t h i s Research
108 I l l 113 115
EXPERIMENTAL WORK AND TECHNIQUES
116
4.1 4.2 4.3 4.4
116 118 121 122
4.5 4.6
Experimental Procedure Analysis of Inclusions T o t a l Oxygen A n a l y s i s I n c l u s i o n E x t r a c t i o n Method 4.4.1 Apparatus and Experimental Procedure C r y s t a l l o g r a p h i c X-ray A n a l y s i s o f Extracted Inclusions Atomic A b s o r p t i o n A n a l y s i s (Spectrophotometry)
123 126 ?
127
vi Chapter 4.7 V
Page Metallographic
RESULTS AND 5.1
DISCUSSION
-^8 •
Mechanism by which E l e c t r o d e are E l i m i n a t e d 5.1.1 5.1.2
5.1.2.2
5.1.3
130 Inclusions 130
Behavior of O x i s u l f i d e I n c l u s ions i n 1 0 2 0 M.S. Electrode Tips *. , . . Removal of Oxide and S u l f i d e I n c l u s i o n s i n 4 340 and Rotor Steels 5.1.2.1
5.2
Analysis
Removal of Oxides and Sulfides i n 4340 electrodes Calcium Aluminum S i l i cates i n a Rotor ( N i Cr-Mo) S t e e l
F i n a l Remarks About the moval Mechanism
Re-
The Chemical I n f l u e n c e of the E l e c t r o d e , Slag and D e o x i d i z e r on the Chemical Composition of I n c l u s i o n s .. 5.2.1
D e s c r i p t i o n of Experimental Findings 5.2.1.1
5.2.1.2 5.2.1.3
5.2.1.4
P r e l i m i n a r y Studies on the E f f e c t of the Slag and the Deoxidation I n t e r m i t t e n t CaSi A d d i t i o n s and the Rea c t i o n Scheme R e f i n i n g of 1 0 2 0 M.S., 2 0 0 mm Diameter Ingots Deoxidized C o n t i n uously with A l 1 0 2 0 M.S. Ingots Deo x i d i z e d Continuously with a CaSi A l l o y ... .....
130 141
144 146 148
151 151
151 157
159 164
5.2.1.5
C o r r o b o r a t i o n and Ext e n s i o n o f Previous F i n d i n g s t o a 4340 S t e e l CaSi ( c o n t i n u ously) Deoxidized
D i s c u s s i o n o f R e s u l t s i n Terms of E l e c t rode and S l a g Composition, Related t o the Second Question 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5
The E f f e c t o f the E l e c t r o d e on the I n c l u s i o n Composition of ESR Ingots E l u c i d a t i o n o f the E f f e c t o f S l a g and D e o x i d i z e r s (preliminary studies) , P r e l i m i n a r y D i s c u s s i o n on the Deoxidation Mechanism Comprehensive D i s c u s s i o n on the Deoxidation Mechanism F i n a l Remarks
F i n d i n g s and D i s c u s s i o n Related t o the T h i r d Question 5.4.1
D e s c r i p t i o n of Experimental Results 5.4.1.1 5.4.1.2 5.4.1.3 5.4.1.4
5.4.2 5.4.3
The I n c l u s i o n Mean Diameter F i n d i n g s from I n d i v i d u a l Experiments Complimentary Studies Summary o f E x p e r i mental F i n d i n g s
P r e c i p i t a t i o n of Inclusions i n the Fe-Al-Ca-O-S (Mn) system D i s c u s s i o n of R e s u l t s » 5.4.3.1 5.4.3.2
N u c l e a t i o n Growth and F l o t a t i o n of Inclusions . . . Comparison between T h e o r e t i c a l and Experimental Results...*
viii Chapter VI
Page THE RADIAL DISTRIBUTION OF INCLUSIONS IN CaSi AND A l DEOXIDIZED INGOTS 6.1 6.2 6.3
VII VIII
Experimental D e t a i l s and Techniques...... Experimental F i n d i n g s D i s c u s s i o n of R e s u l t s
2
2
3
223 2
2
2 2
4
5
CONCLUSIONS
228
SUGGESTIONS FOR FUTURE WORK
2 32
LIST OF REFERENCES
235
FIGURES
251
TABLES
3
APPENDIX . . . ........
5
1
374
ix LIST OF FIGURES Figure
Page
1.
Schematic i l l u s t r a t i o n of an ESR system
2.
P r e d i c t e d and measured temperature p r o f i l e s f o r a 1018 MS e l e c t r o d e 25 mm i n diameter
252
Manganese c o n t e n t o f the metal f o r u n i v a r i a n t e q u i l i b r i u m y - i r o n + "MnO" + "MnS" + l i q u i d (1) f o r Fe-Mn-S-0 s y s tem and u n i v a r i a n t e q u i l i b r i u m Y + "MnS" + l i q u i d s u l f i d e f o r Fe-Mn-S system
253
U n i v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 system i n the presence o f y - i r o n and Mn(Fe)0 phases
254
Univariant e q u i l i b r i a involving s o l i d metal and Mn(Fe)0 i n the Fe-Mn-S-0 system bonded w i t h t e r n a r y Fe-Mn-0 and Fe-S-0 terminal-phase f i e l d s (e) , ,(p) , (f) , (n), (g) and (h)
255
L o c a t i o n o f the p l a n e s i n the quaternary (FeO-MnO-MnS-Si0 ) system
256
E q u i l i b r i u m phases i n t h r e e planes o f the FeO-MnO-MnS-SiC^ system. a) MnS-FeO2MnO«Si02, b) MnS-2FeO«Si0 -2MnO«Si0 and c) MnS-FeO-MnO
256
Behavior o f i n c l u s i o n s e n r i c h e d i n Mn and S i as a f u n c t i o n o f temperature
257
Schematic i l l u s t r a t i o n o f changes i n i n c l u s i o n composition i n a 1020 MS e l e c t rode produced v i a a c i d e l e c t r i c f u r a n c e . . . .
258
Wt. % A l and wt. % Ca and wt. % 0 i n l i q u i d i r o n a t u n i t A l 0 and CaO a c t i v i t y 3
259
Isothermal Fe-Al-Ca-0 p r e c i p i t a t i o n (Henrian a c t i v i t i e s ) diagram
260
3.
-
4.
5.
6.
i
r
o
....
n
2
7.
2
8. 9.
10.
2
11.
251
2
X
Figure 12. 13.
Page Ternary A l 0 ~ ( C a , X ) 0 - S i 0 diagram 2
3
2
inclusion 261
Slag chemical composition used i n the ,.(34,53,83) , a. • 4.past and p r e s e n t i n v e s t i g ation
262
14.
Schematic i l l u s t r a t i o n of the ESR arrangement used i n t h i s i n v e s t i g a t i o n
26 3
15.
Schematic i l l u s t r a t i o n of the " i n c l u s i o n extractor"
264
16.
T y p i c a l i n c l u s i o n s from 1020 MS ( o p t i c a l microscopy) *
265
17.
Deformed i n c l u s i o n s i n 1020 MS and t h e i r
18.
19.
20.
21.
22. 23.
24. 25.
electrodes electrodes
X-ray spectrum a n a l y s i s
(SEM)
...
266
M a c r o s t r u c t u r e of a 1020 MS e l e c t r o d e t i p where l i q u i d f i l m , p a r t i a l l y molten and f u l l y r e c r y s t a l l i z e d areas are shown
267
M a c r o s t r u c t u r e s o f a 4340 e l e c t r o d e t i p . D r o p l e t , l i q u i d f i l m , p a r t i a l l y molten, f u l l y and p a r t i a l l y r e c r y s t a l l i z e d zones are shown
268
M a c r o s t r u c t u r e o f a r o t o r (Ni-Cr-Mo) s t e e l . L i q u i d f i l m , and p a r t i a l l y molten areas are shown
269
Schematic i l l u s t r a t i o n o f 1020 MS e l e c t r o d e tip (acid e l e c t r i c furnace produced) s u b j e c t e d t o ESR-thermal g r a d i e n t s
270
M u l t i p h a s e ( r e l a t i v e l y grown) i n c l u s i o n s i n a 1020 MS e l e c t r o d e t i p
271
S i n g l e phase i n c l u s i o n s i n p a r t i a l l y and f u l l y molten r e g i o n s i n a 1020 e l e c t r o d e tip
272
Complex Ca-Al-Si-Mn i n c l u s i o n s l o c a t e d i n the l i q u i d f i l m and d r o p l e t s
273
Spectrum X-ray a n a l y s i s o f Ca-Al-Si-Mn i n c l u s i o n s i n a 1020 MS e l e c t r o d e l o c a t e d i n the l i q u i d f i l m and d r o p l e t s
274
xi Figure 26.
27.
28.
29.
30.
31.
32.
33
34.
35.
36.
37.
Page Changes i n i n c l u s i o n chemical composition i n a 4 340 e l e c t r o d e t i p s u b j e c t e d t o ESR thermal g r a d i e n t s
275
Changes i n i n c l u s i o n chemical composition i n a 4340 e l e c t r o d e t i p with a strong r e c r y s t a l l i z e d region
276
Behavior of oxide i n c l u s i o n s i n a e l e c t rode t i p of a r o t o r s t e e l subjected t o ESR thermal g r a d i e n t s
277
.
Aluminum s i l i c a t e s i n a 4340 ESR i n g o t 75 mm i n diamter. Precipitated inclusions in a l o c a l i z e d region
278
I n f l u e n c e o f CaSi and FeO i n t e r m i t t e n t a d d i t i o n s on the oxygen content of a 1020 M.S. (RIII-W)
279
Changes i n oxygen content i n a 1020 MS i n g o t as a r e s u l t o f CaSi and FeO i n t e r m i t t e n t a d d i t i o n s (RII-W)
280
Changes i n s l a g chemical composition i n a 1020 MS (RIII-W) as a r e s u l t of CaSi and FeO i n t e r m i t t e n t a d d i t i o n s
281
Changes i n s l a g chemical composition as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s of CaSi and FeO i n s l a g d u r i n g r e f i n i n g (RII-W)
282,283
Changes i n i n g o t chemical composition as a r e s u l t of CaSi and FeO a d d i t i o n s i n s l a g during r e f i n i n g (RIII-W)
284
E f f e c t of CaSi and FeO a d d i t i o n s i n the s l a g on the chemical composition of a 1020 MS i n g o t (RII-W)
285
Changes i n i n c l u s i o n composition and s i z e i n a 1020 MS i n g o t (RIII-W) as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s o f CaSi and FeO i n the s l a g
286
Chemical a n a l y s i s o f s l a g samples i n R I - I l .
287
xii Figure
Page
38.
Ingot chemical a n a l y s i s i n R I - l l
288
39.
S l a g chemical a n a l y s i s (wt. %) i n a cont i n u o u s l y A l d e o x i d i z e d 1020 MS i n g o t (RII-Il)
289
40.
Slag chemical a n a l y s i s
290
41.
I n c l u s i o n mean diameter and t o t a l oxygen content i n a c o n t i n u o u s l y (Al) d e o x i d i z e d ingot, (RII-Il)
291
42.
T o t a l oxygen content and i n c l u s i o n mean diameter i n i n g o t (RII-I2)
292
43.
I n c l u s i o n chemical composition (at. %) as a f u n c t i o n o f c o n t i n u o u s l y i n c r e a s i n g deoxidation rates i n RII-Il
293
I n c l u s i o n chemical composition (at. %) as a f u n c t i o n of the i n g o t h e i g h t (or continuously increasing deoxidation r a t e s ) i n RII-I2
294
45.
Ingot chemical a n a l y s i s i n R I I - I l
295
46.
Ingot chemical a n a l y s i s i n RII-I2
296
47.
"Alumina g a l a x i e s " , (EPMA), a s s o c i a t e d t o MnS I I i n i n c i p i e n t aluminum d e o x i d i z e d i n g o t s , ( R I I - I l and RII-I2)
297
"Alumina g a l a x i e s " (EPMA) and MnS I I i n A l deoxidized ingots
29 8
Faceted alumina (a-A^C^) i n samples from l i q u i d p o o l and i n g o t d e o x i d i z e d with A l ..
299
Calcium aluminates low i n Ca from h i g h l y A l d e o x i d i z e d i n g o t s . A l , Ca and S composition RII-I2
300
Composition dependence o f s u l f i d e phases on the Ca:Al r a t i o i n the oxide phase ( R I I - I l )
301
44.
48. 49. 50.
51.
(wt. %) i n R I I - I l . . .
xiii Page
Figure 52.
5 3
•
54.
55.
56.
Composition dependence o f s u l f i d e phases on Ca-aluminate i n c l u s i o n s phases i n RII-I2 .. 302 Segregated m a t e r i a l i n an A l d e o x i d i z e d i n g o t ( l i q u i d pool) . . Dependence o f "FeO" contents i n s l a g on the Ai2 0-.:CaO r a t i o i n s l a g o f a c o n t i n u ously A l deoxidized ingot (RII-Il) Dependence o f "FeO" contents i n s l a g on the A ^ O ^ t C a O r a t i o i n s l a g o f a c o n t i n u o u s l y A l d e o x i d i z e d i n g o t (RII-I2)
3
0
3
3
04
3
05
Changes i n t o t a l oxygen content and i n c l u s i o n mean diameter i n a c o n t i n u o u s l y CaSi deoxidized ingot (RIII-Il)
306
I n c l u s i o n mean diameter and t o t a l oxygen content i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t (RIII-I2)
307
58.
I n c l u s i o n chemical composition as a f u n c t i o n of d e o x i d a t i o n r a t e s i n R I I I - I l
308
59.
I n c l u s i o n chemical composition as a funct i o n o f d e o x i d a t i o n r a t e s i n RIII-I2
309
60.
Changes i n s l a g chemical composition i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t (RIIIIl)
310
Changes i n s l a g chemical composition i n a continuously CaSi d e o x i d i z e d i n g o t (RIII12)
311
Changes i n A l and S i i n R I I I - I l as a consequence o f c o n t i n u o u s l y i n c r e a s i n g CaSi deoxidation rates
312
Changes i n i n g o t composition as a consequence o f c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n RIII-I2
313
57.
61.
62.
63.
XIV
Figure 64.
65.
66.
67.
68.
69.
Page Dependence o f "FeO" contents i n s l a g samples on the d e o x i d a t i o n r a t e s i n RIII-Il •
314
Dependence o f "FeO" contents i n s l a g samples on the d e o x i d a t i o n r a t e s i n RIII-I2
315
S u l f u r (as s u l f i d e s ) content i n i n c l u s i o n s as a f u n c t i o n of the Ca:Al r a t i o i n the Ca-aluminate i n c l u s i o n phases i n R I I I - I l ..
316
S u l f u r (as s u l f i d e s ) content i n i n c l u s i o n s as a f u n c t i o n o f the Ca:Al r a t i o i n the Ca-aluminate i n c l u s i o n phases i n RIII-I2 ..
317
Chemical composition o f i n c l u s i o n s (as Ca:Al r a t i o s ) as a r e s u l t o f c o n t i n u o u s l y i n c r e a s i n g d e o x i d a t i o n r a t e s i n RIII-I2, (a) and s u l f u r (as s u l f i d e ) i n i n c l u s i o n s i n Ca-aluminates, (b) . s
318
Segregate e n r i c h e d i n A l , Ca and S i i n a sample e x t r a c t e d from the l i q u i d p o o l of i n g o t R I I I - I l
319
S l a g chemical a n a l y s i s o f a 4340 i n g o t c o n t i n u o u s l y d e o x i d i z e d w i t h a CaSi a l l o y , [R-4340 (1)]
320
71.
Ingot chemical composition i n R-4340 ( 1 ) . . .
321
72.
I n c l u s i o n s i z e d i s t r i b u t i o n and t o t a l oxygen content i n R-4340 (1)
322
Changes i n "FeO" contents i n the s l a g as a consequence o f the c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n R-4340(1)
323
I n c l u s i o n chemical composition (as Ca:Al r a t i o s i n a t . %) i n samples o f l i q u i d p o o l and i n g o t i n R-4340 (1)
324
I n c l u s i o n composition as Ca:Al r a t i o s and S content i n R-4340 (1)
325
70.
73.
74.
75.
XV
Page
Figure I n c l u s i o n composition (oxide and s u l f i d e phases i n a r o t o r s t e e l d e o x i d i z e d with S i based a l l o y s , namely: Ca-65 wt.% S i , Al-65% S i and "Hypercal". R-RS(I), R-RS(II) and R-RS(III)
326
77.
Segregate e n r i c h e d i n A l , Ca and S i from the A l S i d e o x i d i z e d i n g o t , R-RS(II)
327
78 .
I n c l u s i o n p r e c i p i t a t i o n sequence i n a s t e e l c o n t a i n i n g two l e v e l s o f s u l f u r
328
79.
S t a t i s t i c a l determination c l u s i o n diameter
329
80.
C e - d i s t r i b u t i o n i n a i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l
330
81.
Ce and La d i s t r i b u t i o n i n an i n c l u s i o n of a sample e x t r a c t e d from the l i q u i d p o o l . La and Ce come from a RE w i r e l o c a t e d i n the q u a r t z t u b i n g
331
A l , Ca and Zr d i s t r i b u t i o n s i n an i n c l u s i o n of a sample e x t r a c t e d from the l i q u i d p o o l . Zr was i n the q u a r t z t u b i n g
332
D i s t r i b u t i o n o f oxide formers i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d pool
333
76.
82.
83.
84.
85.
86.
87.
of the mean i n -
,
D i s t r i b u t i o n o f o x i d e - s u l f i d e former i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l
334
Inclusion d i s t r i b u t i o n i n a dendritic s t r u c t u r e o f 1020 MS samples taken from l i q u i d pool during r e f i n i n g
335
Inclusion d i s t r i b u t i o n i n a dendritic s t r u c t u r e o f a 4 34 0 sample from the l i q u i d pool
336
Isothermal (1823 K) p r e c i p i t a t i o n (Fe, A l , Ca, 0, S) diagram a t 0.1 a c t i v i t y o f aluminum
337
xvi Figure 88.
Page E f f e c t o f the a c t i v i t y o f A l ( h = 0.001, 0.01 and 0.1) on the " p r e c i p i t a t i o n sequence" o f Ca-aluminates
338
E f f e c t o f the a c t i v i t y of S (h = 0.01, 0.01 and 0.001) on the " p r e c i p i t a t i o n sequence" o f Ca-aluminates
339
Arrangement o f aluminates i n r e l a t i v e l y low CaSi d e o x i d i z e d ESR-ingots
340
T y p i c a l arrangement o f i n c l u s i o n s i n a r e l a t i v e l y low CaSi or high A l deoxidized ingots
341
X A1 0_• Y CaO/CaS i n t e r f a c e i n an ESR i n g o t , R-RS ( I I I ) , d e o x i d i z e d with "hypercal". X-ray spectrum analyses are a l s o i n c l u d e d
342,343
93.
Secondary DAS i n a round 1020 MS ESR i n g o t
344
94.
Secondary DAS i n a 1020 MS ESR i n g o t
345
95.
Secondary DAS i n a 4340 ESR i n g o t
346
96.
R a d i a l s i z e d i s t r i b u t i o n of i n c l u s i o n s i n an A l d e o x i d i z e d i n g o t , (RII-I2)
347
Radial i n c l u s i o n size d i s t r i b u t i o n i n a low CaSi d e o x i d i z e d i n g o t ( R I I I - I l )
348
Radial i n c l u s i o n size d i s t r i b u t i o n i n a 200 mm ESR i n g o t CaSi d e o x i d i z e d , ( R I I I - I l )
349
Radial i n c l u s i o n size d i s t r i b u t i o n i n a 4340 (ESR) i n g o t CaSi d e o x i d i z e d
350
89.
90. 91.
92.
97. 98. 99.
A 1
2
(200 mm
i n diameter)
xvii
L I S T OF
TABLES Page
Table I. II.
III. IV.
V. VI. VII.
VIII. IX. X.
XI.
Correction factor
to the
Stokes'
351
Law
Thermochemical data f o r a) I n v a r i a n t e q u i l i b r i a i n Fe-S-0 s y s t e m and b) E s t i m a t e d d a t a f o r i n v a r i a n t e q u i l i b r i a i n Fe-Mn-0, Fe-Mn-S and Mn-S-Q t e r n a r y systems
353
Estimated data for i n v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 q u a t e r n a r y s y s t e m
355
C a l c u l a t e d and p u b l i s h e d f r e e f o r F e - O - C a - A l s y s t e m a t 1823
356
E q u i l i b r i u m constants reactions
energy d a t a K (1550°C)...
for deoxidation
Equations f o r i n v a r i a n t e q u i l i b r i a i s o t h e r m a l (Fe-O-Ca-Al) system
357
i n the
Chemical a n a l y s i s o f e l e c t r o d e s used this research
in
E x p e r i m e n t s and t h e i r this investigation
in
f e a t u r e s used
Chemical c o m p o s i t i o n of d e o x i d i z e r s used i n the p r e s e n t i n v e s t i g a t i o n a)
I n c l u s i o n c o m p o s i t i o n as a r e s u l t o f r e m e l t i n g 4340 e l e c t r o d e s i n a s m a l l E S R - f u r n a c e (75 mm i n d i a m e t e r )
b)
Slag-deoxidizer effect composition
on
inclusion
c)
I n c l u s i o n c h e m i c a l c o m p o s i t i o n o f 4340 e l e c t r o d e s u s e d i n t h e s m a l l ESRfurnace
C h e m i c a l e f f e c t o f s l a g and e l e c t r o d e s u r f a c e p r e p a r a t i o n on i n c l u s i o n c o m p o s i t i o n . (A 1020 MS and a r o t o r (Ni-Cr-Mo) s t e e l were r e f i n e d i n t h e 200 mm i n d i a m e t e r E S R - f u r n a c e t h r o u g h s e v e r a l s l a g s y s t e m s ). .
358
359
360
361
362
362
362
xviii Page
Table XII.
XIII.
Slag chemical a n a l y s i s o f ESR (Ni-Cr-Mo) i n g o t s d e o x i d i z e d with S i based d e o x i dizers Chemical with: a) b) c)
XIV.
XV. XVI.
a n a l y s i s of ingots deoxidized
the Al-65% S i a l l o y the Ca-65% S i a l l o y and the CaSiAlBa (hypercal) a l l o y
D e r i v e d equations f o r i n v a r i a n t ( i s o t h e r m a l ) e q u i l i b r i a i n the Fe-O-Ca-Al-S system Computed compositions i n Table XV and e ^ and e * =
XVII.
365 366 367
T y p i c a l data recorded from EPMA a n a l y s i s of i n c l u s i o n s . a) l i q u i d p o o l and b) i n g o t
C
364
1
368 369
370
based on data g i v e n
= - 25,
e ^ 0
= -62
-40
3
7
1
3
7
2
Computed compositions i n the Fe-Ca-Al0-S system by u s i n g i n f o r m a t i o n i n Table XV, v a r i a b l e e~r
(-535, -400, -300, Al -250 and -200) i n a d d i t i o n t o the e = -62 and e = -110 Q
C
a
s
XVIII.
E f f e c t o f i n i t i a l number of i n c l u s i o n s on growth d u r i n g c o o l i n g o f l i q u i d metal
373
xix LIST OF SYMBOLS a c t i v i t y o f the i component
l
'A' s p e c i e s i n s l a g
(A)
'A' element i n s o l u t i o n i n l i q u i d iron r a t i o of A t o B s p e c i e s
[A], A A: B A
(g)'
A
(l)' (s) A
deoxidant, composition o f which i s Al-65 wt.% S i . (Table IX)
AlSi
A l
'A' s p e c i e s i n gaseous, l i q u i d or s o l i d state
alumina as a primary d e o x i d a t i o n product
2°3*
atomic p e r c e n t
at. %
i o n i c species with e i t h e r a p o s i t i v e or negative v a l e n c e allotropic
a-Fe a-Al 0 2
state of iron
corundum; i t i s a l s o g i v e n as 'A' when i t i s r e f e r r e d t o as a p a r t o f the Ca-aluminates p r e c i p i t a t i o n sequence
3
degrees i n the C e l s i u s grade) s c a l e
(centi-
s u p e r s a t u r a t i o n r a t i o i n terms of c o n c e n t r a t i o n s
C:C»
(1)'(s)
and C A 3
2
l i q u i d o r s o l i d CaO s t o i c h i o m e t r i c Ca-aluminates as g i v e n by the pseudo b i n a r y (CaO-Al 0 ) phase diagram, i.e., 2
3
CaO«Al 0 ,
CaO-2Al 0 ,
CaO«6Al 0 ,
12CaO«7Al 0
2
3
2
2
3
3CaO«2Al 0 2
3
3
2
3
and
XX
(CaO) *
p e r i p h e r a l phase on a c a l c i u m aluminate oxide i n c l u s i o n
(Ca,Mn)S
double
CaS
phase heterogeneously precipitated on a Ca-aluminate phase
(CaS)*
p e r i p h e r a l c a l c i u m s u l f i d e phase i n e q u i l i b r i u m w i t h the CaO from the Ca-aluminate and oxygen and sulfur i n solution in iron
s u l f i d e w i t h Ca and
Mn
deoxidant, composition of which i s given i n Table (IX)
CaSi CaSiAlBa
deoxidant ("hypercal"), composition of which i s given i n Table IX
DAS
d e n d r i t e arm
DAS
secondary
11
D c 6„ or Fe
6-iron
spacing
d e n d r i t e arm
spacing
c r i t i c a l drag f o r c e particle
on a
a l l o t r o p i c state
iron
of
spherical
electron
e i
i n t e r a c t i o n c o e f f i c i e n t ; the e l e ment f o r which the a c t i v i t y coe f f i c i e n t i s being c a l c u l a t e d i s designated j and the element c a u s i n g the e f f e c t i s d e s i g nated i .
EPMA
electron-probe-micro
f
Henrian
FeO"
activity
i r o n oxide,
(Fe O) x
analyses
coefficient
xxi Fe(x,y,z)-0-S
pseudo t e r n a r y i n c l u s i o n phase diagrams w i t h an oxide and a s u l f i d e p h a s e ; ( H i l t y and c o ,(129) workers)
f^
liquid fraction
GR
product thermal
of growth r a t e by gradients
Y, k, or 8-Al C>2
a l l o t r o p i c s t a t e s o f the alumina
Y^
a c t i v i t y c o e f f i c i e n t of species A
h^
Henrian
HIC
hydrogen induced
HSLA
high s t r e n g t h low a l l o y
kV
excitation
K
a b s o l u t e degrees(absolute) s c a l e
2
Kg t o n
£
- 1
£^ L
cracking steel
voltage i n k i l o v o l t s i n the K e l v i n
d e o x i d a t i o n r a t e i n kilograms of deoxidant per (metric) tonne of remelted i n g o t liquid
1
a c t i v i t y of s p e c i e s A
oxisulfide
l i q u i d metal and L„
l i n e s d i v i d i n g the t e r n a r y i n e l u s i o n and s l a g compositions suggesting the formation of low m e l t i n g phases, F i g u r e s (12) and (13)
X
wave l e n g t h i n X-rays
m(CaO) • nfA^O.j)
m and n are c o e f f i c i e n t s o f the Ca-aluminate phases which are e q u i v a l e n t t o those i n the CaOA l 0 pseudo-binary phase diagram 2
3
xxii manganese s u l f i d e type III
MnS(I,II,III)
I, I I , or
y
viscosity
yA
specimen c u r r e n t d e n s i t y i n (EPMA) microamperes u n i t l e n g t h , microns
ym
oxide of the type Mn(Fe)0 o,
"o",
or o x i
concentration
ppm
R I I I - I l and
( 1 0 2 0 ) ESR i n g o t s A l - d e o x i d i z e d (200 mm i n diameter)
RII-I2 RIII-I2
R-43040 (1) R-RS(I), R-RS(II) R-RS(III)
million
i n g o t s i n which CaSi and FeO were added ( 2 0 0 mm i n diameter)
RII-W, RIII-W R I I - I l and
i n p a r t s per
and
( 1 0 2 0 ) ESR i n g o t s CaSi ( 2 0 0 mm i n diameter) ( 4 3 4 0 ) ESR i n g o t CaSi ( 2 0 0 mm i n diameter)
deoxidized deoxidized
Rotor (Ni-Cr-Mo) s t e e l d e o x i d i z e d with C a S i , A l S i CaSiAlBa a l l o y s
and
P
density
a
interfacial
u
r e s u l t i n g vector
V
velocity
+
degree of accuracy (plus or minus) i n chemical a n a l y s i s less
<
-«-
or
s
or ^
=
< tension velocity
vector
than
reaction in equilibrium approximately gaseous phase
ACKNOWLEDGEMENTS
I would l i k e t o express my s i n c e r e g r a t i t u d e t o my s u p e r v i s o r Dr. A l e c M i t c h e l l f o r h i s c o n c i s e a d v i s e .
I am
a l s o t h a n k f u l t o P r o f e s s o r s R. B u t t e r s and B. Hawbolt f o r t h e i r c o n t r i b u t i o n s and d i s c u s s i o n s d u r i n g t h i s work.
I
a l s o a p p r e c i a t e the t e c h n i c a l a s s i s t a n c e o f A. L a c i s , G. S i d l a , R. Cardeno, H. Tump, R. McLeod and M. Mager. I would l i k e t o thank the Banco de Mexico, Consejo N a c i o n a l de C i e n c i a y T e c h n o l o g i a N a c i o n a l Autonoma de Mexico
(CONACyT), U n i v e r s i d a d
(Departamento de M e t a l u r g i a de
l a UNAM) and the Department o f M e t a l l u r g i c a l E n g i n e e r i n g of the U n i v e r s i t y o f B r i t i s h Columbia f o r the f i n a n c i a l given d u r i n g my p r o f e s s i o n a l s t u d i e s .
support
The author i s a l s o
g r a t e f u l f o r the f i n a n c i a l a s s i s t a n c e o f the American Iron and S t e e l I n s t i t u t e
( P r o j e c t No. 32-445).
T h i s work i s s p e c i a l l y brothers
and
s i s t e r s and
reach my
goal.
dedicated
everyone who
t o my
has
parents,
contributed
to
1 CHAPTER I INTRODUCTION In
today's technology
where there i s the demand f o r
e x t r a - h i g h - q u a l i t y m a t e r i a l s , there are o n l y three ary
steelmaking p r o c e s s e s capable o f f u l f i l l i n g
q u i r e d s t r i n g e n t standards
the r e -
1) E l e c t r o n Beam M e l t i n g (EBM),
2) Vacuum A r c R e f i n i n g (VAR) and (ESR).
second-
3) E l e c t r o s l a g R e f i n i n g
The p r o p e r t i e s r e s u l t i n g from any o f the above p r o -
c e s s e s can be c a t e g o r i z e d a s :
crystal structure,
chemical
homogeneity, s u l f u r and phosphorus c o n t e n t and i n c l u s i o n chemistry and s i z e d i s t r i b u t i o n .
The EBM and the VAR p r o -
cesses o f f e r the lowest gas content.
The v e r s a t i l i t y i n
c o n t r o l and o p e r a t i o n , c r y s t a l s t r u c t u r e , r e l a t i v e cal
electri-
e f f i c i e n c y and r e p r o d u c i b i l i t y are the main f e a t u r e s o f
the ESR p r o c e s s . * Research
c a r r i e d o u t s i n c e 1967
has w i d e l y demonstrated
t h a t the ESR-process o f f e r s d e f i n i t e advantages over v e n t i o n a l p r a c t i c e and i n some r e s p e c t s a l s o o f f e r s tages over other secondary
steelmaking p r a c t i c e s .
conadvan-
The con-
tinuous demand f o r h i g h q u a l i t y m a t e r i a l s has i n c r e a s e d s i n c e 1967.
From 1960 t o 1973 the western world i n c r e a s e d
i t s ESR p r o d u c t i o n from 2 600 t o about 120 000
tonne/year
and i t i s f o r e c a s t t o i n c r e a s e t o 600 000 tonneVyear i n 1985. The
S o v i e t Union's p r o d u c t i o n i s about three times t h a t
* First
I n t . Symp. on ESR
2 of the Western world.
T h i s marked i n c r e a s e i n p r o d u c t i o n
i n d i c a t e s the a c c e p t a b i l i t y of the products manufactured the
by
ESR-technology. M a t e r i a l s produced f o r p a r t i c u l a r purposes such as
r o t o r s used i n thermal and n u c l e a r e l e c t r i c a l p l a n t s ,
land-
i n g gear used i n a i r c r a f t , crank s h a f t s used i n l a r g e v e s s e l s , gun b a r r e l s , s u p e r a l l o y s used i n t u r b i n e b l a d e s , h i g h q u a l i t y t o o l and b a l l b e a r i n g s t e e l s , e t c . are examples o f the wide v a r i e t y o f m a t e r i a l s produced by the ESR-process.
These components are s u b j e c t
to d r a s t i c
temperature and environmental c o n d i t i o n s and/or to dynamic s t r e s s e s .
These two adverse c o n d i t i o n s by them-
s e l v e s generate m i c r o c r a c k s which are u s u a l l y a s s o c i a t e d w i t h chemical inhomogeneities and/or with i n c l u s i o n s i n the metal m a t r i x . I n c l u s i o n s p l a y a major r o l e i n f a i l u r e s under described situations.
the
Thus t h e i r index o f s p h e r i c i t y ,
degree o f cohesion with the metal matrix, i n t e r p a r t i c l e d i s t a n c e , volume f r a c t i o n , s i z e d i s t r i b u t i o n ,
plasticity,
thermal c o n t r a c t i o n and expansion c o e f f i c i e n t s w i t h r e s p e c t to the m a t r i x and chemistry are the parameters determine the s e r v i c e l i f e ,
which
i n terms of i n c l u s i o n s , f o r
a given material. The p o t e n t i a l of the ESR-process, because of i t s v e r satility,
can be extended to o t h e r types o f uses such as
3 E l e c t r o s l a g C a s t i n g (ESC) I t i s important
and E l e c t r o s l a g Welding
(ESW).
to note t h a t w h i l e these p r o c e s s e s
very r a r e l y used i n North America,
are
i n the S o v i e t Union's
technology they are w i d e l y p r a c t i c e d . The ESR process because of i t s m u l t i p l e degrees
of
freedom a l s o o f f e r s a wide range of parameters to be modif i e d and improved without modifying the standard f u r n a c e . To o p t i m i z e the mechanical
p r o p e r t i e s which are
r e l a t e d to i n c l u s i o n s i n a ESR-product, a s e r i e s of
strictly inter-
a c t i o n s between a l l the components of the process should be e v a l u a t e d , i . e . e l e c t r o d e , s l a g , d e o x i d i z e r and f y i n g i n g o t should a l l be c o n s i d e r e d .
solidi-
I f the mechanisms
by which i n c l u s i o n s are formed are known, then the
ESR-
process c a p a b i l i t i e s and r e s t r i c t i o n s i n t h i s r e s p e c t can be d e f i n e d .
4 CHAPTER II LITERATURE REVIEW 2.1
L i t e r a t u r e Survey on E l e c t r o d e From the thermal p o i n t of view
should be c o n s i d e r e d
as one
Inclusions the e l e c t r o d e t i p
of the sources by which
one
p a r t of the t o t a l heat produced by the s l a g i s consumed, Figure
(1).
T h i s amount of thermal energy which i s t r a n s -
f e r r e d from the s l a g to the e l e c t r o d e p l a y s s e v e r a l r o l e s : 1.
I t i s p r i m a r i l y converted to s e n s i b l e heat, thus
producing a f i n e l i q u i d f i l m which afterwards w i l l droplets, 2. and
form
and I t a l s o determines the temperature g r a d i e n t s
below the slag/gas
interface.
above
Thus, i t e s t a b l i s h e s
amount of p o s s i b l e s u r f a c e o x i d a t i o n and
the
the d i s s o l u t i o n
of c e r t a i n second phase p a r t i c l e s or i n c l u s i o n s i n the e l e c trode . (1-5) T h e o r e t i c a l and
experimental
s t u d i e s have been per-
formed to determine whether i n c l u s i o n s from the e l e c t r o d e e l i m i n a t e d before
are
or a f t e r the metal d r o p l e t i s formed.
Heat and mass t r a n s f e r models have a l s o been developed to p r e d i c t the maximum i n c l u s i o n diameter which can be s o l v e d under g i v e n
dis-
ESR-conditions. (6)
M i t c h e l l , J o s h i and
Cameron
have s t u d i e d the temp-
e r a t u r e d i s t r i b u t i o n above the slag/gas l a b o r a t o r y ESR
furnace.
interface in a
They have i n d i c a t e d t h a t gradients
the r a d i a l
i n a larger electrode-ingot
came s i g n i f i c a n t .
Their
c o n f i g u r a t i o n b<
r e s u l t s a l s o suggest
s o l u t i o n o f second phase p a r t i c l e s tent
temperature
that di;
to a varying
ex-
i s feasible. (7)
Maulvault
and E l l i o t t
who
have d e v e l o p e d a one
d i m e n s i o n a l model have t a k e n i n t o a c c o u n t t h e cal
movement o f t h e e l e c t r o d e .
w h i c h have b e e n b a s e d file,
Their
i n an assumed
verti-
computations,
parabolic
pro-
h a v e shown a r e a s o n a b l e a g r e e m e n t w i t h t h e expe
mentally
(37 mm
diameter electrode)
determined
values
(8) M e n d r y k o w s k i e t a l . ' s work fied the
one-dimensional-heat electrode
part
immersed
found t h a t w h i l e n e i t h e r vection play tions, the
sults
model and
a simpli-
considering
i n the s l a g have
also
r a d i a t i o n n o r gas p h a s e
a major r o l e ,
the convective
electrode
flow
by u s i n g
f o r a given
set of
con-
condi-
heat t r a n s f e r from the s l a g t o
i s i n d e e d more s i g n i f i c a n t .
suggest that conduction along
Their r e -
the e l e c t r o d e
pre
d o m i n a t e s a s t h e h e a t - t r a n s f e r - c o n t r o l l i n g mechanism. (9)
Tacke e t a l . f o r m e d a t U.B.C.
along (6,10) have
t h e l i n e s w i t h work p e r coupled
two m o d e l s
(one
6
to determine the s l a g temperature and the other to determine the heat f l u x e s ) t o c a l c u l a t e the e l e c t r o d e temperature, i t s m e l t i n g p r o f i l e and i t s depth o f immersion i n the s l a g .
I t has been claimed t h a t computed
v a l u e s o b t a i n e d by t h i s two-dimensional flow are i n agreement with the experimental e f f e c t was"also t h e o r e t i c a l l y yzed.
findings.
The r a d i a l
and e x p e r i m e n t a l l y
anal-
These r e s u l t s i n agreement with M i t c h e l l e t
(6)
al.
show t h a t the temperature g r a d i e n t s become
steeper i n the e l e c t r o d e nearer the l i q u i d f i l m . A r e p r e s e n t a t i v e example o f t y p i c a l g r a d i e n t s i n an e l e c t r o d e are shown i n F i g u r e
(2).
I t i s important
to mention t h a t i n a l l the above models the thermal energy spent f o r r e c r y s t a l l i z a t i o n or g r a i n growth, as shown by s e v e r a l r e s e a r c h e r s ^ ' 11-14)
n
Q
t
j
3 e e n
considered. The
i n c l u s i o n d i s s o l u t i o n phenomenon has a l s o
been approached by s e v e r a l r e s e a r c h e r s from the mass
(12) t r a n s f e r view p o i n t ,
Kay and Pomfret
f i r s t r e s e a r c h e r s t o have suggested
were the
and modelled the
d i s s o l u t i o n o f oxide i n c l u s i o n s ( s i l i c a and alumina) i n the e l e c t r o d e f i l m under normal ESR c o n d i t i o n s . They c l a i m t h a t
7 although i n c l u s i o n s can be d i s s o l v e d as a r e s u l t of l i q u i d f i l m - l i q u i d slag i n t e r a c t i o n during formation
stage,
t h e i r computed values
r a t e would o n l y r e q u i r e the time t h a t spends before
i t becomes l i q u i d .
d i s s o l u t i o n of alumina and meters were 4 and
20
ym,
silica
the
droplet
for dissolution an e l e c t r o d e
Mitchell
material
Their c a l c u l a t i o n s
for
i n c l u s i o n s whose d i a -
were performed under the
sumption t h a t thermodynamic e q u i l i b r i u m a t the t i p / s l a g i n t e r f a c e was
the
reached a t 1800
and
as-
electrode
2000°C.
based on heat t r a n s f e r c a l c u l a t i o n ^ '
has
r e c a l c u l a t e d the d i s s o l u t i o n of i n c l u s i o n s (12) u s i n g the c o n d i t i o n s o f Pomfret and Kay . Mitchell's r e s u l t s show t h a t even by u s i n g a two-fold
superheating (8)
(70°
C) above t h a t found by Mendrikowski e t a l .
s o l u t i o n i s p r e d i c t e d below 1600° C.
no
Hence the i n c l u s i o n -
d i s s o l u t i o n mechanism i n the s o l i d e l e c t r o d e t i p was considered
not
to s t r o n g l y i n f l u e n c e the o v e r a l l i n c l u s i o n
removal. (16) Hajra and
Ratnam
f e r c a l c u l a t i o n s and ESR-furnace.
have a l s o performed mass t r a n s experimental r e s e a r c h
T h e i r approach was
previously described with M i t c h e l l ' s
works.
in a
laboratory
on the same b a s i s as
Their results
show t h a t slag/metal
i n agreement
reactions play
important r o l e i n the e l e c t r o d e - i n c l u s i o n removal. a l s o found t h a t oxide p a r t i c l e s c h a r a c t e r i s t i c of e l e c t r o d e were not t r a c e d i n the
ingot.
the
an They
the
8 Experimental and
t h e o r e t i c a l work, so f a r des-
c r i b e d , has o n l y been concerned with l a b o r a t o r y
ESR
(17) furnaces.
Medovar e t a l .
800
mm
- 1200
also reported
that, i n
consumable e l e c t r o d e s r e f i n e d by
ESR,
the i n c l u s i o n removal o c c u r s i n the molten metal or i n the p r o c e s s of d r o p l e t formation.
film
They have a l s o
i n d i c a t e d t h a t i n c l u s i o n s i n d r o p l e t s d i f f e r e d from those i n the e l e c t r o d e . shape, s i z e s and
They c l a i m t h a t the i n c l u s i o n
d i s t r i b u t i o n i n the s o l i d
were s i m i l a r i n nature to those i n the ESR
Research c a r r i e d out on a q u a n t i t a t i v e b a s i s i n the e l e c t r o d e d u r i n g cated
claimed
has
'
suggested t h a t i n c l u s i o n s
r e f i n i n g are s p e c i f i c a l l y l o they have a w e l l
defined
Based on these f i n d i n g s i t has
t h a t i n c l u s i o n s are mechanically
c a l l y removed by
ingot. (19 20)
i n the S o v i e t Union
i n the l i q u i d f i l m and
size distribution.
droplets
and
been
chemi-
the s l a g . (19)
On
the other hand Roshchin e t a l
w i t h other
investigators^ ''have
due
"high temperature h e a t i n g "
to the
1
i n agreement established
that
manganese s u l f i d e s
9 are f i r s t l y
spherodized and afterwards d i s s o l v e d .
I t has
(19) been observed
that s i l i c a t e
i n c l u s i o n s were
sphero-
d i z e d , transformed and s l i g h t l y enlarged, i n c o n t r a d i c t i o n to s e v e r a l i n v e s t i g a t o r s ' r e s e a r c h reach the l i q u i d f i l m .
The
1
3
^
b e f o r e they
same c o n t r a d i c t i o n i s found
with r e s p e c t to second phase p r e c i p i t a t e s .
While some
r e s e a r c h e r s b e l i e v e t h a t d i s s o l u t i o n occurs i n the stage^
solid
o t h e r s have r e p o r t e d t h a t t h i s takes p l a c e i n
the l i q u i d stage
and s t i l l others ^
t h a t they do not d i s s o l v e and
have
suggested
serve as n u c l e a t i n g agents
i n the r e f i n i n g i n g o t . Roshchin e t a l . ' s work was
performed
u s i n g o p t i c a l and o p t i c a l - q u a n t i t a t i v e d i s t r i b u t i o n ) techniques.
exclusively
(inclusion
These r e s e a r c h e r s c l a i m t h a t
s i m u l a t e d heat t r e a t e d samples
(under an i n e r t atmo-
sphere) s u b j e c t e d to s e v e r a l p e r i o d s of time and e r a t u r e ranges, served i n a c t u a l Other
produced
size
temp-
e q u i v a l e n t r e s u l t s t o those
ob-
ESR-electrodes. (13)
studies
i n l i n e with the p r e v i o u s work,
u s i n g d i f f e r e n t schedules have agreed with the above f i n d ings.
The major disadvantage
of these simulated e x p e r i -
ments i s t h a t the c a l c u l a t e d thermal g r a d i e n t s ^ the time-temperature
and
schedules are so d i f f e r e n t to t h a t
experienced by the e l e c t r o d e t i p s t h a t a s e l f - c o n s i s t e n t
c o n c l u s i o n cannot be
derived,
(15) Studies
c a r r i e d out on a q u a n t i t a t i v e b a s i s
oxygen content and
i n c l u s i o n chemical a n a l y s i s ) have
mined t h a t i n c l u s i o n s are d i s s o l v e d i n the l i q u i d
(total deter-
film.
These a n a l y t i c a l s t u d i e s however were performed e x c l u s i v e l y on. m a t e r i a l belonging The
to the molten
family.
idea which supports the e x i s t e n c e
r e o x i d a t i o n due
to continuous i n c l u s i o n d i s s o l u t i o n , from
the heat a f f e c t e d r e g i o n to the e l e c t r o d e has
a l s o been p r o p o s e d
1
3
^.
The
these i n c l u s i o n s , however, was
not
Theoretical s t u d i e s ^ ' ^ ' ^ ^ electrode-mold
of a continuous
liquid
film,
chemical nature of investigated.
indicate that for a
diameter c o n f i g u r a t i o n some
given
superheating
i s expected at the e l e c t r o d e t i p , although f o r a s h o r t of time.
On
period
t h i s b a s i s i t has
been a n t i c i p a t e d t h a t i f (18) i n c l u s i o n s c o n t a c t the s l a g or e a r l i e r i f they are s i l i c a type, t h e i r d i s s o l u t i o n r a t e should be extremely high (21) f o r a l l common s l a g - i n c l u s i o n combinations (22) Paton e t a l .
have a l s o suggested t h a t the
l i q u i d u s - s o l i d u s l e n g t h of each a l l o y system and trode-steelmaking
p r a c t i c e a l s o p l a y an important
T h e i r s t u d i e s were performed on and
a gradual
served.
The
1200
mm
diameter
d i s s o l u t i o n of s u l f i d e s was critical
intrinsic
the e l e c role. electrodes
( o p t i c a l l y ) ob-
length at which changes i n s u l f u r con-
c e n t r a t i o n s were observed was
about one
centimeter above
the
"fusion l i n e . " (23)
Zhengbang e t a l . ' s s t u d i e s
based on the
con-
95 c e n t r a t i o n s of a r t i f i c i a l
Zr
0
2
i n c l u s i o n s have shown that
the chemistry of i n c l u s i o n s during gradually
from the e l e c t r o d e to the
the ESR ingot.
p r o c e s s change Other
research-
ers c l a i m t h a t the major r e a c t i o n s i t e where i n c l u s i o n s from the e l e c t r o d e are e l i m i n a t e d i s a t the l i q u i d f i l m (23 24) (15) slag interface ' . Mitchell who has r e f i n e d electrodes
containing
c a l c i u m aluminum s i l i c a t e s has
p o r t e d small i n c l u s i o n s i n the
liquid film,
the
re-
composition
of which d i d not correspond to the s t o i c h i o m e t r i c 2FeO«Si0 phase.
2
2.2
L i t e r a t u r e Review on S l a g - L i q u i d Metal and
2.2.1
t h e i r I n f l u e n c e on the ESR Ingot
P r i n c i p l e s o f the R e a c t i o n Among the c o n v e n t i o n a l
Reactions
12
Chemistry
Scheme i n the ESR
Process
and secondary steelmaking
prac-
t i c e s the ESR-process r e p r e s e n t s one of the most complex metallurgical reactors. study
The degree of d i f f i c u l t y
inits
a r i s e s because r e a c t i o n s take p l a c e a t s i t e s
(elect-
r o d e - s l a g , d r o p l e t - s l a g and l i q u i d p o o l i n t e r f a c e s ) which have separate
and d i s t i n c t chemical
and e l e c t r o c h e m i c a l r e -
(26 2 7 )
gimes
'
.
The d r o p l e t , due t o i t s s i z e
sees no
p o t e n t i a l d i f f e r e n c e between i t and the surrounding
slag
t h e r e f o r e i t r e a c t s under the thermochemical c o n d i t i o n s d i c t a t e d by the s l a g . and
The e l e c t r o d e
(liquid film) - slag
the molten l i q u i d p o o l - s l a g i n t e r f a c e s r e a c t almost
e n t i r e l y by imposed e l e c t r o c h e m i c a l p o t e n t i a l s . a t these and
Reactions
s i t e s are c o n t r o l l e d by the s u r f a c e environments
they are not d i r e c t l y i n f l u e n c e d by the s l a g
chemistry.
I t i s worthwhile t o mention t h a t the above p a t t e r n s are mainly a p p l i e d t o DC-ESR and t o a g i v e n extent to the AC-ESR (26) (2728) operation . Several researchers ' have suggested t h a t even i n t h i s l a t t e r o p e r a t i n g mode
slag-metal ex-
change and s u r f a c e s are r u l e d by the p o l a r i z a t i o n (28 29 ) " Several studies t i a l behavior
'
on the c u r r e n t
behavior.
density-poten-
have shown t h a t s i n c e there i s not a l i n e a r
r e l a t i o n s h i p between these parameters used i n ESR, then p o l a r i z a t i o n e x i s t s .
f o r DC and AC ranges Schwerdtfeger s 1
(28) studies
have a l s o shown t h a t a f t e r the l i m i t i n g
r e n t i s approached
f o r a g i v e n s l a g system
cur-
a plateau i s
reached.
T h i s l i m i t i n g c u r r e n t can be
i n c r e a s e d again
i f the p o t e n t i a l i s markedly i n c r e a s e d . tude o f the l i m i t i n g c u r r e n t potential relationship
has
only
Thus, the magni-
from t h i s c u r r e n t
density-
given a c l e a r i n d i c a t i o n that
2+ a s u r f a c e s a t u r a t i o n i n Fe
r e s u l t s i n the s e p a r a t i o n
of
an i r o n - r i c h phase which remains f i x e d on the anode s u r face by
i n t e r f a c i a l tension f o r c e s ^ ^ . 3
incomplete i r r e v e r s i b i l i t y i n the s l a g and
leads to a net
Therefore, "FeO"
this
production
a l s o to a net s o l u t i o n of aluminum or
cal-
cium i n the i r o n . Besides the r e c t i f i c a t i o n of AC c u r r e n t caused by i n t e r (30 32) f a c i a l e f f e c t s there i s evidence ' i n the l i t e r a t u r e which e s t a b l i s h e s t h a t r e c t i f i c a t i o n due to c u r r e n t p a s s i n g 2+ through the slag-skin/mould bulk,
i n c r e a s e s the Fe
i n the s l a g
thus r a i s i n g a l l o x i d a t i o n r a t e s i n the
ESR-reaction
(33) scheme.
Hawkins e t a l .
have shown t h a t i f 5% - 30%
the t o t a l c u r r e n t i s passed through the mould w i t h an c i e n c y of 2% f o r the anodic
reaction
of oxygen would occur, under normal (29) I t has been s p e c u l a t e d
of
effi-
a r i s e of about 40
ppm
ESR-conditions.
t h a t the mechanism which con-
t r o l s t h i s type of r e c t i f i c a t i o n i s the presence of s m a l l arc c o n t a c t s which pass through the s l a g - s k i n i n t o the s l a g . (27) Mitchell temperature and the
reaction
has a l s o i n d i c a t e d t h a t due high c u r r e n t - d e n s i t y slag-metal scheme
is
probably
not
a
to the
high
interface
well-defined
14 Faradaic i n t e r f a c e . sible
Thus e l e c t r o l y t i c
o n l y to the extent p e r m i t t e d by
r e a c t i o n s are possuch p o l a r i z a t i o n
phenomena. (28 The
30)
suggested FeU) Ca
2 +
* + 2e
' Fe
r e a c t i o n scheme i s as f o l l o w s : + 2e
2 +
* Ca
,
(1) (2)
X
Ca t (Ca) s l a g or [Ca] and at h i g h c u r r e n t d e n s i t i e s :
(3)
X
Al
3 +
Fe I t has
2 +
+ 3e
t
+ 2e
t .Fe
[Al]
(4) (5)
( £ )
a l s o been c l a r i f i e d t h a t other r e a c t i o n s with
higher decomposition p o t e n t i a l s than those allowed above scheme w i l l not take
by
the
place. (26)
From the above r e a c t i o n scheme t h a t d u r i n g the anodic h a l f c y c l e adjacent gen
to the metal s u r f a c e
i t has been
envisaged
i r o n oxides w i l l
form
e i t h e r by d i s c h a r g e of oxy-
i o n s or by d i s s o l u t i o n of Fe which w i l l r e p l a c e Ca-ions
locally.
T h i s leads to a high i r o n oxide a c t i v i t y
(
a F e 0
^
W 1
th
consequent d i s s o l u t i o n of oxygen i n t o the i r o n b u l k . 2+ 3+
Simult-
aneously
the
FeO
or Fe
(or Fe
) w i l l be t r a n s p o r t e d by
hydrodynamic regime i n t o the bulk of the s l a g c a u s i n g a ual
grad-
i n c r e a s e i n the a„ . The c a t h o d i c h a l f c y c l e w i l l d i s FeO charge A l 3+ , Ca 2+ or Fe 2+ . Any of these ions w i l l contribute to reduce the a _ in the slag. I t can also be established that i f in this n
last e l e c t r o c h e m i c a l r e a c t i o n there i s not s u f f i c i e n t
Ca
2+
or
15
(33) a slag deoxidation i s
i f Ca i s e x t e n s i v e l y evaporated necessary
to a v o i d the e l e c t r o d e s a c r i f i c i a l
Up t o t h i s p o i n t i n t h i s review
deoxidation.
only the r e a c t i o n s as
a r e s u l t o f the i n h e r e n t e l e c t r o c h e m i c a l nature of the ESRprocess
have been c o n s i d e r e d .
There are, however, other (38)
types o f r e a c t i o n s i n v o l v i n g the s l a g
atmosphere
inter-
f a c e which a l s o a f f e c t i t s o v e r a l l r e a c t i o n p a t t e r n s .
Holz-
gruber ( ^ 34
has claimed
that i f remelting
i s c a r r i e d out
under a pure oxygen atmosphere the oxygen content ranges from 1.8 t o 3.8 times t h a t o b t a i n e d atmosphere. content try.
In t h i s work
i n ingots
under an argon
i t i s a l s o shown t h a t oxygen
i n ESR-ingots i s very dependent on the s l a g chemis(1 37)
S e v e r a l r e s e a r c h e r s have e s t a b l i s h e d
v
'
' that i f
r e m e l t i n g i s not c a r r i e d out under an i n e r t atmosphere and if
the s l a g i s not d e o x i d i z e d then the oxygen content (and
the l o s s of r e a c t i v e elements) i n the i n g o t can only be c o n t r o l l e d by the s l a g (oxygen p o t e n t i a l ) . results (38)
a l s o i n favour o f the above theory
the lowest oxygen content s l a g chemistry
Miska e t a l . ' s show t h a t
i s c o n t r o l l e d s t r i c t l y by the
and i n t e r m e d i a t e oxygen contents
i n f l u e n c e d by the s l a g - e l e c t r o d e
are strongly
chemistry.
While some r e s e a r c h e r s ( 3 8 ) have found t h a t the i n t r o d u c t i o n o f oxygen i n t o the s l a g i s a mass t r a n s f e r c o n t r o l l e d process
others d ' 3 3 ) b e l i e v e t h a t i n a d d i t i o n t o t h i s
mechanism there i s an "oxygen s i n k " face) which a c t s as a d r i v i n g f o r c e .
(at the slag-metal
inter-
I t i s thought t h a t the
d e s u l f u r i z a t i o n r e a c t i o n i s c o n t r o l l e d by t h i s dual mech(1, 12)
anism
I t i s g e n e r a l l y accepted i n t r o d u c t i o n of i r o n oxide
t h a t there
i s a continuous
i n t o the melt, due t o the
continuous o x i d a t i o n of the e l e c t r o d e s u r f a c e . has p o i n t e d out t h a t the ESR-reaction
Mitchell
v
p a t t e r n i s more
s t r o n g l y i n f l u e n c e d by t h i s phenomenon than by the oxygen i n t r o d u c e d as a r e s u l t o f r e a c t i o n s t a k i n g p l a c e a t the slag-atmosphere i n t e r f a c e .
Other s t u d i e s have a l s o
shown t h a t by r e f i n i n g e l e c t r o d e s with d i f f e r e n t (36,39)
o
r
different surface preparation
wise e q u i v a l e n t ESR-conditions,
under o t h e r -
d i f f e r e n t composition
d i f f e r e n t mechanical p r o p e r t i e s a r e observed. havior
chemistry
or
T h i s be-
although i t i s i n d i r e c t , has been a t t r i b u t e d t o
the i n t r o d u c t i o n o f v a r i o u s q u a n t i t i e s of i r o n oxide
into
the s l a g as ( e l e c t r o d e ) s c a l i n g . (40 41) There a r e r e p o r t s i n the l i t e r a t u r e ' i n d i c a t e t h a t the e v a p o r a t i o n
x
'
' which
of gaseous f l u o r i d e com-
pounds i n c e r t a i n s l a g systems a l s o a f f e c t s the r e a c t i o n pattern.
The r e a c t i o n :
(A1 0 ) + 3 ( C a F ) 2
2
3
l a r g e l y c o n t r i b u t e s t o s h i f t the A l 0 : C a O r a t i o . 2
r e a c t i o n becomes very
(8)
t 3(CaO) + 2A1F +
3
important where the c a l c i u m
a c t i v i t i e s are l e s s than 10
-2 (42, 43)
Mitchell
This oxide (36)
17 has p o i n t e d out t h a t i n order to t r a c e the a c t u a l s h i f t i n g i n the chemical
composition
the CaF« and A l F ^ 3
p a r t i c u l a r l y i n s l a g s where
have about the same vapour p r e s s u r e ,
a n a l y s i s i n the 0
2-
:F
-
r a t i o as w e l l as the Ca
2+
: Al
an
3+
should be considered. Complementary r e a c t i o n s are: (CaF ) + H 0 2
2
t
( g )
(CaO)
+ 2HF+
(9)
and 2(CaF ) + 2
Chouldhury e t a l .
K i i i i )
(Si0 ) 2
±n
t
(CaO)
+ SiF^
a r e c e n t communication have
p o i n t e d out t h a t by r e m e l t i n g i n g o t s with low current
(10)
the S i l o s s e s from an a c i d i c s l a g are
frequency negligible.
They n o t i c e , however, t h a t f o r a s l a g where the CaO:Si0
2
r a t i o i s g r e a t e r than 4, S i l o s s e s r i s e to 65% d u r i n g r e melting. gations
T h i s f i n d i n g i s a l s o supported (40, 45)
.
t h a t r e a c t i o n (9)
m
i n previous
.. , , „. ^, . (39) T o b i a s ' and Bhat's work
can be c o n s i d e r e d
of oxygen i n the system.
investi-
suggests
as an a d d i t i o n a l source
In t h i s work
although
i s not c l e a r l y s p e c i f i e d , i t i s c o n s i d e r e d
a mechanism
t h a t moisture
as a condensed phase i n moulds, water vapour from the atmosphere or c h e m i c a l l y bonded moisture i n the f l u x markedly a l t e r s the recovery of t i t a n i u m and
s i l i c o n i n ESR-ingots.
2.2.2
On the Nature of the ESR-reaction
Scheme
A g r e a t d e a l of a t t e n t i o n has been d e d i c a t e d to i n v e s t i g a t e the o r i g i n , sequence and consequence o f the r e a c t i o n s i n the ESR-process.
The major o b j e c t i v e o f these
s t u d i e s have been to c o n t r o l the i n g o t composition out s a c r i f i c i n g i t s chemical
integrity.
I t i s c o n v e n t i o n a l l y accepted
t h a t the
broadest
c l a s s i f i c a t i o n of r e a c t i o n s t a k i n g p l a c e d u r i n g can be s u b d i v i d e d Reactions
with-
refining
as f o l l o w s : which are c o n t r o l l e d by the oxygen p o t e n t i a l
[Me] + [0]
(11)
* (MeO)
and r e a c t i o n s as a r e s u l t of the exchange between
two
liquids: [Me] + (MO) t
(MeO) + [M]
(12)
Among the r e a c t i o n s comprised i n the f i r s t category,
type
(11), a r e : [Ca] + [0] t
(CaO)
2[A1] + 3[0] t
'
( 4 8
6
(A1 0 ) 2
[Si] + 2 [ 0 ] t
(Si0 )
[Ti] + 2[0] t
(Ti0 )
2
(11-i)
)
( 3 6
3
'
4 8
"
5 2
'
6 2 )
(26, 33,35,36,49-51,63,64)
2
( 5 2
2
'
5
8
m i r I -*• /i-i ^ \ (26,33,35.36,63,64) x[Fe] + y[o] (Fe 0 ) ' ' ' • ' x y t
2(Ti 0 )
[Ti] + 2 ( T i 0 )
t
( T i 0 ) + (TiO)
2
2
2
2
n
_
i
i
i
)
. (11-v) (11-vi)
( 5 2 )
3
3
(
(11-iv)
)
[Ti] + 3 ( T i 0 )
(11-ii)
( 5 2 )
(11-vii)
The group of r e a c t i o n s of the k i n d (12) the
so c a l l e d d e o x i d a t i o n (FeO) t-
[Mn]+
subdivided i n
s
r e a c t i o n s , (12a),
namely:
(MnO) + Fe (57,59-61)
(12-i)
[Si]+ 2(FeO) t
( S i 0 ) + 2Fe d,57,60,61)
[Til + 2 (FeO) t
( T i 0 ) + 2Fe (52,58,60)
(12-ii)
2
(12-iii)
2
2[A1]+ 3(FeO) t [Ca] + (FeO) t and
±
( A 1 0 ) + 3Fe (35,48,57,60) 2
(12-iv)
3
(CaO) + Fe
(12-v)
( 6 2 )
the exchange r e a c t i o n s which a l s o i n v o l v e the r e a c t i v e
species,
(12-b):
3[Ti] + 2(A1 0 ) t 2
3
2[Ti] + (Si0 ) t
3(Ti0 )
2(Ti0 )
2
+ 2 [ T i ] (52,58)
2
3 [ S i ] + 2(A1,0-) t ^
+ 4[A1] (18,39,46-51)
2
3(SiCO
J
+
4[A
Z
(12-vii)
i]d/44,46,47,49,55) (12-viii)
2[Mn] + ( S i 0 ) t
2(MnO) + [ S i ] ( /56,57,76)
2[A1]
( A l ^ )
44
2
+ 3(MnO) J
+
Other r e a c t i o n s i n c l u d e d in laboratory
3
[Mn]
(ESW) experiments are (12-C): ( C u C l ) + [Al] t
Cu +
2
3(Cu 0) + 2[A1] t 2
2
0
Cu +
3
(Al 0 ) 2
S i + 2(Fe O)
(MnO) + Fe t
2 Fe +
C + (Fe O) t
CO
x
(A1C1 )
N i + (FeO)
( S i 0 ) + 2 Fe t
( g )
(12-ix) (12-x)
( 5 7 )
i n t h i s c a t e g o r y observed
( N i 0 ) + Fe t
(12-vi)
(Si0 ) 9
+ Fe
3
-(^1)
20
Although the d e p i c t e d
c a t e g o r i z a t i o n of the
reaction
scheme has been presented i n an o v e r s i m p l i f i e d manner i t s t h e o r e t i c a l basis
should be enunciated to e s t a b l i s h •
the r e a c t i n g c o n d i t i o n s under which i t takes p l a c e
and
the governing r e a c t i n g mechanism. A wide range of o p i n i o n s
and
sometimes
c o n t r o v e r s i a l r e s u l t s are found i n the
apparently
literature in re-
gard to the approach p r e d i c t i n g the E S R - r e a c t i o n sequence. While some i n v e s t i g a t o r ' s work
(63)
support the theory
there e x i s t s a s t a t e of e q u i l i b r i u m ,
other
studies
that
(58)
(33)
based i n thermodynamic data and
experimental
r e s u l t s have
found t h a t e i t h e r a "dynamic e q u i l i b r i u m " or k i n e t i c f a c t o r s govern the r e a c t i o n p a t t e r n .
I t i s w e l l recognized^®^
t h a t i f an ESR-furnace i s c o n s i d e r e d
s t r i c t l y as a
even i n the absence of e l e c t r o c h e m i c a l (65
such t h a t t r u e thermal e q u i l i b r i u m and
hence i t should be
operates under three
f a c t o r s , i t s nature i s 66)
'
i s never reached
instead considered
as a r e a c t o r which
d i f f e r e n t regimes, namely:
unsteady s t a t e which holds f o r about three
times
i n g o t diameter from bottom.
2)
for
time
and
3)
of
the
refining
stage
most
of
which
the is
refining at
the
end
Other p e c u l i a r i t i e s o f the ESR the r e a c t i o n sequence are caused by
i t s r a d i a l and
reactor
a quasi-steady
p r o c e s s which
the
1)
an
the state hot
top
time.
influence
i t s hydrodynamic regime v e r t i c a l temperature g r a d i e n t s
(30
'
65,67)^
Thus, s t r i c t l y
speaking an a c t u a l s t a t e of e q u i l
brium i s not reached because of the changing thermal cond t i o n s , hence i n f l u e n c i n g i t s chemical n a t u r e .
From t h i s
d e s c r i p t i o n and from the e l e c t r o c h e m i c a l p r i n c i p l e s a l ready d e s c r i b e d
i t can be seen t h a t the r e a c t i o n scheme
must be c o n s i d e r e d a c c o r d i n g to both thermal regime i t s resulting kinetic factors. p o r t e d by Kay's s t u d i e s d ' reaction pattern.
4 8
)
o
and
These i d e a s have been sup the behavior o f the
n
In t h i s work
ESR
i t has been suggested
t h a t s l a g - m e t a l composition r e l a t i o n s h i p s are governed by (33) kinetic factors.
Hawkins e t a l .
have c l e a r l y shown
t h a t t h i s p a r t i c u l a r s t a t e o f e q u i l i b r i u m i s not unique but i t can be r e p r e s e n t e d as a thermal-parameter denominated " c h a r a c t e r i s t i c temperature." was
T h i s parameter
c a l c u l a t e d on a thermochemical b a s i s i n d i c a t e s
the system may
see simultaneous r e a c t i o n s a t t h e i r
responding thermal r e g i o n s .
Although t h i s
which that cor-
"characteris-
t i c temperature" as a parameter does not have any p h y s i c a l meaning
i t does r e p r e s e n t the unsteady
thermal-chemi
c a l behavior of the ESR p r o c e s s . (33 61) I t has been proposed actions
are
the
result
' of
that o v e r a l l a
well defined
of steps which i n v o l v e mass t r a n s f e r t i o n and hydrodynamic
(ESR) r e -
(diffusion,
series convec-
flow) and chemical f a c t o r s (reorgan
z a t i o n o f the r e l a t i v e p o s i t i o n o f i o n s , atoms or mole-
cules).
The
i s r u l e d by:
k i n e t i c aspect of e l e c t r o a c t i v e the a c t i v i t i e s of r e a c t i n g
interfaces
species
on
both
s i d e s of t h i s s i t e , d i f f u s i o n c o e f f i c i e n t s , temperature and
concentration
gradients
extending from the
inter(33)
face to the
l i q u i d i r o n or s l a g b u l k .
Hawkins
have a l s o suggested t h a t a t h r e e f o l d - s t a g e
et a l .
reaction
se-
quence can be envisaged, namely i)
Transport of reactants
to the s l a g - m e t a l i n t e r -
face.
T h i s s t e p i s a t t a i n e d by d i f f u s i o n and
of the
two
c o n t r i b u t i n g phases
i i ) • Electrochemical
liquid
metal).
r e a c t i o n s which i n v o l v e
e l e c t r o n exchange p r o c e s s , iii)
(Slag and
convection
the
and
T r a n s p o r t of r e a c t i n g products away from
interface.
This
Experimental
(ESW)
work
( ^ 6
has
shown t h a t
dependent upon the
products a t the e l e c t r o a c t i v e i n t e r f a c e s . found t h a t l i q u i d m i s c i b l e
the reaction
I t has
been
r e a c t i o n products r e a d i l y
are e f f i c i e n t l y t r a n s p o r t e d
reacting interface.
away from
the
Gaseous r e a c t i o n p r o d u c t s which
are formed at the e l e c t r o - a c t i v e i n t e r f a c e r e a c t i o n by
the
step i s again r u l e d as stage ( i ) .
r a t e of r e a c t i o n i s s t r o n g l y
d i f f u s e and
ion-
slow
the
i n t e r f e r i n g with the d i f f u s i o n products
through the boundary l a y e r .
And
solid reaction
u c t s a l s o slow the r e a c t i o n r a t e by b l o c k i n g area a v a i l a b l e f o r r e a c t i o n .
Patchet
(^D
off
has
prodthe
also
i n v e s t i g a t e d " i n d u s t r i a l cases" component e l e c t r o d e and
i n ESW
s l a g systems.
these experiments t h a t r e a c t i o n s can taneously
and
involving multiI t i s noted i n
take p l a c e
simul-
they a l t e r the composition of the r e f i n e d (28
product.
Work c a r r i e d out by
57,
has
suggested t h a t although the process operates under
5 8
(chemical
in
and
agreement
'
33,
a
)
several investigators w i t h Patchet's f i n d i n g s
k i n e t i c ) dual regime, the s t a r t i n g thermo-
dynamic c o n d i t i o n s a t l e a s t can be used to i n i t i a t e c a l c u l a t i o n s i n v o l v e d i n p r e d i c t i n g the equilibrium" conditions.
On
et a l .
t h a t during
have r e p o r t e d
the other
metal drops l e a v i n g the e l e c t r o d e
"dynamic hand, Cooper
AC-melting;
i n terms of s u l f u r ,
reach chemical e q u i l i b i r u m with the s l a g and extent
that
of the r e a c t i o n s between l i q u i d pool and
They a l s o c l a i m t h a t the
r e a c t i o n s which o c c u r r e d
at t h i s
to minor temperature and
Hawkins e t al.(58)
who
differences
T h i s apparent
d i c t i o n i s c l a r i f i e d by M i t c h e l l
( 2 7
'
3 0
'
4 1
?
contraand
have e s t a b l i s h e d that although
an a c t u a l thermodynamic e q u i l i b r i u m may
not be
attained
i n i n d u s t r i a l ESR-operation; the k i n e t i c s of the c e s s , however, are so f a v o r a b l e brium i s reached. s l a g s and
only
( l a t t e r ) s i t e were
compositional
w i t h those of the e l e c t r o d e .
the
slag
were almost n e g l i g i b l e .
due
the
I t has
pro-
t h a t a s t a t e c l o s e to e q u i l i -
a l s o been found t h a t low. v i s c o s i t y
h i g h l y e f f e c t i v e r e a c t i n g area enable
the
r e a c t i o n s to reach
such a s t a t e of n e a r - e q u i l i b r i a
6378) .
Several studies
shown t h a t
on C a F ~ A l 0 2
2
although t h i s s l a g system has
concentrations
of A l , S i and Mn
tendency to achieve
3
'
s l a g s have
high
viscosity
i n ESR-ingots have the
(
6 3 ,
'
6 9
7 0
^
have a l s o found
t h a t r e g a r d l e s s of the number of e l e c t r o c h e m i c a l k i n e t i c parameters of the ESR-process, a simple chemical
has
or thermo-
( e q u i l i b r i u m ) approach i s s u f f i c i e n t to p r e (71)
d i e t the f i n a l i n g o t composition. s t u d i e d the S i - S i 0 t h a t i f there
2
Mitchell
r e a c t i o n , has
i s a constant
the s l a g i n which y°
i s high
a l s o sug-
i r o n oxide
source i n
then i t i s f e a s i b l e
t h a t the e f f e c t i v e oxygen p o t e n t i a l w i l l be t h a t of Fe-FeO e q u i l i b r i u m . which supports the and
53
the t h e o r e t i c a l e q u i l i b r i u m .
Other r e s e a r c h e r s
gested
'
(168)
'
who
(49
Petersen's
Perhaps (ESR)
(72, 73)_
the most t y p i c a l work
e q u i l i b r i u m theory I n
the
^h^g
W O
rk
i s Holzgruber
i t has been es-
t a b l i s h e d t h a t s u l f u r removal i s e n t i r e l y dependent upon the s l a g chemistry.
Other s t u d i e s along
of the p r e v i o u s work
a l s o c a r r i e d out by Miska e t
was
the
lines
(38) al.
•
.
These r e s e a r c h e r s
Holzgruber e t a l . ' s p r o p o s a l . obtained
by r e m e l t i n g
deoxidizer who
have a l s o agreed with Miska e t a l . ' s f i n d i n g s
low a l l o y s t e e l u s i n g A l as a
were not i d e n t i c a l to Holzgruber e t a l . ' s
used d i f f e r e n t e l e c t r o d e chemistry
practices.
and
Si-deoxidation
They have a t t r i b u t e d these d i f f e r e n c e s to
the d e o x i d a t i o n
p r a c t i c e and a l s o t o the presence of
Mn and A l i n the e l e c t r o d e . been s t u d i e d under s e v e r a l
The S i - S i C ^ r e a c t i o n has (ESR) s l a g systems.
g r u b e r ^ ^ , Holzgruber and P l o c k i n g e r 7 5
Holz-
^ *^ and Miska 7
(38) and
Wahlster
furnaces
have found t h a t i n i n d u s t r i a l
ESR-
t h i s r e a c t i o n reaches a s t a t e of e q u i l i b r i u m .
(75) influence of several a l l o y s and the i n f l u e n c e (38) of the A1 C>2 i n the s l a g i s a l s o shown. Kusamichi (77) The
2
et a l . ' s f i n d i n g s
i n agreement with p r e v i o u s work,
have a l s o shown t h a t the S i - S i C ^ behavior i s l i n e a r l y r e l a t e d t o the b a s i c i t y index of the s l a g . there
Although
are i n d i c a t i o n s of the v a l i d a t i o n of the thermo-
chemical e q u i l i b r i u m achieved d u r i n g should be p o i n t e d
refining i t
out t h a t t h i s e q u i l i b r i u m i s very
temperature-dependent^ ^. 48
Retelsdorf
and Winterhager
^ ^ 9
f
Boucher
and
(79) Jager and Kuhnelt
have s t u d i e d the A l - A ^ O ^ r e -
a c t i o n and conclude t h a t the A l and the oxygen content from ESR-ingots indeed f o l l o w the t h e o r e t i c a l (thermodynamic)
equilibrium.
(46 47 49-51) Abundant i n f o r m a t i o n ' ' ' exists i n the l i t e r a t u r e which e s t a b l i s h e s the v a l i d i t y of the v
(83) equilibirum-reaction
theory.
Rehak e t a l . ' s s t u d i e s
on the A l and S i d i s t r i b u t i o n i n ESR-ingots
a l s o favour
the thermodynamic approach of the ESR-reaction system.
They c l a i m t h a t r e a c t i o n s i n v o l v i n g these s p e c i e s are r u l e d by the e l e c t r o d e composition and by the i n d i v i d u a l a c t i v i t y of the components of the s l a g . (76) Holzgruber and P l o c k i n g e r ' s
work
and Choudhury
(44) et a l . ' s
are a l s o i n agreement with Holzgruber and (72
Petersen's
73) '
.
T h e i r thermodynamic approach on
s l a g chemistry as a f u n c t i o n of the a c i d i t y - b a s i c i t y concept and A l d e o x i d a t i o n
techniques
in industrial
p r a c t i c e , c l e a r l y r e v e a l t h a t indeed e q u i l i b r i u m i s reached. Kamardin e t a l . low
who have r e f i n e d 0.38 wt. % carbon
a l l o y Cr-Mo s t e e l s d e o x i d i z e d
with aluminum
have
concluded t h a t d e s p i t e t h e i r approximate method t o c a l c u l a t e the a c t i v i t y of the s l a g components
(by means o f
t e r n a r y diagrams o f the CaD-A^O^-SiG^-system) , the pred i c t i o n o f the A l and S i - c o n c e n t r a t i o n s
i n r e f i n e d ingots
can be estimated u s i n g a thermodynamic treatment. The p r e v i o u s phasized gory
d e s c r i p t i o n has e s s e n t i a l l y been
on r e a c t i o n o f the type
which i n v o l v e s r e a c t i n g
has a l s o been e x t e n s i v e l y of t h e i r study
( 1 1 ) . The other
s p e c i e s between two
studied.
i s t h a t they l a r g e l y
a l t e r the c h e m i s t r y o f
em-
liquids
The importance c o n t r i b u t e to
i n d u s t r i a l ESR - i n g o t s .
m o d i f i c a t i o n of the i n g o t chemistry
cate-
The
( " l o n g i t u d i n a l seg-
27 r e g a t i o n " ) becomes more c r i t i c a l where h i g h a c t i v i t y r e a c t i v e elements i s p r e s e n t . r o l e p l a y e d by
the T i
Because of the
in either superalloys
s t a b i l i z e d s t a i n l e s s s t e e l s , a considerable
of
important or T i -
e f f o r t has
been devoted to understand the mechanism by which a homogeneous l o n g i t u d i n a l T i - d i s t r i b u t i o n i s reached in refined ingots.
Although there are evidences i n
1-4. a. literature
71,
t h e r e are
(37, • few
74)
. . . . ,. ^ , which i n d i c a t e the mechanism,
s t u d i e s which c l e a r l y r e v e a l
(46 studies
48, •
it.
Pateisky's
47) '
have shown t h a t the r e a c t i o n
(12-vi)
indeed a t t a i n s e q u i l i b r i u m .
It i s also indicated
this equilibrium
a f f e c t e d by
i s strongly
Krucinski's
ment w i t h P a t e i s k y ' s
have a l s o i n d i c a t e d t h a t
brium.
studies
also pointed
out
that Ti-oxides
i s the r e a c t i o n
have remelted ingots
tility
the
(11-vi and
11-vii)
studied
A l l i b e r t et a l .
under S i C ^ - s l a g s
'
'
'
of lower v o l a -
have shown t h a t t h i s r e a c t i o n does f o l l o w i t s
stoichiometric slope
has
from the i n d u s t r i a l (47 49 55)
been e x t e n s i v e l y
(12-viii).
equili-
of lower valency i n
Another i n t e r e s t i n g r e a c t i o n viewpoint which has
the
Krucinski
s l a g s h o u l d be c o n s i d e r e d , i . e . r e a c t i o n s
who
i n agree-
(12-vi) a c t u a l l y reaches a s t a t e of In a d d i t i o n to the above f a c t s
that
the thermal (52)
reaction conditions.
reaction
the
i s 0.781
ratio.
The
[Al] vs
[Si] p l o t whose
indeed c o r r o b o r a t e s t h i s f a c t and
also
i n d i c a t e s the r e v e r s i b i l i t y which i s reached as a manif e s t a t i o n of a s t a t e o f e q u i l i b r i u m .
Kay's
studies^
suggest t h a t t h i s r e a c t i o n i s not i n f l u e n c e d by the oxygen p o t e n t i a l .
This conclusion
i s a l s o supported
by O p r a v i l (81) . Choudhury e t a l . (78) who have r e f i n e d ingots
(2300 mm
i n diameter) u s i n g 2.5 Hz AC. ESR
s t u d i e d the r e a c t i o n
(12-ix).
ment with Holzgruber s
Their r e s u l t s
have
i n agree-
and Holzgruber and P l o c k i n g e r s
1
1
^
c l e a r l y show t h a t the s l a g b a s i c i t y p l a y s a s i g n i f i c a n t r o l e i n the Si-Mn d i s t r i b u t i o n i n ESR-ingots.
Choudhury s 1
r e s u l t s a l s o show t h a t the type of c u r r e n t does not i n f l u e n c e the i n g o t c h e m i s t r y .
I t i s a l s o p o i n t e d out
t h a t Mn l o s s e s take p l a c e o n l y when the CaOtSiC^ r a t i o i n the s l a g i s l e s s than 3.
They a l s o c l a i m t h a t
the continuous A l - a d d i t i o n d u r i n g r e f i n i n g and
Mn are unavoidable.
The s t o i c h i o m e t r y
despite
the l o s s of S i of t h i s r e a c t i o n
was not i n v e s t i g a t e d . (37) Buzek and Hlineny recovery
rates
concerned w i t h the low Mn-
(50-58%) have used i s o t o p i c oxygen
18 {O
} above the s l a g t o determine the r e a c t i o n mechanism.
T h e i r f i n d i n g s * i n d i c a t e t h a t by A l - d e o x i d a t i o n proved Mn-recovery i s a t t a i n e d .
Although they have not s p e c i -
f i c a l l y e s t a b l i s h e d i t s thermodynamic behavior i n d i c a t e i t s high e f f e c t i v e n e s s . reduction-oxidation
im-
they d i d
They c l a i m t h a t the
mechanism i s r u l e d by the r e a c t i o n
(12-x). Regarding the has
s o - c a l l e d deoxidation
suggested the use
of extreme care i n any
s i n c e s e v e r a l r e a c t i o n s may has
been p o i n t e d
instances action
out t h a t r e a c t i o n
( 1 2 - i i ) may
has
a well-defined
(8).
^
approach
operate s i m u l t a n e o u s l y .
be c o n t r o l l e d by r e a c t i o n
(12-i)
r e a c t i o n s , Kay
It
i n some
Since the
re-
e q u i l i b r i u m constant
of a v a l u e c l o s e to u n i t y i n the range of ESR-temperatures, Fraser
has
date i t s mechanism.
d e l i b e r a t e l y s e l e c t e d i t to
He has
may
proceed to the
and
subsequently r e v e r s e
the s l a g - i n g o t
quently
noted t h a t t h i s r e a c t i o n
l e f t a t the e l e c t r o d e - s l a g
This proposal
steady s t a t e c o n d i t i o n s
d i f f e r e n c e between the two Mitchell the type
( 3 0 )
has
extended t h i s p r o p o s a l
are an
h
the A l d i s t r i b u t i o n s by
fre-
the
thermal
to r e a c t i o n s
of
i n d i c a t i o n of the
"deoxidation
a
v
e
studied
the S i , T i ,
r e f i n i n g i n g o t s under
have found a " s a t i s f a c t o r y " stab-
of these elements.
a t t a i n e d during on
which are
the
(12-vi).
s e v e r a l s l a g systems ility
l e d to
major e l e c t r o a c t i v e s i t e s .
K r i c h e v e c e t a l . (^O) and
has
observed i n r e a c t i o n s of t h i s type are a con-
sequence of a dynamic balance c r e a t e d by
Mn
interface
a t the h i g h e r temperature of
interface.
b e l i e f t h a t the
eluci-
They c l a i m t h a t these f i n d i n g s "practical" equilibrium
refining. reactions"
conditions
T h e i r s t u d i e s were performed (12-iv).
30
As d e s c r i b e d i n p r e v i o u s s e c t i o n s
the formation of
i r o n oxide d u r i n g r e f i n i n g i s almost unavoidable, e i t h e r as a r e s u l t of e l e c t r o c h e m i c a l r e a c t i o n s or as a r e s u l t of the r e a c t i o n s between the s l a g and the atmosphere d u r i n g r e f i n i n g . • These sources o f i r o n o x i d e i n c o n j u n c t i o n with the oxide on the e l e c t r o d e s u r f a c e b e f o r e and d u r i n g r e f i n i n g ,
formed
i n the presence of the oxide
components of the s l a g generate a l i q u i d with e x t e n s i v e (1 immiscibility
38 '
.
t o u n i t y a t very low
"FeO"
binary
(CaF ~FeO) ^ , 2
Al 0 ~FeO) ^ 2
'
82) Hence, the
F
e
0
concentrations.
rapidly
S t u d i e s on
t e r n a r y (CaF -CaO-FeO) ^ *,
and i n quaternary
3
rises
a
1
2
(CaF ~ 2
(CaF -Al 0 -CaO-Al 0 -FeO) ^ 2
2
3
2
3
systems have shown t h i s b e h a v i o r . A CaF
2
s l a g can permit very l i t t l e oxygen b e f o r e i t
becomes o x i d i z i n g with r e s p e c t to i r o n .
Consequently,
any
element which forms an o x i d e more s t a b l e would then be o x i d i z e d from the metal i n t o the s l a g . more c r i t i c a l where r e a c t i v e metals T i are p r e s e n t .
T h i s f a c t becomes
such as A l , S i , Zr, and
S e v e r a l techniques have been proposed such a problem:
1) A complete
to overcome
removal of s c a l e on the
e l e c t r o d e s u r f a c e and the use of an i n e r t atmosphere (74) (He or N ) , 2) p a i n t i n g the e l e c t r o d e s u r f a c e a f t e r s c a l e i s removed w i t h an A l or a magnesia-alumina s p i n e l (38) p a i n t to prevent o x i d a t i o n of the e l e c t r o d e , 3) en2
r i c h i n g electrodes i n oxidable Zr, A l , S i , e t c . , oxide
(FeAl or FeSi) ^ ^ 84
(CaF -Ca>
( 8 5
2
(83)
such as
4) continuous a d d i t i o n s of a)
formers as elements
alloys
elements
strong
( A l , S i , T i , Zr, e t c . ) , and
b) f e r r o
c) s l a g - d e o x i d i z e r composites
' >. 8 6
(34)
Holzgruber
suggests t h a t
use of a p r o t e c t i v e atmosphere d a t i o n i s achieved
i n a d d i t i o n to
a more e f f i c i e n t
i f a deoxidizer
the
deoxi-
( A l , S i or T i ) i s added
i n a s l a g system which does not c o n t a i n i t s oxide. Other . (39 , 46, 55, 60) . _ ^ researchers ' ' ' have proposed t h a t i f an element i s prone to o x i d a t i o n
l i k e T i , S i , Zr,
during
ESR-process then a d d i t i o n s of i t s r e s p e c t i v e oxide vents i t s l o s s e s .
Kay's
^
f i n d i n g s i n d i c a t e t h a t by
f i n i n g a l l o y s which c o n t a i n A l , T i and oxide
slags
Zr i n f r e e - t i t a n i u m
As the amount of Ti02 i n the s l a g i n c r e a s e s
the d e o x i d a t i o n
i s only c a r r i e d out by A l and
and
a l s o found t h a t by adding 15%
Zr.
The
the Si-decrement i n the i n g o t are con-
t r o l l e d by the exchange r e a c t i o n
containing
re-
the three elements i n the e l e c t r o d e a c t as
deoxidizers.
Al-increment
pre-
Ti0
2
(12-viii).
0.5% Zr.0
2
Kay
to the s l a g
has initially
i s s u f f i c i e n t to p r o t e c t the Zr
con-
(79)
t e n t of the r e f i n e d a l l o y .
Jager e t a l .
t h a t the e f f e c t of the A l - c o n t e n t
from the e l e c t r o d e or
a d e o x i d i z e r i s very dependent upon the s l a g The
net content
of A l t r a n s p o r t e d
have shown as
chemistry.
i n t o the i n g o t i s almost
constant f o r a given A^O^-content the s l a g
(up to 24 wt. %) i n
and a l s o f o r a g i v e n CaO: S i 0
ratio
2
(up t o 2 ) .
If these two parameters a r e i n c r e a s e d the n e t A l - c o n t e n t of the ESR-ingot
increases d r a s t i c a l l y
hence l e a d i n g t o (78)
d e l e t e r i o u s mechanical (79) and Jager e t a l . proved
properties.
Chouldhury e t a l .
have claimed t h a t by u s i n g an "im-
technique" a maximum A l content of 0.01 wt %
can be a t t a i n e d i n i n d u s t r i a l
125 tonnes
ESR-ingots.
In these two communications the d e o x i d a t i o n r a t e s , how(55) ever, a r e not g i v e n .
Kajioka e t a l .
have s t u d i e d the
e f f e c t o f A l - d e o x i d a t i o n under s e v e r a l s l a g systems, namely CaF ~CaO, C a F - A l 0 2
2
2
and C a F - A l 0 - C a O - S i 0 . They have
3
2
2
3
2
found
t h a t d e o x i d a t i o n r a t e s between 0.05 t o 0.1 wt. % A l produce the b e s t " r e s u l t s " , i n the i n g o t .
i . e . an almost
steady
Al-distribution (34)
On the other hand, Holzgruber
proposes
a d e o x i d a t i o n r a t e o f 6.2 wt. % A l . 2.2.3
Thermodynamic Approach o f the ESR-Slag Systems Another important
area o f the ESR-slag
thermo chemical approach. important,
In t h i s f i e l d
system i s i t s
although
very
very l i t t l e i n f o r m a t i o n has been r e p o r t e d .
(45) Mitchell A1 0 2
has found t h a t i n the common system CaO +
+ Si0
3
2
+ CaF
2
there a r e only three f l u o r i d e - c o n t a i n i n g
compounds other than the i n d i v i d u a l f l u o r i d e s , i . e . C
11 7 ' 3 3 A
F
C
A
F
a
n
d
C
9 3 ' S
F
w
n
e
r
e
c
' ' A
F
a
n
d
s
stand f o r
33 CaO, has
A 1 0 , CaF 2
3
2
and
Si0
respectively.
2
This
been taken as an i n d i c a t i o n t h a t the C a F
s i d e r e d as an
observation may
2
be
con-
i n e r t d i l u e n t i n h i g h l y b a s i c areas of
these systems, s i n c e the acid-base i n t e r a c t i o n s i n v o l v i n g 20 would be 54) who 30 wt.
stronger
than those f o r F .
(53 A l l i b e r t et a l . '
have remelted a l l o y s through 70 wt. %
% A1 0 2
3
with 0,
2,
5,
10,
and
15 wt.
C a F
% Si0
p e c t i v e l y , have a p p l i e d M i t c h e l l ' s c r i t e r i a .
2
res-
2
Their
f i n d i n g s show t h a t the acid-base i n t e r a c t i o n s i n the ernary
CaO
+ A l ^ O ^ + Si0
2
+ CaF
same as those i n the t e r n a r y
are approximately
2
CaO
+ A^O^
'
+ SiC^
s
Y
quatthe
s t e m
f
d i l u t e d i n the C a F . There are o t h e r i n d i c a t i o n s i n the 1 -4. t.. *_ , ^ • , (38, 58, 88 , 89) l i t e r a t u r e which a l s o support t h i s theory (14 53 54) 2
A l l i b e r t et a l .
'
'
a l s o suggest an a l t e r n a t e method
f o r r e a c t i o n s r e l a t e d p r i m a r i l y to b a s i c i t y , i . e . the C a O / S i 0 r a t i o concept which i s s t r o n g l y supported i n the (34, 49-51, 72-76) . , . , . (38) German l i t e r a t u r e ' ' . Miska and Whalster 2
M
who
have s t u d i e d
the C a F - C a O - A l 0 - S i 0 - F e O system 2
2
3
found t h a t i f the A l 0 : C a O r a t i o i s g r e a t e r 2
the C a F
2
than
3
a t ESR-temperatures remains i n e r t and
composition behaves as i t were i n the C a O - A l 0 2
Chai's and fluxes
Eagar's s t u d i e s o n
have
2
3.0,
the
slag
binary.
3
CaF ~metal oxide welding 2
have concluded t h a t the o x i d i z i n g p o t e n t i a l of
these types of s l a g s i s reduced o n l y by these s p e c i e s
i n the C a F
2 <
The
the d i l u t i o n
a d d i t i o n of C a F
2
of
i n these
34
s l a g systems has i d e s and
almost no e f f e c t on the more s t a b l e
hence the C a F
2
was
v i r t u a l l y considered
ox-
as a
diluent. 2.2.4
O v e r a l l View on the M o d e l l i n g
of ESR-Reactions
(57) A r e c e n t work
has
c l e a r l y revealed
understanding of the E S R - r e a c t i o n system.
the
I t has
i n d i c a t e d above t h a t there are e s s e n t i a l l y two proach the r e a c t i o n p a t t e r n . r e a c t o r and
the
These are the
current been
ways to
equilibrium
" s i n g l e - s t a g e r e a c t o r " concepts.
e q u i l i b r i u m - r e a c t o r method i s by
f a r a simpler
The
approach.
I t i s supported by the i d e a t h a t an a c t u a l s t a t e of brium i s reached d u r i n g r e f i n i n g ,
as p r e v i o u s l y
equili-
indi-
cated.
I t s p r i n c i p l e i s to
a
s l a g w i t h an e l e c t r o d e of a given composition
(ESR)
ap-
(thermodynamically) e q u i l i b r a t e This
technique i n t r i n s i c a l l y assumes a unique e q u i l i b r i u m tempe r a t u r e and ume.
a mass t r a n s f e r flow through a f i x e d s l a g v o l -
These two
major assumptions
as a l r e a d y
indicated,
are not n e c e s s a r i l y t r u e . The t a c t and pointed
second approach c o n s i d e r s
a t r a n s i t i o n a l phase con-
a "lumped m a s s - t r a n s f e r c o e f f i c i e n t . "
I t has
out t h a t although t h i s model resembles the
e q u i l i b r i u m nature of the process
non-
i t r e l i e s on a mass-
t r a n s f e r c o e f f i c i e n t which does not have a t h e o r e t i c a l background i n i t s computation.
Another disadvantage of
been
t h i s technique i s t h a t r e a c t i o n s o f the type
i t i s not able to account f o r (12). M i t c h e l l has a l s o p o i n t e d out 2+
t h a t both techniques r e l y on the Fe i n p u t datum.
c o n c e n t r a t i o n s as an
T h i s parameter, however, i s unknown and has
to be determined e x p e r i m e n t a l l y . As d e s c r i b e d here, these two concepts have both advantages
and disadvantages.
N e v e r t h e l e s s , i t can be un-
m i s t a k e a b l y seen t h a t the main o b j e c t i v e of these two a l t e r n a t i v e s i s to p r e d i c t and c o n t r o l the i n g o t chemical homogeneity .
36 2.3
P r e c i p i t a t i o n of
2.3.1
General
Inclusions
Since endogeneous i n c l u s i o n s are no longer as f o r e i g n p a r t i c l e s
but
" n a t u r a l " components of
today's technology demands from m e t a l l u r g i s t s
considered steel,
skillful
c o n t r o l of them to y i e l d products which c o u l d f u l l y i s f y the r e q u i r e d s t r i n g e n t standards.
sat-
A v a s t amount of
(90-98) r e s e a r c h has been devoted d e o x i d i z e r s and
to study the e f f e c t s of
deoxidation
techniques
i s known t h a t s i n c e elemental liquid iron at
(0.168 and
0.20
o r d i n a r y steelmaking
i n the p a s t .
oxygen i s h i g h l y s o l u b l e i n
wt.
% a t the monotectic
d e o x i d i z e r can be s e l e c t e d to maintain
oxygen content
to a g i v e n l e v e l .
with is has
The
first
s u l f u r i n the melt.
i n p a r t i c u l a r cases The
capability
simultaneously
second important requirement
i t s a b i l i t y to be removed from the melt once o x i d a t i o n taken p l a c e . „
. ..
..
. ,.
(99-106) .
S o l i d i f i c a t i o n - p r e c i p i t a t i o n studies shown t h a t the
tinuous
have
i n c l u s i o n p r e c i p i t a t i o n sequence, as a
measure of the degree of d e o x i d a t i o n
and
the
requirement
d e o x i d i z e r i s o b v i o u s l y a high
to r e a c t with oxygen and
and
temperatures r e s p e c t i v e l y ) , then
an a p p r o p r i a t e
expected from any
It
processes.
i s a s e r i e s of con-
These comprise the n u c l e a t i o n , growth
e l i m i n a t i o n of the d e o x i d a t i o n
products.
The
nucle-
a t i o n phenomena can be homogeneous or heterogeneous
and
i t can take p l a c e i n the l i q u i d stage or during fication.
To homogeneously n u c l e a t e a phase
sary t o o r i g i n a t e
solidi-
i t i s neces-
a s u p e r s a t u r a t i o n and i t can be reached
by u n d e r c o o l i n g o f the s p e c i e s i n s o l u t i o n ,
by a d d i t i o n s (9
of e i t h e r a d e o x i d i z e r or oxygen and during
solidification
If there a r e some s o l i d p a r t i c l e s i n a melt where deoxida t i o n products ation
can d i f f u s e t o
(precipitation) At steelmaking
then a heterogeneous n u c l e -
occurs.
temperature some oxides, o x i s u l f i d e s and
s u l f i d e s a r e g e n e r a l l y found
i n s o l u t i o n with l i q u i d
Once s o l i d i f i c a t i o n s t a r t s , s e g r e g a t i o n
(due to incomplete
d i f f u s i o n i n the s o l i d ) i n the i n t e r d e n d r i t i c As soon as t h i s i n t e r d e n d r i t i c cipitation clusions
liquid
l i q u i d i s saturated
takes p l a c e .
c o n t i n u e s u n t i l the s o l i d u s
i s reached. further
of i n c l u s i o n s
steel.
occurs. pre-
P r e c i p i t a t i o n of i n temperature o f the melt
Under p a r t i c u l a r circumstances
as w i l l be
d e s c r i b e d , p r e c i p i t a t i o n takes p l a c e a t even lower
temperature ranges.
I n c l u s i o n s i z e , shape, q u a n t i t y and
d i s t r i b u t i o n i s p r i n c i p a l l y given by the s o l i d i f i c a t i o n r a t e and by the s o l u b i l i t y i n the l i q u i d s t e e l
.
of certain
chemical
species
Maximum s o l u b i l i t y o f these
s p e c i e s i n f l u e n c e s the p r e c i p i t a t i o n sequence d u r i n g dification. solubility
soli-
As an a p r i o r i r u l e , f o r s p e c i e s which have low i n liquid steel
precipitation
c i p i e n t s o l i d i f i c a t i o n i s observed.
s t a r t s when i n -
These types o f i n -
38 e l u s i o n s w i l l have longer time f o r growth. O x i - s u l f i d e s and
s u l f i d e s which are p r e c i p i t a t e d as
a r e s u l t of monotectic r e a c t i o n s are i n c l u d e d i n t h i s
cate-
gory.
high
On the other hand, i f s o l u b i l i t y i s r e l a t i v e l y
p r e c i p i t a t i o n takes p l a c e at the l a s t stage of c a t i o n and
hence these phases are c o n f i n e d to
solidifilocalized
areas. While i n the f i r s t case i n c l u s i o n s are g l o b u l a r , large ond
and
group
have l a r g e i n t e r p a r t i c l e d i s t a n c e s , i n the i n c l u s i o n s are very
around g r a i n s or d e n d r i t e s .
small and u s u a l l y l o c a t e d
S i n g l e phase or composite
f i l m s around d e n d r i t e s are a l s o i n c l u d e d i n t h i s kind.
The
second
s o l u b i l i t y of some s p e c i e s i n l i q u i d s t e e l
a l t e r the s u l f i d e chemistry
sec-
and
, . (90,106,107) sequence and s i z e '
can
hence i t s p r e c i p i t a t i o n
2.3.2
Nucleation
2.3.2.1
Homogeneous N u c l e a t i o n
According
and Growth of I n c l u s i o n s
to the homogeneous n u c l e a t i o n theory
posed by Volmer and Weber-Becker the f o r m a t i o n
and
pro-
Doring^®^'^
o f a new phase from a l i q u i d phase
occurs
o n l y i f s u p e r s a t u r a t i o n e x i s t s i n the parent phase. , , (99,101,110,111) e r a l researchers ' • the i n t e r f a c i a l saturation Popel^
1 1
^
interfacial
tension
(a)
Sev-
. i T x. have r e v e a l e d t h a t
and the degree of super-
(C:C») of a melt i n f l u e n c e the n u c l e a t i o n r a t e . has c a l c u l a t e d the r a t e s o f n u c l e a t i o n f o r t e n s i o n s ranging
from 180 to 100 ergs/cm
and s u p e r s a t u r a t i o n r a t i o s from 1 t o 10.
2
His s t u d i e s
show t h a t f o r systems (FeO-MnO) where the a = 180 ergs/cm , 2
28 he obtained
a n u c l e a t i o n r a t e of about 10
a t i o n r a t i o s as low as .1.5.
a t super s a t u r -
With C:C°° r a t i o s o f about 10, 35
the n u c l e a t i o n r a t e s were i n c r e a s e d to 10
.
On the other
hand i n systems (FeO-MnO-Si0 ) where the i n t e r f a c i a l 2
t e n s i o n i s about 700 ergs/cm
2
i n c l u s i o n s i s extremely small
the n u c l e a t i o n r a t e o f -79 (10 ) for supersaturation
40
r a t i o s of l e s s than 3.
I t becomes a p p r e c i a b l e , however,
a t C:C°° r a t i o s of about 10. about 1000
ergs/cm
2
For i n t e r f a c i a l
t e n s i o n s of
as i n the CaO-A^O^-SiC^ system,
homogeneous n u c l e a t i o n of i n c l u s i o n s becomes very cult.
diffi-
These c o n c l u s i o n s are s i g n i f i c a n t f o r d e o x i d a t i o n
d u r i n g c o o l i n g and
solidification.
During
c o o l i n g of a
w e l l - d e o x i d i z e d melt which does not c o n t a i n any i n c l u s i o n s there i s a p o s s i b i l i t y interfacial
of formation of an oxide with
t e n s i o n , e.g.
T u r p i n and c l a s s i c a l theory
Elliot
FeO'A^O^ and
FeO-rich
lower
silicates.
u s i n g Volmer and Weber's ^^8)
obtained
an e x p r e s s i o n f o r c r i t i c a l
super-
s a t u r a t i o n i n terms of the f r e e energy f o r homogeneous n u c l e ation.
They have found t h a t h e r c y n i t e was
formed i n i r o n
melts where thermodynamically alumina should have p r e cipitated.
Thus, they
suggested t h a t s u p e r s a t u r a t i o n i s
r e q u i r e d t o produce homogeneously n u c l e a t e d Chipman ^
X 1 1
^
has
alumina phases.
suggested t h a t both A l ^ O ^ and
p r e c i p i t a t e simultaneously
FeO'A^O-j
may
i f there i s not complete mixing (112-113)
i n the melt.
McLean and Ward
have i n d i c a t e d t h a t
h e r c y n i t e may
a l s o p r e c i p i t a t e a f t e r an i n i t i a l alumina p r e -
41 c i p i t a t i o n when the metal i s d e p l e t e d brium i n t h i s case is between A^O^,
in A l .
The
FeO-A^O^
equili-
dissolved (99)
oxygen and
the l i q u i d i r o n .
shows t h a t i f the c r i t i c a l nucleate
A^O^
Turpin*s
and
E l l i o t ' s work
f r e e energy to homogeneously
were much g r e a t e r than t h a t f o r h e r c y n i t e ,
the p r e c i p i t a t i o n s of the l a t t e r phase becomes more f e a sible.
These r e s e a r c h e r s
concentrations
have a l s o concluded t h a t a t high
of d e o x i d i z e r or a l t e r n a t i v e l y of oxygen
r e l a t i v e to normal bath compositions i n e q u i l i b r i u m with pure oxide e f f e c t and
i s r e q u i r e d to overcome the s u r f a c e
tension
thus to p r e c i p i t a t e phases homogeneously.
They have a l s o p o i n t e d out t h a t the common method of adding the d e o x i d i z e r to a molten p o o l p r o v i d e s s a t u r a t i o n to form very c l u s i o n was
sufficient
small i n c l u s i o n s .
super-
T h i s con-
a l s o reached by Turkdogan ^^1)
showed
t h a t i f the deoxidant i s assumed to be evenly d i s t r i b u t e d i n the melt b e f o r e n u c l e a t i o n . then the s u p e r s a t u r a t i o n
at-
t a i n e d would be an order of magnitude l e s s than t h a t necessary f o r homogeneous n u c l e a t i o n .
He
therefore
postulated
t h a t the d i s s o l u t i o n of d e o x i d i z e r i n l i q u i d s t e e l
takes
a f i n i t e time d u r i n g which c e r t a i n r e g i o n s of the melt are expected
to be very r i c h i n s o l u t e c o n c e n t r a t i o n .
these r e g i o n s
l i q u i d metal a t t a i n s s u f f i c i e n t l o c a l
super-
s a t u r a t i o n f o r homogeneous n u c l e a t i o n . I n v e s t i g a t i o n s c a r r i e d out by Von
Bogdandy^ ^' on 114
In
n u c l e a t i o n of aluminum c o n t a i n i n g phases showed t h a t when the deoxidant i s c a r e f u l l y i n t r o d u c e d
i n t o the melt
the
i n c l u s i o n s form i n a l a y e r at a d e f i n i t e time and l o c a t i o n . They have p o s t u l a t e d t h a t very h i g h s u p e r - s a t u r a t i o n
ratios
14 (10 ) are r e q u i r e d f o r homogeneous n u c l e a t i o n of these oxides. These values are s e v e r a l o r d e r s of magnitude (99) higher
2.3.2.2
than those obtained
Heterogeneous
In a c t u a l p r a c t i c e
by
Turpin
Nucleation l a r g e degrees o f
supersaturation
are not r e q u i r e d i f the p r e c i p i t a t i o n of i n c l u s i o n s take
, . , s u r .f a c e s (115)
-i
p l a c e on s o l i d
From the above d i s c u s s i o n i t i s e v i d e n t t h a t
nucle-
a t i o n of i n c l u s i o n s i n s t e e l i s not the r a t e c o n t r o l l i n g step because high s u p e r s a t u r a t i o n
i s reached near
r e g i o n s where the d e o x i d i z e r s are t r a n s p o r t e d l i q u i d pool.
These n u c l e i are u n i f o r m l y
to s t i r r i n g of the melt f u r t h e r oxides
the
i n t o the
d i s t r i b u t e d due
(during r e f i n i n g ) and p r e c i p i t a t e
as c o o l i n g and
solidification
takes p l a c e .
However, the presence of p r e - e x i s t i n g i n c l u s i o n s from electrodes
( i f any), make heterogeneous n u c l e a t i o n more
f a v o r a b l e where r e f i n i n g c o n d i t i o n s are not optimum.
2.3.3
Growth of
Inclusions
By u s i n g Shewman's f o r m u l a t i o n ^ among the phenomena which c o n t r i b u t e clusions gots gen
from n u c l e i
(2-4 and
ym),
the
(0.1
ym)
can
see
to s i z e s found i n ESR
p r e c i p i t a t i o n on
i s the mechanism which i n the
the
nuclei
l e a s t amount of time
process.
The
in(oxy-
generate i n c l u s i o n s i z e s i n the range
a r i l y found i n the ESR
that
to growth of i n -
growth by d i f f u s i o n of s o l u t e s
d e o x i d i z e r s ) and
sees.) c o u l d
one
(^
1-2
ordin-
above c a l c u l a t i o n s 7
are very dependent on cm ). 5 - 3
(10
Turkdogan
) at the
the number of n u c l e i p r e s e n t u s e (
j
a
d i f f e r e n t number of
s t a r t i n g conditions
and
hence h i s
showed t h a t a d i f f e r e n t maximum r a d i u s (23
ym)
was
(6 sees ).
of
nuclei
calculations
inclusions
reached i n a s l i g h t l y h i g h e r p e r i o d The
(10
of
time
above i n f o r m a t i o n p l u s some o t h e r t h e o r (117)
e t i c a l c a l c u l a t i o n s performed by
Lindberg and
i n a s i m i l a r a p p l i c a t i o n of Wert's and
Torsell
Zener s model^ 1
1 1 8
^
c l e a r l y i n d i c a t e t h a t t h i s growth mechanism i s a very f a s t process. Experimental work performed by s e v e r a l r e (107 117 119 120) searchers ' ' ' agree w i t h p r e v i o u s c a l c u l a t i o n s . During c o o l i n g
and
solidification
the growth of
inclusions
becomes more s i g n i f i c a n t as p r e c i p i t a t i o n c o n t i n u e s on existing particles.
Iyengar^ ^ 1 2
has
pre-
formulated a model
44 to p r e d i c t the growth under the above c o n d i t i o n s .
His r e -
s u l t s have shown t h a t the time f o r completion of growth i s dependent on the i n i t i a l
s i z e of i n c l u s i o n s .
almost n e g l i g i b l e .
Thus, these
are c l e a r l y i d e n t i f i e d w i t h r e s u l t s found 27
de-
6 7 With 10 -10 nuclei/cm
creases with i n c r e a s e i n r a d i u s . the growth was
T h i s time
in
3
results E S R ' " ' '
2
1
'
30) '
l i q u i d p o o l s and
i n g o t s , i . e . growth i s almost
en-
t i r e l y achieved by d i f f u s i o n of s o l u t e s . (117 The
second phenomenon which has been observed
'
120-122) to l a r g e l y c o n t r i b u t e t o the growth of
inclusions
i n c o n v e n t i o n a l m e l t i n g p r a c t i c e s i s the c o l l i s i o n a l e s c e n c e mechanism.
T h i s mechanism i s s t r i c t l y
t o the motion o f oxide i n c l u s i o n s i n l i q u i d
co-
related
steel.
For a g i v e n s i z e d i s t r i b u t i o n of i n c l u s i o n s i n a melt there i s a d i s t r i b u t i o n of r i s i n g v e l o c i t i e s '
2 1
^.
The
l a r g e r i n c l u s i o n s w i l l l e v i t a t e more r a p i d l y than the s m a l l e r , ,,. . (117,122) ones and as a r e s u l t c o l l i s i o n may occur ' The c o a l e s c e n c e o f i n c l u s i o n s depends on
impact,
speed and angle, s u r f a c e p r o p e r t i e s such as s u r f a c e t e n s i o n , chemical composition l i q u i d or
and t h e i r p h y s i c a l s t a t e ( i . e .
solid).
I t has been observed
t h a t the motion of
inclusions
i n s t e e l f a l l s w i t h i n the v i s c o u s flow regime where the Reynolds number of the p a r t i c l e
i s l e s s than one.
This
45
includes
i n c l u s i o n s i z e s i n the 0-50 ym range.
condition, Stokes
1
Under t h i s
Law (13)
Ust = i s a p p l i c a b l e provided
the system i s c o n s i d e r e d
t o be d i -
l u t e and p a r t i c l e i n t e r a c t i o n can be n e g l e c t e d . a t i o n o f Stokes' L a w ^ tions:
126
^
depends upon the f o l l o w i n g
1) i n c o m p r e s s i b i l i t y o f the medium,
extent of the medium, velocity,
4) r i g i d i t y of i n c l u s i o n s ,
The parameter i n v o l v e d Ust = t e r m i n a l
condi-
2) i n f i n i t e
3) very small and c o n s t a n t
at the f l u i d - p a r t i c l e i n t e r f a c e and cles.
The d e r i v -
terminal
5) absence o f s l i p p i n g 6) s p h e r i c i t y o f p a r t i -
i n t h i s expression a r e :
v e l o c i t y according
t o Stokes' Law,
(cm/sec.) p
s
, p = density
pectively,
o f the p a r t i c l e and the medium r e s -
(g/cm ) 3
r - r a d i u s o f the sphere, (cm) y = v i s c o s i t y of the medium, The
above c o n d i t i o n s
in reality.
Corrections,
(g/cm. sec.)
are very d i f f i c u l t
however, can be a p p l i e d t o ac-
count f o r the d e v i a t i o n from i d e a l i t y . the a v a i l a b l e c o r r e c t i o n s . provided
to s a t i s f y
Table
(I) l i s t s
Stokes' Law i s a p p l i c a b l e ^
1 2 6
^
t h a t g r a v i t y i s the only e x t e r n a l f o r c e a c t i n g on
inclusions.
I f an i n c l u s i o n i s i n a melt
as i n the ESR
46
p r o c e s s , which i s i t s e l f spherical
i n motion, then the drag on a
p a r t i c l e i s g i v e n by: Dc = -6iryr (v-u)
where
v = velocity
(vector) of sphere
u = resulting velocity rounding
(14) due to g r a v i t y and
(vector) due t o movement o f the s u r -
fluid.
In order t o o b t a i n an e x p r e s s i o n f o r the v e l o c i t y of the i n c l u s i o n s i s necessary location
r e l a t i v e to a f i x e d c o o r d i n a t e system
t o know the r e s u l t i n g v e l o c i t y
it
(u) a t every
i n the melt.
Iyengar's
work' ^ 2 1
has c l e a r l y r e v e a l e d
through
e r a l mathematical approaches
t h a t growth of i n c l u s i o n s
any other mechanism i s almost
negligible.
sevby
47
2.3.4
Sulfides The
i d e a of "hot s h o r t n e s s " was
l a s t century.
conceived
i n the
T h i s t o p i c , however, r e c e i v e d more a t t e n t i o n (127
i n the e a r l y 30's
128) '
.
The
so c a l l e d
"steel
burning"
or "overheating phenomenon" has been s t u d i e d s i n c e then. Research through s u l f u r was
the years has l e d to the c o n c l u s i o n t h a t
l e s s d e t r i m e n t a l when manganese was
present.
Since then Mn has been used to modify the s u l f i d e phase. I f Mn
i s absent or p r e s e n t i n i n s u f f i c i e n t amounts
f o r m a t i o n o f FeS
i s almost
inevitable.
the
T h i s phase has
a
very low m e l t i n g p o i n t (1190° C) and when i t i s combined with i r o n or FeO phase
(940°C).
i t forms a lower m e l t i n g p o i n t e u t e c t i c T h i s e u t e c t i c p r e c i p i t a t e s between g r a i n s
(129-132) or d e n d r i t e s
. I f t h i s s t e e l i s to be heated
a u s t e n i t i c temperatures
f o r f u r t h e r mechanical
at
working
then g r a i n detachment o c c u r s ^ ^ " ^ ^ . T h i s problem (133) • (overheating") has been observed even i n ESR-materials.
Thus Mn
has the c a p a b i l i t y to modify the
phase from a l i q u i d temperatures the Mn:S
"FeS"
to a s o l i d
(1900- 1200°C) .
"MnS"
a t hot working
T h i s t r a n s i t i o n occurs where (92)
r a t i o i s h i g h e r than 4
s u l f i d e i n c l u s i o n s i n low carbon
.
The
i d e a l form f o r
s t e e l s i s to have a pure
MnS-phase which melts a t about 1610°C. k i n d s of MnS
sulfide
Three d i f f e r e n t (90 134) have been u s u a l l y r e p o r t e d ' , MnS I - I I I .
T h e i r s t a b i l i t y depends on the c o o l i n g r a t e and on chemistry of the melt (136-139) ^
T
^
e
t
r
a
n
s
-L i t
o
f
n
r
the o
m
type I to I I o c c u r s i f the oxygen content i n the s t e e l i s d i m i n i s h e d to l e s s than 100 ppm. II
The
t r a n s i t i o n of type
to I I I i s o b t a i n e d by the i n f l u e n c e of two
parameters,
a low oxygen content and a high a c t i v i t y of s u l f u r . has been r e p o r t e d t h a t the presence C a
(140
142)
p
r
o
m
0
4 -
and H i l l e r t ' ^ 3
tem
of C, S i , P, A l and
f o r m a t i o n of MnS
e
who
It
III.
Fredriksson
have s t u d i e d the Fe-O-S t e r n a r y s y s -
have claimed t h a t as a r e s u l t of a c o o p e r a t i v e -
eutectic reaction
where MnS
forms as a c r y s t a l l i n e phase
t o g e t h e r with the F e - r i c h phase, a MnS-type IV i s formed. The morphology o f these s u l f i d e s has g e n e r a l l y been desc r i b e d as g l o b u l a r , b r a n c h e d rod and i d i o m o r p h i c f o r type (93 I,
I I and I I I , r e s p e c t i v e l y
142) '
.
which they are formed i s as f o l l o w s . type I
The mechanism by Sulfide
inclusions
are u s u a l l y a s s o c i a t e d with o x i - s u l f i d e s
(eutectic
type) and are p r e c i p i t a t e d as a r e s u l t of a monotectic reaction. almost
Since p r e c i p i t a t i o n of s u l f i d e s takes p l a c e
s i m u l t a n e o u s l y with the deoxidaton process
an o x i d e ^ s u l f i d e and a s u l f i d e w i l l be formed.
(type I) e n r i c h e d phase
The phase which p r e c i p i t a t e s f i r s t i s (91 142)
r i c h e r i n oxygen than the second phase or
then
'
.
Rimmed
s e m i k i l l e d i n d u s t r i a l i n g o t s (with r e l a t i v e l y h i g h
oxygen content and low s u l f u r s o l u b i l i t y ) c o n t a i n t h i s
49 type of s u l f i d e .
Ingots which have been d e o x i d i z e d
the
t h e o r e t i c a l required
low
oxygen content and
deoxidation initially reaction ^
1 3
amount of aluminum w i l l have
high s u l f u r s o l u b i l i t y .
p r a c t i c e produces MnS
thought to be ^
.
II.
This
T h i s type
was
formed as a r e s u l t of a e u t e c t i c
More r e c e n t
ideas i n d i c a t e t h a t i t i s
o r i g i n a t e d by a c o o p e r a t i v e monotectic r e a c t i o n . also believed
with
It i s
that t h i s s u l f i d e p r e c i p i t a t e s at i n (91)
c i p i e n t s o l i d i f i c a t i o n stages. out
t h a t s i n c e alumina and
t o g e t h e r but
MnS
f o r the
frequently
to p r e c i p i t a t e MnS
These c o n d i t i o n s
observed
lower s u l f u r s o l u b i l i t y
are
I I I i n s t e e l s , than i n MnS
II.
are a t t a i n e d because of the excess of A l
This
s u l f i d e p r e c i p i t a t e s i n the e a r l y stages
of s o l i d i f i c a t i o n as a s i n g l e phase. that the
pointed
s u l f i d e (type I I ) .
Lower oxygen content and
in solution.
II are
has
as d i s t i n c t phases then the alumina phase
a c t s as a s u b s t r a t e
required
Kiessling
I t has
been o b s e r v e d ^
t h r e e types are p r e c i p i t a t e d i n between g r a i n s
or
dendrites. Recent c o m m u n i c a t i o n s ^ MnS
IV
'
1 4 3
^
which p r e s e n t s a "ribbon"
c a t i o n of e i t h e r I - I I I who
1 3 8
have s t u d i e d
( 1 3 9 )
or I I
the k i n e t i c s and
have suggested
pattern (
1
4
3
)
.
is a Ito et
that
modifial.
chemical i n f l u e n c e
(
1
3
9
of
melts on the MnS-shape
c l a i m t h a t type II r e s u l t s from
a e u t e c t i c r e a c t i o n and
type I and
III
(type N)
are
)
pre-
142
^
50 c i p i t a t e d from s o l i d s t e e l . given.
Steinmetz e t a l . d
4 3
A mechanism, however was not )
who have s t u d i e d the Fe-Mn-O
and the F e - S i - 0 systems a t 1500° and 1600°C
have shown
t h a t there are areas of s t a b i l i t y f o r the three MnS
types
when the [S] v s . [0] and the [S] v s . [Mn] are p l o t t e d . In t h i s work, i t i s a l s o proposed t h a t MnS-morphology
is
very dependent upon the l o c a l a c t i v i t y c o n d i t i o n s o f oxygen and the degree of d e o x i d a t i o n
( S i or Mn).
a s u c c e s s i o n of d i f f e r e n t c o n d i t i o n s
Thus, i f
i n terms of l o c a l
a c t i v i t y or degree o f d e o x i d a t i o n of melts
i s made then
a continuous s e r i e s of m o r p h o l o g i c a l changes i n MnS's would take p l a c e , i . e . from s p h e r i c a l
( o x i s u l f i d e ) a t h i g h oxy-
gen a c t i v i t i e s , r o d l i k e , d e n d r i t i c and " s k e l e t o n " shape a t medium oxygen a c t i v i t i e s and pseudo and h i g h l y talline last
(MnS) a t very low oxygen
"transition"
(MnS I I t o MnS
(local) a c t i v i t y .
crysThis
I I I ) has been observed
when a melt i s d e o x i d i z e d e i t h e r by A l , Ca or Ca-bearing (140,142,144,145) a l l ovc:
'
'
'
51
2.3.5
Specific
Sulfides
K i e s s l i n g and Lange
(91)
(92) and S a l t e r and P i c k e r i n g
have e s t a b l i s h e d t h a t double s u l f i d e s of the type are f r e q u e n t l y found. elements
Me r e p r e s e n t s any o f the f o l l o w i n g
T i , V, N i , Cr, Fe, Zr, Mg and Ca.
Pickering ^ h a v e
(Mn, Me)s
S a l t e r and
s t u d i e d the replacement o f Mn by Fe
i n the double s u l f i d e . 0.5 to 32 wt. % Fe.
They found t h a t i t ranges
from
The maximum s o l u b i l i t y l i m i t , however, (91)
d i s a g r e e s w i t h p r e v i o u s work performed by K i e s s l i n g (41.0).
The Cr s u b s t i t u t i o n f o r Mn i n these
has a l s o been s t u d i e d by these r e s e a r c h e r s .
,
sulfides While
Salter
(92) and P i c k e r i n g
have r e p o r t e d a replacement o f Mn by (91)
Cr ranging from 0-5 to 25 wt. % ( C r ) , K i e s s l i n g
who
has s t u d i e d these compounds i n s y n t h e t i c s u l f i d e s found a maximum replacement of 26 wt. % Cr.
has
Perhaps
the
most important double s u l f i d e which has become a f o c u s o f a t t e n t i o n with the advent o f the C a - i n j e c t i o n processes i s the (Ca, Mn)S. , .^
.
literature
There i s abundant i n f o r m a t i o n i n the
(140, 144, 158) '
'
...
^ , ,. ,
.
.
which e s t a b l i s h e s t h a t t h i s com-
pound i s p r e c i p i t a t e d on complex Ca-aluminates a p e r i p h e r a l envelope.
S a l t e r and P i c k e r i n g
forming d ^) 4
n
a
v
e
found t h a t s i n c e CaS i s isomorphous with the MnS (NaCl type o f l a t t i c e ) then e x t e n s i v e CaS s o l u b i l i t y i n MnS should be expected.
They have a l s o found a l i m i t e d s o l u b -
i l i t y of FeS
(4% Fe)
i n the above
l i n g and W e s t m a n ' ^
(CaS-MnS) system.
Kiess- ,
have determined the e x i s t e n c e of a
4
( t r i a n g u l a r shaped) m i s c i b i l i t y gap which shows a maximum
i m m i s c i b i l i t y a t approximately 120 0°C and a t 50
Ca + Mn,
(in at.%).
A t approximately 1000°C i t i s i n c r e a s e d
from 2 5 to 8 5 Ca/Ca + Mn.
These r e s e a r c h e r s
t h i s m i s c i b i l i t y gap
may
i.e.
r i c h phases.
C a - r i c h and Mn
d i v i d e the
ment with r e s p e c t to the Ca and Mn or MnS 6.0
phases.
wt.%
Mn
S a l t e r and from 1.0 ively.
(Ca, Mn)S
i n t o two
and
from 3.0
s o l u b i l i t i e s i n the
to 7.0
wt.
4
wt.
% f o r Mn
i n CaS
and
CaS
from 3.0
% Ca i n to 12.0
Ca i n MnS
to
MnS.
wt.
% and
respect-
Eklund s t u d i e s ' ^ ^ ^ supported by K i e s s l i n g and
man's f i n d i n g s o n
types
There i s c e r t a i n d i s a g r e e -
P i c k e r i n g ' * ^ r e p o r t from 1.0
to 19.0
suggest t h a t
Church e t a l . ' ^ ® ^ have r e p o r t e d
i n CaS
Ca/
West-
the i n i t i a t i o n of c o r r o s i o n i n i n c l u s -
i o n s , has a l s o i d e n t i f i e d the e x i s t e n c e of these phases. t h i s study i t i s shown t h a t while remains almost i n e r t severely attacked. l i n g and
the s u l f i d e phase e n r i c h e d
i n Ca
T h i s f i n d i n g i s i n agreement with
Westman's who
have a l s o observed the CaS
i t i o n to hydrogen s u l f i d e and sence of water.
Ca-sulfide enriched
in
In Mn
was Kiess-
decompos-
c a l c i u m hydroxide i n the
pre-
53 2.3.6
Oxisulfides
2.3.6.1
The
Fe-Q-S System
Rosenqvist and Dunicz
(161)
and
Turkdogan e t a l .
(162)
have determined the s o l u b i l i t y o f s u l f u r i n high p u r i t y iron.
I t i s e s t a b l i s h e d t h a t the maximum s o l u b i l i t y of
s u l f u r i n d e l t a - i r o n i s 0.18 wt.% a t 1365°C.
A t the same
temperature the gamma-iron holds o n l y 0.06 wt.%. bility
g e n e r a l l y decreases w i t h temperature but a l p h a -
i r o n a t 913°C holds 0.02 wt.%. has
The s o l u -
been s t u d i e d e x t e n s i v e l y .
The Fe-O-S t e r n a r y
system
H i l t y and C r a f t s ^ ^ ^ have 3
determined the l i q u i d u s s u r f a c e based on chemical and m e t a l l o graphic
analysis.
T h e i r r e s u l t s show t h a t the Fe-FeS-FeO
as the most important p a r t o f the Fe-O-S system i n the range o f p r a c t i c a l i n t e r e s t , i s c o n s t i t u t e d by a t e r n a r y e u t e c t i c a t 67 wt.% Fe, 24 wt.% S, 9 wt.% 0 920°C.
and about
A m i s c i b i l i t y gap which extends i n t o the system
from the Fe-0 s i d e to a s u l f u r content a t 21.5 wt.% a minimum p o i n t Fe,
with
( p l a i t p o i n t ) a t approximately 81.5 wt.%
16.5 wt.% S, 2 wt.% O and a t 1345°C.
The s o l u b i l i t y o f
oxygen i n i r o n a t s e v e r a l temperatures has a l s o been d e t e r mined by H i l t y and C r a f t s ^ ^ 3 ) ^
j t i s indicated that f o r
increasing s u l f u r concentrations
the oxygen content o f
i r o n f i r s t decreases s l i g h t l y up t o about 0.1% S and then increases r a p i d l y .
The s o l u b i l i t y o f s u l f u r i n i r o n as a
54 r e s u l t o f the oxygen i n f l u e n c e has been determined dogan e t a l .
166)^ T h e i r f i n d i n g s i n d i c a t e t h a t i n
the e q u i l i b r i u m Fe-S-O. s a t u r a t e d with w u s t i t e temperature
by Turk-
i n the
range between 913°C t o 1375°C, there i s a p r o -
nounced expansion on the s u l f u r s o l u b i l i t y curve which reaches a maximum o f 143 ppm o f S a t about v a l u e corresponds
1200°C.
This
to almost h a l f o f t h a t of the s o l i d u s on
the Fe-S diagram. Yarwood e t a l . ' ^ " ^
have proposed
an i n c l u s i o n pre-
c i p i t a t i o n model f o r the Fe-FeS-FeO system. mgs
Their f i n d -
4. - 4 . U 4-v, u (90,134,135, 163) i n agreement with other r e s e a r c h e r s ' ' ,
show t h a t the p r e c i p i t a t i o n sequence monotectic r e a c t i o n ,
as a r e s u l t o f the
i s indeed a f f e c t e d by the %0:%S r a t i o ,
(0:S), i n the a l l o y .
I f t h i s r a t i o i s g r e a t e r than 0.05.
i n c l u s i o n s w i l l have a wide range of compositions.
They a l s o
found t h a t w h i l e the maximum oxide content i n i n c l u s i o n s was
dependent on the i n i t i a l J m
was
not.
i J
0:S r a t i o , the minimum content
• (164-166)
Kor and Turkdogan's
ment w i t h Yarwood e t a l . ' s '
0 5
.
-it,
, •
i n qualitative ^
agree-
i n d i c a t e t h a t f o r 0:S
r a t i o s g r e a t e r than 0.12 two l i q u i d s form a t a g i v e n tempe r a t u r e and composition.
T h e i r experiments
on an a l l o y
con-
t a i n i n g 0.02% C and an 0:S r a t i o o f 0.29, c l e a r l y r e v e a l the presence o f the l i q u i d
oxysulfide.
55 2.3.6.2
The Fe-O-S-Mn
"Equilibrium"
H i l t y and C r a f t s ^ ter
1 2 9
'
i
n
t h e i r aim t o g a i n a b e t -
understanding of the d e o x i d a t i o n p r a c t i c e and the i n -
c l u s i o n chemistry
have
s t u d i e d the Fe-S-O,
Fe-S-Mn, Mn-O-S
and the Fe-O-Mn systems t o develop the Fe-O-S-Mn
system.
They have suggested t h a t the Fe-S-0 i s s t r o n g l y m o d i f i e d if
the Mn content i n the a l l o y
i s h i g h enough t o enhance
the p r e c i p i t a t i o n o f the s u l f u r - f r e e oxide and the oxygenfree sulfides,
s i m u l t a n e o u s l y with the s o l i d i f i c a t i o n of
the m e t a l l i c phase.
S e m i - q u a n t i t a t i v e work performed on
the Fe-O-S system
by these r e s e a r c h e r s
by adding 0.3% Mn
the i m m i s c i b i l i t y r e g i o n s from the Fe-O-S
and the Fe-S-Mn a r e encountered m i s c i b l e r e g i o n i s formed.
indicates
and hence a continuous im-
They propose
t h a t the metal
oxide and metal s u l f i d e e u t e c t i c s are i n i t i a l l y to
that
formed c l o s e
the i r o n c o r n e r , d i a g o n a l l y i n t e r s e c t the i m m i s c i b i l i t y
r e g i o n and meet the " t e r n a r y " e u t e c t i c .
I t was a l s o
t h a t the e u t e c t i c i n the m o d i f i e d t e r n a r y remained i n the same l o c a t i o n as i n the o r i g i n a l Fe-O-S Van V l a c k e t a l . ^ s h o r t n e s s " problem
1
3
^
almost
system.
a l s o concerned w i t h the "hot
have observed t h a t i f the Mn content
i s about 0.8% i n the Fe-O-S system, d u r i n g quenching
found
this alloy
originates
duplex o x i d e - s u l f i d e i n c l u s i o n s .
The
s u l f i d e phase e n r i c h e d i n Mn was a r e s u l t o f a primary crystallization.
I t was a l s o noted t h a t i f the Mn content
56 i n the t e r n a r y a l l o y
(Fe-O-S) was low then FeS and Mn-
r i c h oxide phases were p r e c i p i t a t e d . (164-166)
. m
Turkdogan and Kor
,
f
.. . _
a s e r i e s o f papers have compiled
i n f o r m a t i o n concerning the Fe-Mn-S-0 system.
thermodynamic Oxygen and
s u l f u r p o t e n t i a l diagrams which a r e i n v o l v e d i n t h i s q u a t e r (93) nary have been developed
'.
Turkdogan and Kor based
on H i l t y and C r a f t s o b s e r v a t i o n s ' * * ^ and on t h e o r e t i c a l 3
thermodynamic
data developed by Darken and Gurry
have p r o -
posed t o r e p r e s e n t the s t a b i l i t y phase f i e l d s f o r the Fe-Mn-S-0 system under s e v e r a l c o n d i t i o n s .
They have
esti-
mated t h e c o e x i s t e n c e o f gamma i r o n , Fe(Mn)0, FeS, Mn(Fe)S and a l i q u i d o x y s u l f i d e , £^ , as the e q u i l i b r i u m phases a t about 900°C, F i g u r e
( 3 ) . The a
mated t o be u n i t y and 0.4 r e s p e c t i v e l y
p
e
S
and a
(condensed) M
n
g
were e s t i -
and hence t h e e q u i l i _3
brium manganese i n gamma i r o n was computed
t o be lOppm (10
%).
The f o u r f o l d phase e q u i l i b r i u m i n v o l v i n g the gamma i r o n , Mn(Fe)0, Mn(Fe)S and l i q u i d o x y s u l f i d e
(£^), c o n s i d e r e d as
perhaps the most important u n i v a r i a n t e q u i l i b r i u m i n the quaternary
(Fe-O-S-Mn) system
has been estimated on the
premise o f an i d e a l l i q u i d o x y s u l f i d e s o l u t i o n , i . e . a + a + a _ + = i. They c l a i m t h a t s i n c e FeO FeS MnO MnS a
J
ideal
mixing behavior i s observed i n the FeO-FeS l i q u i d i n e q u i l i brium with gamma i r o n and MnO-MnS and s i n c e the FeO-MnO forms an i d e a l s o l u t i o n
then the i d e a l behavior c o n s i d e r e d i n
the FeO-FeS-MnO-MnS i s a reasonable assumption.
The behavior
of Mn i n i r o n under the above c o n d i t i o n s i s g i v e n i n F i g ure
(3) and Table ( I I ) . The r e a c t i o n scheme used t o e s t a b l i s h the phases i n -
v o l v e d i n such e q u i l i b r i a a r e :
M n 0
M n S
(s)
+
(s)
+
F e
F e
( s ) * FeO (s)
t
FeS
+ Mn
( 1 )
MnO
(s)
t MnO
MnS
( s )
t
M n S
+ Mn
( 1 )
(15)
( s )
(16)
( s )
< ) 17
(1)
(i)
( 1 8
I t has been e l u c i d a t e d t h a t i f a., _ = a.. _ s 1 MnS MnO
)
(be-
cause o f t h e i r low Fe i n s o l u t i o n and the Mn a c t i v i t i e s or atom f r a c t i o n s i n i r o n ) then an e x p r e s s i o n i s o b t a i n e d to r e p r e s e n t the Mn content o f s o l i d i r o n f o r t h i s
equili-
brium: 1 -N (K, + K_) ( — - — — ) + Mn
K-, + K. = 1 ; where N = atom
fraction.
By t a k i n g a., „ = 0.4 and a., = 0.5 a t the i n v a r i a n t MnS MnO 3
e q u i l i b r i u m l o c a t e d a t 900°C and u s i n g the above e x p r e s s i o n , the d o t t e d curve
i n Figure
(3) i s o b t a i n e d .
The Mn contents
o f gamma i r o n i n e q u i l i b r i u m w i t h s o l i d Mn(Fe)S and l i q u i d s u l f i d e , i n curve
(k) have been e s t a b l i s h e d u s i n g the "FeS"-
"MnS" phase diagram.
Raoult's
Law was assumed f o r the s o l u b -
i l i t y o f "FeS" i n "MnS". The curves
j and k show the s t r o n g e f f e c t o f oxygen on the
m e l t i n g p o i n t o f t h e o x y s u l f i d e phase i n the Fe-Mn-O-S (j) and
58 the
Fe-Mn-S (k) systems r e s p e c t i v e l y .
a l i q u i d phase l e s s than 10
I t i s seen t h a t w h i l e
(point A) i s formed when the Mn content i s % i n the former system ( j ) , the minimum Mn
content t o suppress the l i q u i d phase on the Fe-Mn-O-S system at
1200°C i s 1%.
The i n v a r i a n t e q u i l i b r i u m
(j)
which i n -
v o l v e s the gamma i r o n , Mn(Fe)0, Mn(Fe)S and the l i q u i d s u l f i d e phases
oxy-
i s the most important e q u i l i b r i u m i n the
Fe-Mn-O-S system by which the "hot s h o r t n e s s " can be avoided. Turkdogan and Kor have shown t h a t as long as the s t e e l cont a i n s Mn(Fe)0 and Mn(Fe)S i n e q u i l i b r i u m with the metal, a l i q u i d o x y s u l f i d e may
form between 900° and 1225°C
on the c o n c e n t r a t i o n o f Mn i n s o l u t i o n i n s t e e l . the
Mn-content i n s o l u t i o n
depending The h i g h e r
the h i g h e r i s the temperature
above which a l i q u i d phase i s p r e s e n t . (165 Experimental work performed by Kor and Turkdogan
'
166) have
clearly
shown
the
above
by
(0.34% Mn and 150 ppm S) a t about 900°C.
oxidizing
iron
They found a de-
p l e t i o n of Mn and accumulation of S i n the metal c l o s e t o the
scale-metal i n t e r f a c e .
These changes b r i n g about the
f o r m a t i o n of l i q u i d o x y s u l f i d e near the s u r f a c e above 900°C and the p r e c i p i t a t i o n of p y r r h o t i t e below 900°C. of
low i n t e r f a c i a l
tension
Because
the l i q u i d o x y s u l f i d e has been
seen to p e n e t r a t e i n t o the g r a i n boundaries i n the metal and the s c a l e .
They have a l s o observed t h a t most of the
l i q u i d phase i s found a t the s c a l e - m e t a l i n t e r f a c e . o b s e r v a t i o n s have a l s o been r e p o r t e d by other 1 6 9
)
These (130,
researchers
who have s t u d i e d more complex systems. Turkdogan and Kor who have taken as a b a s i s the i n -
formation and technique
used t o c o n s t r u c t f i g u r e
have extended t h e i r experimental table
( I I I ) , t o d e s c r i b e the Mn behavior
of other
(terminal) phase f i e l d s .
Mn-S-0 and Fe-Mn-O. low
and t h e o r e t i c a l
s o l u b i l i t y o f oxygen i n i r o n
the Fe-S-O, t h a t due t o the
stable deoxidation
u c t s i n commercial s t e e l s must be present. nary Fe-Mn-O-S system
data,
i n the presence
Namely
They have suggested
(4),
prod-
In the q u a t e r -
the Mn(Fe)0 has been taken as the
most s t a b l e oxide which i s p r e s e n t a t a l l temperatures o f interest.
As shown i n F i g u r e
(4),
the M n - p o t e n t i a l
i s given by two i n v a r i a n t s a t two temperatures, 900 and 1225°C: m-n-j
1) the i n v a r i a n t
g i v e n by the i n t e r s e c t i o n o f the
u n i v a r i a n t s which i s c o n s t i t u t e d by the gamma i r o n ,
Mn(Fe)0 as ( o x i ) , FeS, i^, "MnS" and the gaseous phase a t about 900°C and
2) the i n v a r i a n t given by the i n t e r s e c t i o n
of the u n i v a r i a n t s j , p and q.
The i n v o l v e d phases i n
t h i s e q u i l i b r i u m are an Fe/Mn s o l i d phase, "MnS", "MnO", l i q u i d oxide
(SL^) and l i q u i d metal
{l^) a t about
1225°C.
The most complete r e p r e s e n t a t i o n o f the phase changes i n c l u d i n g the l i q u i d , d e l t a and gamma i r o n developed Figure
by Kor and Turkdogan
(5).
The i n v a r i a n t VII
has a l s o been
^ and i t i s g i v e n i n r e p r e s e n t s the immiscible
r e g i o n i n the Fe-Mn-0 system
a t 1527°C.
I t i s important
to p o i n t o u t t h a t t h i s i n v a r i a n t was assumed t o be e q u i v a l e n t t o the Fe-0 m i s c i b i l i t y gap.
The phases i n e q u i l i -
brium a t V I I are d e l t a - i r o n , Mn(Fe)0, (£ ^) and l i q u i d metal previously described involved
"i^- •
system, a r e d e l t a - i r o n "MnO" a low s o l u b i l i t y product
oxide
The u n i v a r i a n t s V and VI were
i n Figure
i n the u n i v a r i a n t e
(Oxi), l i q u i d
(4).
The e q u i l i b r i u m phases
which are f o r the Fe-Mn-0 and l^-
Since
the "MnO" has
a t high M n - a c t i v i t i e s
(>1% Mn)
the e q u i l i b r i u m oxygen i n s o l u t i o n i s so low t h a t the s o l i dus
i n the Fe-Mn-0 i s almost e q u i v a l e n t
The
u n i v a r i a n t g was a l s o assumed e q u i v a l e n t
binary
system.
In g e n e r a l
g and f r e p r e s e n t liquid
t o the Fe-Mn system. t o the Fe-Mn
i t can be s a i d t h a t the u n i v a r i a n t s
the gamma t o d e l t a and the d e l t a t o
i r o n transformations
respectively.
The three
phase f i e l d s i n t h i s f i g u r e a r e the d e l t a - i r o n
new
+ Ox +
which i s l i m i t e d by the e - f u n i v a r i a n t s , the gamma-iron + Ox + £
2
which l i e s between
6 i r o n + Ox + g and f .
f';^ e u n i v a r i a n t s and the
which i s l o c a t e d between the u n i v a r i a n t s
The f - f ' u n i v a r i a n t s correspond t o the Fe-Mn-0
system a l r e a d y
described
i n Figure (4).
C r a f t s and H i l t y ' s w o r k '
2 9
' * ) on
i n c l u s i o n p r e c i p i t a t i o n diagrams representation
6 7
pseudo-equilibrium
has a l s o i n c l u d e d the
o f the Fe-O-Si-Mn-S system as a pseudo-
t e r n a r y , Fe(Mn, S i ) - 0 - S .
I t i s proposed t h a t t h i s
system
61
i s i n t e g r a t e d by metal-oxide,
m e t a l - s u l f i d e and s u l f i d e -
oxide m i s c i b i l i t y gaps which i n t e r s e c t themselves ucing an almost i s o m e t r i c i n t e r n a l t r i p l e
liquid
prodregion.
E q u i v a l e n t t o t h e i r proposed Fe(Mn)-0-S pseudo-ternary there are metal-oxide and metal s u l f i d e e u t e c t i c s which g i n a t e i n the metal corner and pass through f o l d immiscible
region.
ori-
the t h r e e -
These b i n a r y e u t e c t i c s c o n t i n u -
o u s l y decrease i n temperature u n t i l they reach the pseudotriple eutectic.
I t i s a l s o p o s t u l a t e d t h a t while the
above " t e r n a r y " i s u s e f u l t o r e p r e s e n t melts
silica
saturated
a pseudo t e r n a r y which c o u l d d e s c r i b e low S i t o Mn
r a t i o s should be d i f f e r e n t . fluxes s i l i c a
They c l a i m t h a t s i n c e the Mn
a s h i f t of the metal o x i d e - e u t e c t i c towards
the o x i d e c o r n e r o f the diagram would be expected.
I t has
a l s o been proposed t h a t s i n c e there i s s o l u b i l i t y between "MnS" and MnO-SiC^ may disappear
then the s u l f i d e - o x i d e m i s c i b i l i t y gap
and the pseudo-ternary e u t e c t i c would move
towards the oxide c o r n e r . granular higher
I t i s a n t i c i p a t e d t h a t more i n t e r -
s u l f i d e s are expected i n t h i s case than i n the
silicon
steels.
62
2.3.6.3
The Fe-Si-O-S-Mn
System
Other more complex systems have a l s o been g e n e r a l i z e d i n the m o d i f i e d p s e u d o - t e r n a r i e s , namely the F e ( S i ) - 0 - S , Fe(Mn, S i , h i g h A l ) - 0 - S , Fe(Mn, S i , low Al)-0-S and the Fe(Al,Ca)-0-S s y s t e m s
( 1 2 9 ,
1
6
7
)
.
The e x t e n s i v e e f f o r t d e d i c a t e d to c o n t r o l the "hots h o r t n e s s " problem i s c l e a r l y r e v e a l e d by C r a f t s and H i l t y (129) studies
.
I t i s seen t h a t the search f o r adequate de-
o x i d i z e r s which c o u l d promote the formation of h i g h m e l t i n g p o i n t phases has been the main aim.
The most common
f e a t u r e o f these diagrams i s t h a t the l a s t l i q u i d to solidify
i s a ternary e u t e c t i c .
as t h e i r authors have s t a t e d
These t e r n a r y diagrams
are n o t t r u e t e r n a r i e s and
hence "the r a t i o n a l i z a t i o n o f the problem i s i n t u i t i v e i n c h a r a c t e r and l i a b l e t o c o n s i d e r a b l e e r r o r , but should be h e l p f u l i n the e f f o r t t o b r i n g i n c l u s i o n s under c o n t r o l " . Silverman^ problem
a l s o concerned with the "hot s h o r t n e s s "
has s t u d i e d the Fe-Mn-Si-S-0
system.
He has
claimed t h a t i f the m e t a l l i c phase i s r e l a t i v e l y
neglected
the i n c l u s i o n chemistry o f the f i v e f o l d system can be reasonably w e l l r e p r e s e n t e d by the MnS-MnO-FeO-Si0 T h i s system was " s l i c e d " ,
as d e p i c t e d i n F i g u r e
t e r n a r y p l a n e s , shown i n F i g u r e are pseudo t e r n a r i e s FeO-MnO-MnS.
(7a-c).
2
system.
(6)
Two o f these
i n three planes
the 2FeO«Si0 -2MnO«Si0 -MnS and the
The t h i r d plane.
2
2
FeO-MnO•Si0 ~MnS 2
i s more d i f -
63
f i c u l t t o analyze because of i t s f i v e primary phase The
fields.
"A" area i s p r e s e n t i n the three planes and i t r e p -
r e s e n t s the "FeS" s t a b i l i t y
field.
The primary c r y s t a l l i z a t i o n 2MnO«Si0 -MnS-plane i s a s o l i d 2
2FeO«SiC>
2
and 2MnO«SiC> . 2
product on the 2FeO«SiC> 2
s o l u t i o n c o n s i s t i n g of
The second and t h i r d
products
are the FeS'-phase a t "A" and a mixture o f two i m m i s c i b l e l i q u i d s a t "B". as f o l l o w s : silicates
Silverman's o b s e r v a t i o n s can be summarized
1) The MnS-FeO-MnO•Si0
2
plane shows t h a t
liquid
e n r i c h e d i n "FeO" a l l o w more "MnS" i n s o l u t i o n
than l i q u i d
silicates
e n r i c h e d i n "MnO".
2)
This plane
a l s o shows t h a t "MnS" i s more s o l u b l e i n "FeO" than i n the l i q u i d
silicates
content o f the l i q u i d
i n t h i s plane.
s i l i c a t e decreases and the S i 0
t e n t i n c r e a s e s , the s o l u b i l i t y decreases.
3) As the "FeO"
o f "MnS" i n l i q u i d
2
con-
silicate
4) Samples from area "A" i n the MnS-FeO-MnO«Si0
2
plane suggest t h a t the "FeS"-phase s o l i d i f i e s as a e u t e c t i c a t about 910°C.
Silverman^
MnS i s f l u x e d by s i l i c a t e s
has concluded t h a t s i n c e
and oxides i n the planes s t u d i e d
then i n c l u s i o n s i n t h i s system are p a r t i a l l y and f i n i s h i n g
liquid
temperatures.
Van Vlack e t a l . ' s r e s e a r c h ' ^ i n l i n e with 3
work'^ ^ 9
at r o l l i n g
Silverman's
has s e m i - q u a n t i t a t i v e l y shown how the s i l i c o n
a f f e c t s the i n c l u s i o n chemical behavior i n v a r i o u s
systems.
64
In
t h i s work the m e t a l l i c phase n e g l e c t e d by Silverman i s
now
taken i n t o account.
Van V l a c k e t a l . ' s f i n d i n g s
be summarized i n the f o l l o w i n g p o i n t s :
can
1) I f s i l i c o n i s
added i n "small or moderate" q u a n t i t i e s to an Fe-S
alloy
u n d e t e c t a b l e changes i n i n c l u s i o n shape and composition w i l l be observed.
"FeS" was
the o n l y phase p r e s e n t .
Fe-S-0 a l l o y
s i l i c o n was
a l s o added.
n o n - m e t a l l i c phases were p r e s e n t . in
One
In t h i s a l l o y
2
3) I f s i l i c o n
i s added to a t e r n a r y Fe-Mn-S a l l o y whose Mn:S i n c l u s i o n s remain
(about
1200°C).
were observed.
solid at austenitic
ratio
(Mn,Fe)S
4) I f s i l i c o n and oxygen were added to (they generate the Fe-Mn-Si-S-0 system)
a l i q u i d phase s i l i c e o u s i n c h a r a c t e r was
observed.
a s s o c i a t e d with s a t u r a t e d MnS.
observed t h a t i f the S i : 0 r a t i o was
This
They a l s o
l a r g e r than t h a t
r e q u i r e d to form Si02 then a g l a s s y type of i n c l u s i o n formed d u r i n g c o o l i n g . was
smaller
On the o t h e r hand, i f t h i s
the g l a s s y phase disappeared.
a l s o observed t h a t i f oxygen was content then the l i q u i d
i n excess
composition was
phase was
was
ratio
Van V l a c k e t a l . of the
silicon
s h i f t e d from the
s i l i c e o u s range to a more o x i d i z i n g compositions. latter
was
temperatures
G l o b u l a r i n c l u s i o n s of the type
the Fe-Mn-S system
l i q u i d phase was
two
phase was e n r i c h e d
"FeS" and the other e n r i c h e d i n " S i 0 " .
3:1,
2) In an
This
s i m i l a r i n nature to t h a t encountered i n
the Fe-Mn-O-S-system.
T h i s f i n d i n g was
a l s o observed by
65 H i l t y and C r a f t s <
1 2 9
'
l 6 7 )
.
Van V l a c k e t a l . ' s work based on t h e i r own and a l s o on Silverman's work have
illustrated
the
(MnS-MnO-FeO-Si0 ~system)
phase
2
changes
l i q u i d phase u s i n g F i g u r e s (8 a-b) MnS-MnO-FeS-Si0 -system. 2
in
the
which r e p r e s e n t the
I t has been p o i n t e d out t h a t
although t h i s system i s q u a l i t a t i v e
i n c h a r a c t e r and
m e t a l l i c phase i s " t e m p o r a r i l y " ignored used
findings
the
approach
i n t h e i r experimental work indeed d e s c r i b e s phase
changes t o which the i n c l u s i o n s are s u b j e c t e d . et a l . d
3 (
^
have proposed
e n r i c h e d composition temperature
ranges)
ary e q u i l i b r i u m .
(C)
Van
Vlack
t h a t s i n c e the l i q u i d phase
v a r i e s from a s i l i c a e n r i c h e d composition
(A) to a
then the quaternary
can be r e p r e s e n t e d
MnO
(at h i g h
by a Mn0-Si0
2
Once the s o l u b i l i t y product f o r S i 0
the melt i s reached
the excess s i l i c o n goes i n t o
i n the metal and the excess oxygen r e a c t s with Mn MnO
the
(and l i m i t e d l y with i r o n to produce
FeO).
binin
2
solution to
produce
These r e -
a c t i o n products w i l l generate a composition B i n F i g u r e which f l u x e s the MnS, Figure
as i n d i c a t e d by Silverman's work i n
(76).
The r e s u l t i n g l i q u i d w i l l be composed of 50 % "MnS" about
(8)
1320°C
of "MnS" Rhodonite
at
and hence, d u r i n g s o l i d i f i c a t i o n a mixture
and a s i l i c a t e
either tephroite
(Mn0«Si0 ) depending o
(2MnO*Si0 ) or
on the MnO:Si0
2
9
ratio
will
p r e c i p i t a t e a t low a u s t e n i t i c temperature. have a l s o observed
Van Vlack e t a l . ^
and q u a l i t a t i v e l y p r e d i c t e d with
1 3 0
this
s i m p l i f i e d model t h a t the l i q u i d phase becomes a s i l i c e o u s g l a s s i f the l i q u i d c o n t a i n s an e x c e s s i v e amount o f s i l i c o n . Under t h i s c o n d i t i o n a l i q u i d
which i s r a p i d l y
can remain as a " g l a s s y " i n c l u s i o n a t room Composition
C
i n Figure
(8a)
solidified
temperature.
i s a t t a i n e d i f the oxygen
content exceeds the s i l i c o n content.
Under t h i s
circumstance
the l i q u i d phase d i s s o l v e s a c o n s i d e r a b l e amount of "MnS" and the excess oxygen may r e a c t with some Mn from the MnS. I t i s a l s o b e l i e v e d t h a t some o f the i r o n i s t r a n s f e r r e d i n t o the l i q u i d t o balance the s u l f u r . compositions
are sketched
i n Figure
These s h i f t s i n
(9). In subsequent
s o l i d i f i c a t i o n stages the f o r m a t i o n o f FeS i s expected. 2.3.7
Oxides
2.3.7.1
Aluminates
Experimental
and t h e o r e t i c a l s t u d i e s on the A l - 0 e q u i l i -
brium have been t r a c e d i n the l i t e r a t u r e s i n c e e a r l y i n t h i s century.
The d i f f i c u l t i e s presented i n determining the
thermodynamic e q u i l i b r i u m a r e o b v i o u s l y observed
i n F i g u r e (10).
This summarizes the e q u i l i b r i u m v a l u e s found by s e v e r a l researchers
( 1 7
° "
1
8
3
)
a t 1600°,
1800° and 1900° C.
l a t e s t e q u i l i b r i u m v a l u e s g i v e n by Gustafsson and
The
Melberg^ ^
.. - work , from s e v e r a, are summarized l r e s e a r c h e r s (176, 177, u
179—18 2) Gustafsson and Melberg
c l a i m t h a t t h i r d order
17
67 polynomial (regression) parameters should be i n c l u d e d i n the determination
of the i n v o l v e d a c t i v i t i e s where there e x i s t s
s t r o n g oxygen-metal
(Al or Ca)
interaction.
Their tech-
nique u n f o r t u n a t e l y o n l y works when b i n a r y oxygen-aluminum or oxygen-calcium systems are c o n s i d e r e d .
Sims^ ^ 9
has
p o i n t e d out t h a t the observed d i s c r e p a n c i e s can be r e c o n c i l e d on the b a s i s t h a t the oxide phase i n e q u i l i b r i u m with Fe-O-Al i s not pure A^O^
but i n s t e a d FeO'A^O^ and
t h i s s p i n e l phase w i l l always be p r e s e n t .
the
hence
Other s t u d i e s on
t h i s matter have shown t h a t by d e o x i d i z i n g a melt with aluminum at s e v e r a l l e v e l s served: melt
three g e n e r a l stages can be
1) I f i n s u f f i c i e n t aluminum i s added to an
ob-
iron
( i . e . there i s an excess o f oxygen i n s o l u t i o n ) f e r r o u s
oxide
and h e r c y n i t e should be p r e c i p i t a t e d
as d i c t a t e d by
(112-113) the FeO-Al^O^ e q u i l i b r i u m diagram mediate A l - l e v e l s *
(about
.
.
0.4-0.5% Al) a mixture of •
-a-
4-
^d83,
n i t e and alumina i s p r e c i p i t a t e d
184) '
n i t e phase w i l l be the major phase present high Al-contents found'
8 3
'
1 8 4 )
F a r r e l l ^^5)
steel
_. .
hercy-
.
The and
inter-
hercy3) At
i n an i r o n melt almost pure A^O^
is
.
According and
2) At
to the d e o x i d a t i o n diagram proposed by a
f n u
v
kin
e <
3 carbon or low
alloy
d e o x i d i z e d with aluminum, the s o l i d i f i c a t i o n of
m e t a l - o x i d e - s u l f i d e system s t a r t s by s o l i d i f y i n g crystals
(A^O^) i n s t e a d of metal.
As the
Hilty
oxide
temperature
the
68 decreases
s o l i d i f i c a t i o n o f metal and some oxide
takes
p l a c e s i m u l t a n e o u s l y u n t i l the metal-oxide b i n a r y e u t e c t i c i s reached.
S o l i d metal, s o l i d oxide and a phase r i c h i n
sulfide w i l l p a r t i a l l y precipitate i n further stages.
solidification
The remaining phase r i c h i n s u l f i d e w i l l
precipitate,
finally
i n the same manner as the Fe-O-S system, as
the temperature
approaches the t e r n a r y e u t e c t i c .
McLean
(112-113) and coworkers
who have s t u d i e d the thermodynamic
behavior of the Fe-O-Al system c l e a r thermochemical
have found t h a t there a r e
c o n d i t i o n s under which e i t h e r
A ^ O ^ o r h e r c y n i t e a r e formed.
In t h i s work
pure
i t has been
p o i n t e d o u t t h a t t o p r e v e n t the f o r m a t i o n o f h e r c y n i t e the oxygen a c t i v i t y a t 1600°C.
should be reduced
to l e v e l s below 0.058
A c t i v i t i e s o f oxygen equal t o 0.058 r e p r e s e n t
the l o c a t i o n o f the (A^O^-FeO• A^O^) t r a n s i t i o n p o i n t . S e v e r a l r e s e a r c h e r s have a l s o agreed
that k i n e t i c
fac-
t o r s a r e i n v o l v e d i n the FeO-FeO'A^O^-A^O^ p r e c i p i t a t i o n sequence.
T o r s e l l and O l e t t e ^
i n the submicron Hammar's'^^
1 2
^
s i z e s one second
have observed
a f t e r aluminum was added.
t h e o r e t i c a l p r e d i c t i o n s a r e i n agreement with
T o r s e l l * s and O l e t t e s f i n d i n g s . 1
Hammar s e x p e r i m e n t a l 1
work, however, d i d not f o l l o w such a b e h a v i o r . t h a t the f i r s t
*
inclusions
t r a n s f o r m a t i o n i s g i v e n by
He c l a i m s
FeO'A^O^dT
FeO'A^O-jCs) and i t i s very dependent o f the i n c l u s i o n
size.
T h i s t r a n s f o r m a t i o n has been t r a c e d 17 seconds a f t e r the Al-addition.
L a t e r d e o x i d a t i o n stages t r a n s f o r m the
F e O ' A ^ O ^ s ) t o almost pure A^O^.
The mechanisms proposed
to c o n t r o l these t r a n s f o r m a t i o n s a r e the simultaneous
dif-
f u s i o n o f oxygen from the p a r t i c l e and d i f f u s i o n of aluminum i n t o the p a r t i c l e .
Since, Hammar s r e s u l t s were not i n 1
agreement w i t h h i s theory
i t was proposed t h a t i n c l u s i o n s
may have a p e r i p h e r a l case of FeO-A^O^Csf which enclose the FeO « A 1 0 ( i f 2
thus d i f f u s i o n o f A l i n t o l i q u i d
3
ates was prevented.
precipit-
T h i s p r o p o s a l was indeed c o r r e c t ,
„ . ,. (184, 186-188) , . . , s i n c e EPMA-studies ' showed an e n r i c h e d A l - c a s e p n u
surrounding state.
the FeO'Al^O^ which was o r i g i n a l l y i n l i q u i d
Another i n t e r e s t i n g o b s e r v a t i o n t r a c e d by Hammar
was t h a t the FeO-phase was not detected one second a f t e r the (18 7) a d d i t i o n o f aluminum. t h a t a sharp decrease
Wadby and S a l t e r i n oxygen
have noted
as w e l l as pure alumina
i n c l u s i o n s a r e seen w i t h i n a p e r i o d o f 30 seconds. and D r i o l e s t u d i e s '
8 9
Cremer
^ on the i n f l u e n c e o f e l e c t r o m a g n e t i c
s t i r r i n g and the removal of i n c l u s i o n s , have e s t a b l i s h e d t h a t a f t e r 20 seconds o f the aluminum a d d i t i o n p a r t i c l e s were grown i n s i d e c l u s t e r s .
spherical
Hammar has a l s o ob-
served r e l a t i v e l y l a r g e FeO-A^O^ i n c l u s i o n s transforming t o pure A ^ O ^ i n t h e p e r i o d o f one t o three minutes a f t e r the a d d i t i o n o f A l i n t o the molten i r o n . * F e O « A l 0 i s not intended t o i n d i c a t e s t o i c h i o m e t r y and i n f a c t the F e O « A l 0 ( s ) would have a d i f f e r e n t A l 0 / F e O r a t i o 2
3
2
than
3
FeO«Al 0 (1). 2
3
2
3
70 Straube and P l o c k i n g e r ^ '
1 9 1
^
who
have s t u d i e d the p r e -
c i p i t a t i o n of alumina i n melts c o n t a i n i n g some manganese, have s t a t e d t h a t the primary d e o x i d a t i o n p r o d u c t s are lean i n alumina and c o n t a i n e s s e n t i a l l y Mn-oxides.
The
A^O^-
content i n c r e a s e d very r a p i d l y d u r i n g the next few u n t i l the composition reached t h a t of the s p i n e l A^O-j.
I t was
partially
seconds
(Fe,Mn)0«
observed t h a t i n c l u s i o n s were i n a f l u i d or
f l u i d state.
(18 7) Waudby e t a l . have a l s o agreed (190 191)
with Straube and P l o c k i n g e r ' s f i n d i n g s
'
.
Waudby
(187) et a l . noted t h a t once the s p i n e l type was formed i t r e a c t e d with A l i n f u r t h e r stages to produce i r r e g u l a r h i g h l y aluminous
i n c l u s i o n s which e n c l o s e d i r o n .
Morgan
(188) et a l .
who
have s t u d i e d the d e o x i d a t i o n e f f e c t on the
i n c l u s i o n chemistry have a l s o observed s i l i c a t e d e o x i d a t i o n products p e r i p h e r a l l y p r e c i p i t a t e d on A^O^ phases.
or FeO'A^O^
Waudby's and S a l t e r ' s experiments were performed
a t s e v e r a l A l - d e o x i d a t i o n l e v e l s , namely 0.05, and 0.5 wt.
%.
0.15,
0.3
T h e i r samples were quenched and heat t r e a t e d
afterwards f o r 7 days at 1150°C.
Under the above experimental
c o n d i t i o n s , i t was
found t h a t by d e o x i d i z i n g the i r o n
melt w i t h 0.5%
i n as c a s t c o n d i t i o n duplex h e r c y n i t e -
Al
alumina i n c l u s i o n s were observed.
A f t e r the heat t r e a t -
ment, however, i n c l u s i o n s d i s s o l v e d more oxygen u n t i l hercynite •has
equilibrium
composition
was
a l s o i d e n t i f i e d s i m i l a r compounds,
reached.
the
Hammar
(Fe,Ni) 'A^O^,
71 i r r e s p e c t i v e of the quenching time.
The o u t s t a n d i n g c r y s (183)
t a l l o g r a p h i c work performed by Watanabe and coworkers (192)
along the l i n e s of Sloman's and Evan's work inum d e o x i d i z e d melts
has c l e a r l y r e v e a l e d the nature of (183)
the t r a n s f o r m a t i o n i n the Fe-O-Al system. was
on alum-
T h e i r work
c a r r i e d out by m e l t i n g l e v i t a t e d samples under a p u r i -
f i e d Ar-atmosphere and s o l i d i f i e d under three cooling conditions.
The 0:A1
r a t i o was
different
1.45 which i s c l o s e
to the s t o i c h i o m e t r i c r a t i o found i n the A 1 0 2
3
phase.
Ex-
t r a c t e d i n c l u s i o n s from the m e t a l l i c m a t r i x were a n a l y z e d by X-ray (powder) d i f f r a c t i o n u s i n g Cr-Ka r a d i a t i o n . r e s u l t s showed t h a t s i n c e the F e O « A l 0 2
3
phase had
Their
inter-
p l a n a r spacing approximately e q u i v a l e n t t o the y ' - A ^ O ^ a ' ) then the y'-A^O^ was though to o r i g i n a t e from the s p i n e l phase, as f o l l o w s : F e O A l 0 -•• Y ' - A l 0 ( a ' ) -> y - A l 0 ( a ) l
2
3
The f i n a l Y
, -
2
A1 0 2
3
2
3
3
+
Y'-AljOg
i s o b t a i n e d a c c o r d i n g to the degree of
simultaneous m i g r a t i o n of i r o n and aluminum out and the o r i g i n a l F e O « A 1 0 2
3
phase.
s i n c e i n the p r o c e s s o f K - A 1 0 2
phase d i s a p p e a r s and Y ' - A 1 0 2
i s d e r i v e d from Y ' ~ 2 ° 3 ^ • a 1
i n t h e i r experiments a-Al 0 . 2
3
( b )
The a - A l 0 2
3
I t was 3
a l s o proposed t h a t
formation the F e 0 « A l 0 2
3
(b) shows up, then K - A 1 0 2
T n
e
third cooling
produced Y ' - A 1 0 2
3
into
phase was
3
3
condition
(b), 0 - A l O 2
3
and
the more abundant phase.
Hence, the o v e r a l l t r a n s f o r m a t i o n sequence
was
proposed
to be: FeO-Al 0 2
3
+ y ' - A l 0 (a') 2
-* 6 - A l 0 2
2
Since y' -A1 C> was was
A 1
+ ^' ~ 2 ° 3 A l
"*" * ~ 2 ° 3
( b )
A l
3
found i n a l l the c o o l i n g c o n d i t i o n s , i t
3
suggested t h a t the r a t e of t r a n s f o r m a t i o n from t o y '-A1 C> i s f a s t and t h a t the y '-A^C^
FeC"Al 0
3
a-Al 0
is relatively
2
2
3
2
3
2
studied.
(b) to
slow.
The morphology of Al C>
who
°3 > (a
2
a-Al 0 .
3
2
y'
3
3
type of i n c l u s i o n s has been widely
T o r s e l l and O l e t t e ^
1 2
^
were the f i r s t r e s e a r c h e r s
proposed t h a t i n a d d i t i o n to a l o c a l s u p e r s a t u r a t i o n , a
continuous d i f f u s i o n of aluminum and oxygen i n t o these r e g i o n s i s r e q u i r e d t o p r e c i p i t a t e the d e n d r i t i c type of inclusions.
Under these c o n d i t i o n s
t h a t d e n d r i t i c alumina was
i t has been proposed
a r e s u l t of a homogeneous n u c l e (189)
ation.
Cremier and D r i o l e
have suggested t h a t
alumina i n c l u s i o n s are products of heterogeneous T h i s type grows i n areas low i n d e o x i d i z e r .
spherical
nucleation.
Torsell
and
O l e t t e have a l s o proposed t h a t c l u s t e r s are not formed i n r e g i o n s e n r i c h e d i n aluminum. c l u s t e r s of alumina
I t i s also indicated
that
which are very commonly observed i n
aluminum d e o x i d i z e d melts
are formed due to c o l l i s i o n of
s i n g l e p a r t i c l e s as a r e s u l t o f thermal, mechanical or e l e c t r o m a g n e t i c a g i t a t i o n of the molten bath.
Cremier and
D r i o l e have concluded t h a t the importance
of magneto-hydro-
dynamic phenomena on the k i n e t i c s of d e o x i d a t i o n o f s t e e l i s mainly a p h y s i c o - c h e m i c a l p r o c e s s , i . e . shape and type of i n c l u s i o n s i n the Fe-Al-0 system are c o n t r o l l e d by the l o c a l flow and a c t i v i t y c o n d i t i o n s .
Steinmetz
et a l . '
8
4
^
who have s t u d i e d the above system under s e v e r a l c o n d i t i o n s ( i n d u c t i o n - s t i r r i n g , c o n v e c t i o n - f r e e and i n the gas phase) have a l s o agreed with t h a t p r o p o s a l .
They found t h a t w i t h
an oxygen supply h i g h enough compared to the supply of r e s p e c t i v e elements, cipitate.
l i q u i d phase o f h i g h F e O - a c t i v i t y p r e -
I t i s a l s o suggested
t h a t t h e i r growth i s a l -
most s t r i c t l y c o n t r o l l e d by the flow c o n d i t i o n s a t which the g i v e n r e g i o n i s s u b j e c t e d .
They c l a i m t h a t the s p h e r i -
c a l contours become u n s t a b l e and change t o " r o s e t t e s " and f i n a l l y t o d e n d r i t e shape as the " p h a s e - s p e c i f i c concent r a t i o n s " or " m a t e r i a l s flow" are changed.
The degree o f
l o c a l d e o x i d a t i o n and the type and shape of oxides and s u l f i d e s have a l s o been shown i n t h i s work. o f p l a t e - l i k e alumina
and the MnS
The a s s o c i a t i o n
I I I are g i v e n where the
l o c a l c o n c e n t r a t i o n of aluminum i s h i g h e r
(2 t o 3%).
At
i n t e r m e d i a t e d e o x i d a t i o n (0.25-1.0% A l ) a mixture of coarse s u l f i d e type I I and a c i c u l a r oxide i n the presence of s u l f i d e are found.
Between these two ranges
a mixture of MnS
I I and I I I i s expected
aluminum contents
(1.25-1.75% A l ) and a t very low
(0-0.25%) o x y s u l f i d e s , primary
I I and d e n d r i t i c oxides may be formed. Steinmetz
s u l f i d e s , type (184) et a l . have
74 a l s o proposed the mechanism a l r e a d y d e s c r i b e d f o r s u l f i d e s for
the alumina, i . e .
1) d e n d r i t e s and coarse g l o b u l a r
hercynite at high i n i t i a l
oxygen contents,
2)
initial
g l o b u l a r to " c o r a l " shape alumina f o r low oxygen contents under very d r a s t i c c o o l i n g c o n d i t i o n s . gen o n l y d e n d r i t i c A ^ O ^
i s expected.
Above 0.019% oxySlower growth i s r e -
q u i r e d f o r the b r a n c h e d - i r r e g u l a r shape alumina type.
They
have a l s o proposed t h a t under low i n i t i a l oxygen contents r a d i a t e d - c r y s t a l l i n e to compact n i t r i d e s are grown on the alumina. Braun e t a l . ^ stirring
l 9 3
^ , who have s t u d i e d the i n f l u e n c e of
time, s t i r r i n g r a t e and i n i t i a l oxygen i n i r o n melts
have c l a s s i f i e d the morphology of the alumina i n c l u s i o n s f i v e types, namely:
d e n d r i t i c , faceted,
s p h e r i c a l and c l u s t e r s . not
into
plate-like,
I t was found t h a t these types are
e x c l u s i v e l y found as a unique type but as a mixture f o r
a g i v e n s e t of experimental c o n d i t i o n s .
They have a l s o
observed t h a t i n c l u s i o n s which i n t e g r a t e the c l u s t e r s change from d e n d r i t i c to p l a t e - l i k e shapes a t low oxygen contents t o s p h e r i c a l a t high oxygen l e v e l s . Olette et
( 1 2 0 )
al. (
l 9 5
^
,
Braun e t a l .
(
1
9
3
)
,
T o r s e l l and
Okohira e t a l .
and Cremer and D r i o l e ^
1 8 9
^
(
1
9
4
)
,
Ooi
have agreed on the
mechanism by which alumina c l u s t e r s are formed, i . e . c o l l i s i o n and
coalescence o f s i n g l e p a r t i c l e s as a r e s u l t of f l u i d
motion i n the melt.
Ooi e t a l . 's s t u d i e s on n o n - s t i r r e d
75 and s t i r r e d melts
have shown t h a t under the former
condi-
t i o n d e n d r i t i c and alumina c l u s t e r s are the major t y p e s . S p h e r i c a l i n c l u s i o n s were almost absent. type o f experiment produced
Their
second
1) i n c l u s i o n s l a r g e r than
20 ym i n diameter with adhered p a r t i c l e s of about 0.5 2.0
-
ym i n diameter and 2) c l u s t e r s composed of v e r y small
s p h e r i c a l i n c l u s i o n s with the maximum diameter o f which about 2 ym.
Ooi e t a l . ^
1 9
~^
have c o r r o b o r a t e d the
was
"collision
coalescence and s i n t e r i n g theory" on the f o r m a t i o n o f alumina c l u s t e r s by measuring
the neck growth and assuming
volume
d i f f u s i o n as the c o n t r o l l i n g mechanism. H i l t y and C r a f t s ^
1 6 7
^
have found t h a t 0.5%
Mn
in liquid
i r o n enhances the A l - d e o x i d a t i o n power as much as f i v e times. McLean^
113
^
suggests t h a t Mn
lowers the oxygen and
the A l c o n c e n t r a t i o n f o r u n i v a r i a n t t r a n s i t i o n from Al 0 2
3
to
Sims^ ^ 9
h l ^ O ^ i
as suggested by P l o c k i n g e r
raises (Fe, Mn).
) and Waudby ^
has s t u d i e d the dual A l - S i d e o x i d a t i o n of melts
(0.4% A l and 0.5%
S i ) . He noted t h a t the i n c l u s i o n s are
c h a r a c t e r i s t i c o f those e x c l u s i v e l y d e o x i d i z e d with A l and s t r o n g e r d e o x i d a t i o n was Al-deoxidized.
reached than when the melt i s
Sims p o i n t s out t h a t i f s i l i c o n i s added
b e f o r e o r with the aluminum
one minute
o b t a i n the maximum c l e a n l i n e s s studies^
l 9
^
•
i s s u f f i c i e n t to
Waudby s and Wilson's 1
on p r o g r e s s i v e d e o x i d a t i o n o f iron-oxygen
melts by A l - S i a l l o y s
(0.3, 0.6
and 0.9%
A l - S i ) . have
1 8 7
\
76 found t h a t because o f the much more r a p i d f o r m a t i o n of alumina compared with s i l i c a ,
the alumina c o n t e n t o f
the i n c l u s i o n s p r o p o r t i o n a l l y i n c r e a s e with the A l - S i addition.
Hence, they concluded t h a t the dual
(Al-Si)
d e o x i d i z e r behaves i n a complex manner only when a melt is
(Al-Si) deoxidized i n r e l a t i v e l y c r i t i c a l
additions.
D e o x i d a t i o n of melts by l a r g e q u a n t i t i e s of A l - S i behave as c o n v e n t i o n a l a d d i t i o n s o f the s t r o n g e s t element deoxidizer.
As proposed by S i m s ^ ^ 9
c l u s t e r s i s expected.
i n the
formation o f alumina
G a t e l l i e r et a l . '
9
^
i n agree-
ment with Waudby's and Wilsons's and Sim's f i n d i n g s have noted t h a t i f aluminum i s f i r s t l y metal bath the s i l i c o n remains
i n t r o d u c e d t o the
as a p a s s i v e d e o x i d i z e r .
G a t e l l i e r e t a l . ' s t h e o r e t i c a l c o n s i d e r a t i o n have shown t h a t t h r e e d i f f e r e n t b e h a v i o r s might be observed, a t 1600°C: 3/4 1) I f the a / A l ° ° / alumina should be p r e c i p i t a t e d , 3 /4 2) i f a / A l " 1400/ pure SiC> p r e c i p i t a t e s and 3) i n the 3/4 a
s
6
0
i
a
2
i n t e r m e d i a t e range o f these s t a b i l i t y ranges a A
l
(600 S a c
/
i 1400), m u l l i t e i s the most s t a b l e phase.
2.3.7.2
Calcium aluminates
Although the use o f c a l c i u m as a d e o x i d i z e r and des u l f u r i z e r i n i r o n melts has become an a t t r a c t i v e
alternative
(198) s i n c e S p o n s e l l e r ' s and F l i n n ' s r e s e a r c h the foundry i n d u s t r y ,
i t s use i n
to d e s u l f u r i z e , i n o c u l a t e and to
77
enhance t h e s p h e r o i d i z a t i o n o f g r a p h i t e early has of
i n this
century.
been c o n s i d e r e d research
Sponseller's
t h a t has c o n c l u s i v e l y c o n t r i b u t e d
Al,
C/ N i , S and Au.
liquid
iron.
i t s i n t e r r e l a t e d e f f e c t s with
calcium
in liquid
1880°K.
At t h i s
1.87
-
( l 9 8 )
In
light
other
of Sponseller's
( 1 4 4
'
reducing Al,
1
5
5
'
1
9
7
'
9
9
_
2
0
2
) .
i t s vapour pressure
i s 0.032% a t
a t about
t o improve
1780°K
W
o
r
k
( 1 9 9 )
.
inten-
i t s solubility,
respect
i t s vapour p r e s s u r e 1
elements, i . e .
and F l i n n ' s f i n d i n g s
t o overcome t h e p r o b l e m o f d e n s i t y w i t h
years
also
i t s vapour p r e s s u r e i s
has been d e d i c a t e d
i r o n and t o d i m i n i s h
to the develop-
the s o l u b i l i t y of
atm. and i t b o i l s
( 1 9 9 )
pieces
They have
i r o n under p r e s s u r e
temperature
1.645
sive research
They f o u n d t h a t
since
and F l i n n ' s work
a s one o f t h e most f u n d a m e n t a l
ment o f t h e C a - t r e a t m e n t o f l i q u i d studied
has been used
to liquid
i n the l a s t
20
has been devoted t o
by a l l o y i n g
i t with
Ba o r a s m u l t i p l e m i x t u r e s o f v a r i o u s
S i , C,
elements,
CaAlSi,
(9 5) CaAlSiFe, the
CaAlBaFe, e t c .
who
has reviewed
s t a t e o f t h e a r t o f oxygen and i t s r e a c t i o n s w i t h
ferent deoxidizers, of
Philbrook
has d e s c r i b e d
C a - t r e a t m e n t up t o 19 77.
Sweden, t h e F i r s t Metallurgy
the current
dif-
understanding
I n June o f t h e same y e a r i n
I n t e r n a t i o n a l C o n f e r e n c e on I n j e c t i o n
took p l a c e .
In the proceedings o f t h i s
a new d i r e c t i o n on t h e d e o x i d a t i o n
meeting^ *^
practice i s clearly
9
seen.
78
Thermodynamic and k i n e t i c theory t o support the e x p e r i mental work, f i n a l l y g i v e c r e d i t t o the d e o x i d a t i o n capab i l i t y o f Ca-bearing m i x t u r e s .
The second conference on (97)
i n j e c t i o n p r o c e s s e s a l s o h e l d i n Sweden more, r e c o n f i r m s the advantages
i n 1 9 8 0 , once
( d e o x i d i z e r and d e s u l f u r -
i z e r ) and disadvantages (low y i e l d ) of i t s usage. i n a more r e c e n t communication
Holappa^ ^ 98
a l s o p r e s e n t s an o v e r a l l
view of the Ca-treatment i n the l a d l e . In a d d i t i o n t o the p r e v i o u s l y d e s c r i b e d advantages o f the usage o f Ca-bearing mixtures
the major a t t r i b u t e s o f
t h i s d e o x i d a t i o n p r a c t i c e i n terms o f i n c l u s i o n s a r e : 1)
the e l i m i n a t i o n o f c l u s t e r s and angular alumina i n -
c l u s i o n s which otherwise would be formed from the A l deoxidation p r a c t i c e ' ^ 4
1 6 8 ) ^ ) ^he t r a n s i t i o n o f 2
MnS type I I t o MnS I I I o r p e r i p h e r a l c a l c i u m s u l f i d e around C a - a l u m i n a t e s
( 1 4 4
'
1 4 5
'
1 4 7
'
1 6 8
'
1 9 7 ]
.
The presence
of the MnS I I I has been observed a t r e l a t i v e l y low Cacontent
(< 20 ppm) and the "CaS" a t much h i g h e r Cat
O A
,
.
,^
(157, 158, 168)
_ .
,
content (> 20 ppm) i n the melt ' • . I t has a l s o j. * • *.u T * . (146, 159, 160) _ . been r e p o r t e d i n the l i t e r a t u r e • • that i n a d d i t i o n t o the above c h a r a c t e r i s t i c s
TJ
e x c e l l e n t de-
79
(96—98) oxidation, desulfurization (157,
ation
158, 204)
'
'
processes. added"to ^ ( 2 0 4 ) t
and some dephosphoriz,
,
,
i
.
.
. .
a r e reached by the c a l c i u m i n j e c t i o n
Gaseous
and m e t a l l i c c a l c i u m has been
the s t e e l stream d u r i n g tapping ^ , ' p l u n g i n g ' 8
o
s n
r
ooting
i t as b u l l e t s i n t o
the metal bath.
When m e t a l l i c c a l c i u m i s added to the melt i t t u r n s i n t o vapour bubbles which r a p i d l y r i s e t o the metal s u r f a c e and subsequently r e a c t v i o l e n t l y with the s l a g and the oxygen i n the a i r producing c o n s i d e r a b l e f l a r e , s p l a s h i n g and fumes.
B u r n - o f f and r e a c t i o n s with the s l a g and l i n i n g
m a t e r i a l s reduce the y i e l d o f the Ca-treatment t o about 10-50% (
l
9
7
'
2
0 5 )
m
Thus, new means t o u t i l i z e c a l c i u m as
calcium-composite wires
(97)
o r i r o n tube c o n t a i n i n g Ca(155)
a l l o y s have been developed techniques o b v i o u s l y
.
In a d d i t i o n to these
the simultaneous d e o x i d i z e r a d d i t i o n s
(as mixtures of d e o x i d i z e r s with o r without s l a g s ) e i t h e r top or bottom blown i n t o the c o n v e r t e r have a l s o been industrially
practiced.
I t i s a general p r a c t i c e
in
c o n v e n t i o n a l steelmaking, to f i r s t l y d e o x i d i z e e f f i c i e n t l y the melt w i t h A l and secondly by the c a l c i u m t r e a t m e n t ^ . Regarding the mechanical p r o p e r t i e s , i t i s g e n e r a l l y accepted t h a t g l o b u l a r i n c l u s i o n s improve (92
of the mechanical p r o p e r t i e s
the a n i s o t r o p y
95-97)
'
. I t has been pro-
posed as a p r i o r i r u l e s t h a t e i t h e r a Ca:S r a t i o g r e a t e r than 1 . 2 5
(
1
5
3
)
or more than 2 0 - 3 0
ppm of C a
( l 5 1 )
i s required to
80 achieve the t r a n s i t i o n from the alumina
(clusters) to
c a l c i u m aluminates and the MnS I I t o a t l e a s t MnS I I I or t o p e r i p h e r a l c a l c i u m s u l f i d e s .
Gatellier et a l . '
have found i n experimental melts t h a t a complete of A l 0 2
3
(144) 9
7
^
elimination
as c l u s t e r s i s a t t a i n e d when the 0:Ca r a t i o
(wt %) i n i n c l u s i o n s i s about to be independent
three.
T h i s r u l e was found
of the i n g o t chemical composition.
(209) Faulring et a l .
have r e p o r t e d t h a t the n o z z l e b l o c k -
age by the aluminate type o f i n c l u s i o n s i s e l i m i n a t e d when the Ca:Al r a t i o
( i n wt.%) i s g r e a t e r than 0.14.
This
r a t i o r e p r e s e n t s compositions which c l o s e l y correspond (133) to the CaO • 2 A 1 0 2
3
phase.
gested t h a t "burning"
Boldy e t a l .
have sug-
which occurs even i n ESR-ingots
where the s u l f u r content i s u s u a l l y thousandths
of a
p e r c e n t might be e l i m i n a t e d o n l y by r a r e - e a r t h or Catreatments.
These r e s e a r c h e r s have r e p o r t e d t h a t the
problem was e l i m i n a t e d , i n c o n v e n t i o n a l p r a c t i c e
:
when
manganese s u l f i d e s were completely transformed t o CaS. (157 158) Japanese r e s e a r c h e r s drogen
'
who have s t u d i e d the hy-
induced c r a c k i n g (HIC) on p i p e l i n e s t e e l s
have
concluded t h a t a Ca:S r a t i o g r e a t e r than or equal t o 1.5 i s r e q u i r e d t o prevent the r e o x i d a t i o n of Ca d u r i n g the teeming
o f the melt.
t a n t or t o t a l l y
Under these c o n d i t i o n s high r e s i s -
i n s u s c e p t i b l e s t e e l s t o HIC were developed.
I t has a l s o been e s t a b l i s h e d t h a t Ca-aluminates
are a l s o
81 p r e s e n t i n s t e e l s produced v i a the b a s i c e l e c t r i c a r c furnace^ ^^. 2
T h e i r presence a r i s e s due t o the aluminum
which i s used as a d e o x i d i z e r and the b a s i c i t y of the s l a g or by the Ca-(Si) treatment.
While some work i n the
l i t e r a t u r e r e p o r t s the presence o f Ca-aluminates by the Ca-treatment 19 7
( 1 4 4
'
1 4 7
'
1 4 8
'
1 5 1
'
1 5 3
'
2 0 7 )
,
others
( 9 6
'
97
<
20 8) '
have shown t h a t complex c a l c i u m - a l u m i n u m - s i l i c a t e s (159)
are formed.
Church e t a l . ' s
s t u d i e s on a s t e e l
processed under two d i f f e r e n t c o n d i t i o n s , a i r melt and d e o x i d i z e d i n the l a d l e and carbon d e o x i d i z e d i n vacuum have found g l o b u l a r type o f i n c l u s i o n s .
( g a l a x i t e ) o x i d e s , s u l f i d e s and
stringer
In the s t e e l t r e a t e d under vacuum,
i n c l u s i o n s were s m a l l e r , fewer and were l e s s complex than i n t h a t t r e a t e d under a i r . These
inclusions consisted
o f a nucleous of g a l a x i t e surrounded by a C a - A l - S i matrix. Whereas the a i r melted s t e e l c o n t a i n e d (Mn, Ca)S around g l o b u l a r oxides and MnS
the
I with some Ca, Cr and Fe i n
s o l u t i o n , i n the s t e e l melted under vacuum o n l y the l a t t e r type was
observed.
The presence of s l a g i n some c o n v e n t i o n a l
processes and the chemistry of the d e o x i d i z e r s employed i n the Ca-treatment p l u s the chemistry o f the melt indeed c o m p l i c a t e the e l u c i d a t i o n of the mechanism(s) by which the i n c l u s i o n chemistry i s c o n t r o l l e d .
Ja*ger and H o l z -
(202) gruber
have found t h a t a l l o y s of Ca with A l , Mn o r S i
used as deoxidants i n 18-8
s t e e l s a f t e r the A l - t r e a t m e n t
i n c r e a s e the Ca y i e l d when 0.1 wt.%
(Ca + Ba) i s a l s o
present. CaO
D^type of i n c l u s i o n s c o n s i s t i n g of 40-60 ^2°3
and 60-40 wt.%
under t h i s
w
i
t
wt.%
p e r i p h e r a l CaS are found
h
treatment.
S a l t e r and P i c k e r i n g '
^
4 0
i n t h e i r s t u d i e s on
C-Cr
b e a r i n g s t e e l s dexodized with a CaSi a l l o y and H i l t y coworkers' ' 4 4
1 6 8
^ who
used C a S i , CaSiB'a and
and
CaSiBaAl
a l l o y s to d e o x i d i z e an i r o n melt and C a S i T i to d e o x i d i z e some c a s t i n g melts, have h i g h l i g h t e d the p r e c i p i t a t i o n scheme.
These r e s e a r c h e r s have found t h a t
inclusions
g e n e r a l l y obey the sequence of phases g i v e n by the pseudobinary Ca0-Al 0 2
diagram.
3
Although these phases d i d not
necessarily follow a stoichiometric relationship c a l c i i m aluminates i d e n t i f i e d were: CaO-2Al 0 2
3
(CA ), C a O - A l ^ 2
CaO*f>Al 0 2
(CA) , 12CaO• 7 A l 0 2
3
3
the
(CAg), (C A ). 1 2
7
S a l t e r and P i c k e r i n g have r e p o r t e d as an e x c e p t i o n a l case a Ca-aluminate
the composition of which corresponded
c l o s e l y to the C ^ A . 2
Pickering s^
o x i d a t i o n i n the l a d l e , of
reactions.
2 <
have
9
de-
have a l s o found the same sequence
In these s t u d i e s the C^A^
Faulring et a l . ^ ^ ^ (201, 207)
s t u d i e s on
1
7
and S a l t e r e t a l . '
4
was (
^
identified.
and o t h e r s
agreed t h a t f o r a g i v e n l e v e l of d e o x i -
d a t i o n with c a l c i u m
a mixture of a t l e a s t two
s t o i c h i o m e t r i c c a l c i u m aluminate phases
different
are found.
(144) H i l t y and coworkers
have approached
the i n -
c l u s i o n f o r m a t i o n mechanism as another p a r t i c u l a r case of the g e n e r a l theory t o e x p l a i n the metal-oxide
sulfide
83 co-precipitation. to
These r e s e a r c h e r s ' work c o i n c i d e n t a l l y
S a l t e r ' s and P i c k e r i n g • s
190,
210)
A^O^
S U
gg
( 1 4 0 J
( 1 4 7
'
1 4 8
'
t h a t s i n c e CaO s u b s t a n t i a l l y f l u x e s
e s t
then the CaO decreases
the m e l t i n g p o i n t of the
" A l 0 " to produce Ca-aluminates 2
and o t h e r s
3
range o f steelmaking
which melt w i t h i n the
temperatures.
Hilty et a l . ^ ^ ^ 8
propose t h a t the pseudo t e r n a r y e u t e c t i c i n t h e i r t e r n a r y ( m e t a l - o x i d e - s u l f i d e ) diagram should be moved c l o s e r t o the oxide corner and hence a h i g h e r m e l t i n g p o i n t " e u t e c t i c " should be expected.
The Ca-aluminate
p r e c i p i t a t i o n se-
quence g i v e n by H i l t y and F a r r e l l suggest t h a t t h i s i s m o d i f i e d by the s u l f u r content, i . e . while a s t e e l t a i n i n g 0.015% S p r e c i p i t a t e s
con-
( C A ) , a s t e e l with 0.005% S 2
and the same Ca- content ('v, 40 ppm) , i t w i l l
precipitate
(CA) . Laboratory and i n d u s t r i a l work performed
by
Takenouchi
(154) and Susuki described.
have agreed w i t h the r e s u l t s p r e v i o u s l y The shape c o n t r o l o f the Ca-aluminates
disappearance
and the
of the manganese s u l f i d e s was a l s o o b t a i n e d .
The d e o x i d i z e r used was a CaAl a l l o y as wires 4.8 and 7 mm diameter
s h i e l d e d with a s t e e l p l a t e 0.2 mm
Emi e t a l . ^
X
1
^
w
i n thickness.
h o have used the same d e o x i d i z e r and
technique, have r e p o r t e d e s s e n t i a l l y the same trend o f (144) r e s u l t s as t h a t g i v e n by H i l t y and F a r r e l l
.
The
s t o i c h i o m e t r i c C^A-y phase was c l e a r l y seen a t a p p r o x i mately
75-80 ppm o f Ca i n the (HSLA) s t e e l .
84 Researchers a t
(Wakayama works) Sumitomo Metal i n -
dustries i n Japan^^3) et a l . ' s and
Emi
i
a
o
n
g
et a l . ' s work
Ca treatment) have introduced b u l l e t shooter" L.D.
the l i n e s of Takenouchi (pipeline
The
the above r e s e a r c h . aluminates) and
i n the
CaO
to A^O^
The
presence of the
the e x t e r n a l
and
the C a - a l l o y by the " A l -
i n t o the S t e e l contained
converter.
steels
r a t i o was
160
ton
equivalent
internal
(A^O^-MnS and
CaS)
(Ca-
phases
have shown a c l e a r dependence on the t o t a l c a l c i u m t e n t of the p r e v i o u s l y Saxena and
(Al)-deoxidized
coworker's
'
previously deoxidized
con-
steel.
research
j e c t i o n of CaO-bearing s l a g s i n t o the was
to
(30 kg)
on i n melt which
with aluminum, have shown t h a t
by t h i s treatment alumina c l u s t e r s i n t o the melt changed to CaO-A^O^ i n c l u s i o n s and
that MnS
are
gradually
'disappears." I t i s a l s o i n d i c a t e d t h a t the i n c l u s i o n s , present a f t e r the p r e f u s e d
slag i s injected
are s p h e r i c a l
aluminates with p e r i p h e r a l s u l f i d e s . 1
4
8
J
Saxena e t a l .
have proposed t h a t as soon as the
s l a g i s i n c o n t a c t with the melt two place,
calcium (147,
CaO-bearing
primary r e a c t i o n s
take
namely:
mCaO, , . + (slag)
nAl_0 * t 2 3
mCaO-'n A1,0,(1) 2 3
(19)
and
3 C a 0
(slag)
+
2 [ A 1 ]
*
Al 0 *(s) 2
3
+ 3[Ca]
(20-a)
85 where the c o e f f i c i e n t s m and n i n r e a c t i o n (19) r e p r e s e n t s t o i c h i o m e t r i c f a c t o r s a c c o r d i n g t o the e q u i l i b r i u m pseudo * b i n a r y (CaO-A^O^) phase diagram. A l ^ O ^ r e p r e s e n t s the primary
(Al) d e o x i d a t i o n
Gatellier et a l .
products.
(19 7)
and Holappa
(210)
also
support
the d e o x i d a t i o n mechanism g i v e n by the r e a c t i o n (20). Holappa g i v e s an e q u i v a l e n t r e a c t i o n which comprises
both
e q u i l i b r i a ; namely A l - d e o x i d a t i o n and Ca-treatment: x[Ca]
+ y(Al 0 ). 2
3
n
c
l
u
s
Saxena and c o w o r k e r s ^ reactions
i
o
1 4 7
t
n
'
1 4 8
xCaO.[y-Kr]Al 0 2
^
+ |x.[Al]
3
(20-b)
have p o i n t e d out t h a t these
(19) and (20) o r (21) take p l a c e i n s o f a r as the
bath c o n t a i n s s u f f i c i e n t aluminum and hence low oxygen
acti-
vity. Since a simultaneous ation^
'
'
'
d e o x i d a t i o n and d e s u l f u r i z ;
i n C a - i n j e c t i o n processes
, . , _ (147,148) , ,^ has been observed then Saxena has proposed t o r e p r e s e n t t h i s e q u i l i b r i u m by the r e a c t i o n : (CaO)* + [S] = (CaS)* + [0]
(21)
I t i s a n t i c i p a t e d t h a t i f the CaO and CaS have u n i t a c t i v i t i e s then a ^ = 0.0266 a and hence Saxena and c o O s workers p r e d i c t the p r e c i p i t a t i o n o f CaS s o l e l y i f the oxygen l e v e l i n the melt
i s lower than or equal t o 10 ppm.
Thus, i f a strong d e o x i d a t i o n i s obtained oxygen l e v e l s
pure CaS would p r e c i p i t a t e .
t o reach
such
They propose
86 t h a t s i n c e the CaO has a l s o a very h i g h a f f i n i t y f o r A l 0 2
3
then a s e r i e s o f c a l c i u m aluminates would be formed, namely: CaO + 6A1_0_
Z
Ca0«6Al_0 2 3
(CA,) 6
(19-a)
CaO + 2 A 1 0
3
t
Ca0-2A1 0
(CA )
(19-b)
CaO +
3
t
CaO-Al 0
(CA)
(19-c)
12CaO + 7 A 1 0
3
t
12CaO-7Al 0
3CaO + 2 A 1 0
3
t
3Ca0*2Al 0
2 -i
2
A1 0 2
2
2
Although
o
2
2
3
3
2
(
3
2
2
3
C
A 1 2
7
)
(19-d)
(C^)
i n these l a b o r a t o r y s t u d i e s '
4 7
(19-e) '*
4 8
^
r i c h e d i n c a l c i u m were i d e n t i f i e d , r e a c t i o n which p r e c i p i t a t e the C ^ A 2
, c l e a r l y revealed. the
CaO-CaF
and the C A
7
3
2
oxides en(19d) and (19e)
phases were not
, (147,148) ^, ^ Saxena e t a l . propose t h a t
s l a g s do not c o n t r i b u t e to form CaS on i n -
2
c l u s i o n s u n l e s s the A 1 0 2
aluminates.
i s f i r * s t l y transformed i n t o Ca-
3
Hilty et a l .
Nashiwa e t a l . ' * ^ 5
(
1
6
8
)
,
Salter et a l .
(
1
4
0
)
and
have a l s o agreed w i t h Saxena' s p r o p o s a l .
Gatellier et a l .
(
1
9
7
)
,
Saxena e t a l .
(
1
4
7
,
1
4
8
)
and
Holappa( *°) h o have s t u d i e d the d e o x i d a t i o n i n l a d l e s w i t h 2
w
Ca-treatments have suggested t h a t the i n c l u s i o n morphology can
be r e t a i n e d i n the f i n a l i n g o t only i f sources o f oxy-
gen, which produce r e o x i d a t i o n
are r e s t r i c t e d .
(159) Church e t a l .
have proposed t h a t n u c l e a t i o n o f
Ca-bearing s u l f i d e s take p l a c e e x c l u s i v e l y on Ca-aluminates. • ^ - . - ^ • , ^ , (147,148) Experimental evidence g i v e n by Saxena and Engh shows t h a t as the i n j e c t i o n time o f CaO-slags i n t o the melt
87 increases., the amount o f s u l f u r i n the (Ca) s u l f i d e phase a l s o i n c r e a s e s g r a d u a l l y up to a l e v e l which i s thought t o be the maximum s u l f u r s o l u b i l i t y i n c a l c i u m a l u m i n a t e s . As a f u r t h e r c o r r o b o r a t i o n of these o b s e r v a t i o n s chemical a n a l y s e s o f samples
e x t r a c t e d d u r i n g the i n j e c t i o n
process show a g r a d u a l and continuous increment o f
Ca
which reaches a p l a t e a u a t approximately 20 ppm a t l a t e r i n j e c t i o n stages.
Saxena's and coworkers
previous lab-
o r a t o r y work on CaO-CaF2 i n j e c t i o n has been extended to industrial t r i a l s ^ oratory scale
2 1 4
have
).
Although the r e s u l t s on a l a b -
indicated a r e l a t i v e l y high y i e l d , i n
terms o f t r a n s f o r m a t i o n o f A l ° 3 2
to
t
o
Ca-aluminates and MnS I I
C a - s u l f i d e s , the i n d u s t r i a l s c a l e t r i a l s
d i d not show
such e f f i c i e n c y . The MnS I I was o n l y transformed t o duplex(Ca,
Mn)S- s u l f i d e In
and pure CaS by i t s e l f was not t r a c e d .
an apparent disagreement with a l l o f the p r e v i o u s l y
, , . (140, 147, 148, 159, 168) . .. described investigations with r e s p e c t to the r e q u i r e d c o n d i t i o n s t o change the A ^ O ^ and the MnS I I morphology, i t has been r e p o r t e d ^
2 1 !
^ that
"pure" CaS i s formed e x c l u s i v e l y a f t e r the "A^O^" c o n t e n t i n the Ca-aluminates
i s reduced by Ca t o l e s s than about
40.0%, i . e . when the CaO:Al C>2 r a t i o i s 3.0 or when the 2
3CaO«Al 0.j s t o i c h i o m e t r i c compound i s formed. 2
i n d i c a t e d t h a t once t h i s r a t i o i s reached
I t i s also
the CaS i s
sharply increased. (209) F a u l r i n g and H i l t y
have observed CaS i n the p r e -
88 sence of CaO-A^O^ and C a O ^ A ^ O ^ as the major and minor compounds r e s p e c t i v e l y .
According to the schematic
formation model proposed by T a h t i n e n e t a l .
(97)
trans-
and sup-
(94)
p o r t e d by Holappa
i t i s seen t h a t f a c e t e d
probably as the hexagonal
Ca-aluminate
inclusions,
which corresponds
to CaO'GA^O^, r e p r e s e n t the i n c i p i e n t t r a n s i t i o n o f the a-A^O-j to the Ca-aluminates
and the simultaneous
tran(94)
s i t i o n o f the MnS to (Ca, Mn) ,S. G u s t a f f s o n and Melberg (209 217) Faulring et a l . ' have observed these phases i n (15) Ca-treated ingots. phases
Mitchell
has a l s o r e p o r t e d these
i n ESR-ingots.
The most comprehensive
work which a n a l y z e s , on thermo-
dynamic p r i n c i p l e s , the p r e c i p i t a t i o n sequence o f A ^ O ^ and Ca-aluminates
i s t h a t developed by F a u l r i n g and
Ramalingam^ ^.
These r e s e a r c h e r s have developed a
21
t e r n a r y Al-O-Ca e q u i l i b r i u m , i s o t h e r m a l (1550°C, 1823°K) p r e c i p i t a t i o n diagram based on Henrian a c t i v i t i e s . have e s t a b l i s h e d t h a t although diagrams
They
o f t h i s k i n d (three
components, i s o t h e r m a l and Henrian behavior) are hypot h e t i c a l i n nature, these a r e very h e l p f u l
i n the
understanding and p r e d i c t i n g of the i d e n t i t y o f i n c l u s i o n s from the c h e m i s t r y o f the bath o f v i c e v e r s a . I t i s a l s o emphasized
by these r e s e a r c h e r s , t h a t
Henrian a c t i v i t y behavior was assumed due t o the i n c o n s i s t e n c y found i n the thermodynamic data a v a i l a b l e f o r
89 calcium. was
T h i s t h r e e dimensional diagram
developed
(h^, ^ c a ' ^ A l ^
by p r o j e c t i n g the i s o t h e r m a l Al-O,
and Ca-Al b i n a r y e q u i l i b r i a .
Ca-O
Thus, o r i g i n a t i n g the
sat-
u r a t e d and unsaturated s u r f a c e s which w i l l g i v e the volume of s t a b i l i t y ,
Figure (11).
Thermodynamic data used to
c o n s t r u c t t h i s diagram i s condensed i n t a b l e s (IV, V and VI) . F a u l r i n g ' s and Ramalingam's experimental and
theoreti-
c a l f i n d i n g s are condensed i n the f o l l o w i n g p o i n t s : 1)
The Ca:Al r a t i o determines
c l u s i o n phases.
2)
The
the i d e n t i t y o f the i n -
amount of c a l c i u m f o r a g i v e n
amount of aluminum v a r i e s over a narrow range f o r each aluminate phase.
3)
If h ^ A
> 0.01
i n s t e e l , c a l c i u m has
a n e g l i g i b l e e f f e c t as a d e o x i d i z e r but does a l t e r
the
composition and thus the morphology of the i n c l u s i o n s 4)
as the major phase
F i n a l l y , F a u l r i n g and Ramalingam have determined p i r i c a l l y s e v e r a l c o r r e c t i o n parameters based on C a
and
Close c o n t r o l of the Ca:Al r a t i o to o b t a i n a d e s i r e d
Ca-aluminate
h
Ca-
:
h l A
a n <
3
t
n
e
%Ca:%Al r a t i o s
h
i.e.
Ca "Al
2.3
Ca
_
Al
'
x 10~
6
from Ca
f
the
Al
f o r CA , C
• %Ca %
CA
0
A
1
and CA and when
em-
90
alumina
i s present as one of the phases
= 10 x 10 r
2.3.7.3
u
.
Al
Complex Oxides (92)
Pickering
i n h i s aim to c l a s s i f y the nature o f
n o n - m e t a l l i c i n c l u s i o n s i n complex s i l i c a t e systems d e f i n e d f i v e d i f f e r e n t c a t e g o r i e s-,namely: 2)
Olivines,
ierites.
3)
Garnets,
4)
has
1) Pyroxenes,
F e l d s p a r s and
5)
At the same time, these c a t e g o r i e s can be
Cordsub-
c l a s s i f i e d as f o l l o w s : 1)
Pyroxenes, these are compounds of the
MO«Si0 .
Where M can be Fe, Mn
2
grunerite
(FeO«Si0 ), 2
(MgO«Si0 ), 2
the d i o p s i d e
2
and MgO
and
enstatite
Since t h e r e i s e x t e n s i v e s o l u ^ i n the presence
of S i 0
2
then
be c o n s i d e r e d as a mix-
2
2
T h e i r names are
(MnO«Si0 ) and
(CaO«MgO•2Si0 ) may
t u r e of CaO*Si0 2)
rhodonite
respectively.
b i l i t y between CaO
and Mg.
type
MgO«Si0 2
O l i v i n e s , t h i s category comprises
the same e l e -
ments as the p r e v i o u s c l a s s i f i c a t i o n ; t h e i r s t o i c h i o m e t r y , however, i s g i v e n as: (2FeO-Si0 ), 2
2 MO«Si0 . 2
Thus,
t e p h r o i t e (2MnO«Si0 ) and 2
fayalite
forsterite
(2MgO«Si0 ) are the main phases of t h i s k i n d . 2
w i t h Ca i n this category i s not i n c l u d e d due ionic size.
A compound
to t h i s l a r g e
I t i s a n t i c i p a t e d , however, t h a t s i n c e the
main t h r e e phases have complete mutual s o l u b i l i t y d i s s o l v e up to 50%
CaO.
they
can
3) general
Garnets.
T h i s s e r i e s of compounds f o l l o w s the
stoichiometry
given by 3 M 0 « A 1 0 • 3SiC> 2
case can be Fe, Mn, Mg and Ca. A1 0 «3Si0 ), spessartite 2
3
2
(3MgO«Al 0 «3Si0 ) 2
3
3
Thus, almandine 2
(3FeO*
3
2
and g l o s s u l a r i t e (3CaO•A1 0 •3Si0 ) a r e
2
2
show v i r t u a l l y complete mutual
form:
M i n this
( 3 M n O « A 1 0 • 3 S i 0 ) , pyrope
the s u b c l a s s i f i e d phases i n t h i s group.
4)
.
2
3
2
A l l these phases
solubility.
The f e l d s p a r group i n c l u d e s phases o f the general
MO•A1 0 •2Si0 2
3
where M represents
2
Mn and Ca. These
phases a l s o show mutual s o l u b i l i t y and take i n t o s o l u t i o n c e r t a i n q u a n t i t i e s o f FeO or MgO r e p l a c i n g MnO o r CaO. 5)
Cordierites.
T h i s i s a group which
compounds o f the f o l l o w i n g g e n e r a l 5Si0 .
M there
2
represents
K i e s s l i n g and Lange
encompasses
chemistry:
2MO«2Al 0 « 2
3
Fe, Mn and Mg. (91)
(92) Pickering
i n agreement w i t h
have c l a s s i f i e d the most common compounds i n the C a O - A l 0 ~ 2
Si0
2
(C-A-S) system, i n the f o l l o w i n g manner:
anorthites.
2)
C A«S, gehlenite. 2
C o r d e r i t e and 4)
3)
2
2
Lange have e s t a b l i s h e d t h a t the C « A « S , C « A « S C
2* 2* 5 A
S
t v
P
e s
a
r
e
n
o
t
,
5
K i e s s l i n g and
3
2
2
C « A « S , Ca-
C «A«S , glossularite. 3
1) C « A « S
3
3
3
and the
common i n c l u s i o n phases. (9192)
I t i s g e n e r a l l y agreed
'
that to avoid
chemical a n a l y s i s by EPMA, due t o the extensive
misleadin
mutual s o l u -
92 bilities
and the wide v a r i a t i o n o f compositions
around the
s t o i c h i o m e t r i c v a l u e s , i t i s r e q u i r e d t o know not only the Ca, A l and S i but a l s o the amount o f Mn, Mg, Fe and T i . (91) A summary o f work performed
by K i e s s l i n g and Lange
i n the C-A-S system i s g r a p h i c a l l y shown i n F i g u r e (12). The L^ and
l i n e s r e p r e s e n t the maximum and the minimum
MeO:SiC>2 r a t i o s i n the phases o f the i n c l u s i o n s .
Although
the b i n a r y oxide MeO p r i n c i p a l l y r e p r e s e n t s CaO, i t can f r e q u e n t l y c o n t a i n v a r i o u s amounts o f FeO, MnO and MgO. I t has a l s o been p o i n t e d out t h a t the c e n t r a l between L^ and L
2
l a r g e l y corresponds
p a r t s o f the above systems.
t o the low-melting
The open c i r c l e s r e p r e s e n t
chemical composition o f indigeneous by K i e s s l i n g and Lange.
area
inclusions
determined
The major area, on the A l 0 2 - S i 0 2 2
s i d e are chemical a n a l y s i s o f e x t r a c t e d samples from a Ca-Si A • a. (207) d e o x i-Ad i z e dA ingots (91 92) I t i s suggested
'
the d e o x i d a t i o n products
t h a t t o t r a c e the o r i g i n o f a knowledge o f the furnace and
l a d l e s l a g and r e f r a c t o r y composition as w e l l as the deoxidation practice i s required.
S a l t e r and P i c k e r i n g ' ^ 4
have r e p o r t e d t h a t i n c l u s i o n phases i n the range of the C2*A'S-C2* * 2 types a r e commonly found i n Ca-Si de(208) M
S
o x i d i z e d melts.
Other
studies
on d e o x i d a t i o n o f s t e e l
w i t h complex d e o x i d i z e r s ( C a S i A l and MgSiAl) have r e p o r t e d i n c l u s i o n compositions
as f o l l o w s : A^O^/
5.0 - 82.7 %,
93
CaO,
6.6
- 37%;
FeO,
1.4
- 6.0%;
Lindon and B i l l i n g t o n ^ alumina
content i n the C-S-A
pure alumina
1 1 5
^
and S i 0 , 2
2.4
- 64.4%.
have a l s o found t h a t the
products i n c r e a s e s to approach
as the A pet. 0: pet. A l added decreases
l e s s than the s t o i c h i o m e t r i c r a t i o .
to
The c h e m i s t r y of the
d e o x i d a t i o n products i n d i c a t e t h a t the degree of u t i l i z a t i o n (181 of c a l c i u m i s maximum o n l y f o r a s h o r t p e r i o d of time 202 •'
'
20 5) .
Hence, i f there i s not s u f f i c i e n t r e s i d u a l
cium i n the melt
although CaO
cal-
i s present i n the d e o x i d a t i o n
p r o d u c t , i t w i l l mainly c o n t r i b u t e to reduce
the
activity
of s i l i c a and thus to achieve a lower oxygen content. (94) Holappa's r e s u l t s Experiments
also e x h i b i t s i m i l a r trends.
i n t h i s r e s e a r c h show t h a t the aluminum i n
s o l u t i o n c o n t r o l s the A l 0 : C a 0 r a t i o and a l s o the 2
3
content i n the d e o x i d a t i o n p r o d u c t s . s o l u t i o n i n c r e a s e s from 0.05
to 0.4%
a l s o i n c r e a s e s whereas the S i 0 the endogenous
Si0
2
I f the aluminum i n the A l 0 : C a O 2
3
ratio
g r a d u a l l y decreases i n
2
p r e c i p i t a t i o n products.
As d e p i c t e d i n the C a 0 - S i 0 ~ A l 0 2
2
3
ternary, t h i s (91)
h a v i o r agrees w i t h K i e s s l i n g ' s and Lange's i . e . i n c l u s i o n chemistry w i l l f o l l o w a tendency w i t h i n the area of low m e l t i n g p o i n t
be-
proposal, to
e n c l o s e d by
fall and
94 2.4
I n c l u s i o n s i n ESR-ingots In s p i t e of the improvement i n mechanical p r o p e r t i e s
mainly due to i n c l u s i o n s i z e and q u a n t i t y
o b t a i n e d by the
ESR-process/ l i t t l e work has been p u b l i s h e d with r e s p e c t to the i n c l u s i o n c h e m i s t r y .
One of the major drawbacks found
i n approaching the i n c l u s i o n chemistry m e t a l l o g r a p h i c o r microprobe t r a c t i o n methods
e i t h e r i n s i t u by
(EPMA) techniques
o r by
ex-
i s the s m a l l i n c l u s i o n s i z e .
While
en-
dogeneous (primary d e o x i d a t i o n products) i n c l u s i o n s i n conv e n t i o n a l steelmaking p r a c t i c e s are 15-40 products
manufactured
by
the
between 2 to 10 ym i n diameter.
ym i n diameter,
ESR-technology
;
they range
The second major d i f f i c u l t y
of t h e i r study i s the complexity of the r e a c t i o n scheme. The p r e c i p i t a t i o n of i n c l u s i o n s i n the ESR-process been s t u d i e d by B e l l
( 2 1 8 )
and M i t c h e l l
f e r e n t s l a g and d e o x i d a t i o n p r a c t i c e s . the Fe-O-Al system and CaF ~30% A^O^ 2
( 1 5
'
under
2 1 9 )
has
dif-
B e l l ' s f i n d i n g s on slag,
indicate
that
the f i n a l i n c l u s i o n composition cannot be e x p l a i n e d by the c l a s s i c a l n u c l e a t i o n theory a p p l i e d t o the l i q u i d i.e.
i n s u f f i c i e n t supersaturation for nucleation.
observed, however, t h a t t h i s requirement was e x c l u s i v e l y i n l a t t e r stages of
pool,
I t was
fulfilled
solidification.
(15) Mitchell
i n an attempt t o i n f l u e n c e the p r e c i p i t -
a t i o n s i t e i n l a b o r a t o r y ESR-ingots
has induced an i n s t a n t -
aneous s u p e r s a t u r a t i o n by adding f e r r o s i l i c o n i n t o the
95 metal p o o l through was
the s l a g .
Under these c o n d i t i o n s , i t
a n t i c i p a t e d t h a t the i n c l u s i o n s i z e d i s t r i b u t i o n i n the
i n g o t would show the e f f e c t of growth time and flotation. produced inclusion
possibly
His r e s u l t s i n agreement with B e l l ' s , however,
no d e t e c t a b l e change i n e i t h e r oxygen content or distribution.
Other s t u d i e s on F e - C u which e x h i b i t w e l l developed
( 1 5 )
and F e - N i
( 2 1 8 )
(ESR)-alloys
d e n d r i t e s , have shown e i t h e r
i n c l u s i o n s a l i g n e d along the i n t e r d e n d r i t i c r e g i o n or d e n d r i t e s f o l d e d around i n c l u s i o n s . enabled them to suggest
These o b s e r v a t i o n s have
that inclusions
i n the f i r s t
case
were formed a t e a r l y stages and i n the second case - they might be formed a t the beginning of s o l i d i f i c a t i o n . Hence, i t was
concluded
t h a t d e o x i d a t i o n i n the ESR process
occurs
by chemical e q u i l i b r a t i o n of oxygen and deoxidant with s l a g and
the
s i n c e almost a l l i n c l u s i o n s are n u c l e a t e d and
grown i n i n t e r d e n d r i t i c r e g i o n s d u r i n g s o l i d i f i c a t i o n , i n c l u s i o n f l o t a t i o n mechanism (15 Mitchell
was
the
discarded.
i
' has r e p o r t e d t h a t o n l y very few
inclusions
from the e l e c t r o d e p e n e t r a t e to the l i q u i d p o o l bulk
and
those which do so are s u b s t a n t i a l l y a l t e r e d i n composition. I t has been widely r e c o g n i z e d t h a t due area a v a i l a b l e f o r thermochemical a c t i o n s and temperature
to the s u r f a c e
and e l e c t r o c h e m i c a l r e -
d i f f e r e n c e s i n ESR-furnaces;
two
96 d i f f e r e n t behaviors a l s o observed.
i n terms o f i n c l u s i o n chemistry
are
Work on the Fe-O-Al and on the Ni-O-Al
(218 220) systems performed a t U.B.C. ' i n agreement with (38) Miska's and Wahlster's work i n l a b o r a t o r y ESR-furnaces has shown t h a t the A l - 0 behavior does not obey the s t o i c h i o (218) metric who
r a t i o expected from e q u i l i b r i u m c o n d i t i o n s .
has remelted e l e c t r o d e s i n CaF -25% A^O^
under an argon
2
atmosphere
has found t h a t i f an
t o t a l oxygen content of 30 ppm
(anodic) e l e c t r o d e
with a
i s remelted, a d r a s t i c i n -
crement of oxygen i s observed a t the d r o p l e t s and t h i s i s reduced down t o about 70 ppm passed through the c a t h o d i c
Bell
ppm)
a f t e r they have
ingot surface.
c o n d i t i o n s h e r c y n i t e or a mixture e n r i c h e d alumina as i n c l u s i o n s would be expected.
1600
Under the above i n hercynite
and
Miska e t a l . ' s
(38) work
on aluminum a l l o y e d s t e e l s remelted i n a l a b o r -
a t o r y ESR-furnace under alumina s a t u r a t e d C a F ~ s l a g s has 2
a l s o shown t h a t the oxygen content f a r exceeded brium,
2 3 [Al] [0] , product.
B e l l has a l s o performed
(ESR)
laboratory scale experi-
ments i n which aluminum d e o x i d a t i o n was trodes c o n t a i n i n g 700 and 30 ppm through a CaF ~25 wt% 2
levels
the e q u i l i -
(1.15, 10.3
A l 2
°3
s l a
and 44.0
d e o x i d i z e r i n the melt was
9~ ' s
c a r r i e d out.
Elec-
of oxygen were r e f i n e d deoxidized a t various
grams).
The i n t r o d u c t i o n of
c a r r i e d out by a t t a c h i n g aluminum
97 wires to the e l e c t r o d e s .
R e s u l t s o f these s e r i e s of ex-
periments showed an 'apparent e q u i l i b r i u m temperature' of 2000 to 2100°C
r a t h e r than 1700°C.
/
Thus, whereas the
metal was expected t o l o s e aluminum and oxygen as alumina to the s l a g
sometimes the opposite
was observed.
I t was
suggested t h a t t h i s d i f f e r e n c e i s due to the i n e f f i c i e n c y of the aluminum d e o x i d a t i o n i s required
and t h a t an excess of aluminum
to lower the oxygen content.
Since c a l c u l a t i o n s
have shown t h a t l o s s e s of aluminum to atmospheric o x i d a t i o n would be as important as the s l a g d e o x i d a t i o n
reaction
then i t was proposed that the r e a c t i o n s : 2A1
( 1 )
+ 3(FeO) t
2A1
( 1 )
+ |
F
e
(i)
+
Al 0 (s) 2
3
(12-iv)
and
take p l a c e .
(O)
t Al 0 (s) 2
3
(ll'-ii)
T h i s l a s t r e a c t i o n was the most probable,
since
the condensation s i t e would be the c o l d mold w a l l where the aluminum i s not r e f l u x e d but removed from the system. Miska e t a l . ' ^ 8
2 2 0
in
^
have
found
i n agreement w i t h B u r e l ' s findings'"'"'
. t h a t the amount o f alumina or h e r c y n i t e
(ESR) l a b o r a t o r y
s c a l e i n g o t s was s t r o n g l y
as compared t o the i n i t i a l q u a n t i t y
increased
t r a c e d i n the e l e c t r o d e .
(55) Kajioka achieved
et a l .
have r e p o r t e d
that better c l e a n l i n e s s i s
i n l a r g e r r a t h e r than i n smaller ESR-furnaces.
e r a l explanations
Sev-
have been proposed to account f o r the above
98
facts; than
i t i s , however, accepted t h a t e l e c t r o c h e m i c a l r a t h e r chemical
reactions
control
the
ingot
and
hence
(63)
the
inclusion
chemistry.
Boucher's
work
on e q u i v a l e n t s l a g compositions to the p r e v i o u s works have suggested t h a t i n i n d u s t r i a l ESR-ingots i s a l a r g e r s u r f a c e area exposed
where t h e r e
t o the s l a g , chemical
i n s t e a d o f e l e c t r o c h e m i c a l r e a c t i o n s govern the i n g o t and thus the i n c l u s i o n chemistry. w i t h some s c a t t e r
Boucher's
findings,
show t h a t there i s a l i n e a r
although
relationship
between the "FeO" content i n the s l a g and the aluminum i n the i n g o t .
T h i s behavior was an i n d i c a t i o n that thermo-
dynamic e q u i l i b r i u m was p r a c t i c a l l y achieved.
While
Bell's
f i n d i n g s suggest an "apparent e q u i l i b r i u m temperature" i n the 1900° t o 2000°C range f o r alumina i n s m a l l Boucher's an almost 1700°C.
i n d u s t r i a l s c a l e ESR-experiments
ESR i n g o t s ,
suggest t h a t
t r u e thermodynamic e q u i l i b r i a i s reached a t He a l s o c l a i m s t h a t almost pure alumina
were i d e n t i f i e d when the p r o t e c t i v e
inclusions
(Ar) atmosphere was
t i g h t l y maintained throughout the r e f i n i n g p e r i o d . R e t e l s d o r f and W i n t e r h a g e r ^ ^ 9
i n t h e i r aim t o produce
alumina f r e e h i g h carbon ferrochrome and metal chrome by ESR.
have found t h a t r e l a t i v e l y l a r g e diameter
about 200 mm,
ingots,
c o n t a i n e d e i t h e r a-A^O^ 'C^O^ or a-alumina
(corundum) and the aluminum and oxygen contents always c o r -
responded
to the A l - 0 e q u i l i b r i u m .
Their "unsuccessful"
f i n d i n g s were claimed to be due t o the high o x i d a t i o n p o t e n t i a l of the s l a g
(CaF -CaO-Al C> 2
2
3
w i t h 30%
Al 0 ) 2
3
and to the i n e f f i c i e n c y of the p r o t e c t i v e atmosphere. (15) Mitchell complex
who
has remelted e l e c t r o d e s c o n t a i n i n g
(calcium alumina s i l i c a t e ) i n c l u s i o n phases
r e p o r t e d t h a t i n g o t s remelted through CaF ~20 wt.%
A1 0
2
and h i g h aluminum d e o x i d a t i o n (0.5% A l ) t a i n calcium bearing i n c l u s i o n s .
has 2
3
are prone to con-
I t has a l s o been r e p o r t e d
i n t h i s study t h a t although l e s s than one p e r c e n t of these i n c l u s i o n s c o n t a i n e d s i l i c a , where i t was h i g h as
found i t was
as
50%. (74)
Holzgruber's work CaF ~CaO-Al 0 2
2
levels
3
on the e f f e c t of s i l i c a of the
s l a g system,
has found t h a t a t low
silica
(4.2%) i n the s l a g , c a l c i u m aluminates c o n t a i n i n g
84% Al C» , 12% CaO 2
3
and about
sulfide phase—probably Another 32% A l 0 ^ 2
1% s i l i c a w i t h a p e r i p h e r a l
( C a M n ) s — a r e commonly found.
p e c u l i a r i n c l u s i o n composition
and 56% CaO)
(14%
r e p o r t e d by Holzgruber
c o n t a i n e d a p e r i p h e r a l s u l f i d e phase
was
Si0 , 2
which a l s o
obtained under
the above experimental c o n d i t i o n s , the s i l i c a i n the however was t h a t about
about
12.0
wt.%.
12-15% s i l i c a
Holzgruber's f i n d i n g s
slag, indicate
i n the s l a g y i e l d s the h i g h e s t Ca
100
content i n i n c l u s i o n s . These r e s u l t s were l a t e r confirmed by A l l i b e r t e t (53 al.
54) '
.
I t should be mentioned t h a t Holzgruber's e x p e r i -
ments were performed though s i l i c o n was
under v a r i a b l e CaOrSiC^
used as d e o x i d i z e r
r a t i o s and a l -
the amount was
not
specified. (53 A l l i b e r t et a l . ' s studies
54) '
on the a c i d - b a s i c
r e a c t i o n s i n the CaF2-Al202-CaO-SiC>2 s l a g system i n agreement with Holzgruber's
f i n d i n g s have r e p o r t e d t h a t a t
low
s i l i c a content i n the s l a g , c a l c i u m aluminates a s s o c i a t e d with a s u l f i d e phase are c o i n c i d e n t a l l y Holzgruber's of
precipitated.
and A l l i b e r t ' s e t a l . ' s f i n d i n g s i n terms
s l a g and i n c l u s i o n chemical composition a r e shown i n (53 54)
Figures
(12) and
(13).
A l l i b e r t et a l .
'
have c l a s s i -
f i e d the i n c l u s i o n composition i n oxides p l u s s u l f i d e s sulfides.
The
and
f i r s t types are l o c a t e d i n the t e r n a r y where
a r e l a t i v e l y high a c t i v i t y of s i l i c a The s u l f i d e zone
i s found, Zone (1).
(2) i s l o c a t e d a t moderate s i l i c a
activities.
Holzgruber*s r e s u l t s , c i r c l e s e n c l o s i n g a s o l i d square,
also
r e f l e c t s i m i l a r trends. (74) I t has been r e p o r t e d the ESR-slag
t h a t i f th,j s i l i c a content i n
i s h i g h e r than 10%,
the percent of s i l i c a i n
i n c l u s i o n s w i l l be higher than the p e r c e n t i n the s l a g . Simu l t a n e o u s l y to t h i s s i l i c a increment
the s i z e of
inclusions
w i l l be l a r g e r and hence the t o t a l oxygen w i l l a l s o be i n creased. (92) Holzgruber i n agreement with P i c k e r i n g and Lange (91) has a l s o found t h a t higher s i l i c a
and K i e s s l i n g content
101 i n the s l a g , the alumina s i l i c a t e phase i n i n c l u s i o n s c o n t a i n s e i t h e r CaO or MnO, but n o t both compounds t o g e t h e r . Holzgruber has a l s o noted t h a t i f r e f i n i n g i s c a r r i e d out
i n alumina f r e e CaO-CaF
2
slags
manganese s i l i c a t e s which c o n t a i n
small alumina f r e e a maximum o f 10 wt %
CaO w i l l be the most common type o f i n c l u s i o n s
found.
(83) Rehak e t a l .
who have s t u d i e d
the e f f e c t of e l e c -
trode and s l a g chemistry on i n c l u s i o n s i n ESR-ingots remelted a s t e e l (CSN 19.426 used f o r c o l d r o l l i n g
have
rods)
produced v i a e l e c t r i c a r c furnace under e i t h e r CaSi or A l deoxidation
practices.
clusions i n electrodes
The chemical composition o f i n Al-deoxidized
2.23 wt% CaO and 5.43 wt % MgO. electrodes
i t was as f o l l o w s :
CaO, 5.36 wt. % S i 0
2
is:
92.25 wt% A^O^,
In the CaSi
deoxidized
58.48 wt.% A l 0 , 2
3
19.46 wt. %
and 16.7% MgO.
Three major s l a g types were s e l e c t e d t o r e f i n e these electrodes;
namely b a s i c , n e u t r a l and a c i d i c .
s e r i e s o f aluminum d e o x i d i z e d i n i n c l u s i o n s and only
ingots
While the
showed almost pure
Al 0
t r a c e s of Ca ( l e s s than 1%), s i l i c a
was d e t e c t e d e x c l u s i v e l y i n one case where the s i l i c a
con-
t e n t i n t h e s l a g was as h i g h as 25%. The
CaSi d e o x i d i z e d
after refining
s e r i e s of e l e c t r o d e s
a h i g h e r Ca-content
showed,
(2.41 t o 6.91%). The
e f f e c t o f the s i l i c a content i n the s l a g was s t r o n g l y
2
3
r e f l e c t e d i n the i n c l u s i o n chemistry.
The
s l a g and
chemistry are a l s o shown i n Figures (12 and t a i n i n g 50% C a F
2
30% CaO
and 20% S i 0
both c o n s i d e r e d as n e u t r a l duced S i 0
2
v a r i e d from 2.4 1.5
to The
(53.0
from 27.0
to 5.0%.
and a pure C a F
2
The MgO
t o 71.36% S i 0 ) . 2
t o 39.4%. ranged
The CaO
from
con-
slag,
Their
content
approximately
3.5%. CaSi s e r i e s of e l e c t r o d e s remelted through b a s i c
s l a g s showed a s l i g h t l y higher CaO-contents than i n the p r e v i o u s ESR s i o n s of about 0.3
ingots.
to 0.57%
were
on the other hand v a r i e d from 5.1 content
A slag
and the h i g h l y a c i d i c s l a g s p r o -
enriched inclusions
alumina content ranged
2
13).
inclusion
which was
(3.2 to 6.9 5%)
Traces of s i l i c a i n i n c l u f o u n d s
The MgO
t o 10.0%
the major component, was
contents,
and the
alumina
86-87%.
Rehak e t a l . have concluded t h a t oxide i n c l u s i o n s are s e q u e n t i a l l y formed as t h e i r thermochemical oxygen i s d i c t a t e d .
They have suggested
affinity for
t h a t the a-A^O^
(corundum) w i l l form f i r s t and as the a c t i v i t y of aluminum in for
the melt decreases other elements with lower
affinity
oxygen, such as c a l c i u m - a l u m i n u m - s i l i c a t e i n c l u s i o n s ,
w i l l subsequently be formed.
Thus, the parameters which i n f l u e n c e the f i n a l i n c l u s i o n chemical composition are the s l a g chemical composition trode
(49 51 53 54 74)
( 8 3 )
o f the e l e c -
.
Several obtained
and the d e o x i d a t i o n
s t u d i e s on mechanical p r o p e r t i e s o f ESR-ingots
under d i f f e r e n t p r a c t i c e s have been r e c e n t l y pub(133)
lished.
Work c a r r i e d out by Boldy e t a l .
w i t h the e f f e c t of s u l f i d e i n c l u s i o n s on the phenomenon.
has d e a l t "overheating"
Overheated m a t e r i a l s , as a r e s u l t of p r e c i p i -
t a t i o n o f manganese s u l f i d e s onto h i g h temperature 1400°C) a u s t e n i t i c g r a i n boundaries toughness.
These r e s e a r c h e r s
(1100°-
show a r e d u c t i o n i n
describe
t h a t a f a c e t e d ap-
pearance of the f r a c t u r e s u r f a c e i s c h a r a c t e r i s t i c of an "overheated" m a t e r i a l . I t has been found t h a t although r e f i n i n g processes such as ESR and VAR i n g o t s
a r e capable o f r e d u c i n g the
s u l f u r content i n i n g o t s down t o very
low l e v e l s and hence
promoting the p r e c i p i t a t i o n o f a f i n e d i s p e r s i o n o f s u l -
104
f i d e s , i t enhances the i n t e r g r a n u l a r ( a u s t e n i t i c ) p r e c i p i t a t i o n which causes o v e r h e a t i n g .
S e v e r a l c o u n t e r a c t i n g measures
have been proposed t o overcome such a problem, i . e . changes i n i n g o t chemistry o r d e o x i d a t i o n p r a c t i c e s o r c o o l i n g r a t e s other
than a i r c o o l i n g (^100°C/min).
Another communication
(221) which has e v a l u a t e d and compared mechanical p r o p e r t i e s between VAR and c a l c i u m - t r e a t e d ESR-ingots under s e v e r a l s l a g s and d e o x i d a t i o n r a t e s , has shown t h a t impact s t r e n g t h i s s t r o n g l y a f f e c t e d by these v a r i a b l e s . at h i g h c a l c i u m d e o x i d a t i o n r a t e s
T h i s work shows t h a t
(0.14% Ca) the aluminum
and oxygen and p a r t i c u l a r l y the s i l i c o n content are s h a r p l y increased during remelting.
The ESR i n g o t s e x h i b i t e d a
g r a d u a l increment i n the i n c l u s i o n s i z e as the Ca-deoxidation l e v e l was i n c r e a s e d
(0.032%, 0.047% and 0.14% Ca).
As a
r e s u l t o f the above parameters the lowest toughness was a t the h i g h e s t c a l c i u m d e o x i d a t i o n l e v e l s . studies
found
In these
n e i t h e r the i n c l u s i o n chemical composition
nor a
s e l f - c o n s i s t e n t e x p l a n a t i o n as t o why the mechanical prope r t i e s e x h i b i t e d such a behavior, Although
the Ca/CaF
2
have been c o n s i d e r e d .
s o l u t i o n has been used
industri-
(86) ally and
i n ESR f o r removing phosphorous from s t a i n l e s s (85) s u l f u r from r o t o r s t e e l s
and as a r e s u l t
improved
mechanical p r o p e r t i e s have been r e p o r t e d , the i n c l u s i o n chemical composition
has not been i n v e s t i g a t e d .
steels
105
Viswanatan
and Beck (222) have r e c o n f i r m e d f i n d i n g s from R a t l i f f
(223) and Brown
i n terms of determining the i n f l u e n c e o f
A l i n the mechanical p r o p e r t i e s o f a r o t o r Their results c l e a r l y (more than 230 ppm) trides,
(Cr-Mo-V) s t e e l .
show t h a t the presence o f aluminum
i n solid solution
without forming n i -
markedly reduces the r u p t u r e d u c t i l i t y and hence
leads to premature
failures.
106
CHAPTER I I I NATURE OF THE PROBLEM A comprehensive work on s e m i - i n d u s t r i a l o r f u l l - s c a l e ESR
experiments, which would account f o r a l l o f the s t e p s -
a t the e l e c t r o d e , e l e c t r o d e - s l a g , s l a g - l i q u i d p o o l and i n the process
of s o l i d i f i c a t i o n during r e f i n i n g and the e f -
f e c t s o f s l a g s and d e o x i d i z e r s on the f i n a l i n g o t and hence the i n c l u s i o n chemistry,
3.1
has y e t not been performed.
I n c l u s i o n s i n the E l e c t r o d e (2-5) Several studies
have attempted t o e l u c i d a t e the
nature o f the t r a n s f o r m a t i o n s to i n g o t s d u r i n g r e f i n i n g . have analysed
of i n c l u s i o n s from e l e c t r o d e s
Mathematical m o d e l s ^ ^ which 9
the thermal h i s t o r y o f e l e c t r o d e s
s t r a t e d that c r i t i c a l
have demon-
thermal g r a d i e n t s are developed a t
the e l e c t r o d e t i p . Regarding the mechanism by which i n c l u s i o n s i n the e l e c t r o d e a r e removed, c o n t r o v e r s i a l and i n c o n s i s t e n t models -,(1,5) have been proposed ' .
., . (1,12,13,15,16) While some r e s e a r c h e r s '
have r e p o r t e d t h a t i n c l u s i o n s are g r a d u a l l y d i s s o l v e d
as a
consequence o f the thermal g r a d i e n t s a t the e l e c t r o d e t i p , (17 19 20) others (?
ers
'
•' 35
have r e p o r t e d the o p p o s i t e .
Other
research-
i
have suggested t h a t the e l i m i n a t i o n o f i n c l u s i o n s
from e l e c t r o d e s i s by mechanical a c t i o n .
On the other hand,
107 (15) studies
performed on i n c l u s i o n s a t the l i q u i d f i l m have
demonstrated t h a t i n c l u s i o n s do not c h e m i c a l l y show any l a r i t y with i n c l u s i o n s i n areas where e l e c t r o d e s (22) low thermal g r a d i e n t s .
Other s t u d i e s
simi-
experience
i n f u l l scale
(ESR)
e l e c t r o d e s , i n agreement with t h i s p r o p o s a l , have a l s o suggested
t h a t there i s a c r i t i c a l l e n g t h above the l i q u i d
where c e r t a i n v o l u m e t r i c Russian
changes of i n c l u s i o n s take (19 20)
investigators
'
film
place.
have a l s o p o i n t e d
out
t h a t the c h a r a c t e r i s t i c
l i q u i d u s - s o l i d u s l e n g t h of
a l s o p l a y s an important
r o l e i n the removal of i n c l u s i o n s
from the e l e c t r o d e .
seen i n t h i s summarized review,
As
there i s a v a s t q u a n t i t y of q u a l i t a t i v e i n f o r m a t i o n
alloys
but
o n l y a l i m i t e d amount of q u a n t i t a t i v e i n f o r m a t i o n a v a i l a b l e . Since the chemical
nature of i n c l u s i o n s i s r e l a t e d to
t h e i r t r a n s f o r m a t i o n as a r e s u l t of the steep thermal g r a d i ents a t the e l e c t r o d e t i p i t has qualitative basis
only been approached on a
( i n terms of the chemical
composition
of
the e l e c t r o d e ) and q u a n t i t a t i v e a n a l y s i s ( i n terms of i n clusion size distributions),
i t was,
however, very c l e a r
t h a t a deeper study which c o u l d r a t i o n a l i z e the r e s e a r c h , would be very
valuable.
reported
108 3.2
The
Chemical I n f l u e n c e of the ESR
Components on
the
Composition of I n c l u s i o n s TT
•
(37,55,58,75-77,79) .
Various to o p t i m i z e by the ESR melting
-
,
have been performed
the chemical homogeneity of i n g o t s manufactured technology.
I t i s widely
accepted
that i f r e -
i s conducted under atmospheric c o n d i t i o n s , an
hanced and occurs.
studies
.
continuous
accumulation
of i r o n oxide
en-
i n the s l a g
I t i s a l s o known t h a t the o x i d a t i v e s t a t e of
the
s l a g with r e s p e c t to the l i q u i d p o o l i s r e l a t e d to the s l a g ^ (38,48,82) system ' ' On an a p r i o r i b a s i s , i t i s understood t h a t i f d e o x i d a t i o n i s not c a r r i e d out d u r i n g r e m e l t i n g then a
sacrifi-
c i a l o x i d a t i o n of r e a c t i v e a l l o y i n g elements takes
place.
S e v e r a l w o r k e r s ' ^ ' ^ ' ^ ' have p o i n t e d out t h a t the
chemical
composition
of the s l a g s t r o n g l y enhances or suppresses c e r -
t a i n reactions during r e f i n i n g . (28 29 58 71) oxides
and
The
net p r o d u c t i o n of
iron
the p r o d u c t i o n of c a l c i u m or alum-
inum a t the e l e c t r o - a c t i v e i n t e r f a c e s d i c t a t e s the o x i d a t i v e s t a t e of the molten p o o l and hence the f i n a l ESR-ingot and i n c l u s i o n chemical
composition.
I t has been proposed t h a t p o l a r i z a t i o n due p a s s i n g through the slag-^skin/mould
w a l l i n t e r f a c e , which
generates s m a l l arc c o n t a c t s , i n c r e a s e s the i n the A.C.
ESR
process
and hence
symetry of r e a c t i o n s (1-5).
to c u r r e n t
rectification
i t enhances the net
as-
This p o l a r i z a t i o n increases
the
109 Fe 2+ content
of the s l a g bulk
a t i o n r a t e s i n the system. p l a i n the chemical
and
thus, accentuates a l l o x i d -
T h i s p r o p o s a l has been used to
composition
of i n c l u s i o n s i n the
ex-
Fe-Al-0
. (219,220) system • ' . The b a s i c i t y index of the s l a g chemical
p o t e n t i a l ) and
(as a measure of i t s
i t s e f f e c t on the chemical
composition
(49-51) of i n g o t s
and
to a l i m i t e d extent on the chemical
t u r e of i n c l u s i o n s ' ' 8
7 4
the German l i t e r a t u r e .
na-
^ , has been s t r o n g l y supported i n These s t u d i e s , however, have not
c l u s i v e l y determined the r o l e of the d e o x i d i z e r , the of the s l a g and/or d e o x i d i z e r , and/or the chemistry
con-
chemistry of
the
e l e c t r o d e or the combined e f f e c t of these parameters on i n c l u s i o n chemical
composition
of ESR
the
ingots.
S e v e r a l d e o x i d a t i o n p r a c t i c e s have been suggested i n / ^ g 74 the l i t e r a t u r e ^
'
8 3)
'
.
Among the uneconomic
deoxidation
techniques,
to overcome l o s s e s of r e a c t i v e elements ( A l ,
Ti,
e t c . ) , i t has been proposed t o :
S i , Mn,
eliminate
the
hard s c a l e from r o l l e d e l e c t r o d e s , d e l i b e r a t e l y i n c r e a s e
the
r a t i o of these s p e c i e s i n the e l e c t r o d e , use p r o t e c t i v e p a i n t i n g s based on Mg or A l , to d e p o s i t o x i d a t i v e elements on electrode surface, etc. nique
The most f r e q u e n t d e o x i d a t i o n
developed e x c l u s i v e l y on an e m p i r i c a l b a s i s
the
tech-
has
been the e x t e r n a l a d d i t i o n of e i t h e r aluminum or s i l i c o n
as
wire, p e l l e t s , f e r r o a l l o y s , e t c . i n t o the s l a g to achieve
a
d e s i r e d i n g o t chemistry.
The
conventional
widespread
deoxi-
110
d a t i o n l e v e l i s about 0.2 wt. % A l o r S i .
I t has been p r o -
(74) posed
t h a t e f f i c i e n t d e o x i d a t i o n i s achieved when a de-
o x i d i z e r i s i n t r o d u c e d i n t o the s l a g which does not c o n t a i n i t s oxide.
On the other hand, other r e s e a r c h e r s have p r o -
(39 48) posed
'
t h a t i f an element i s prone t o o x i d a t i o n ( i . e .
r e a c t i v e elements as T i , S i , Z r , A l etc.) d u r i n g r e f i n i n g , then a d d i t i o n s o f i t s r e s p e c t i v e oxide i n t o the s l a g p r e vents i t s l o s s e s .
The p o t e n t i a l harm o f i n a p p r o p r i a t e de-
o x i d a t i o n w i l l m a n i f e s t i t s e l f i n an uneven d i s t r i b u t i o n (55 75 79) of c r i t i c a l a l l o y i n g elements i n i n g o t s ' ' and r e (221) s u i t i n d e l e t e r i o u s mechanical p r o p e r t i e s These s t u d i e s , however, have not approached the r e a c t i o n mechanisms and hence i n g o t and i n c l u s i o n composition has remained unexplored.
chemical
In summary, although
the need t o i n t r o d u c e a deoxidant i n t o the s l a g , has been i d e n t i f i e d , the net e f f e c t o f i t has not been e l u c i d a t e d . Thus, t o a l a r g e extent the e x p l a n a t i o n f o r the i n g o t chemi s t r y and hence the composition o f i n c l u s i o n s has remained obscure.
In a d d i t i o n , s i n c e the r e a c t i o n mechanisms which
c o n t r o l the chemistry of i n g o t s have not been completely understood,
the e x p l o r a t i o n o f o t h e r a l t e r n a t i v e means of
d e o x i d a t i o n — w i t h t h e i r p o t e n t i a l advantages and d i s a d v a n t a g e s — h a s never been p r o p e r l y i n v e s t i g a t e d .
Ill 3.3
The
P r e c i p i t a t i o n of I n c l u s i o n s from L i q u i d Pool
to
Ingot ,
. ,.
(1,33,36,48,58,61,64)
Several studies
'
' • '
'
'
proached the r e a c t i o n scheme i n the ESR
'
.. . , which have
process
have c l e a r l y
demonstrated the e x i s t e n c e of o x i d a t i o n - r e d u c t i o n a t the e l e c t r o a c t i v e ( e l e c t r o d e t i p - s l a g and
ap-
reactions
slag-liquid
pool) i n t e r f a c e s which l a r g e l y c o n t r i b u t e to c o n t r o l the (218—220) i n g o t and ried
the i n c l u s i o n chemistry.
out a t U.B.C.
has
Research
c l e a r l y r e v e a l e d the
carelectrochemical
nature of i n c l u s i o n p r e c i p i t a t i o n i n the Fe-O-Al system. Chemical a n a l y s i s ( i n s i t u by m e t a l l o g r a p h i c microscopic
techniques
and e l e c t r o -
and by e x t r a c t i n g i n c l u s i o n s and
an-
a l y z i n g them by X-ray techniques) have c o n c l u s i v e l y shown t h a t a s t a t e of thermochemical e q u i l i b r i u m i s only i v e l y obeyed. alumina was
qualitat-
From thermochemical c o n d i t i o n s i n s l a g s
where
expected as the o n l y type of i n c l u s i o n , a mix-
t u r e of i r o n oxide
and h e r c y n i t e , h e r c y n i t e and
found i n s t e a d of pure alumina. The m a j o r i t y of s t u d i e s on the chemical
alumina were
composition
i n c l u s i o n s have been performed on samples from the
of
liquid
(15) film
(at the e l e c t r o d e t i p ) , d r o p l e t s i n process
of form-
a t i o n which have been i n c o n t a c t with the s l a g ' ^ ' ^ " ^ ( a l s o at the e l e c t r o d e t i p ) and ingots.
from samples of a l r e a d y
solidified
112
I t should be p o i n t e d out t h a t these s t u d i e s have been performed i n i n g o t s r e f i n e d i n l a b o r a t o r y ESR-furnaces as p r e v i o u s l y c i t e d , the i s smaller
s u r f a c e area
than i n i n d u s t r i a l
and
available for reactions
s i z e furnaces.
p h y s i c a l l i m i t a t i o n s i n the s m a l l furnaces
In a d d i t i o n
( i . e . electrode
mould w a l l spacing) pose another drawback f o r e x t r a c t i n g samples from e i t h e r l i q u i d p o o l or s l a g . not allowed
researchers
These f a c t o r s have
to e l u c i d a t e the o r i g i n of i n c l u s i o n s .
Thus, the need to i n v e s t i g a t e the thermochemical or e l e c t r o chemical
i n f l u e n c e of the s l a g - l i q u i d p o o l i n t e r f a c e on
chemical
composition
of i n c l u s i o n s and
the
t h e r e f o r e t o unambigu-
ously i d e n t i f y t h e i r o r i g i n i s e s s e n t i a l .
113 3.4
D i s t r i b u t i o n of Inclusions during I t i s g e n e r a l l y accepted
b u t i o n s i n ESR-ingots a r e
Solidification
that i n c l u s i o n size
distri-
markedly s m a l l e r compared t o
i n g o t s produced under c o n v e n t i o n a l and most of the secondary ( r e f i n i n g ) steelmaking
processes.
While i n c o n v e n t i o n a l processes
localized
concen-
t r a t i o n o f i n c l u s i o n s have been widely r e p o r t e d
due to
t h e i r c h a r a c t e r i s t i c c r y s t a l l i z a t i o n mode, i n s e m i - i n d u s t r i a l or f u l l
s c a l e ESR-ingots t h i s phenomenon has almost never been
reported. ESR-ingots
Other i n t e r e s t i n g f e a t u r e s commonly observed i n o b t a i n e d under c o n v e n t i o n a l d e o x i d a t i o n p r a c t i c e s , (224)
are t h e i r i n c l u s i o n s i z e d i s t r i b u t i o n s
(about 2 t o 12ym) (225)
and t h e i r r a d i a l l o c a l s o l i d i f i c a t i o n times
, expressed
as a r e g u l a r d e c r e a s i n g v a r i a t i o n o f t h e i r primary
and second-
ary d e n d r i t e arm spacings along t h e i r r a d i a l d i r e c t i o n s from (65) the c e n t r e l i n e towards the mould w a l l . Several d e t a i l e d (218) s t u d i e s on i n c l u s i o n s i n ESR i n g o t s
where r e f i n i n g o f a
f e r r o u s N i e n r i c h e d a l l o y was performed through a CaF^^CaO s l a g , have found round i n c l u s i o n s a l i g n e d along d e n d r i t e arms.
primary
These o b s e r v a t i o n s l e d to the b e l i e f t h a t
p r e c i p i t a t i o n o f i n c l u s i o n s takes p l a c e homogeneously from the i n t e r d e n d r i t i c l i q u i d . (15 219) formed a t U.B.C. In t h i s study
'
Complementary s t u d i e s
also per-
have a l s o c o r r o b o r a t e d t h i s p r o p o s a l .
i t i s r e p o r t e d t h a t i n c l u s i o n s were l o c a t e d i n
i n t e r d e n d r i t i c spaces and very r a r e l y were d e n d r i t e arms seen
114 f o l d e d around i n c l u s i o n s . Since a t t e m p t s ^ ^ 15
t o generate a s i l i c o n
supersaturation
i n l a b o r a t o r y ESR melts d i d not produce any d e t e c t a b l e
change
i n the i n c l u s i o n s i z e or i n the t o t a l oxygen a n a l y s i s , i t was proposed t h a t n u c l e a t i o n and growth o f i n c l u s i o n s takes almost e x c l u s i v e l y as a r e s u l t of r e j e c t i o n of s o l u t e s solidification.
during
I t was t h e r e f o r e concluded t h a t under a con-
v e n t i o n a l degree o f d e o x i d a t i o n
the i n c l u s i o n f l o t a t i o n mech-
anism was not a p p l i c a b l e , i n disagreement with other ers
place
research-
(1,12,35) ' ' As p r e v i o u s l y s t a t e d
s i n c e there are p h y s i c a l
limit-
a t i o n s and d i f f e r e n t k i n e t i c s a t the e l e c t r o a c t i v e i n t e r f a c e s i n s m a l l ESR furnaces
researchers
have not been able t o ap-
p r o p r i a t e l y monitor a l l o f the r e a c t i o n s i n the v a r i o u s
com-
ponents and stages of r e f i n i n g , a more complete i n v e s t i g a t i o n is
required.
115
3.5
E s t a b l i s h m e n t of the P r o p o s a l and O b j e c t i v e s Sought Through t h i s
Research
A c l e a r n e c e s s i t y to understand
and thereby to c o n t r o l
the sequence of events to which i n c l u s i o n s and the
liquid
metal are s u b j e c t e d i n the v a r i o u s stages of r e f i n i n g i s r e q u i r e d , as seen from the p r e v i o u s review.
Thus, i n order t o
cover a l l the e x i s t i n g gaps and to extend our p r e s e n t unders t a n d i n g r e g a r d i n g the nature of i n c l u s i o n s i n t h i s f i e l d s e r i e s of f o u r q u e s t i o n s was
a
addressed:
1)
How
are e l e c t r o d e i n c l u s i o n s removed?
2)
Is the i n c l u s i o n composition c o n t r o l l e d
by
the chemistry of e l e c t r o d e s , s l a g s or d e o x i d i z e r s ? 3)
Are i n c l u s i o n s i n the l i q u i d p o o l the same as i n the i n g o t ? and
4)
Is the i n c l u s i o n s i z e d i s t r i b u t i o n r e l a t e d to r a d i a l d i s t a n c e s from the c e n t r e l i n e to the mold w a l l of ESR i n g o t s .
These q u e s t i o n s were s t a t e d i n such a way
t h a t a l l of the
phenomena i n v o l v e d i n the process of r e f i n i n g , i n terms of inclusions
were addressed.
the o r i g i n of i n c l u s i o n s
Once the mechanisms which
( r e a c t i o n s ) were determined
the deoxidant, d e o x i d a t i o n technique and the s l a g
govern
then
chemical
composition would be s e l e c t e d and a comparison between r e sults
as a f u n c t i o n of e l e c t r o d e and s l a g compositions
w e l l as deoxidants c o u l d be c a r r i e d out.
as
116 CHAPTER IV EXPERIMENTAL WORK AND TECHNIQUES 4.1
Experimental Procedure Ingots were r e f i n e d through s e v e r a l s l a g systems u s i n g
l a b o r a t o r y and s e m i - i n d u s t r i a l s c a l e ESR-furnaces cribed e l s e w h e r e ^ ^ ' 2 2
2 2 7
^.
des-
E l e c t r o d e s of s e v e r a l chemical
compositions and diameters were r e f i n e d u s i n g s e v e r a l systems and
(commercial grades) and deoxidants.
slag
Tables (VII)
(VIII) summarize t h i s i n f o r m a t i o n . E l e c t r o d e s 31.75 and 44.75 mm
i n the l a b o r a t o r y s i z e ESR-furnace from
1.2 t o 1.5 Kg m i n . - 1
i n diameter were melted at melting rates ranging
1020, 4340 and r o t o r (Ni-Cr-Mo)
s t e e l s which were 76.2, 88.9 and 114.3 mm remelted i n the s e m i - i n d u s t r i a l
(200 mm)
m e l t i n g r a t e s o f approximately 1 Kg min use l i n e frequency A.C. power.
i n diameter were ESR-furnace a t .
Refining
with and without a p r o t e c t i v e atmosphere.
Both furnaces
was c a r r i e d out In the f i r s t
case
the system e n c l o s e d an argon gas s h i e l d and deoxidant a d d i t i o n s c o u l d be made a t monitored r a t e s , F i g u r e (14). The d e o x i d i zers were g r a n u l a r aluminum 99.99% p u r i t y , c a l c i u m s i l i c i d e a l l o y s and aluminum 65 wt.% S i , i n the s i z e range o f 8-32 mesh-
S p e c i f i c compositions are g i v e n i n Table ( I X ) . S e v e r a l d e o x i d a t i o n p r a c t i c e s were f o l l o w e d , namely i)
Constant a d d i t i o n i n s m a l l ESR-ingots,
117 ii)
i n t e r m i t t e n t a d d i t i o n s and
iii) The
continuously
increasing.
l a s t two p r a c t i c e s were performed i n i n g o t s 200 mm i n
diameter.
Experiments t o determine the i n c l u s i o n removal
mechanisms i n e l e c t r o d e
t i p s were c a r r i e d out i n 1020 m i l d
s t e e l produced v i a a c i d e l e c t r i c furnace, 4340 C a - S i - A l steel pleted
t r e a t e d , and 114 mm diameter r o t o r
Ca-Si-Al
treated.
electrodes
Once r e f i n i n g
scopic
(Ni-Cr-Mo)
experiments were com-
were r a p i d l y withdrawn from s l a g s t o achieve
as f a s t a c o o l i n g r a t e as p o s s i b l e . sectioned
89 mm diameter
and m e t a l l o g r a p h i c
Electrode
t i p s were
( o p t i c a l ) and e l e c t r o - m i c r o -
(SEM and EPMA) a n a l y s i s were performed.
Qualitative
d i s p e r s i v e - X - r a y - s p e c t r u m a n a l y s i s by the SEM and backs c a t t e r e d and e l e c t r o n composition maps by the EPMA as w e l l as q u a n t i t a t i v e a n a l y s i s
(by EPMA) on i n c l u s i o n s were c a r r i e d
out. Samples from l i q u i d p o o l s and slags were taken as deoxidation
and r e f i n i n g was t a k i n g p l a c e .
samples were e x t r a c t e d
L i q u i d metal
by s u c t i o n from l i q u i d p o o l s and s l a g
samples by means of a s m a l l copper c h i l l .
Chemical a n a l y s i s
of i n c l u s i o n s i n samples d i s c r e t e l y e x t r a c t e d p o o l s as w e l l as from s o l i d i f i e d EPMA.
The
liquid
i n g o t s were c a r r i e d out by
Oxygen a n a l y s i s by vacuum f u s i o n
of samples
from
a l s o on both types
were performed. chemical composition o f s l a g samples
were analyzed
118 by standard spectrophotometric techniques.
The chemical
composition o f i n g o t s was c a r r i e d out by s p e c t r o g r a p h i c a n a l y s i s along the v e r t i c a l a x i s of i n g o t s . F i n a l l y , complementary experiments
to determine
where and when i n c l u s i o n s were n u c l e a t e d and grown were performed.
S i l i c a tubes which c o n t a i n e d e i t h e r r a r e e a r t h metals
(mischmetal) the s l a g
o r Zirconium wires were i n t r o d u c e d through
w h i l e helium was g e n t l y blown
i n t o the l i q u i d
p o o l to e x t r a c t l i q u i d metal by the s u c t i o n technique. wards
After-
samples were p o l i s h e d and q u a l i t a t i v e and q u a n t i t -
a t i v e a n a l y s i s o f i n c l u s i o n s were performed. s t u d i e s on i n c l u s i o n s t o determine
EPMA and SEM
t h e i r chemical
and the d i s t r i b u t i o n o f t h e i r phases
composition
(composition maps) were
c a r r i e d out.
4.2
Analysis of Inclusions A t r i p l e spectrometer
J e o l c o JXA-3A e l e c t r o n
probe and an E t e c "Autoscan"
scanning e l e c t r o n
micro-
microscope
w i t h a d i s p e r s i v e X-ray a n a l y s e r were used to determine the chemical nature o f i n c l u s i o n s . Since the diameter
o f the e l e c t r o n beam which e x c i t e s
the sample, the specimen c u r r e n t d e n s i t y and the a c c e l e r a t i n g v o l t a g e determine signals
the s t e a d i n e s s and the magnitude o f the
(X-rays, secondary
and b a c k s c a t t e r e d e l e c t r o n s , e t c . )
119
emitted they were c o n t i n u o u s l y c a l i b r a t e d t o g i v e a beam approximately
1.0 ym i n diameter when the e x c i t a t i o n
age was 25 kV and the specimen c u r r e n t d e n s i t y was 0.08 yA .
voltabout
Hence, the e l e c t r i c a l - o p t i c a l c o n d i t i o n s i n these
instruments were c a l i b r a t e d i n such a manner t h a t the maximum
p o s s i b l e c u r r e n t was o b t a i n e d i n the s m a l l e s t e l e c t r o n
probe. Aluminum, c a l c i u m , s i l i c o n ,
s u l f u r , manganese, chromium,
t i t a n i u m , and magnesium were determined f l u o r i n e were determined
a t 10 kV.
a t 25 kV.
Oxygen and
The i d e n t i f i c a t i o n o f
i n c l u s i o n phases was a l s o o b t a i n e d by the v i s i b l e l i g h t uced by the e l e c t r o n beam and photon r a d i a t i o n
prod-
(cathodo-
luminescence). Since compound standards are known t o produce
more a c -
(228229) c u r a t e and r e p r o d u c i b l e a n a l y s i s l i k e CaC0 , A^O^, 3
S l
0 ' 2
standards t o determine inclusion
M (
? ' 0
Z
n
S
a
' n
d
,
compounds
pure Mn were used as
the chemical composition
of the
phases.
Raw data
(specimen background, a c c e l e r a t i n g v o l t a g e ,
t a k e - o f f angle, specimen counts, compound standard i n f o r m a t i o n , background from standards, X-ray counting time, e t c ) were t r a n s l a t e d i n t o chemical composition, t a k i n g i n t o account c o r r e c t i o n f o r atomic number e f f e c t s , a b s o r p t i o n and secondary f l u o r e s e c e n c e , by Colby's MAGIC IV p r o g r a m ' * with U.B.C.'s 3 0
120 AMDAHL computer.
R e l a t i v e accuracy of ± 7-10%
was
obtained.
These v a l u e s are i n f a i r agreement with r e p o r t s a v a i l a b l e i n the l i t e r a t u r e '
0 6
'
2 2 8
'
2 2 9
!
(±5-7%).
to mention t h a t , as r e p o r t e d i n the
I t i s also
worthwhile
literature'
4 0
the c a l c i u m to aluminum r a t i o i n i n c l u s i o n s i n the
'
2 1 6
'
2 1 7
^
Ca-deoxidized
i n g o t s gave a c l o s e r i n d i c a t i o n of the d e o x i d a t i o n sequence. These r a t i o s et a l . • s
( 2 0 9
'
3 1 6 )
(Ca:Al)
i n agreement with F a u l r i n g ' s
and S a l t e r ' s and P i c k e r i n g • s '
4 0 }
findings
were found to approximate the corresponding s t o i c h i o m e t r i c of those phases given by the pseudo-binary
ratios
CaO-A^O^ diagram.
S p e c t r o g r a p h i c and oxygen a n a l y s i s of samples from i n gots and l i q u i d p o o l
and
spectrophotometric and
graphic a n a l y s i s of i n c l u s i o n s
crystallo-
(by Debye-Scherrer
and d i f -
f r a c t o m e t e r techniques) e x t r a c t e d from i n g o t s c o r r o b o r a t e d (207) these f i n d i n g s . aluminate
Based on a r e p o r t e d work
on c a l c i u m
i n c l u s i o n s a minimum o f twenty and a maximum of
50 s i n g l e assays were performed
to o b t a i n a r e p r e s e n t a t i v e
a n a l y s i s o f a sample, i . e . t h i s r e p r e s e n t s one p o i n t on
the
graphs. The
i n c l u s i o n s were grouped a c c o r d i n g to s i z e , chemi-
c a l composition, tities.
f l u o r e s c e n c e , shape and r e p r e s e n t a t i v e quan-
I n c l u s i o n s s m a l l e r than 3 ym i n diameter were chemi-
c a l l y analyzed; they were, however o n l y q u a l i t a t i v e l y
con-
s i d e r e d due t o the cumbersome i n t e r a c t i o n e f f e c t s o f the i n c l u s i o n chemical composition and
the metal m a t r i x .
Aluminum
121
d e o x i d i z e d i n g o t s c o n t a i n e d e i t h e r FeO-A^C^, pure or
c a l c i u m hexaluminate
as i n c l u s i o n s phases which were
very s m a l l s i n g l e or c l u s t e r e d . were l e s s than 6-8 pm
alumina,
Since i n c l u s i o n
diameters
i n c l u s i o n s s m a l l e r than 3.0 ym were
a l s o a n a l y s e d on a q u a l i t a t i v e b a s i s . Analyses were c a r r i e d out by scanning d i a g o n a l l y a c r o s s the sample and the i n c l u s i o n s so t h a t r e s u l t s s t a t i s t i c a l l y r e p r e s e n t e d the i n c l u s i o n chemistry of the sample. T y p i c a l i n c l u s i o n s o f a g i v e n sample were microphotographed, o p t i c a l , scanning and b a c k s c a t t e r e d (EPMA) analyses and composition maps were a l s o o b t a i n e d .
4.3
T o t a l Oxygen Analyses The
t o t a l oxygen content of samples e x t r a c t e d from
l i q u i d p o o l s and i n g o t s was determined
by the standard
inert
gas vacuum f u s i o n technique u s i n g a Leco 537 i n d u c t i o n f u r nace
(507-800) and a Leco oxygen analyzer
weighing
(509-600).
Samples
1.0 - 1.5 grams were c u t , ground, and washed, u l t r a -
s o n i c a l l y cleaned and r i n s e d with anhydrous 1,1,1, t h r e e chloroethane.
Since the accuracy and r e p r o d u c i b i l i t y of
t h i s a n a l y s i s was s t r o n g l y i n f l u e n c e d by the weight o f the sample and i t s p r e p a r a t i o n ,
a
meticulous procedure
was
f o l l o w e d to o b t a i n a minimum of t h r e e assays with a maximum o f 2-5% d e v i a t i o n amongst them.
I f the d e v i a t i o n i n analyses
were g r e a t e r than t h i s , a new s e t of t h r e e analyses was p e r -
122
formed. To o b t a i n an a p p r o p r i a t e
c a l i b r a t i o n of the
analy-
t i c a l equipment standards of known oxygen content were analyzed.
A n a l y s i s on samples c o n t a i n i n g
an upper and
l i m i t of oxygen as w e l l as a blank t e s t to check the a t i o n i n gas
(helium) flow r a t e were c o n t i n u o u s l y
to m a i n t a i n them c o n s t a n t l y Samples e x t r a c t e d
throughout any
lower
vari-
performed
s e r i e s of
analyses.
from l i q u i d p o o l s were c a r e f u l l y s e l e c t e d
because p o r o s i t i e s and
s l a g entrapment were o c c a s i o n a l l y
de-
tected .
4.4
Inclusion
E x t r a c t i o n Method
I t i s an accepted f a c t t h a t c h e m i c a l e x t r a c t i o n methods
of n o n - m e t a l l i c
i n c l u s i o n s followed
by a n a l y s i s p r e -
sent s e v e r a l advantages over chemical a n a l y s i s performed i n s i t u . ( b y microprobe or scanning E.M.). vantages are the 1.
The
major
ad-
following:
A n a l y t i c a l r e s u l t s are f a r more
representative
because a much l a r g e r sample i s taken f o r e x t r a c t i o n than f o r i n s i t u methods. 2.
Phases can be
specifically identified after
ex-
traction. 3.
The
t o t a l oxygen content and
the t o t a l amount
of most phases i n s t e e l can be estimated by chemical a n a l y s i s of the
residue.
123
There are, however, s e v e r a l disadvantages as w e l l . 1.
Some phases cannot be q u a n t i t a t i v e l y e x t r a c t e d .
T h i s f a c t i s due t o e i t h e r i n c l u s i o n s i z e (< 5ym i n d i a meter) o r t o the chemical nature o f i n c l u s i o n s and r e agents
(too a g r e s s i v e ) . 2.
Phases c o n t a i n i n g
common elements and amorphous
or/and isomorphic s t r u c t u r e s may i n t e r f e r e with c e r t a i n a n a l y sis . 3. small
Since i n c l u s i o n s i z e i n ESR-materials i s r e l a t i v e l y
(S 10ym i n diameter) a n a l y s i s by X-rays i s r a t h e r
dif-
ficult. S e v e r a l chemical methods o f i n c l u s i o n e x t r a c t i o n were performed.
Among them
bromine i n methanol,
a n o l , bromine-ester-methanol methanol.
i o d i n e i n meth-
and i o d i n e - m e t h y l a c e t a t e -
From a l l the above methods only the l a s t two were
s u i t a b l e t o t h i s purpose.
The iodine-methanol-methyl a c e t a t e
however, was found to be the most convenient because o f i t s accuracy and r e p r o d u c i b i l i t y . 4.4.1
Apparatus and Experimental Procedure The apparatus used was i n t e g r a t e d i n f o u r u n i t s .
f i r s t unit
(I) was used to pour i o d i n e c r y s t a l s and the
methyl acetate-methanol mixture sphere c o n s i s t i n g of) anhydrous
under a p r o t e c t i v e atmoargon.
T h i s p a r t o f the s y s -
tem was a l s o used as a d i s s o l u t i o n chamber. s o n i c c l e a n e r o r a magnetic erature
The
An u l t r a -
s t i r r e r w i t h c o n t r o l l a b l e temp-
served t o speed up the i o d i n e d i s s o l u t i o n .
The second u n i t
(II) c o n s i s t e d of a m i l l i p o r e
which c o n t a i n e d a whatman paper No. pore f i l t e r
(0.5 ym) .
u n i t . T h i s was served as
was
or a t e f l o n
a g l a s s c o n t a i n e r w i t h four o u t l e t s which
a) b r e a t h i n g system
b) r e a g e n t - l e v e l r e g u l a t o r ,
d) a r g o n - f l u x
valve.
T h i s cham-
i n s i d e the u l t r a s o n i c a g i t a t o r which was
speed up the d i s s o l u t i o n of the metal sample. unit
(IV) was
milli-
The r e a c t i o n chamber was the third (III)
c) vacuum c o n t r o l l e r and ber
50
filter
used to
The
fourth
a l s o equipped w i t h another m i l l i p o r e
filter
s i m i l a r t o the one used i n u n i t no. 2 but t h i s had a ym diameter porous s i z e f i l t e r
0.5
(made of teflon), F i g u r e
(15) .
Since humidity i s one of the major concerns i n any halogen-methanol-methyl a c e t a t e technique cedure was
followed.
Reagents used
methyl a c e t a t e were 99.99% i n p u r i t y
a c a r e f u l pro-
such as methanol
and
and i o d i n e c r y s t a l s
were p r e v i o u s l y d r i e d i n a d e s s i c a t o r which c o n t a i n e d gel
and
silica
drierite.
T h i s e x t r a c t i o n method was based on Rooney's and S t a p l e (231) ton's
, i t was,
however, improved i n terms of a v o i d i n g
c e r t a i n complexity In i t s d e s i g n and m i n i m i z i n g the r i s k of
contaminating the apparatus by moisture and o t h e r vapours
c a r r i e d away during e v a c u a t i o n and h e a t i n g .
Combustion
tube
c o n t a i n i n g s p i r a l s o f copper and n i c k e l as w e l l as s u l f u r i c a c i d and contaminated
i r o n t u r n i n g s were a l s o avoided.
125 Experimental Procedure 20-30 grams of an E S R - s t e e l sample cleaned
with 1,1,1-trichlorethane
were i n t r o d u c e d
and d r i e d w i t h h o t a i r
i n t o the r e a c t i o n chamber.
completely dehydrated by p a s s i n g taning d r i e r i t e ,
Argon was
i t through 3 U-tubes con-
s i l i c a - g e l - i n d i c a t i n g and a c t i v a t e d carbon
i n a U-tuhe immersed i n l i q u i d n i t r o g e n . functions:
f r e e o f oxide,
The argon had two
t o sweep out t h e a i r and humidity i n the f o u r
u n i t s and to pump the l i q u i d s from one u n i t t o another. t h i s l a s t purpose The
a vacuum was a l s o used.
whole d r y i n g o p e r a t i o n
was executed i n two hours.
Once the system was f r e e o f moisture and a i r the p r e d r i e d
For
dissolution of
i o d i n e c r y s t a l s was c a r r i e d out.
The next
step
i n t h i s technique was t o pump the i o d i n e s o l u t i o n e i t h e r by vacuum or by argon t o the f i r s t
f i l t e r i n g unit.
Then the
s o l u t i o n was pumped t o the r e a c t i o n chamber. When the s t e e l sample was completely d i s s o l v e d a f t e r 10-24 was
hours, the l i q u o r c o n t a i n i n g
sent t o the l a s t f i l t e r i n g u n i t .
r i n s i n g o f the f i l t e r e d was
inclusions
At t h i s l a s t u n i t ,
i n c l u s i o n s w i t h 99.99% methyl a l c o h o l
performed s e v e r a l times u n t i l the f i l t e r e d
completely c o l o r l e s s , i . e . was
the e x t r a c t e d
iodine free.
alcohol
This l a s t
was
operation
performed under an argon atmosphere. Extracted
i n c l u s i o n s were d r i e d and weighed
a f t e r s u l f i d e i n c l u s i o n s were e l i m i n a t e d .
b e f o r e and
Samples from sev-
126
e r a l ESR
i n g o t s were s u b j e c t e d under t h i s e x t r a c t i o n t e c h -
nique f o r v a r i o u s purposes, namely EPMA i n c l u s i o n chemistry
1) to c o r r o b o r a t e the
by q u a n t i t a t i v e
and q u a l i t a t i v e c r y s t a l l o g r a p h i c
(spectrophotometry)
(X-rays) a n a l y s i s
v e r i f y the v a l i d i t y of the t o t a l oxygen a n a l y s i s and determine how
4.5
2) to 3) to
i n c l u s i o n s were p r e s e n t i n the f i n a l product.
C r y s t a l l o g r a p h i c X-ray A n a l y s i s of E x t r a c t e d I n c l u s i o n s The e x t r a c t e d i n c l u s i o n s were c r y s t a l l o g r a p h i c a l l y
an-
a l y s e d by a P h i l i p s high angle d i f f r a c t o m e t e r and a DebyeS c h e r r e r camera was
114.83 mm
40 kV and 15 uA.
meter was
1° 26/min.
The
i n diameter.
The machine s e t t i n g
scanning r a t e used i n the d i f f r a c t o -
The camera i s designed such t h a t 2
measured on the f i l m corresponds to 1° 6.
mm
The d i s t a n c e along
the f i l m between the zero p o i n t and the r e f e r e n c e end i s 180mm. In both X-ray techniques the i r o n ka^ r a d i a t i o n was
(X = 1.9 36)
used. Although the amount of e x t r a c t e d i n c l u s i o n s ranged
from
10 t o 30 m i l l i g r a m s , p r i o r t o t h e i r X-ray a n a l y s i s , microphotographs
and q u a l i t a t i v e SEM
a p o r t i o n of the sample.
a n a l y s i s were performed
The c r y s t a l l o g r a p h i c X-ray
o f i n c l u s i o n s c l e a r l y showed a sequence of A ^ O ^ and 12 CaO*7Al C> 2
3
(as g i v e n by the C a O - A l 0 2
3
on
analysis
up t o C a O * A l 0 2
3
pseudo b i n a r y phase
127
diagram) as the Ca-Si d e o x i d a t i o n l e v e l was
increased.
It
i s worthwhile to mention t h a t i n the c a l c i u m aluminates riched i n calcium
(CaO•2Al 0 ~CaO•A1 0 2
3
2
3
and
CaO•Al 0^-12CaO• 2
7 A l 0 ) very wide d i f f r a c t i o n peaks and bands were 2
3
T h i s was
en-
observed.
a c l e a r i n d i c a t i o n of t h e i r lower degree of c r y -
stallinity.
The d i f f r a c t i o n bands corresponding
12CaO«7Al 0 2
3
to the
were very weakly t r a c e d .
G e n e r a l l y , the c r y s t a l p a t t e r n s showed from 6 to 16 p r i n c i p a l d i f f r a c t i o n bands with v a r i o u s i n t e n s i t i e s . t u r e s of at l e a s t two
i n c l u s i o n c r y s t a l s t r u c t u r e s and some
n i t r i d e s and c a r b i d e s were
4.6
observed.
Atomic A b s o r p t i o n A n a l y s i s A P e r k i n Elmer 306
model HGA-220 was
(Spectrophotometry)
spectrophotometer with a c o n t r o l l e r
used to analyze
c l u s i o n s from metal m a t r i c e s .
s l a g s and e x t r a c t e d i n -
The
l i t h i u m metaborate f u s i o n (232
procedure The
Mix-
a v a i l a b l e i n the l i t e r a t u r e
233) '
was
followed.
c o n c e n t r a t i o n of the elements of i n t e r e s t were determined
by u s i n g a p p r o p r i a t e l y matched standards
and blanks with
r o u t i n e procedure given i n the g e n e r a l i n f o r m a t i o n of Perkin-Elmer
manual.
s o l u t i o n a n a l y s i s was F + 0.2%,
Mg
G e n e r a l l y speaking Ca ± 0.2%,
the
the
the accuracy of the
A l ± 0.06%, S i ± 0.04%, .
± 0.002% and Fe ± 0.001
wt
%.
Stoichiometric
balances were c a r r i e d out on the bases t h a t Ca, A l , S i , Fe, and F were p r e s e n t as CaO, pectively.
Al 0 , 2
3
Under t h i s assumption
S i 0 , FeO, 2
MgO
and C a F
2
res-
the s t o i c h i o m e t r i c c a l c u -
l a t i o n s gave 10 0% with a minimum accuracy of +
1.0%.
Mg,
128 4.7
Metallographic
Analysis
Ingots were s e c t i o n e d l o n g i t u d i n a l l y i n such a manner t h a t a s l i c e 2.5 cm i n t h i c k n e s s across the diameter was obtained.
These p l a t e s were s u r f a c e ground and etched with a 50%
HCl-H^O s o l u t i o n a t 70-80°C f o r approximately
one hour.
l i q u i d p o o l marks made with m e t a l l i c tungsten
powder to
identify vealed.
deoxidation
Thus
l e v e l s and i n g o t s t r u c t u r e were r e -
L o n g i t u d i n a l d i s c r e t e sampling
(matching the pro-
g r e s s i v e sampling o f l i q u i d p o o l s and s l a g s ) t o perform spectrographic, were thus
i n c l u s i o n chemical
and t o t a l oxygen a n a l y s i s
obtained.
Samples o b t a i n e d
r a d i a l l y were used t o determine i n -
c l u s i o n s i z e d i s t r i b u t i o n s and d e n d r i t e arm s p a c i n g s .
The
o p t i c a l a n a l y s i s was performed u s i n g a Z e i s s u l t r a p h o t i n d i f f e r e n t i a l i n t e r f e r e n c e mode. tips,
Samples from e l e c t r o d e
l i q u i d pools and r a d i a l and l o n g i t u d i n a l specimens
from i n g o t s were ground on emery paper and diamond p o l i s h e d . P o l i s h i n g was c a r r i e d o u t t o determine i n c l u s i o n s i z e s and
t h e i r l o c a t i o n with r e s p e c t t o d e n d r i t e s i n samples ex-
t r a c t e d from l i q u i d p o o l and i n g o t s u s i n g : pastes met,
(Metadi
diamond compound
II) down t o 0.25 ym diamond p a r t i c l e s i z e , t e x -
m i c r o c l o t h and n y l o n p o l i s h i n g (Buehler)
cloth
( o i l and
water r e s i s t a n t and a l c o h o l and an o i l based l u b r i c a n t , (Geomet t h i n n e r M i c r o m e t a l l u r g i c a l MM218). By f o l l o w i n g the above sequence
removal o f i n c l u s i o n s
from metal m a t r i c e s i n any s i z e range was completely avoided. To determine the l o c a t i o n o f i n c l u s i o n s and d e n d r i t e arm spacings
standard O b e r h o f f e r ' s reagent was used t o l i g h t l y
e t c h these specimens.
Four and f i v e f a c e s of each
specimen
were p o l i s h e d , etched and microphotographs were taken a t a m a g n i f i c a t i o n such t h a t r e p r e s e n t a t i v e number of i n c l u s i o n s were i n each photograph.
The m a g n i f i c a t i o n used was very
dependent on the l e v e l o f d e o x i d a t i o n and the c h e m i s t r y o f the deoxidant.
130 CHAPTER V
RESULTS AND 5.1
DISCUSSION
Mechanism by Which E l e c t r o d e I n c l u s i o n s are In the l i t e r a t u r e review on i n c l u s i o n s
emphasis has
Eliminated
particular
been given to the p r e c i p i t a t i o n sequence.
has been e s t a b l i s h e d t h a t i n c l u s i o n s
according
It
to the
de-
o x i d a t i o n technique
e x h i b i t s e q u e n t i a l changes i n t h e i r
chemical
as s o l i d i f i c a t i o n takes p l a c e .
composition
t r a n s i t i o n s may
take p l a c e a t s u b s o l i d u s
These
temperatures;
parti-
c u l a r l y where s u l f i d e phases p r e c i p i t a t e . Thus, to f u l l y understand the mechanism by which i n c l u s i o n s are removed, e l e c t r o d e t i p s from 1020 and
rotor
(Ni-Cr-Mo) s t e e l s were s t u d i e d .
M.S.,
1020
4340
M.S.
ingots
were o r i g i n a l l y produced by a c i d e l e c t r i c furnace p r a c t i c e . The
4340 and
the r o t o r s t e e l were c a l c i u m aluminum t r e a t e d
in
the l a d l e .
Subsequently,
i n t o e l e c t r o d e s 76.2,
88.9
and
they 114.3
were mm
hot
rolled
i n diameters r e s -
pectively. 5.1.1
Behavior of O x i s u l f i d e I n c l u s i o n s i n 1020 Electrode The
and 1020
Tips
most complete p i c t u r e of the i n c l u s i o n d i s s o l u t i o n
the t r a n s f o r m a t i o n M.S.
M.S.
electrodes.
of the metal matrix
i s g i v e n by
the
Typical inclusions i n electrodes i n
t h i s s e r i e s of experiments, as r e c e i v e d , are shown i n Figures
(16)
and
(17).
T h e i r q u a l i t a t i v e (SEM)
chemical
131
composition are a l s o presented Two
(spectrum X-ray
w e l l - d e f i n e d phases are i d e n t i f i e d .
analysis).
The darker phase
i s e n r i c h e d i n S i and the l i g h t phase i s e n r i c h e d i n manganese s u l f i d e .
Iron was
a l s o found i n both phases.
M e t a l l o g r a p h i c s t u d i e s o f e l e c t r o d e t i p s which were subjected to c r i t i c a l
(ESR)
thermal g r a d i e n t s have c l e a r l y r e -
v e a l e d the e x i s t e n c e of s e v e r a l heat a f f e c t e d areas, F i g u r e s (18) t o
(21).
F i n d i n g s from t h i s r e s e a r c h
agreement w i t h p r e v i o u s t h e o r e t i c a l 19 20 '
(8)
in qualitative
and experimental work
(13
'
22) '
. show t h a t a u s t e n i t i c g r a i n growth and changes i n
the morphology of i n c l u s i o n s occurs between 0.5 the l i q u i d f i l m .
S u l f i d e i n c l u s i o n s are f i r s t
and subsequently
- 0.8
spherodized
d i s s o l v e d i n t h i s r e g i o n as w e l l .
i c a l composition of i n c l u s i o n s determine
cm above
The chem-
the c r i t i c a l l e n g t h
at which the above changes take p l a c e . The d r i v i n g f o r c e s t o produce these changes i n order of importance of
are:
the heat produced
by the h i g h r e s i s t i v i t y
the s l a g and hence the a u s t e n i t i c g r a i n growth of the e l e c -
trode t i p .
The deformation of i n c l u s i o n s and metal matrix which
produce sharp c o n c e n t r a t i o n g r a d i e n t s and the n o n - e q u i l i b r i u m nature of the i n c l u s i o n p r e c i p i t a t i o n — a s
indicated i n Figure
(5)
by the s i n g l e d o t t e d l i n e — c a n a l s o p r o v i d e a d r i v i n g f o r c e f o r this
sequence
'
6
4
~
1
6
6
\
The
Mn
depletion
around
i n c l u s i o n s i n the metal m a t r i x should another d r i v i n g f o r c e ' inclusions tory
according
166,199)^
6 4
a l s o be c o n s i d e r e d T h e
c n e m
i
c a
to t h e i r appearance and
( l o c a t i o n ) can be c l a s s i f i e d a s :
phase o x i - s u l f i d e s and
-]_
as
nature of
thermal h i s -
a) Deformed double
deformed s u l f i d e s , F i g u r e s
(16,17).
These i n c l u s i o n s were commonly found i n areas where i n c i p i e n t g r a i n growth was s u l f i d e s and
observed,
b)
Comparatively l a r g e
o x i s u l f i d e s which were l o c a t e d i n r e l a t i v e l y grown
a u s t e n i t i c grains, Figure
(22).
dark i n appearance, F i g u r e p r e c i p i t a t e d complex
c) S p h e r i c a l s i n g l e oxide phas
(23)
and d) R e l a t i v e l y small
(Ca, A l and
Si) o x i d e s .
of i n c l u s i o n s were l o c a t e d i n p a r t i a l l y and q u i d areas.
globular
The
l a s t type was
These two
rekinds
completely
li-
p r e f e r e n t i a l l y l o c a t e d i n the
l i q u i d f i l m and
i n droplets, Figures
As
shown i n
Figures
(20), areas at which p h y s i c a l and
chemical
(18)
to
(24,25).
changes take p l a c e e i t h e r i n i n c l u s i o n s or i n the metal t r i x are very w e l l d e f i n e d . previously of
time
described at
which
a l l y affected. conditions Figures ive
(SEM)
presence of the d r i v i n g f o r c e s
compensate the r e l a t i v e l y the
volume
of
(5).
the
Based on
and q u a n t i t a t i v e
e l e c t r o d e t i p and
predicted the
short
electrode
T h i s promotes q u a s i - e q u i l i b r i u m
approaching
(4) and
The
ma-
is
therm-
thermo-chemical
changes
given
experimental
(EPMA) i n f o r m a t i o n
periods
qualitat-
about how
i n c l u s i o n s are p h y s i c a l l y and
formed as a p r i n c i p a l consequence of the thermal
in
the
chemically gradients
tran
and
the chemical
describes
composition
of
inclusions,
a mechanism w h i c h
the removal of o x y s u l f i d e i n c l u s i o n s
is
proposed.
Once a g i v e n r e g i o n i n t h e e l e c t r o d e t i p i s a f f e c t e d by
the heat
metal
coming from
matrix
oidization
start
of
the l i q u i d
to experience
sulfides
and
slag
the
certain
oxisulfides
inclusions
changes.
takes place
simultaneously
t o the growth o f the a u s t e n i t i c
metal
Experimentally estimated
matrix.
positions
i n t h e e l e c t r o d e and
the
The
spher-
almost
grains of
temperatures
theoretical
and
the
along
axial
calculations
(8) indicate occur
that this
a t a b o u t 0.5
electrode 21).
transition
t o 0.8
cm
above t h e
i s a t a temperature
This finding
(a + p e a r l i t e -»• y) liquid
o f about
approximately
i r o n p l u s p e a r l i t e t o gamma i r o n
f i l m where
corresponds
t o the
transformation.
1350°C) s u l f i d e s
e n r i c h e d i n manganese a r e a l m o s t
the
(about
should
a l s o be
166)^
4
Figures
d e p e n d e n t on
literature'°"*' "'" * . 1
3
(4) and
t h e Mn:S
Oxisulfide
(5). ratio
(2,
zone
1000°C t o totally
dis-
a f a c t w h i c h i s i n a g r e e m e n t w i t h T u r k d o g a n ' s and
workers' f i n d i n g s ^ ^
in
the
alpha
In the
l a r g e g r a i n s were o b s e r v e d
sults
to
850-950°C, Figures
where r e l a t i v e l y
solved,
starts
co-
These r e as
indicated
inclusions containing
s i l i c o n , a c c o r d i n g t o Van V l a c k e t a l . ' * , Silverman'^ * * r, (129,163,168) ,. ., , . . and H i l t y and C r a f t s • a r e d i v i d e d i n two c a t e g o r i e s , 3
namely those
i n which the
Si:0 r a t i o
0
i n wt.
9
% i s either
smaller
or g r e a t e r than u n i t y . Low
S i phases, S i : 0 r a t i o s
obey T u r k d o g a n e t a l . ' s ' * *
4
less
than u n i t y
* equilibrium
qualitatively
stability
phase
diagram.
In the temperature
e q u i l i b r i u m phases
i n the Fe-Mn-S-0 system are r u l e d by the
u n i v a r i a n t h i n F i g u r e (5). by the gamma i r o n , "0"as oxisulfide. it
range of 900° t o 1225°C the
This univariant i s constituted
[Fe(Mn)0],
Under normal
"MnS"
and
%^ as
liquid
ESR-operating c o n d i t i o n s , however,
i s not expected t h a t the composition of i n c l u s i o n s
l y follows t h i s univariant
(h).
Instead
strict-
the b e h a v i o r given
by the " t r i p l e - d a s h e d " - l i n e s i n t h i s diagram i s expected, Figure
(5).
cumulated
Simultaneous w i t h the above changes
s o l u t e ac-
i n g r a i n boundaries, growth of some i n c l u s i o n s
and s u l f u r d e p l e t i o n from s u l f i d e i n c l u s i o n s are observed. These events f u l l y c o i n c i d e w i t h the formation o f oxisulfide,
i^, i n F i g u r e s (4,5).
that the s p e c i f i c temperature
I t i s important to note
a t which
%^ forms, i s s t r i c t l y
a f u n c t i o n o f the o r i g i n a l amount of Mn p r e s e n t and the degree which Mn(Fe)S' commercial content,
6 4
~
1 6 6
^.
(Mn:S
ratio)
the i r o n i s s a t u r a t e d w i t h Mn(Fe)0 and
I t a l s o has to be emphasized
s t e e l s i n these s e r i e s
that with
which have standard S
(0.02-0.05 wt % ) , t h e r e i s s u f f i c i e n t Mn and S i
p r e s e n t t h a t no l i q u i d o x i s u l f i d e e r a t u r e s lower than 1150°C.
u i d o x i s u l f i d e i s expected p e n e t r a t i n g the " o r i g i n a l "
(^)
i s p r e s e n t a t temp-
Above t h i s temperature
(131
was
liquid
*~'
the
liq-
132) to show up as m a t e r i a l
austenitic grainsi
a fact
which
indeed observed. In areas c l o s e r to the f u l l y transformed
(austenitic)
grains
the Mn content i n i n c l u s i o n s , due mainly t o the d i s s o l -
u t i o n o f s u l f u r i n the metal m a t r i x
i s i n c r e a s e d , F i g u r e (4).
Although the Mn content was not s i g n i f i c a n t l y g r e a t e r the i n c l u s i o n composition q u a l i t a t i v e l y obeyed the u n i v a r i a n t h. From approximately 1150° t o 1250°C the composition o f low S i o x i s u l f i d e i n c l u s i o n s changes and £^ i s expected t o f l u x the s o l i d s u l f i d e as S i l v e r m a n ' * ' * and Van V l a c k e t a l . ' 9
have i n d i c a t e d .
3
0
*
Mn w i l l c o n t i n u e i n c r e a s i n g a t slower r a t e s
than i n p r e v i o u s t r a n s f o r m a t i o n s as the temperature i s increased. Upon quenching f u l l y ytransformed
a sample taken from areas c l o s e r t o t h e region, duplex
( r e l a t i v e l y grown) o x i -
s u l f i d e s low i n S i should be p r e c i p i t a t e d ; a f a c t which i s c l e a r l y 'seen i n F i g u r e (22 a-b).
T h e i r major c o n s t i t u e n t s
were i d e n t i f i e d as a Mn r i c h s u l f i d e , Mn(Fe)S, and a Mn r i c h o x i d e , Mn(Fe)0.
At temperatures higher than 1250°C the
manganese s u l f i d e e n r i c h e d phase p r a c t i c a l l y d i s a p p e a r s ; a f a c t which was observed i n the q u a l i t a t i v e
(SEM X-ray
spectrum a n a l y s i s ) and s e m i q u a n t i t a t i v e (EPMA) a n a l y s i s , F i g ures
(23 and 25). A t temperatures
about
1370° t o 1420°C r e l a t -
i v e l y l a r g e a u s t e n i t i c g r a i n s a r e observed. i s exposed
t o t h i s temperature
to d e l t a i r o n t r a n s f o r m a t i o n .
The r e g i o n which
range experiences the gamma This t r a n s i t i o n i s i d e n t i f i e d
i n F i g u r e (5) as the i n t e r s e c t i o n o f the " t r i p l e - d a s h e d "
line
c r o s s i n g the u n i v a r i a n t g_ i n which d e l t a and gamma i r o n , 0
136 and
£^ are
i n equilibrium.
The major changes i n i n c l u s i o n
composition w i l l s t a r t j u s t a f t e r u n i v a r i a n t f i s a univariant i r o n , o, ^
equilibrium
and & , 2
where &
2
f i s reached,
which i s c o n s t i t u t e d i s the l i q u i d metal.
by d e l t a After
f_ i s reached the o n l y s o l i d compounds may be the Fe(Mn)0 and
a very s m a l l amount o f i r o n o x i d e .
I t i s important to
r e c a l l t h a t t h i s event takes p l a c e only i f S i content i s low 4-u i•n these li a tx-ot e r stages (130,169) ' Under t h i s c o n d i t i o n ,
between f_ and e u n i v a r i a n t s
d e l t a i r o n , o and £, are i n e q u i l i b r i u m 2
the remaining S from
i n c l u s i o n s goes i n s o l u t i o n i n d e l t a i r o n . the
Furthermore,
remaining i n c l u s i o n s w i l l be e x c l u s i v e l y c o n s t i t u t e d by
Mn(Fe)0.
This
l a s t step was p a r t i c u l a r l y c l e a r i n the range
a t which the l i q u i d f r a c t i o n was about the
where
l i q u i d f r a c t i o n was g r e a t e r than 0.5
completely d i s s o l v e d
and r e p r e c i p i t a t e d .
0.5.
In areas where
i n c l u s i o n s were Since t h i s
was i n c o n t a c t with the s l a g some r e p r e c i p i t a t e d clusions acter,
(very
few)
Figures
region
small i n -
(24, 25), show the s l a g char-
i . e . , some A l and Ca.
The
second category o f o x i s u l f i d e i n c l u s i o n s which S i : 0
r a t i o i s l a r g e r than u n i t y e x h i b i t an almost e q u i v a l e n t t e r n as the p r e v i o u s behavior l a s t stages. and
(i.e.
pat-
S i : 0 < 1 ) , except i n the
Instead of p r e c i p i t a t i n g Mn(Fe)0 and FeO, S i 0
MnO o r 2Mn0 w i l l p r e c i p i t a t e i n the f u l l y
austenitized
zone and when l i q u i d f r a c t i o n s a r e s m a l l e r than 0.5
2
These t r a n s f o r m a t i o n s as proposed and Van V l a c k e t a l . ^
1 3
^*
9
can be r e p r e s e n t e d by quaternary
diagrams, F i g u r e s (6) and (7). and
by S i l v e r m a n ' * * *
(7) as the temperature
As shown i n F i g u r e s (6)
i n c r e a s e s Mn ( and thus 'MnO')
and the p r o p o r t i o n o f o r t h o s i l i c a t e
i n c r e a s e s . As a r e s u l t
the l i q u i d u s f o r the "MnS" i s decreased, nificant sulfide if
range o f compositions i s increased.
thus over a s i g -
the amount of l i q u i d o x i -
Silverman'** * 9
has p o i n t e d o u t t h a t
the p r o p o r t i o n o f s i l i c a t e i s i n c r e a s e d , as observed i n
t h i s case
then a t temperatures
above 1300°C what i s l e f t
as a s o l i d
(from the p r e v i o u s Fe-O-S-Mn-system, FeO and
Mn(Fe)O) w i l l become almost completely l i q u i d . t r a n s f o r m a t i o n s as proposed from C t o B i n F i g u r e During t h i s
by Van V l a c k e t a l . '
(8a) and C
temperature
These
to B
3
0
*
occur
i n F i g u r e (8b).
i n c r e a s e "FeS", "MnS" and "FeO" a r e d i s -
s o l v e d , F i g u r e (25). Subsequent chemical r e a c t i o n s o f the i n c l u s i o n components which take p l a c e i n the f u l l y a u s t e n i t i z e d meta l and the p a r t i a l l y
l i q u i d zones a r e shown i n macrophotographs
(18a-b) and (21) and photographs
(23a) and 23b). These r e a c t i o n s
are r e p r e s e n t e d by:
2MnO + S i 0
2
Z
2MnO«Si0 «- M n S i 0
2
X
MnO«Si0
2
2
4
or 2MnO + S i 0
2
+ MnO
t Mn
0
+ MnSi0
3
138 I f a sample with t h i s composition and thermal h i s t o r y i s r a p i d l y c o o l e d then
. s i n g l e phase i n c l u s i o n s e n r i c h e d i n
manganese and s i l i c o n must be found, a f a c t which i s l a t e r c o r r o b o r a t e d w i t h the i n c l u s i o n chemical a n a l y s i s . f i n a l composition, a c c o r d i n g t o Van V l a c k e t a l . ' s
Their
work' °V 3
i s d i c t a t e d by the S i : 0 r a t i o and the amount of manganese p r e s e n t i n the e l e c t r o d e .
Thus, i f the S i content exceeds
the amount o f oxygen, as seen i n a n a l y s i s this series
from samples o f _3
(0.25 wt% S i and 90 ppm = 9.0 x 10
wt!)
then
a v i t r e o u s ( s i l i c e o u s ) type of i n c l u s i o n i s formed i n p l a c e of the monophasic t e p h r o i t e
(MnO'SiC^) o r rhodonite
(2MnO'SiO^) as the temperature i s i n c r e a s e d , Some e l e c t r o d e s the
Figures
(23a,b).
which were very r a p i d l y withdrawn from
s l a g showed s m a l l s i l i c e o u s and (iron) s u l f i d e s as r e -
precipitated inclusions exclusively Their q u a l i t a t i v e
(SEM) and s e m i q u a n t i t a t i v e (15)
as reported, i n the l i t e r a t u r e stoichiometric
i n the l i q u i d (EPMA)
film. analysis,
i d e n t i f i e d them as non-
f a y a l i t e ^ F e O S i C ^ ) compounds.
To c o n f i r m the p r e v i o u s l y
described
uence o f t y p i c a l a n a l y s i s
i s shown.
(spectrographic) analysis
i n wt. %
mechanism a seq-
The e l e c t r o d e as r e c e i v e d ,
follows: C
Mn
S
Si
0.19
0.71
0.026
0.025
P 0.01
chemical
i s as
The average i.e.
total
oxygen a n a l y s i s
as r e c e i v e d , was 90 ppm.,
a t c e n t r e l i n e 87 ppm., midradius
93 ppm.
The average
91 ppm.
i n c l u s i o n chemistry i n a t . %
and edges as r e -
c e i v e d , was S 35.0 The average
Si
Mn
Fe
27.0
37.0
balance
chemical composition o f i n c l u s i o n s l o c a t e d b e t -
ween the r e c r y s t a l l i z e d area and l i q u i d
f r a c t i o n s smaller
than 0.5,were ( i n at.%) as f o l l o w s Si
Mn
51.0 T h i s composition roite
( 1 3 0
S
46.0
2.0
immediately
Fe balance
suggest the formation o f teph-
>.
Due t o the number and s i z e of i n c l u s i o n s found i n the neighbourhood o f the l i q u i d
film
chemical a n a l y s i s
from
i n c l u s i o n s l o c a t e d i n l i q u i d f r a c t i o n s g r e a t e r than 0.6 were performed
o n l y on a q u a l i t a t i v e b a s i s .
aluminum i n these i n c l u s i o n s and
(25)
Calcium and
as shown i n F i g u r e s (24)
were t r a c e d .
T h i s p a r t i c u l a r e l e c t r o d e was remelted through a (50 wt% C a F , 30 wt% Al C> 2
2
Ca-Si d e o x i d i z e d . l i q u i d pool
3
and 20 wt% CaO) s l a g which was
The chemical a n a l y s i s o f i n c l u s i o n s
(a) and from the (ESR) i n g o t (b) i n a t . % .
from
140 are as f o l l o w s :
Al
Ca
S
a)
49.0
30.0
20.43
b)
46.0
30. 5
22.80
Thus, i n summary position
Mn
Fe
0.3
balance balance
the change i n i n c l u s i o n chemical com-
i n terms o f s u l f i d e s and low S i - o x y s u l f i d e s and the
m o r p h o l o g i c a l changes o f i n c l u s i o n s take p l a c e i n a u s t e n i t i c temperature
ranges
i n the metal matrix.
In i n t e r m e d i a t e stages
the d i s s o l u t i o n o f s u l f i d e s i n the metal matrix a l s o o c c u r s . These s e r i e s o f events r e p r e s e n t approximately total
10-30% o f the
" t r a n s f o r m a t i o n - d i s s o l u t i o n " mechanism and i t takes p l a c e
a t about
0.4 - 0.8 cm
above the l i q u i d f i l m .
The next 20-
40% o f the t r a n s f o r m a t i o n o f i n c l u s i o n phases occur
either
between the g_-f u n i v a r i a n t s , F i g u r e (5), i n the low S i cont e n t phases o r i n the C-B sequence o f t r a n s f o r m a t i o n s , F i g u r e (8a),
i n the h i g h S i c o n t e n t phases.
The next sequence o f
t r a n s f o r m a t i o n s takes p l a c e between f - e and B-A f o r low and h i g h S i c o n t e n t phases r e s p e c t i v e l y . f u l l y austenitized t i o n does not exceed remaining
I t occurs between the
r e g i o n and the p o i n t where the l i q u i d 0.5.
I t r e p r e s e n t s another 20-40%.
fracThe
" t r a n s f o r m a t i o n - d i s s o l u t i o n " takes p l a c e i n the
neighbourhood
of the l i q u i d f i l m where i n c l u s i o n
dissolution
i s the major mechanism and i n c l u s i o n s l a g r e a c t i o n s (forma t i o n o f lower m e l t i n g p o i n t i n c l u s i o n phases with s l a g chara c t e r ) a c t s as a very l i m i t e d mechanism (^1.0-3.0%).
141 5.1.2
Removal of Oxide and S u l f i d e I n c l u s i o n s i n 4340 and Rotor
Steels
Since the aim of t h i s r e s e a r c h i s t o g a i n an e x t e n s i v e understanding of the i n c l u s i o n - r e m o v a l mechanism; e l e c t r o d e s w i t h d i f f e r e n t m a t r i x - i n c l u s i o n compositions were a l s o a n a l yzed.
4 340-electrodes w i t h alumina type of i n c l u s i o n s and
t o o l s t e e l e l e c t r o d e s with c a l c i u m - a l u m i n u m - s i l i c a t e s were a l s o i n c l u d e d i n t h i s r e s e a r c h program. Macrophotographs
(19) and (20) show the sequence of t r a n s -
formations i n 4340 and r o t o r s t e e l s r e s p e c t i v e l y .
One of
the f i r s t d i f f e r e n c e s t o n o t i c e between these two types of s t e e l s i s t h a t i n the l a t t e r type a u s t e n i t i z a t i o n d i d not occur due t o t h e i r chemical composition the chemical composition of i n c l u s i o n s .
( e l e c t r o d e ) and t o Another
conse-
quence of t h i s i s t h a t s o l u t e p e n e t r a t i o n (between a u s t e n i t i c g r a i n s ) a t s u b s o l i d u s temperatures d i d not take p l a c e . molten
i n the r o t o r
steel
On the other hand i n the p a r t i a l l y
e l e c t r o d e much more"segregated
m a t e r i a l , " as a r e -
s u l t of the i n c l u s i o n d i s s o l u t i o n and the i n t e r a c t i o n o f the e l e c t r o d e with the s l a g , was observed a t l i q u i d
fractions
l a r g e r than 0.5. Once the d i f f e r e n t areas were i d e n t i f i e d
(incipiently
heat a f f e c t e d a r e a , semi or a u s t e n i t i z e d r e g i o n , l i q u i d f i l m i n o r out of the d r o p l e t ) i n each type o f e l e c t r o d e , m e t i c u l o u s c h e m i c a l a n a l y s i s of i n c l u s i o n s
(by EPMA) was
c a r r i e d out a t every 250-300 ym.
R e s u l t s o b t a i n e d from 4340
and r o t o r s t e e l e l e c t r o d e s are shown r e s p e c t i v e l y i n F i g u r e s (26) t o
(28).
Among the most important c o n c l u s i o n s from t h i s are the f o l l o w i n g :
study
a) s i n c e the a u s t e n i t i c t r a n s f o r m a t i o n
i n the r o t o r s t e e l was
almost absent
the i n c l u s i o n
transform-
a t i o n - d i s s o l u t i o n s t a r t e d t o take p l a c e p r i n c i p a l l y i n the partially liquid the s o l i d u s . electrodes
zone.
I t takes p l a c e about 0.3-0.5 cm above
b) A l and S i n i n c l u s i o n s i n both types of
(4340 and r o t o r s t e e l ) were g r a d u a l l y d i s s o l v e d
as the e l e c t r o d e experienced h i g h e r thermal g r a d i e n t s . changes, shown i n F i g u r e s
(26) t o
(28)
s t a r t t o take p l a c e
i n a very d i s c r e t e manner j u s t above the s o l i d u s f o r the r o t o r s t e e l and i n e a r l i e r ents) s u b s o l i d u s temperatures graph
(27), i t can be observed
isotherm
(lower temperature
i n the 4340 i n g o t s .
t h a t due t o a s t r o n g g r a i n
compositions were s h i f t e d i n 2500-4500 ym range. u
163
gradi-
c) In
growth and thus i n t e r g r a n u l a r s e g r e g a t i o n , the A l , Mn
suits
These
and
S
These r e -
. . ... . (1,17,18,129,131-133, i n agreement with p r e v i o u s r e s e a r c h ' ' ' ' '
169)
a
n
(
j^ w
t n
p
r
e
v
i
o
u
s
f i n d i n g s i n the
1020-series
show t h a t s u l f i d e s are the most t h e r m a l l y a f f e c t e d phases. Oxide i n c l u s i o n s i n deformed 4340 e l e c t r o d e s a l s o e x p e r i enced g r a d u a l m o r p h o l o g i c a l changes.
d)
The
largest
changes
i n the i n c l u s i o n chemical composition i n both e l e c t r o d e s a
manner
curred
in
equivalent the
to
partially
the
1020
liquid
M.S. region.
electrodes
in oc-
The presence
of
s t r o n g i n t e r g r a n u l a r and i n t e r d e n d r i t i c (segregated) m a t e r i a l which c o n t a i n e d
inclusion-formers
c l u s i o n s were completely l i q u i d Figure
c l e a r l y indicate that i n -
i n t h i s t r a n s i e n t zone.
(19a) from 4340-electrodes and (20) from the r o t o r
steel electrodes
strongly corroborate
these f i n d i n g s ,
e) Chemical a n a l y s i s i n 4340 e l e c t r o d e s , F i g u r e s
(26,27),
suggest t h a t S i and Mn i n i n c l u s i o n s , p a r t i c u l a r l y i n the liquid film
f o l l o w the same behavior as i n 1020 M.S., i . e .
i n c l u s i o n s get r i c h e r i n S i and Mn j u s t b e f o r e totally
dissolved.
they are
144 5.1.2.1
Removal of Oxides and S u l f i d e s i n 4340-electrodes
The sequence of changes i n the chemical
composition
of i n c l u s i o n s i n these e l e c t r o d e s i s summarized as f o l l o w s . The s p h e r o i d i z a t i o n and a subsequent fides
d i s s o l u t i o n of
sul-
j u s t as i n p r e v i o u s o b s e r v a t i o n s i n the 1 0 2 0
M.S.
e l e c t r o d e s i s the f i r s t
step i n the removal mechanism.
takes p l a c e i n s u b s o l i d u s temperature (26) and
It
ranges. F i g u r e s (19),
(27) i n d i c a t e t h a t these changes occur a t about
2000-
3000 ym above where the s o l i d u s of the a l l o y was m e t a l l o g r a p h i cally identified.
The most d r a s t i c changes, however, take p l a c e
i n areas where complete
a u s t e n i t i z a t i o n was
In f u l l y a u s t e n i t i z e d
observed.
areas and i n the r e g i o n
where the m e l t i n g s t a r t e d the A l and S i n i n c l u s i o n s
de-
crease w h i l e the S i , Mn and the Ca c o r r e s p o n d i n g l y i n c r e a s e . T h i s behavior i s accentuated as the l i q u i d f r a c t i o n i n creases.
A mixture of f e l d s p a r s
and garnets 2AI2O.J
(3M0«Al 0.j *3Si02) °
r
(9192) ' e
v
e
n
2
• 5Si02)
(MO "A^O^
cordierites
i n s t e a d of the o r i g i n a l aluminates
p r e c i p i t a t e as the l i q u i d f r a c t i o n approaches
«2Si02) (2M0* should
unity.
The
a c t u a l s t o i c h i o m e t r y of t h i s compound i s i r r e l e v a n t s i n c e M i n a l l of these compounds cart be e i t h e r Fe, Mn or Ca these s e r i e s of (91 solubility
compounds show v i r t u a l l y complete
and
mutual
92) '
.
The most important f i n d i n g , however,
i s t h a t oxides i n t h i s matrix are suddenly not so much i n s u b s o l i d u s temperature
transformed
ranges
as occurs i n
145 the 1020 M.S. as i n the s e m i - l i q u i d stage.
The presence
of i n c l u s i o n r e l i c s and " l i q u i d " e n r i c h e d i n i n c l u s i o n c o n s t i t u e n t s i s shown i n F i g u r e s (19c) and (2 0a) as i n t e r dendritic
segregates.
In the l i q u i d f i l m ,
about
50ym from the edge o f the
e l e c t r o d e t i p a s i m i l a r e f f e c t as t h a t seen i n the 1020 M.S. e l e c t r o d e s was observed.
Since t h i s volume of l i q u i d
e l e c t r o d e was s u b j e c t e d to a d i r e c t i n t e r a c t i o n with the s l a g a s h i f t i n the chemical composition o f i n c l u s i o n s was detected.
T h i s i n d i c a t e s t h a t the e l e c t r o d e
composition was completely transformed. of i n c l u s i o n s i n the l i q u i d f i l m it
4340 (I)
a) b)
4340 (II)
a) b)
inclusion
The chemical
analysis
(a) i n the d r o p l e t or
are ( i n at.%) as f o l l o w s : Al
Ca
S
19.0 7.0
2.78 3.90
_
8.27 6.30
9.30 11.00
1.5 _
-
Si
Mn
78.0 70 .20
0.22 17.40
56.0 56.0
26.46 27.60
F i n a l l y , the chemical composition o f i n c l u s i o n s i n e i t h e r (a') l i q u i d
434 0 (I)
4340 (II)
(pool) stage o r .(b')the i n g o t correspond t o : a')
Al„0_ and t r a c e s o f s i l i c a + MnS I I
b')
A1 0
a')
Ca«Al 0
b')
2
2
3
3
+ MnS I I
2
3
12CaO-7Al 0 2
3
146
I t i s important t o note t h a t 4340 (I) was A l - d e o x i d i z e d and 4340 (II) was CaSi t r e a t e d . deoxidized
Ingot 4340
(I) was
0.02 kg ton "'') and i n g o t 4340 (II) was h e a v i l y -
CaSi d e o x i d i z e d (10 Kg t o n ) - 1
both i n g o t s were r e f i n e d
through a 50wt % C a F , 30 wt% Al C> 2
2
3
and 20 wt% CaO.
I f the above chemical analyses are compared clearly
slightly
i t can
be seen t h a t i n c l u s i o n r e l i c s from the bulk o f the
e l e c t r o d e , i f any, are d i s s o l v e d and r e p r e c i p i t a t e d i o n s which show the s l a g c h a r a c t e r .
inclus-
I n c l u s i o n s i n the l i q u i d
f i l m are s m a l l and complex i n composition.
Therefore, i n -
c l u s i o n s l o c a t e d i n t h i s narrow f i l m do not r e p r e s e n t i n any way what happened i n the t r a n s f o r m a t i o n - d i s s o l u t i o n o f p r e v i o u s stages.
5.1.2.2
Calcium-Aluminum S i l i c a t e s
i n a Rotor
(Ni,Cr,Mo)
Steel The
i n c l u s i o n chemical composition was m e t i c u l o u s l y
determined
at discrete locations i n electrode tips.
These
a n a l y s i s were c a r r i e d out a t every 250-300 ym s t a r t i n g the l i q u i d f i l m . studies
as i n p r e v i o u s
(1020 and 4340), they were arranged a c c o r d i n g t o
the s p e c i f i c film
For the sake of c l a r i t y
from
area a t which they belonged
i.e., liquid
( i n and out o f d r o p l e t ) , p a r t i a l l y molten
s e v e r a l l i q u i d f r a c t i o n s and a t s u b s o l i d u s
area a t
temperatures.
147 A summary of the r e s u l t s o b t a i n e d by EPMA and t h e i r c l a s s i f i c a t i o n a c c o r d i n g t o the thermal h i s t o r y a t which these volumes were subjected
i s shown i n F i g u r e
Since these e l e c t r o d e s during
(28) *
experienced almost no g r a i n growth
a u s t e n i t i z a t i o n , the composition o f i n c l u s i o n s was
exclu-
s i v e l y changed i n r e g i o n s c l o s e t o the s o l i d u s temperature o f the alloy.
I t i s important t o n o t i c e t h a t the s i z e o f the mushy zone
i n the r o t o r s t e e l (> 2800 pm) i s l a r g e r than i n 1020 M.S. o r the 4340 s t e e l s .
The s l a g - i n c l u s i o n d i s s o l u t i o n ( i n only
remaining i n c l u s i o n s )
took p l a c e
of the o t h e r e l e c t r o d e s ,
i.e.
very few
i n a manner e q u i v a l e n t
liquid
to a l l
film.
T y p i c a l a n a l y s i s o f i n c l u s i o n s from these areas i n a t . %, are as f o l l o w s : Al
Ca
Si
i n g o t (1)
25.18
61.15
8.65
5.0
ingot
25.88
61.36
9.40
3.5
38.48
20.20
34. 85
6.50
61.16
21.63
16.38
0. 82
62.35
2.27
3.16
0.16 1.16
Partially Liquid
Liquid
( f ^ ^ 1)
(2)
S
Mn
Film out in
A f t e r ESR
of droplet droplet
148 These
i n g o t s were r e f i n e d through the 50% C a F , 2
30% A ^ O ^ and 20% CaO s l a g .
T h e i r d e o x i d a t i o n was c a r r i e d
out with the CaSi a l l o y a t approximately
5.1.3
0.1-0.2 Kg ton . 1
F i n a l Remarks About the Removal Mechanism I n c l u s i o n s i n e l e c t r o d e t i p s d u r i n g ESR are removed by
d i s s o l u t i o n i n the metal matrix
i n w e l l d e f i n e d steps a c -
c o r d i n g t o the e l e c t r o d e i n c l u s i o n composition i n the e l e c t r o d e t i p .
and l o c a t i o n
The thermal g r a d i e n t to which the
e l e c t r o d e and hence i n c l u s i o n s are s u b j e c t e d d r i v i n g f o r c e f o r t h e i r removal.
i s the main
T h i s mechanism, however,
does n o t correspond
t o t h a t p r e v i o u s l y d e s c r i b e d i n the
l i t e r a t u r e review.
Gradual d i s s o l u t i o n along the heat
a f f e c t e d zones or s t r i c t d i s s o l u t i o n of i n c l u s i o n s a t the l i q u i d film,
and the "washing o f f " or the mechanical r e -
moval o f i n c l u s i o n s are not o p e r a t i v e mechanisms. stead
In-
a mechanism based on s u b s t a n t i a l experimental
t h e o r e t i c a l evidence chemical
and
which suggests the quasi-thermo-
e q u i l i b r i u m of i n c l u s i o n s and t h e i r l o c a t i o n
is indicated. The
s e r i e s of a c t u a l chemical
transformations
and the
d i s s o l u t i o n of i n c l u s i o n s i n electrode t i p s are s t r i c t l y c o n f i n e d t o a d i s t a n c e no g r e a t e r than 0.5 - 0.8 cm above the l i q u i d f i l m .
S u l f i d e s i n the Fe-Mn-S-0 system and o x i -
s u l f i d e s i n the Fe-O-S-Mn-Si system a r e p a r t i a l l y d i s s o l v e d and p a r t i a l l y transformed
a t subsolidus
temperatures..
149 Reactions between i n c l u s i o n components and the metal matrix leads t o the s o l u t i o n o f c e r t a i n i n c l u s i o n components as
"FeS", "FeO", "MnS", e t c . , which i n i t i a t e
t i o n i n a u s t e n i t i c g r a i n boundaries.
such
solute penetra-
This f a c t implies
that
these i n c l u s i o n s are a mixture o f phases, namely "MnS", "FeO" and
a small amount o f "FeS".
i n c l u s i o n s are subjected
The chemical r e a c t i o n s t o which
and t h e i r d i s s o l u t i o n i n the metal
m a t r i x a r e q u a l i t a t i v e l y p r e d i c t e d by u s i n g diagrams a v a i l a b l e (164 —16 6) i n the l i t e r a t u r e S-0
.
S u l f i d e s belonging
t o the Fe-Mn-
system and o x i s u l f i d e s low i n s i l i c o n which belong t o the
general
Fe-O-S-Si-Mn system i n e l e c t r o d e t i p s f o l l o w a q u a s i -
thermochemical e q u i l i b r i u m d i c t a t e d by the F i g u r e e q u i l i b r i u m phase diagram workers
is
n
o
obtained
(5).
This
by Turkdogan and c o -
t completely obeyed and i n s t e a d a be-
h a v i o r g i v e n by the " t r i p l e dashed l i n e " Inclusions belonging
i s followed.
t o the Fe-Si-Mn-O-S system which
have a s i l i c o n content such t h a t the S i : 0 r a t i o i s g r e a t e r than 0.5, f o l l o w the FeO-MnS-MnO-Si0 quaternary system dev2
eloped ure
by S i l v e r m a n ' * * ^ 9
(9).
The b e h a v i o r o f these i n c l u s i o n s i s a l s o complemented
by the b i n a r y MnO-Si0 ernary (8a)
as i n d i c a t e d by the arrow i n F i g -
2
as p a r t o f the Si0 ~MnO-FeS-MnS quat-
diagram developed by Van V l a c k
and (8b).
This proposal
2
et a l .
, Figures
corresponds l a r g e l y t o t h a t a l (168) ready suggested by H i l t y and C r a f t s , i . e . the pseudo
150 t e r n a r y behavior
of the m e t a l - o x i d e - s u l f i d e phases.
Thermo-
d y n a m i c a l l y more s t a b l e phases such as Mn(Fe)0, MnO, MnO«Si02A
2 M n 0 « S i 0 2 / c a l c i u m aluminates,
uminates, e t c . , a r e transformed bourhood o f the l i q u i d
calcium s i l i c o n a l -
and d i s s o l v e d i n the n e i g h -
f i l m between the f u l l y a u s t e n i t i z e d
area and the f u l l y l i q u i d metal.
Electrode inclusion
( i f any) i n the l i q u i d
f i l m r e a c t , up t o a l i m i t e d
w i t h the s l a g producing
complex i n c l u s i o n phases.
Finally,
relics
extent
i n c l u s i o n s i n ESR i n g o t s which show the e l e c t -
rode i n c l u s i o n c h e m i c a l composition s t a b l e ESR c o n d i t i o n s , "hot t o p p i n g "
Si02^
stages.
a r e found o n l y under un-
i . e . a t the s t a r t i n g and d u r i n g the
151
5.2
The Chemical
I n f l u e n c e o f the E l e c t r o d e , Slag
and D e o x i d i z e r on the Chemical Composition o f Inclusions
5.2.1
D e s c r i p t i o n of Experimental F i n d i n g s
5.2.1.1
P r e l i m i n a r y S t u d i e s on the E f f e c t o f the S l a g and the D e o x i d a t i o n
4340-electrodes
31.75 and 44.75 mm
i n diameter and with
d i f f e r e n t i n c l u s i o n chemical compositions were r e f i n e d t o 75 mm i n diameter
i n g o t s a t m e l t i n g r a t e s o f about
1.3 Kg m i n
through d i f f e r e n t s l a g systems and under a p r o t e c t i v e
- 1
(argon)
atmosphere. The components o f the s l a g systems
(CaF , CaO, Al-^O^ 2
and S i 0 ) were p r e v i o u s l y d r i e d a t 650°C and the " c o l d 2
s t a r t i n g procedure" was f o l l o w e d . through s l a g s which had s e v e r a l S i 0 f e r e n t s l a g systems were chosen CaSi a l l o y and A l , Table form o f p e l l e t s
(99.9%).
E l e c t r o d e s were r e f i n e d 2
contents.
Two
dif-
t o be d e o x i d i z e d w i t h a
(X). The aluminum was i n the The CaSi a l l o y c o n t a i n e d 62.5
152
wt.
% S i , Table
(^ 2.3
(IX).
The d e o x i d a t i o n r a t e s were c o n s t a n t
Kg/ton) and they were performed
when steady r e m e l t i n g
c o n d i t i o n s were observed. The purpose
of these experiments
were:
i ) to
determine
the chemical composition of i n c l u s i o n s as an e x c l u s i v e e f f e c t of the s l a g composition
(and e l e c t r o d e ) .
i i ) to i n -
v e s t i g a t e what changes i n i n c l u s i o n compositions c o u l d be achieved by u s i n g the same s l a g system to compare r e s u l t s from
and d e o x i d i z e r s
( i ) a g a i n s t ( i i ) and
(iii)
and
to d e t -
ermine the most a p p r o p r i a t e s l a g systems to be used i n the 200 mm
i n diameter
ESR-furnace.
Experimental r e s u l t s are shown i n Table s l a g chemical composition i n wt.
%
#
(X)
where the
the i n c l u s i o n chemical
composition i n a t . %, the chemical composition of i n c l u s i o n s i n e l e c t r o d e s and the major i n c l u s i o n phases are g i v e n . i s important to note t h a t although c l u s i o n s was scatter
performed
(± 5.0
- 7.0%)
It
chemical a n a l y s i s of i n -
on a l a r g e number
(30-40) a wide
i n t h e i r a n a l y s i s was
found.
s c a t t e r i s p r i n c i p a l l y a t t r i b u t e d t o the i n c l u s i o n
The size
153
distributions
( l e s s than 5ym
i n diameter) and
steady r e f i n i n g c o n d i t i o n s due s l a g systems.
to the use
of
to the
inappropriate
As a consequence o f t h i s l a c k of
o c c a s i o n a l l y an uneven s u r f a c e of the ingot was and
l i q u i d enriched
un-
stability observed
i n d e o x i d i z e r s and oxygen p r e c i p i t a t e d
alumina type of i n c l u s i o n s i n a c o n f i n e d volume, F i g u r e The
first
oxidizer was
s e t of experiments
performed without a
than 10
wt
%.
Calcium-aluminum s i l i c a t e s i n
i n c l u s i o n s were found above t h i s l e v e l . more than two
i n c l u s i o n phases was
same sample. Table
was
composition
s p e c i f i c a l l y ingots as i n g o t
of i n c l u s i o n s i n i n g o t
showed almost e x c l u s i v e l y c a l c i u m (9)
presence of
commonly observed i n the
second s e r i e s of experiments
c a r r i e d out,
The
(X).
v i r t u a l l y the same behavior
and
de-
showed s i l i c o n i n i n c l u s i o n s where S i C ^ i n s l a g s
higher
The
(29).
i n which (7) and (1).
The
aluminates.
chemical
(1) and
whereas i n i n g o t
higher.
reference
Ingots
(7)
the Ca:Al r a t i o ,
cases.
t e n t of i n c l u s i o n s i n i n g o t s (9). i t was
(9), showed
(1), used as a
a l s o showed c a l c i u m aluminates,
however i s l a r g e r than i n p r e v i o u s
deoxidation
The
s i l i c o n con-
(7) were e q u i v a l e n t ,
I f the a n a l y s i s of i n c l u s i o n s from e l e c t r o d e s used i n ingots
(1) to
(7) are compared a g a i n s t
(9) and
(10)
then
154 i t can be i n f e r r e d t h a t the i n c r e a s e d S i content comes from the e l e c t r o d e , Table
(X).
c a l c i u m aluminates, was
The maximum c a l c i u m c o n t e n t , as
found i n i n g o t s remelted
through
r e l a t i v e l y high CaO
(15-22 wt %) and r e l a t i v e l y low
( l e s s than 10 wt %)
slags.
The and
i n c l u s i o n chemical a n a l y s i s performed
15/15/15) s l a g system, t h e i r composition with and
the
(2)
(55/
without
On the other hand,
f o r e l e c t r o d e s r e f i n e d under the same s l a g system and o x i d i z e d w i t h aluminum; lower
2
i n ingots
(10) shows t h a t by r e f i n i n g e l e c t r o d e s through
Ca-Si d e o x i d a t i o n remains u n a l t e r e d .
Si0
de-
s i l i c o n and r e l a t i v e l y higher
c a l c i u m and hence higher aluminum i n i n c l u s i o n phases i s found. R e s u l t s i n t h i s i n v e s t i g a t i o n c l e a r l y show t h a t the i n trinsic
s l a g e f f e c t i n the chemical composition of
f o l l o w s a very w e l l d e f i n e d p a t t e r n . the S i 0 (5),
2
S l a g systems i n which
content i s lower than 10 wt
(7), and
dominantly
2
2
3
%
as i n i n g o t s (1), (4),
(9) y i e l d e d i n c l u s i o n compositions which p r e -
l i e i n the C a O - A l 0
on the A l 0
inclusions
r i c h side, i . e .
3
pseudo b i n a r y phase diagram
alumina
types and low
CaO-
aluminates. To c o r r o b o r a t e these f i n d i n g s periments
i n the 200 mm
other s e r i e s of
ESR-furnace were performed.
exEx-
p e r i m e n t a l d e t a i l s and a summary of f i n d i n g s are g i v e n i n
155
Tables
(VIII) and
(XI).
The main p o i n t to be c o n s i d e r e d
i n t h i s s e t of experiments (0.02
kg ton
1
i s the low l e v e l of d e o x i d a t i o n
) to which the s l a g - l i q u i d p o o l was
j e c t e d and the e l e c t r o d e s u r f a c e p r e p a r a t i o n . Table
(XI)
sub-
As seen i n
c o n s i s t e n t q u a l i t a t i v e r e s u l t s are found
terms of the chemical composition of i n c l u s i o n s
in
i n both
ESR-furnaces. P a r t i c u l a r emphasis should be g i v e n to r e s u l t s t a i n e d from i n g o t (11).
A rotor steel electrode
ob-
with
chemical composition i s g i v e n i n Table
(VII)
average
( i n at%) as f o l l o w s :
was
i n c l u s i o n chemical composition Al
Ca
Si
S
28.5
24.1
42.0
2.2
Mn
2
12 wt
% Si0
2
and 6 wt
% MgO
Fe
2.5
remelted through a 49 wt % C a F , 16 wt
A^O-j,
slag.
balance % CaO,
(ESR)
chemical ingot,
i s as f o l l o w s :
Al 44.70
Ca 13.60
Si
S
Mn
24.5
7.4
9.2
Since the at.%Mn:at.%S r a t i o i s approximately it
17 wt %
The average
composition o b t a i n e d from 40 i n c l u s i o n s i n the in at.%
and with an
can be assumed t h a t a MnS
s u l f i d e phase was
phase was
Mg + Fe balance one
then
precipitated.
The
commonly found surrounding the oxide phase.
156 X-ray composition p r o f i l e s and maps as w e l l as d i s p e r s i v e X-ray
spectrum
a n a l y s i s confirmed these f i n d i n g s .
oxide phase was
not s p h e r i c a l
The
(as c a l c i u m aluminates-
c a l c i u m s u l f i d e i n c l u s i o n s ) , i n s t e a d angular oxides were observed. maining
I f the above v a l u e s are normalized
then the r e -
elements can be f u r t h e r analyzed; thus the o v e r a l l
composition i s Al
Ca
Si
^54
^16
^30
From these computed v a l u e s the r a t i o s f o r A l , Ca and S i r e s p e c t i v e l y are approximately
4:1:2.
Thus, the f e a s i b l e phase
p r e s e n t i n these type of i n c l u s i o n s c o u l d be: CaO«2Al 0 '2Si0 2
T h i s compound, as i n d i r e c t l y 9 2
^
3
2
s t a t e d i n the l i t e r a t u r e
review*
has not been r e p o r t e d as an i n c l u s i o n phase; i t can
i n s t e a d a f e l d s p a r of the type M 0 « A 1 0 « 2 S i 0 2
can be e i t h e r FeO,
MgO,
MnO
or CaO.
3
2
Based on
i n which
individual
a n a l y s i s of i n c l u s i o n s ; alumina r i c h phases and CaO-Al 0 2
3
MO
complex
s i l i c a t e s were indeed the major phases p r e s e n t .
Hence, the o n l y f e a s i b l e compounds i n t h i s i n g o t are the Al 0 «CaO•2Si0 2
3
Al_0_
2
( a n o r t h i t e ) phase i n c o n j u n c t i o n with
(corundum) e n r i c h e d phase.
an
be
157
5.2.1.2
I n t e r m i t t e n t CaSi A d d i t i o n s and the R e a c t i o n Scheme
Since no d i f f e r e n c e was
found between d e o x i d i z e r s
(Al and the Ca-Si a l l o y ) i n s m a l l ESR-furnace, the chemical composition of i n c l u s i o n s of
(i.e.
i n terms of precipitation
c a l c i u m aluminates and up t o a given e x t e n t c a l c i u m
s u l p h i d e s ) , an e x t e n s i o n of these experiments
i n the
i n d u s t r i a l s i z e ESR-furnace was
These e x p e r i -
ments are l i s t e d
i n Table
c a r r i e d out.
(VIII).
50 grams of
the Ca-Si a l l o y were a l t e r n a t e l y added a t two
FeO
semi-
and
discrete
time
i n t e r v a l s d u r i n g r e f i n i n g under two d i f f e r e n t s l a g systems; namely 50/30/20 and 70/30/0. C a F , A^O^, 2
and the CaO
These f i g u r e s r e p r e s e n t the
compositions
i n wt %.
1020
M.S.
e l e c t r o d e s whose chemical composition and i n c l u s i o n chemi s t r y have a l r e a d y been d e s c r i b e d , were r e f i n e d a t about 1 kg min
1
, with and without
(RIII-W and RII-W r e s p e c t i v e l y )
an argon atmosphere s h i e l d i n g . T o t a l oxygen content, s l a g chemical a n a l y s i s from
samples
taken d u r i n g r e f i n i n g , i n g o t chemical a n a l y s i s and
inclusion
chemical composition as w e l l as s i z e d i s t r i b u t i o n s
from
i n g o t s were determined.
These r e s u l t s are shown i n F i g u r e s
(30) to
(36).
S i , Mo,
Cr, A l and N i were analyzed i n the s l a g s and i n g o t s
respectively.
Ca, F, A l , S i , Mn
and Fe and Mn,
C, P,
S,
Elements with s i g n i f i c a n t changes i n t h e i r
composition are p l o t t e d . Figures
(32) and
(33a-b) from RII-W and RIII-W, show the
158 e f f e c t of the Ca-Si a l l o y
(intermittent) additions.
These
graphs show t h a t the d e o x i d i z e r produces a sharp decrement i n a l l of the s l a g c o n s t i t u e n t s .
Correspondingly,
the chem-
i c a l composition of i n g o t s show a sharp increment i n A l and
S i , Figures
considered
(34,35).
Mn,
Other important p o i n t s to
be
from these graphs are t h a t s u l f u r i s decreased
when the Ca a l l o y was
added and
i r o n oxide a d d i t i o n s i n the
s l a g d i d not produce as sharp changes i n the i n g o t composit i o n as d i d a d d i t i o n s o f the d e o x i d i z e r . comes from the e l e c t r o d e
gradually
as r e f i n i n g takes p l a c e ,
Figure
The
and
response time of the system was
The
i n the s l a g
(33b). a l s o observed.
RII-W
i n about 100-150 seconds
RIII-W w i t h i n 200-250 seconds. The
i n the s l a g and
s i l i c o n which
increased
(32) and
showed a response to the d e o x i d i z e r
The
e f f e c t of the
deoxidizer
i n g o t decrease i n a r e l a t i v e l y slow manner.
sudden changes i n FeO
content
(expressed
as wt
% of
Fe)
i n the s l a g as w e l l as the abrupt changes i n the t o t a l oxygen content and
the i n c l u s i o n chemical composition as a d i r e c t
e f f e c t o f these i n t e r m i t t e n t ( C a - S i )
a d d i t i o n s are the most
important responses i n the r e f i n e d i n g o t , F i g u r e s (33).
I t i s important t o n o t i c e t h a t there was
r e a c t i o n time t o show t h e • i n d i v i d u a l Ca or FeO o f oxygen i n (RIII-W), F i g u r e The
to
not enough e f f e c t s i n terms
(30).
d i f f e r e n c e between RII-W and
s t a r t i n g s l a g compositions and
(30)
RIII-W are
the
the presence o f an argon
s h i e l d i n g atmosphere i n the l a t t e r , T a b l e
(VIII).
Thus
a
159
lower oxygen content
(15-20 ppm)
and observed, F i g u r e s The
(30)
and
i n RIII-W was
expected
(31).
main c o n c l u s i o n from the above r e s u l t s i s t h a t
ESR-process i n terms of s l a g s and plex reactor.
The
s l a g do not occur
d e o x i d i z e r s i s a very com-
s e r i e s o f r e a c t i o n s t a k i n g p l a c e i n the independently
the l i q u i d p o o l and
of the ones t a k i n g p l a c e i n
i n the i n g o t , i . e .
p o s i t i o n i s not c o n t r o l l e d by one 5.2.1.3
the
R e f i n i n g of 1020 Deoxidized
M.S.,
Continuously
the
i n c l u s i o n com-
single factor. 200
mm
Diameter Ingots
with Aluminum
To g a i n a b e t t e r understanding of the above sequence of r e a c t i o n s , complementary and more d e t a i l e d experiments by which r e a c t i o n s i n the l i q u i d monitored were planned.
s l a g l i q u i d p o o l and The
purpose of these experiments was
s l a g compositions.
to d i s c r i m i n a t e the
to i d e n t i f y s e p a r a t e l y the e f -
f e c t of d e o x i d i z e r s on the s l a g d u r i n g the three the r e f i n i n g p r o c e s s . c l u s i o n chemistry a t i o n and / and
f o r other
stages
through an i n i t i a l
% CaO,
was
i n g o t s , CaSi and
of
intrinsic electrode-slag-in-
of a r e f i n e d (1020) i n g o t , without
remelted 20 wt
The
50 wt%
CaF^,
deoxid-
30 wt
%
used as the b a s i s of comparison Al-deoxidized.
the The
intrinsic
e f f e c t o f the e l e c t r o d e i t s e l f on the s l a g ( i . e .
without any d e o x i d i z e r ) . a n d
A^O^
be
next s e t o f experiments i n c l u d e d
r e f i n i n g of e l e c t r o d e s through e q u i v a l e n t
chemical
ingots could
160
The
i n g o t i d e n t i f i e d as R I - I l was
argon atmosphere and "FeO"
r e f i n e d under an
i n the absence of a deoxidant.
i n the s l a g and
the t o t a l oxygen content
approximately constant
i n the i n i t i a l
stages,
The
remained Figure
(37).
I n c l u s i o n s i n samples e x t r a c t e d from the l i q u i d p o o l and
from
the i n g o t were e s s e n t i a l l y i d e n t i f i e d as s p h e r i c a l s i n g l e p a r t i c l e s or as small c l u s t e r s of alumina type and
a-A^O-j) and
The
alumina type was
fides,
l e s s f r e q u e n t l y as f a y a l i t e type
i n the s l a g was
The
to 0.125
wt.%
MnS
II.
The
considerable. up to
s i l i c o n content
(2FeO«Si02) •
u s u a l l y a s s o c i a t e d with manganese s u l -
(Fe,Mn)S and
the bottom and
(FeQ'A^O^
gradual
i n c r e a s e of
I t ranged from 0.75
about 2.0
wt.%
a l y s i s i s shown i n F i g u r e
The
2
at
at the top of the
ingot. up
i n g o t chemical
an-
(38).
Experiments which are e q u i v a l e n t to the s m a l l
M.S.
wt.%
i n the i n g o t ranged from 0.095
from s t a r t to f i n i s h .
and A l ) d e o x i d i z e d
Si0
(Ca-Si
(4340) ingots were a l s o c a r r i e d out.
e l e c t r o d e s were r e f i n e d through e q u i v a l e n t
slags
1020
and
samples from l i q u i d s l a g s and pools were e x t r a c t e d while
continu-
o u s l y i n c r e a s i n g a d d i t i o n s of d e o x i d i z e r s to the s l a g were made.
Table
experiments.
(VIII) summarizes the d e t a i l s of t h i s s e t of Refined
i n g o t s r e f e r r e d to as R I I - I l and
RII-I2 were aluminum t r e a t e d by u s i n g two
different
deoxid-
a t i o n sequences.
Deoxidation
r a t e s were 3.63,
6.1,
6.8
and
7.6
1.21,
3.64,
and
12.12
kg
kg t o n
- 1
and
2.42,
4.85,
6.06
ton
- 1
161 f o r R I I - I l and RII-I2 r e s p e c t i v e l y .
RII-I2 was CaSi (50
grams) d e o x i d i z e d i n the i n i t i a l r e f i n i n g stage. .. The i r o n oxide content, g i v e n as wt- % i r o n i n F i g u r e s (39) and (40), slowly and c o n t i n u o u s l y decreased
from about
0.6 wt.% down t o about
0.4 wt-%
as the aluminum a d d i t i o n
r a t e s were i n c r e a s e d .
While h i g h d e o x i d a t i o n r a t e s
r e l a t i v e l y steady t o t a l oxygen content
( R I I - I l ) and hence
e q u i l i b r i u m behavior i n i n c l u s i o n compositions, o x i d a t i o n r a t e s produced parameters,
(RII-I2),
an o s c i l l a t i n g behavior
Figures
(41, 42) and
F i n d i n g s i n these experiments,
produced
the low dei n both
(43,44).
although not as drama-
t i c as the (Ca-Si) i n t e r m i t t e n t l y d e o x i d i z e d i n g o t s , show t h a t the aluminum as a d e o x i d i z e r a l s o produces s i m u l t aneous exchange r e a c t i o n s between two l i q u i d s o f the g e n e r a l type
(11) and r e a c t i o n s o f the type
.(12).
The elements i n -
v o l v e d i n these r e a c t i o n s , i n a manner e q u i v a l e n t t o the i n termittent itself,
Ca-Si a d d i t i o n s
F i g u r e s (37-40) and
are the S i , Mn and the A l by (43-46).
The most s e n s i t i v e p a r t s of the system t o the aluminum d e o x i d a t i o n were the t o t a l oxygen content and the chemical composition o f i n c l u s i o n s r e p r e s e n t e d by the a t . % C a : a t % A l i n Figures Figure
(43) and (44). (40) from RII-I2
shows t h a t the aluminum was
a b l e t o s l o w l y overcome the s i l i c o n e f f e c t from the e l e c t r o d e .
162 Hence, from the c a l c i u m
t o aluminum, r a t i o of i n c l u s i o n s ,
the chemical composition o f i n g o t s and s l a g , i t i s i n f e r r e d t h a t the major r e a c t i o n s which govern the chemical composition of i n c l u s i o n s d e f i n i t e l y slag.
On the other
i n v o l v e the CaO and A ^ O ^ from the
hand the s i l i c o n - from e l e c t r o d e s ,
although i t i s t r a n s p o r t e d
i n the i n g o t , F i g u r e s
not play a r o l e i n the d e o x i d a t i o n The
(45,46), does
scheme.
sequence o f i n c l u s i o n formation
was as f o l l o w s :
1) i n the bottom p a r t o f these i n g o t s , where r e f i n i n g was unstable
some i n c l u s i o n s (approximately 5%)
contained
silicon.
T h i s was almost i n v a r i a b l y l o c a t e d i n the i n -
c l u s i o n core and a s s o c i a t e d with manganese and c a l c i u m . This i s considered
as a c l e a r i n d i c a t i o n t h a t some i n c l u s i o n s ,
a t low r e f i n i n g e f f i c i e n c i e s , come from the e l e c t r o d e and i n subsequent stages they a r e t r a n s p o r t e d
d i r e c t l y i n t o the
i n g o t which i s a l s o s o l i d i f y i n g under unsteady s t a t e tions.
condi-
The b u l k of these i n c l u s i o n s are, however, mainly
represented
by s m a l l s i n g l e o r c l u s t e r e d type
galaxies) of i n c l u s i o n s , Figures degree o f d e o x i d a t i o n
(47) t o (48).
i s increased,
s i n g l e i n c l u s i o n s were observed
(alumina 2) As the
g l o b u l a r and f a c e t e d
(FeO-A^O^ and a-A^O^ r e s -
p e c t i v e l y ) , F i g u r e (49). These types were u s u a l l y a s s o c i a t e d with a s u l f i d e phase (MnS I I ) and
3) A t the h i g h e s t
deoxidation
rates,
163 a mixture of s p h e r i c a l and f a c e t e d alumina w i t h
hexagonal
aluminates were observed, F i g u r e (50). T h i s l a t t e r type had a p e r i p h e r a l double, are shown i n Graphs a g a i n s t the S:Mn
(Mn,Ca)S, s u l f i d e .
These f i n d i n g s
(51) and (52) where the Ca:Al r a t i o
i n a t . % are p l o t t e d .
These f i g u r e s were
o b t a i n e d from i n c l u s i o n s i n R I I - I l and RII-I2 RII-Il
respectively.
which was a h e a v i l y d e o x i d i z e d i n g o t
very h i g h l y segregated m a t e r i a l .
These segregates
under the e l e c t r o n beam produced
a red fluorescence
showed which occurred
i n the t h i r d d e o x i d a t i o n l e v e l , F i g u r e (53) and t h e i r
typical
composition i n a t %, was as f o l l o w s : Al
Ca
26.23
Si
45.67
17.19
Mn Balance
Composition maps shown i n F i g u r e s (53a-d) are t y p i c a l of these segregates.
T h e i r area ranged from 10ym
2
up t o 65-70ym . 2
T h i s f i n d i n g a l s o confirms the " m u l t i - e x c h a n g e - r e a c t i n g " nature of the d e o x i d a t i o n i n the ESR-process, r e a c t i o n s of the type were commonly
(12 a-b).
e.g.
exchange
These types of segregates
seen i n samples e x t r a c t e d from l i q u i d p o o l s .
In these types of samples
inclusions containing s i l i c o n
and o c c a s i o n a l l y f a y a l i t e type of i n c l u s i o n s were a l s o found. Based on mass balances the "FeO" content of the s l a g d u r i n g r e f i n i n g changed from 0.45 wt % down t o 0.27 wt %
164
i n R I I - I l and
from 0.6
wt % to 0.26
lowest "FeO" l e v e l i n s l a g s was
wt % i n RII-I2.
The
a l s o accompanied by a change
i n the A^O^tCaO r a t i o ; whereas the C a F ^ content was s l i g h t l y changed
(from 0.5
to 1.0
wt % ) .
Thus, the minimum
l e v e l of d e o x i d a t i o n reached without
s h i f t i n g the
composition
% FeO
i s about
0.28
- 0.30
wt
5.2.1.4
(54,
slag
f o r 1.3
C a O i A ^ O ^ r a t i o s i n s l a g s of R I I - I l and RII-I2 Figures
only
and
1.5
respectively,
55).
1020
M.S.
Ingots Deoxidized Continuously with a
CaSi A l l o y Since the e f f i c i e n c y
of the Ca-Si a l l o y i n the s m a l l
4340 i n g o t s and i n the l a r g e diameter intermittently deoxidized
was
(200 mm)
observed *
1020
to be h i g h e r
i n the aluminum d e o x i d i z e d i n g o t s , a s e r i e s of were conducted
than
experiments
u s i n g e q u i v a l e n t s l a g systems and
of d e o x i d a t i o n as w e l l as m e l t i n g r a t e s (1 kg min the CaSi a l l o y .
M.S.
Experimental techniques used t o
degrees *) w i t h determine
the t o t a l oxygen content from l i q u i d pool and i n g o t , the s l a g chemical a n a l y s i s , the i n c l u s i o n composition and
their
s i z e d i s t r i b u t i o n s and the chemical a n a l y s i s of i n g o t s were the same as those used to study the 1020 f i n e d through
the C a F - A l 0 - C a O system. 2
2
3
M.S.
ingots r e -
The Ca-Si a l l o y
was *
added to the s l a g i n R I I I - I l and RIII-I2 i n about e q u i v a l e n t
* N o t i c e t h a t 1 gram A l i s approximately of the CaSi a l l o y ; Table (IX).
e q u i v a l e n t t o 3.12
grams
165 aluminum r a t e s as i n R I I - I l and RII-I2 namely: 16.83, 22.24 and p a r t i a l l y 28.0 kg t o n 16.83, 22.44, 28.05, and 56.1 kg t o n
- 1
- 1
5.11, 11.23,
and 5.11, 11.23,
, Table
(VIII).
The p r i n c i p a l d i f f e r e n c e s between R I I I - I l and RIII-I2 are . t h e i r s l a g chemical composition and t h e i r d e o x i d a t i o n r a t e s . R I I I - I l and RIII-I2 were r e f i n e d through 60/36/4 and 50/30/20; lowest
(CaF , A 1 0 2
2
3
and CaO) r e s p e c t i v e l y .
The t h r e e
(CaSi) r a t e s were added i n s h o r t e r p e r i o d s o f time
a t the bottom o f the i n g o t i d e n t i f i e d as RIII-I2 and the f o u r t h l e v e l of a d d i t i o n s than i n R I I I - I l . analysis
(22.4 4 kg ton ^),was longer
Due to these d i f f e r e n c e s the t o t a l oxygen
shown i n F i g u r e s (56) and (57)
c l u s i o n chemical compositions,
and hence the i n -
F i g u r e s (58) and (59) from
R I I I - I l and RIII-I2 r e s p e c t i v e l y , were the most affected
critically
parameters.
T h e i r s l a g and i n g o t compositions f o l l o w e d e q u i v a l e n t b e h a v i o r , F i g u r e s (60) and (61) and F i g u r e (62) and (63). The S i and Ca contents i n s l a g s g r a d u a l l y i n c r e a s e d the "FeO"and the A l 0 2
3
given as Fe and A l i n wt %
whereas
gradually
decreased as the (Ca-Si) d e o x i d a t i o n r a t e s were i n c r e a s e d . An important p o i n t to note i s t h a t the i r o n oxide i n s l a g s from both i n g o t s was reduced t o about Figures
(64) and (65)
0.2 wt%
as shown i n
without producing s t r o n g changes i n
the composition o f the s l a g s .
These graphs c o n s i s t e n t l y show
166
t h a t the aluminum and
s i l i c o n g r a d u a l l y i n c r e a s e d as
the
l e v e l of d e o x i d a t i o n i s i n c r e a s e d . The
i n c l u s i o n chemical composition
principally
as the a t . % Ca: a t % A l r a t i o i n F i g u r e s R I I I - I l and pattern.
RIII-I2
(58) and
given
(59) f o r
r e s p e c t i v e l y , f o l l o w e d an e q u i v a l e n t
T h i s r a t i o , however, was
l a r g e r i n RIII-I2
to h e a v i e r d e o x i d a t i o n i n i t s f o u r t h l e v e l .
due
Another
import-
ant f i n d i n g i n regard to the i n c l u s i o n composition
was
p r o p o r t i o n a l changes of s u l f u r
Ca:Al
(as a CaS)
with the
r a t i o s and hence with the d e o x i d a t i o n r a t e s , F i g u r e s to
(68).
I n c l u s i o n s a t the bottom of i n g o t s
r a t e s of d e o x i d i z e r were used alumina types,
were mainly
( a - A ^ C ^ and F e O * A l 0 ) . 2
3
where
I I I and
At i n t e r m e d i a t e
de-
(rate) ranges
s p h e r i c a l aluminates
(CaO«2Al 0 , C a O « A l 0 2
3
3
(Mn,Ca)S) were found.
2
3
and
d i t i o n s , as i n RIII-I2 CaS
In the h i g h
aluminates, sulfides
deoxidation
enriched i n calcium,
12CaO•7A1 0 ) 2
p e r i p h e r a l CaS were i d e n t i f i e d .
low round
(a-A^O^ and C a O 6 A l 0 ) as c l u s t e r s , together with (MnS
(66)
f a c e t e d and
grees of d e o x i d a t i o n f a c e t e d alumina and hexagonal 2
the
a s s o c i a t e d with
3
Extreme d e o x i d a t i o n con-
and p a r t i a l l y i n R I I I - I l , produced a
phase w i t h i n c i p i e n t amounts o f aluminum ( u s u a l l y
l o c a t e d i n t h e i r core) and
the l a r g e s t segregated
e n r i c h e d i n d e o x i d i z e r s ( A l , S i , Ca and
sometimes
These r e s u l t s indeed c o r r o b o r a t e the
material Mn).
qualitative
f i n d i n g s p r e v i o u s l y d e s c r i b e d f o r RII-W and RIII-W as w e l l as f o r the small 4340-ingots which were Ca-Si
deoxidized.
167 The above f i n d i n g s RIII-I2) c l e a r l y
(RII-W, RIII W,
RIII-Il
and
i n d i c a t e t h a t the CaSi as a d e o x i d i z e r
p l a y s by f a r a more important r o l e i n the chemical composit i o n of i n g o t and of the
composition
slag.
The A^O^
i n c l u s i o n s than the chemical
low l e v e l of SiC>2 and the gradual decrement of
i n the s l a g , the amounts of S i and A l which are c o n t i n u -
o u s l y i n c r e a s i n g i n the i n g o t and the Ca:Al r a t i o i n i n c l u s i o n s immediately reacting
(ESR)
suggest t h a t the S i i s u t i l i z e d
system as a c a r r i e r .
t h a t simultaneous
I t i s also
i n the
observed
exchange r e a c t i o n s between the two
liquids
(slag and metal pool) d e f i n i t e l y c o n t r i b u t e t o the deoxida t i o n mechanism, F i g u r e s (60-68). t h i s mechanism, r e a c t i o n s of the type
Further evidence t h a t (11) and
(12 a-b) ,
r u l e s the chemistry of the melt, i s seen i n the S i content i n i n c l u s i o n s at h i g h d e o x i d a t i o n r a t e s i n RIII-I2, F i g u r e (68).
Excessive
(CaSi) d e o x i d a t i o n performed
i n t h i s ingot
induced the f o r m a t i o n of c a l c i u m aluminates with p e r i p h e r a l CaS
and some s i l i c o n as w e l l as the formation of
e n r i c h e d i n d e o x i d i z e r s , F i g u r e (69).
segregates
168 5.2.1.5
C o r r o b o r a t i o n and E x t e n s i o n of Previous F i n d i n g s t o a 4340 S t e e l CaSi (continuously) Deoxidized
Once the l i q u i d p o o l - s l a g d e o x i d a t i o n mechanism was unmistakenly
i d e n t i f i e d through the p r e v i o u s work, a f u r -
t h e r s e t o f experiments was c a r r i e d out t o r e c o n f i r m and extend
these r e s u l t s t o more complex d e o x i d i z e r s and a l l o y
systems such as 4340 and a r o t o r (Ni-Cr-Mo) s t e e l .
Re-
m e l t i n g of these e l e c t r o d e s was performed u s i n g the e q u i v a l e n t experimental remelted
c o n d i t i o n s as i n the 4 340 e l e c t r o d e s
by the s m a l l ESR-furnace and the 1020 M.S.
rodes remelted
by the s e m i - i n d u s t r i a l ESR-furnace.
m e l t i n g r a t e s were kept i n the 1 kg min The
1
electThe
range.
l a s t i n g o t i n c l u d e d i n the f u l l y monitored s e t o f
experiments
(through the three r e f i n i n g stages) was a
4 340-electrode
which was r e f i n e d through a 50 wt. % CaF /
30 wt. % A 1 0
and 20 wt. % CaO s l a g and CaSi
2
The
3
2
deoxidized.
degree o f d e o x i d a t i o n was c o n t i n u o u s l y i n c r e a s e d from
4.17 to 41.67 kg (CaSi) t o n
- 1
f o r almost e q u i v a l e n t p e r i o d s
of time as i n R I I I - I l .
The l a s t l e v e l o f d e o x i d a t i o n was
a l s o suddenly
from 41.67 down t o 20.83 kg ton
decreased
Chemical composition
of the s l a g and i n g o t f o l l o w e d
the same p a t t e r n as the 1020-ingots, a l l o y , Figures
d e o x i d i z e d with the CaSi
(70) and (71). The major d i f f e r e n c e found
i n t h i s i n g o t was i t s i r o n oxide and i t s oxygen Figure
(72). The i r o n oxide
given i n Figure
content,
(73)
changed
169 from 0.4
down to 0.15
creased.
The average
10-20
ppm.
deoxidized
as the r a t e of d e o x i d a t i o n was i n t o t a l oxygen content was about
Whereas i n the 1020 the l e v e l ranged
ingots
e i t h e r A l or CaSi
from 30 and up to 80
ppm.
This s u b s t a n t i a l d i f f e r e n c e i s e s s e n t i a l l y a t t r i b u t e d to the t i g h t Ar-atmosphere e n c l o s u r e of the f u r n a c e , the gree of
(Ca-Si) d e o x i d a t i o n of these
ingots
de-
(50-70
ppm
of oxygen) and the chemical composition of the e l e c t r o d e . The chemical composition of i n c l u s i o n s Figures
given i n
(74 a,b), f o l l o w e d the g e n e r a l t r e n d observed i n
the e q u i v a l e n t 10 20 M.S. of i n c l u s i o n s
ingots.
The chemical
composition
i n s i m i l a r manner to p r e v i o u s 1020
i n g o t s d e o x i d i z e d with the CaSi a l l o y
e x h i b i t e d the
a l t r a n s i t i o n from aluminate
to c a l c i u m aluminate
T h e i r p r o p o r t i o n a l increment
i n s u l f u r content
up to 25 a t . % was was
a l s o observed,
increased, Figure A very important
M.S. gradu-
phases.
(as
CaS)
as the d e o x i d a t i o n r a t e
(75). f a c t to address
i s the r a t i o of the S i
in
i n these
the C a S i - a l l o y
i s c o n s t i t u t e d by approximately
62.0
wt.
even
experiments though i t
% S i , i t has
not
p l a y e d a r o l e i n the d e o x i d a t i o n scheme p r e v i o u s l y presented, i.e.
i n v o l v i n g the CaO
and A^O^
of the s l a g and the Ca
and A l i n i n c l u s i o n s and d e o x i d i z e r s .
It i s also
important
to emphasize t h a t the S i from e i t h e r the e l e c t r o d e ( i n
170 the 1020 ported
e l e c t r o d e s ) or the CaSi a l l o y i s v i r t u a l l y c o n j o i n t l y to the A l and
Ca
trans-
i n t o the i n g o t
and
i t does not appear i n i n c l u s i o n s . At t h i s p o i n t i n t h i s d e s c r i p t i o n , i t becomes e s s e n t i a l to r e c a l l t h a t although the A l as a d e o x i d i z e r seems to be o p e r a t i n g w i t h i n the same frame of r e a c t i o n s as the ( s l a g - d e o x i d i z e r and
l i q u i d pool), i t
t o r s , does not d e o x i d i z e CaSi a l l o y .
due
to k i n e t i c
to c o r r o b o r a t e
fac-
the ESR-melt as e f f i c i e n t l y as
In the l i g h t of these f i n d i n g s a new
three experiments was
CaSi
planned.
s e t of
The major purpose
was
the c o n c l u s i o n t h a t the s i l i c o n i n the
de-
o x i d i z e r works e x c l u s i v e l y as a c a r r i e r , to r e c o n f i r m v a l i d i t y of the proposed mechanism
the
( r e a c t i o n scheme) and
to compare the degrees of d e o x i d a t i o n
reached through
d i f f e r e n t d e o x i d i z e r s , Table
Three r o t o r
(VIII).
s t e e l e l e c t r o d e s were r e f i n e d i n the 200 furnace
using e q u i v a l e n t m e l t i n g
deoxidation
r a t e s , Table
were C a S i , SiAlCaBa chemical
(XII).
mm
The and
diameter
ESRand
(Si-based) d e o x i d i z e r s an A l S i a l l o y .
compositions are given i n Tables
Despite
three
(Cr-Mo-V)
r a t e s , s l a g system
("hypercal")
the
the f a c t t h a t the chemical
Their
(XII a - c ) .
composition
of
the
d e o x i d i z e r s i s q u i t e d i f f e r e n t c a l c i u m aluminate phases with p e r i p h e r a l c a l c i u m
s u l p h i d e are p r e c i p i t a t e d .
Ca:Al r a t i o vs. the s u l f u r content
The
are p l o t t e d i n F i g u r e
(76).
171 Again
i t i s shown t h a t exchange r e a c t i o n s of the
(12 a-b)
type
p l a y the most important r o l e i n the d e o x i d a t i o n
( r e a c t i o n ) scheme and s i n c e the S i appears
i n the i n g o t
but i t does not i n i n c l u s i o n s i t s r o l e i s p r i n c i p a l l y
as
a c a r r i e r of Ca and A l i n t o the l i q u i d p o o l and i n g o t . These r e s u l t s support the three p r e v i o u s p r o p o s a l s . The chemical composition of i n c l u s i o n s i n d i c a t e t h a t s i l i c o n free, c a l c i u m aluminates with p e r i p h e r a l c a l c i u m s u l f i d e ( i . e . o t h e r s than C a O 6 A l 0 2
c i p i t a t i n g phases.
The
3
and
(Mn,Ca)S) were the p r e -
s i l i c o n content i n the s l a g
c o n s i d e r a b l y i n c r e a s e d and the "FeO"content was i n the ranges p r e v i o u s l y d e s c r i b e d , Table Furthermore,
was
also held
(XII).
segregates which were found i n the
ex-
c e s s i v e l y and a b r u p t l y A l and CaSi d e o x i d i z e d i n g o t s were the same as observed
i n ( s i z e , f l u o r e s c e n c e under the
ron beam and t h e i r chemical composition) ingot.
elect-
the A l S i d e o x i d i z e d
The d i s t r i b u t i o n of elements i n a segregate e n r i c h e d
i n s t r o n g oxide formers, namely aluminum, s i l i c o n and c u l a r l y c a l c i u m , i s shown i n F i g u r e s composition was
(77a-d).
parti-
Their t y p i c a l
( i n at.%) as f o l l o w s : Ca 40.6
Al 41.5
Si
Mn + Fe
19.7
balance
T h i s f i n d i n g i s c o n s i d e r e d as another evidence t h a t the p r o posed mechanism i s indeed o p e r a t i n g .
172 5.3
D i s c u s s i o n of R e s u l t s
i n Terms of E l e c t r o d e
Slag Composition, Related 5.3.1
The
and
to the Second Question
E f f e c t of the E l e c t r o d e on the I n c l u s i o n Comp-
o s i t i o n of ESR-ingots The
experimental
f i n d i n g s p r e v i o u s l y d e s c r i b e d have
been used to address the second q u e s t i o n III, i . e . chemical
i s the i n c l u s i o n composition
composition
This question
s t a t e d i n Chapter c o n t r o l l e d by
of e l e c t r o d e s , s l a g or
deoxidizers?
as envisaged i n the l i t e r a t u r e review ( i n
terms o f the complexity
of the r e a c t i o n scheme and
c l u s i o n chemical
composition
and
the p r e v i o u s l y d e s c r i b e d r e s u l t s
as shown i n
of r e f i n i n g and
the i n -
of i n g o t s i n the ESR-process) cannot
be answered u n l e s s the r e a c t i o n s between the three f e r e n t stages
the
i t s components
dif-
(electrode,
slag, s l a g - l i q u i d film, deoxidizer, l i q u i d pool-slag
and
ingot) are c a r e f u l l y monitored. Through the f i r s t p a r t of t h i s r e s e a r c h concluded t h a t i n c l u s i o n s from e l e c t r o d e s r e f i n i n g conditions rode t i p . The and
are completely
i t has
under s t a b l e
d i s s o l v e d i n the
Thus, f u r t h e r d i s c u s s i o n assumes t h i s
e l u c i d a t i o n of the r o l e p l a y e d by the
the s l a g on the chemical
composition
been
elect-
fact.
electrode
of i n c l u s i o n s i n
the ESR-ingot have been shown through s e v e r a l experiments: 1)
The
small 4340 i n g o t
.(6), Table
(X), r e f i n e d through
173
an alumina
f r e e s l a g and
a t i v e and deoxidant
(external) sources, i . e .
and without deoxidant. 1020
M.S.
i n the absence of gaseous o x i d -
2) A l a r g e diameter
e l e c t r o d e r e f i n e d through
under (200
M.S.
mm)
a CaF -CaO-Al 0 2
2
s l a g under the above c o n d i t i o n s , ( R I - I l ) , Table and 3) A s e r i e s o f 1020
argon
3
(VIII)
e l e c t r o d e s r e f i n e d i n the 200
mm
i n diameter ESR-furnace which were i n t e r m i t t e n t l y d e o x i d i z e d with CaSi and o t h e r s c o n t i n u o u s l y d e o x i d i z e d with A l and a CaSi
alloy.
1. 31 wt.%
The
i n g o t (6)
C a F , 46 wt. 2
which was
% CaO,
remelted through
and 23.0
wt.
% Si0
a dominant r o l e i n the f i n a l i n c l u s i o n chemical of the r e f i n e d i n g o t .
The
r e p r e s e n t e d as A l i n Table g i v e n as s i l i c o n ,
alumina
has
2
c l u s i v e l y shown t h a t the e l e c t r o d e composition
the con-
indeed p l a y s composition
content i n i n c l u s i o n s
(VIII) with r e s p e c t t o
silica,
shows t h a t the aluminum which came ex-
c l u s i v e l y from the e l e c t r o d e ( i n s o l u t i o n ) has the i n c l u s i o n chemical composition.
controlled
This finding
i n agree-
(83) ment with Rehak s e t a l . ' s 1
i n A l and CaSi t r e a t e d e l e c t r o d e s
c l e a r l y demonstrates t h a t the chemical composition of e l e c t rodes s p e c i f i c a l l y due
to the presence of d e o x i d i z e r s i n
s o l u t i o n , under a g i v e n s l a g system can p l a y an
important
r o l e i n the f i n a l i n c l u s i o n composition of r e f i n e d i n g o t s , i.e.
self-deoxidation.
174 2.
Results
found from a 1020-ingot remelted under a
p r o t e c t i v e atmosphere without the i n f l u e n c e of a are shown i n F i g u r e s illustrate 200
mm
t h a t as the r e m e l t i n g
mould takes p l a c e
s l a g and
a gradual
occurs.
The
and
(37,38). These graphs
from R I - I l
of the e l e c t r o d e
clearly
i n the
an accumulation of s i l i c a
change i n the alumina and
i n the
calcium
oxide
S i C ^ i n the s l a g a c t s e x c l u s i v e l y as a d i l u e n t
only c o n t r i b u t e s
to a g r a d u a l
s h i f t i n the II
r a t i o s and
deoxidizer
CaOiA^O^ (38
II
to c o n t r o l the i n t r i n s i c "FeO"content i n the
slag
I t does not,
however, i n f l u e n c e the chemical composition of
inclusions
A deeper d i s c u s s i o n r e l a t e d to t h i s matter w i l l
r
be pursued i n a subsequent s e c t i o n . clarify
t h a t the change i n the CaOrA^O^ r a t i o was
f l u e n c e d by or HFl)
the formation
s i n c e the f l u o r i n e a n a l y s i s was
The
i n the
as the t o t a l A l and d e p l e t i o n i n the p o i n t out (0.65
i n the
% and
0.09
i n g o t , o n l y aluminates
sulfides
and "FeO"in the
2
Ca content i n F i g u r e
ingot, Figure
wt.
((Fe,Mn)S and
changed only
CaOtA^O^ r a t i o i n the
t h a t i n s p i t e of the to 0.72
MnS
not i n -
(38).
i n the
slag
slag—given
(37)--and an A l
I t i s worthwhile to
(gradual) to 0.13 (A^O^
2
(± 0.2%).
continuous increment of S i 0
produces a s h i f t
to
of v o l a t i l e f l u o r i d e s (AlF^, S i F
measure of the experimental e r r o r ,
Si
It i s pertinent
i n c r e a s e i n Mn wt.
and
% respectively)
and A^O^'FeO)
II) were p r e c i p i t a t e d .
and
3.
A t y p i c a l a l t e r a t i o n o f the otherwise
o u s l y i n c r e a s i n g content
of s i l i c a
S i i n the i n g o t i s shown i n F i g u r e f i e d as RIII-W
was remelted
v a l e n t s l a g to R I - I l . contents
continu-
i n the s l a g and hence (32). T h i s i n g o t
identi-
under argon and under an e q u i -
The abrupt changes i n the S i and Mn
i n the s l a g and i n g o t
and'the Ca:Al r a t i o i n i n -
c l u s i o n s are a r e s u l t from the i n t e r m i t t e n t a d d i t i o n s of the (CaSi) d e o x i d i z e r .
Since the s i l i c o n comes from the e l e c t -
rode and the d e o x i d i z e r a more a p p r o p r i a t e
analysis
should
be performed on the Mn s i n c e i t comes e x c l u s i v e l y from the electrode.
The Mn content
changes from about 0.65 down t o
0.45 wt. % i n the s l a g , F i g u r e (32). The
behavior
o f the S i from the e l e c t r o d e becomes more
important when the 1020 M.S. e l e c t r o d e s are A l d e o x i d i z e d . The
i n g o t i d e n t i f i e d as R I I - I l c l e a r l y shows t h a t as the
degree o f d e o x i d a t i o n
i s increased
i n the s l a g and i n g o t — F i g u r e s a constant
level.
the l e v e l o f S i and Mn
(39) and ( 4 5 ) — a r e
held to
T h i s suggests t h a t the chemical
composition
of the e l e c t r o d e no longer p l a y s a r o l e i n the r e f i n i n g cess.
T h i s i n g o t was r e f i n e d , as shown i n Table
pro-
(VIII),
through a S i and Mn f r e e s l a g under an argon atmosphere. Thus, the o n l y source o f S i (0.25 wt. %) and Mn
(0.6 - 0.7
wt. %) e i t h e r i n s o l u t i o n o r as i n c l u s i o n s i s the e l e c t r o d e . The
above r e s u l t s c l e a r l y i n d i c a t e t h a t i f an e l e c t r o d e
176 c o n t a i n s oxide forming elements i n s o l u t i o n or as i n c l u s i o n s , which are not present as oxides d e o x i d i z e r s than those present d e o x i d a t i o n takes p l a c e .
i n the s l a g and are stronger i n the s l a g , a c o o p e r a t i v e
The mechanism by which these r e -
a c t i o n s take p l a c e i s w i t h i n the g e n e r a l scheme given by reactions
(11) and (12 a-b). The most important
conclusion
from these experiments i s t h a t these r e a c t i o n s predominate s o l e l y i n the absence of or under i n e f f i c i e n t A conventional Al-deoxidation
deoxidation.
(0.05 - 0.2 wt. %) i s able
to overcome the e f f e c t of the S i from the e l e c t r o d e i f the r e f i n i n g s l a g i s low (< 10 wt, %) i n SiO,,.
5.3.2
E l u c i d a t i o n of the E f f e c t of Slag and D e o x i d i z e r s (Preliminary The
Studies)
e l u c i d a t i o n of the e f f e c t of s l a g s and d e o x i d i z e r s
was approached through the s m a l l 4340 i n g o t s . to
(6)
slags,
Ingots
(1)
which were r e f i n e d through d i f f e r e n t S i 0 - c o n t a i n i n g 2
y i e l d e d c a l c i u m aluminate
c a t e phases.
and calcium-aluminum
sili-
The former type of i n c l u s i o n s d i d not exceed
3.75 a t . % Ca and they were i d e n t i f i e d o n l y where the S i 0 ~ 2
content
i n the s l a g was l e s s than
10 wt. %.
Above t h i s
c e n t the l a t t e r type of phases were i d e n t i f i e d . summarizes the main f e a t u r e s of these
Table
experiments.
per(X)
177 I f the above a n a l y s i s i s extended to both s l a g s and i n c l u s i o n compositions
and they are p l o t t e d i n t e r n -
ary diagrams
by A l l i b e r t e t a l . (207)
f o r ESR
as suggested
i n g o t s and
s l a g s and Bruch
(14 53 54) ' '
and K i e s s l i n g
and
(91) Lange
f o r CaSi d e o x i d i z e d i n g o t s i n c o n v e n t i o n a l
making processes c l u s i o n s and Figures
then the chemical compositions
t h e i r probable o r i g i n i s e a s i l y
(12) and
(13) .
of i n -
followed.
S e v e r a l important p o i n t s should
c o n s i d e r e d i n these diagrams:
i ) the s l a g chemical
t i o n i s p l o t t e d under the assumption t h a t the C a F an i n e r t d i l u e n t
( 3 3
'
3 8
steel-
'
4 5
'
5 3
'
8 8
'
8 9 }
.
composia c t s as
i i ) r e g a r d i n g the
nary diagram which d e s c r i b e s the i n c l u s i o n (91) K i e s s l i n g ' s and Lange*s
2
be
ter-
composition,
s t u d i e s as an e x t e n s i o n of
(207) Bruch's have c o n s i d e r e d a replacement of e i t h e r Mn, Mg or Fe by Ca as oxides i n the CaO c o r n e r . The replacement (34) of Mn by Ca as oxides has a l s o been r e p o r t e d by i n ESR
ingots.
the A^O-j
And
the two
Holzgruber
d i v e r g e n t l i n e s which emerge from
corner to the CaO-Si0
2
b i n a r y are l i n e s which r e p -
r e s e n t the maximum and minimum MeO:Si0 respectively, in inclusions.
2
i i i ) The
r a t i o s , L^ and
f i n d i n g s from C a - t r e a t e d
3
(conventional) i n g o t s
al.'s' and
data o b t a i n e d by other r e s e a r c h e r s i n c o n v e n t i o n a l '
'
diagram.
and
i n ESR-research
1 0
^
iv) 4 0
'
15115783) '
2
t r i p l e l i n e which
a l s o emerges from the A l 0 ~ c o r n e r are Holappa e t 2
L
i s also included i n t h i s
1 4 4
'
178
Slags c o n t a i n i n g l e s s than 10 wt.
% Si0
2
c l u s i o n s l y i n g along the A^O^-CaO b i n a r y and l o c a t e d c l o s e r to the A l 0_-corner. 2 3 u s u a l l y a s s o c i a t e d with s u l f i d e s (Ca, Mn)S).
The
produce i n specifically
These types were J
(MnS
c
I I , MnS
I I I or
type and composition of these
sulfides (34)
depended on the Ca:Al r a t i o i n the oxide phase. (14 53 54) and A l l i b e r t e t a l . (12 v i i i ) , Figures
have
also
'
'
who
reported
Holzgruber
have s t u d i e d the r e a c t i o n these
inclusion
phases,
(12,13).
The chemical composition of i n c l u s i o n s which were obt a i n e d from s l a g s c o n t a i n i n g more than 10 wt. l o c a t e d along the S i C ^ - A ^ O ^ a x i s . (8),
(10) and
20 t o 85 wt. about
30 wt.
Bruch's
Ingots
% Si0
2
were
(2), (3),
(11) were l o c a t e d i n an area c o n f i n e d i n the %.
Al 02 2
% CaO.
range along the S i C ^ - A ^ O ^ a x i s
and
These r e s u l t s are i n agreement with
and K i e s s l i n g ' s and L a n g e ' s ^ ^ ' and
with A l l i b e r t ' s et a l . ' s
( 5 3 )
,
Rehak's
( 8 3 )
qualitatively
and Holzgruber ' s
( 3 4 )
F i n d i n g s from the l a t t e r two r e s e a r c h e r s were o b t a i n e d from ESR experiments
where experimental c o n d i t i o n s were not
dir-
e c t l y concerned with the s l a g chemical composition. Thus, i f C a F
2
i s s t r i c t l y c o n s i d e r e d as an i n e r t (234 )
and Rein's and Chipman's data
diluent
are used t o s u b s t a n t i a t e
the thermodynamic behavior of s i l i c a
i n ESR-slags
then i f
.
a_.__ Si0
2
£ 0.01, a , , . AlO^
S 0.5 and a„ . 5 0.1 , aluminates CaO
5
w i l l precipitate.
On the other hand i f the S i 0
of s l a g s exceeds 10 wt. % with some c a l c i u m
then a l u m i n u m - s i l i c a t e i n c l u s i o n s
(up to about 30 wt. % CaO) w i l l
The a c t i v i t y r e l a t i o n s a r e as f o l l o w s : a
C
a
0
< 0.10 and a
content
2
A
1
^ 0.5.
Q
a„.^
precipitate.
^0.01,
SiO„
'
Holappa's r e s u l t s
'
v
1. 5 from C a - t r e a t e d i n g o t s suggest i n the melt i s reduced
t h a t as the a c t i v i t y of A l
and the a c t i v i t i e s o f S i and Ca are i n -
creased, a g r a d u a l change i n composition of the i n c l u s i o n phase as i n d i c a t e d by the ' t r i p l e - d o t t e d ' l i n e i n F i g u r e be observed.
(12) should
T h i s behavior i n ESR i n g o t s (1) t o (6) was not
completely f o l l o w e d and i n s t e a d a mixture o f c a l c i u m -
silicon-
aluminate and aluminate phases were found, Table (X). The b e s t d e o x i d a t i o n in inclusions* * ^ 2 1
3
measured as the C a O : A l 0 2
was found i n the C a F - C a O - A l 0 2
s p e c i f i c a l l y where the C a F
2
2
3
ratio
3
system,
and CaO contents were 50 wt. %
and 20 wt. % r e s p e c t i v e l y i n the s l a g .
Polish researcher's
work ^ ^ ' o n s l a g s b e l o n g i n g to t h i s system have r e p o r t e d a maximum of 71.0% r e d u c t i o n o f n o n - m e t a l l i c i n c l u s i o n s i n r e l a t i o n t o the s t a r t i n g s t e e l e l e c t r o d e i n e x a c t l y the same s l a g composition
(50/30/20) a t which the l a r g e s t
Ca:Al
r a t i o i n i n c l u s i o n s was found i n t h i s r e s e a r c h , Table (X). Thus, through
the p r e v i o u s d e s c r i p t i o n
i t has been
found t h a t the s l a g d e f i n i t e l y p l a y s a r o l e i n the r e f i n i n g process.
What has not been answered y e t i s how l a r g e the
180 s l a g e f f e c t i s i n comparison with
the d e o x i d i z e r .
q u e s t i o n can be answered i n a t r i v i a l manner by r e s u l t s i n Table composition
(X).
of i n g o t
This
analyzing
By comparing the i n c l u s i o n chemical (1) a g a i n s t
(7) and
(9),
can
ob-
serve t h a t the Ca-content i n i n c l u s i o n s i n the l a t t e r
two
i n g o t s i s double that i n the former. b a s i s , one
one
Thus, on an
apriori
could e s t a b l i s h that since deoxidation
s l a g were e q u i v a l e n t
rates
(2.3 kg ton ^, 50/30/20) and
ratios in
i n c l u s i o n s i s twofold
deoxidized
ingots
(7) and
i n the A l and
(9) r e s p e c t i v e l y
the
the
l a r g e r than 1.15
kg ton
And
deoxidation
molten i r o n then a r e l a t i v e l y
ex-
higher
r a t e c o u l d generate aluminates r i c h e r i n c a l c i u m
however, do not r e s t on any do not e x p l a i n why
mechanism and
the A l and
compositions.
62.5
i n c l u s i o n chemical
(2.3 kg ton
wt.%
Si.
The
composition,
r e f i n e d through the 55 wt.% 15 wt.
consequently they produce
i n terms o f i n c l u s i o n
I t i s important to c l a r i f y t h a t although
amounts of d e o x i d i z e r s a l l o y contains
These premises,
the CaSi d e o x i d a t i o n
an almost e q u i v a l e n t t r e n d i n r e s u l t s
and
rates
t h a t s i n c e the Ca i s
and hence much lower t o t a l oxygen c o n t e n t s .
CaO
de-
i f these f i n d i n g s are
t r a p o l a t e d , i t c o u l d be estimated almost i n s o l u b l e i n
Ca:Al
CaSi
then the
o x i d i z e r overcomes the s l a g e f f e c t at d e o x i d a t i o n
and
% Si0
0
1
) were e q u i v a l e n t
the
e f f e c t of d e o x i d i z e r s
i n the s m a l l 4 340
C a F , 15 wt.% 2
the
Al 0 ,
s l a g i s shown i n Table
2
3
(X).
ESR
CaSi
on
ingots
15 wt.
%
the
181
If
ingots
oxidized the
a r e compared
against ingot
The S i C ^ e f f e c t
e v e r , was a l m o s t (Al).
from
completely
( 2 ) , one c a n s e e t h a t
i n diameter
This p a r t i c u l a r
findings
was r e m e l t e d
ingot
a constant rate
i n ingot
by t h e d e o x i d i z e r , a
1020-electrode
under e q u i v a l e n t c o n d i t i o n s .
Kg/ton
).
The e f f e c t o f
(X) and i n c l u s i o n
composition
was n o t enough t o c o u n t e r b a l a n c e
the slag.
( 8 ) , how-
( 1 1 ) , however, was A l - d e o x i d i z e d
(0.02
the d e o x i d i z e r , T a b l e ously c i t e d ,
the s l a g
suppressed
To c o r r o b o r a t e t h e s e
76.2 mm
of
(10) w h i c h were A l and C a S i d e -
C a S i d e o x i d i z e d i n g o t d i d show t h e i n f l u e n c e o f t h e
silica.
at
(8) and
The i n c l u s i o n p h a s e s were
previ-
the SiC^ e f f e c t
" a n o r t h i t e " and
alumina. It
i s worthwhile
t o p o i n t out that the s i l i c o n
in
the i n c l u s i o n phases of i n g o t s
of
magnitude
And
although
sition of
there
silicon
deoxidant
slag
the aluminum-deoxidized
ingots.
i n the chemical
(1) t o ( 8 ) and (9) and (10) (SiC^ i n i n c l u s i o n s ) ,
to the large q u a n t i t i e s
and t h e c h e m i c a l
than
(2) and (8) a r e one o r d e r
i s a difference
content
i s attributed
larger
than
of electrodes
their
fect
the
larger
10 wt. %.
composition
treatment,
contents
s m a l l e r than
10 wt. %.
i n terms
t h e main e f -
of the slag, i . e . ,
Thus, t h e c h e m i c a l
s h o u l d be c a r r i e d
compo-
i n t h e (CaSi)
composition of
a t w h i c h an a p p r o p r i a t e d e o x i d a t i o n
the CaSi
content
i n terms o f
out i s at s i l i c a
182 Hence, the most important
c o n c l u s i o n from p r e v i o u s
f i n d i n g s i s t h a t the d e o x i d a t i o n phenomenon i s a n e t r e s u l t o f c o o p e r a t i v e r e a c t i o n s between d e o x i d i z e r s and s l a g s . Thus, t o o b t a i n an e f f i c i e n t d e o x i d a t i o n
an a p p r o p r i a t e
s e l e c t i o n o f these parameters i s e s s e n t i a l . of these statements
A f u r t h e r proof
w i l l be approached i n the next s e c t i o n .
I t i s a l s o worthwhile to c l a r i f y
t h a t although there i s
a common t r e n d o f r e s u l t s i n both ESR-furnaces the v a l i d i t y of p r e v i o u s f i n d i n g s i s q u a l i t a t i v e .
The
lower
sur-
f a c e area a v a i l a b l e f o r r e a c t i o n s , the higher thermal
gradi-
ents and the unsteadiness o f the s o l i d i f i c a t i o n c o n d i t i o n s i n the small ESR-furnace
a r e f a c t o r s t h a t must be con-
sidered.
5.3.3
P r e l i m i n a r y D i s c u s s i o n on the Deoxidation Mechanism In the l i g h t of p r e v i o u s d i s c u s s i o n o f f i n d i n g s , the
e v a l u a t i o n of the o r i g i n a l q u e s t i o n — I s the i n c l u s i o n compo s i t i o n c o n t r o l l e d by the chemical composition slag or deoxidizers?—becomes
of electrodes,
i r r e l e v a n t and i n s t e a d o t h e r
q u e s t i o n s emerge, i . e . what i s the mechanism by which the deoxidation
( i n i n d u s t r i a l s l a g s and deoxidants)
What i s the r o l e p l a y e d by the s l a g ?
takes p l a c e ?
and What a r e the c o n d i -
t i o n s which an a p p r o p r i a t e d e o x i d a t i o n i s c a r r i e d out under? To s a t i s f a c t o r i l y answer t h i s s e t o f q u e s t i o n s
a summary
183 of experimental i s presented
r e s u l t s c o r r e l a t e d to the g e n e r a l
i n advance.
The
theory
f o l l o w i n g s e c t i o n emphasizes
the r e s u l t s obtained w i t h the 20 0 mm
ESR
ingots continu-
o u s l y or c o n s t a n t l y d e o x i d i z e d . F i n d i n g s from the small suggest
t h a t the chemical
clusions A^O^
(4340) ESR
composition
i n g o t s , Table
of i n g o t s and i n -
(Ca:Al r a t i o s ) i s determined s o l e l y by the
r a t i o i n the s l a g when the Si02 content
10 wt.
% and d e o x i d a t i o n i s absent.
through the 200 mm
(X)
The
i s lower
results
ESR-furnace have confirmed
ings and they have a l s o c o n t r i b u t e d to the
CaO: than
obtained
these
find-
formulation
of a more s e l f - c o n s i s t e n t d e o x i d a t i o n model. The
i n h e r e n t r e a c t i o n scheme (1-5)
a t the e l e c t r o a c t i v e
• ^ * • v „r.T, (27,28,30, 33,34) i n t e r f a c e s i n the ESR-process • ' ' / atmos• (1,34,38) , . . phere-slag-liquid pool i n t e r a c t i o n ( i n terms of t
t
h
e
n
the oxygen t r a n s p o r t ) . and the amount of s c a l e (as a r e s u l t o f the thermal i n the s l a g
h i s t o r y of the e l e c t r o d e )
introduced
are the main f a c t o r s which determine the
oxi-
d a t i v e s t a t e of the s l a g and hence the oxygen p o t e n t i a l i n the l i q u i d
pool.
Thus, the deoxidant,
the sequence and degree of
de-
o x i d a t i o n as w e l l as the s l a g system are parameters which should be adequately without The
s e l e c t e d to optimize
s a c r i f i c i n g the chemical
deoxidation
i n t e g r i t y of
a p p r o p r i a t e c o n t r o l of the '^ed i n the s l a g 1
ESR-ingots. by the
de-
184 oxidation p o o l and The "FeO"
w i l l i n f l u e n c e the l e v e l of oxygen i n the molten consequently the p r e c i p i t a t i o n of i n c l u s i o n s . importance of the e l e c t r o c h e m i c a l r e a c t i o n s on
l e v e l of a melt and
composition Table
(XI).
t h e i r i n f l u e n c e on the
of i n c l u s i o n s i s seen through i n g o t This rotor
the
chemical (14) i n
(Cr-V-Mo) s t e e l e l e c t r o d e was
sur-
face ground, thus s c a l i n g formed during mechanical working was
removed from i t s s u r f a c e
was
a l s o coated
with
The
(ESR)-ingot
vious surface preparation,
c l u s t e r s o f aluminates
i r o n oxides
and
This
chemical
a n a l y s i s of i n -
the argon atmosphere (0.02
kg ton ^ ) , round, s i n g l e
(mostly
s u l f i d e s (FeO,
FeS)
FeO-A^O^ and A^O^) and
(Mn,Fe)S) were
(218) metal i n thermodynamic e q u i l i b r i u m , i.e. (234) Chu
saturated. rates
Kun ' s phase diagram
- 1
s l a g which can be achieved The
i s a minimum "FeO"
"FeO"
de-
according A^O^-
deoxidation l e v e l i n the
for a given deoxidation p r a c t i c e .
e f f e c t of the atmosphere as w e l l as the
introduced
and
slag-liquid
this slag i s
On the other hand, d e s p i t e l a r g e
(10 kg t o n ) there
pre-
enclosure
t e c t e d i n s t e a d of the a-A^O^ expected from the
to Kuo
electrode
show t h a t d e s p i t e the
and a s l i g h t A l - d e o x i d a t i o n and
1 mm).
an Al-Mg s p i n e l p a i n t i n g t o prevent i t s
oxidation during r e f i n i n g . clusions in this
(about
artificially
i n the s l a g and hence i n the l i q u i d
are c l e a r l y shown i n F i g u r e s
(32,33) and
to the i n g o t s i d e n t i f i e d as RII W and
RIII
pool
(34,35) which belong W.
185 The
i n i t i a l stages
s l a g composition "FeO
( 1 , 3 8
mitted
'
8 2 )
.
of r e f i n i n g are c o n t r o l l e d by
which i n i t s e l f allows a g i v e n amount of I f the
"FeO"
content
i n the s l a g i s p e r -
to r i s e above t h i s l e v e l by any of the
mechanisms
the
described
the r e s u l t i s an i n c r e a s e d r a t e of o x i d a t i o n
of the r e a c t i v e s p e c i e s from the e l e c t r o d e or the s l a g , hence moving the system towards unacceptable r e f i n i n g i n terms of s l a g or i n g o t composition. 2[A1] which has
+ 3 (FeO)
t
The
(Al^)
reaction
+ 3Fe
d e p l e t i o n of
A l i n the i n g o t ; i d e n t i f i e d as R I - I l , F i g u r e s
the slag) has gradual
slag
(37,38),
(change i n the C a O i A ^ O ^ r a t i o i n
a l s o been i n f l u e n c e d by the presence of
i n t r o d u c t i o n of "FeO"
(mostly
s l a g as the r e f i n i n g took p l a c e . controlled
(12-iv) (12-iv)
c o n t r i b u t e d to produce the gradual
a t expense of the
conditions,
The
the
as s c a l e ) i n t o the CaOtA^O^ r a t i o i s
by 2[A1]
+ 3(CaO)
J
( A 1 0 ) + 3[Ca] 2
(20-C)
3
Although the extent t o which t h i s r e a c t i o n o c c u r r e d was limited,
i t s r e s u l t s were d e t e c t e d ,
Figures
(37) and
very
(38).
These r e a c t i o n s can take p l a c e only when there i s not enough d e o x i d i z e r to suppress the c o n t i n u o u s l y "FeO"
i n the s l a g .
i n c r e a s i n g amount of
Under these c o n d i t i o n s the major pre-
c i p i t a t i o n r e a c t i o n s are governed by the oxygen p o t e n t i a l as follows:
186 Fe + 2[A1]
t
+ 4[0]
(22)
(FeO«Al„0 ) 2 3 inclusion
or 2[A1]
+ 3[0]
t
(11-i)
(Al 0_) 2 3 inclusion o
These p r e c i p i t a t i o n r e a c t i o n s are c o n t r o l l e d by r e a c t i o n (12-iv) i n the A l d e o x i d i z e d i n g o t . e n t i a l has been decreased finite
"FeO"
content
p l a y s a very Figures
(45) and
RII-I2).
the r e a c t i o n
(46) which r e p r e s e n t the
deoxid-
(RII-Il
and
I t can a l s o be seen t h a t the"FeO"content i n the to about 0.3
i n c l u s i o n composition, FeO«Al 0 2
to a - A l 0
3
CaO«6Al 0 2
2
3
3
wt.
%.
7
Figures
(54,55).
and at. v e r y h i g h d e o x i d a t i o n r a t e s
i n c l u s i o n phase i s p r e c i p i t a t e d , F i g u r e s
(41,42).
of Mn
it
This
the p r e c i p i t a t i o n of the C a O - e A ^ O ^ phase
(up to the same degree) the p a r t i a l s u b s t i t u t i o n
by Ca i n the s u l f i d e phases,. F i g u r e s
consequence of these according
trend,
"deoxidation
Phenomenon" i s a l s o a t t r i b u t e d to the r e a c t i o n (20).
also
the
(47-50).
From a c o n s i d e r a t i o n of these r e s u l t s
i s i n f e r r e d t h a t to a l i m i t e d extent the
r e a c t i o n induces
The
however,•changes g r a d u a l l y from
t o t a l oxygen a n a l y s i s a l s o r e f l e c t s the d e o x i d a t i o n
Figures
and
(20)
behavior
show t h a t the A l as a
i n t r o d u c e d i n t o the i n g o t s
s l a g i s decreased
The
then
but
role.
of the A l - d e o x i d i z e d i n g o t s izer is virtually
as a r e s u l t of the low
i n the s l a g
important
Once the oxygen p o t -
(50,52).
As a
r e a c t i o n s i n c l u s i o n s are p r e c i p i t a t e d
(140,144,147,148,216)
to:
187 m CaO + n A l 0 2
J
3
[m(CaO) « n ( A 1 0 ) ] i n c l u s i o n 2
(19)
3
or i n a more s p e c i f i c f o r m u l a t i o n : CaO
+ 6(A1 0 ) t 2
CaO-6Al 0
3
2
(19-a)
3
Since these r e a c t i o n products are i n e q u i l i b r i u m w i t h oxygen and s u l f u r according
then a s u l f i d e phase can be p r e c i p i t a t e d
(147, 148,197,210,215),. ' ' ' ' to: CaO
ic
+ [S] t
For low CaO content phases
ic
CaS
+ [0]
such as the C a O « 6 A l 0 , a 2
s u l f i d e phase such as the double s u l f i d e be
expected
3
(Mn, Ca)S should
t o (heterogeneously) p r e c i p i t a t e on o x i d e s .
Although very r a r e Ca,
(21)
when the s u l f i d e phase d i d not c o n t a i n
i t was f a c e t e d and c o n t a i n e d o n l y Mn and S.
Hence, i t
was c l e a r l y i d e n t i f i e d as MnS I I I . The
1020-M.S. i n g o t s i n t e r m i t t e n t l y d e o x i d i z e d with
the CaSi a l l o y have c l e a r l y r e c o n f i r m e d t h a t the d e o x i d a t i o n r e a c t i o n s are n o t e x c l u s i v e o f each o t h e r .
Instead a
c o o p e r a t i v e process between the d e o x i d i z e r , s l a g and l i q u i d metal takes p l a c e .
At a g i v e n d i s c r e t e
addition
of CaSi i n t o the s l a g i t s "FeO" content decreases, F i g u r e s (32) and (33).
Simultaneously t o t h i s change an increment
of A l i n the i n g o t and a decrement o f A l 0 ^ in. the s l a g 2
i s a l s o observed. reactions
As a r e s u l t of the above c o i n c i d e n t a l
a net change i n t o t a l oxygen content
which i s
a consequence of the i n c l u s i o n q u a n t i t i e s and compositions i s expected.
A r e d u c t i o n from 75 down t o 30 ppm was ob-
it r e p r e s e n t s a p e r i p h e r a l phase on i n c l u s i o n s
188 served. Another i n t e r e s t i n g f i n d i n g i s t h a t the r e d u c t i o n of t o t a l oxygen content was very dependent on the m e l t i n g conditions.
RII-W was melted under a i r w h i l s t RIII-W
was under an argon b l a n k e t .
The i n c l u s i o n phases
identified
i n t h i s experiment (RII-W and RIII-W) were e s s e n t i a l l y a-A^O^ and FeO-A^O^ as c l u s t e r s of s m a l l s p h e r i c a l p r e cipitates.
The samples c r i t i c a l l y
of d e o x i d i z e r — F i g u r e
a f f e c t e d by the a d d i t i o n s
(36)—showed Ca:Al r a t i o s
(at. %)
which c l o s e l y correspond to the f o r m a t i o n of the C a O « 6 A l 0 2
phase.
T h i s phase was m e t a l l o g r a p h i c a l l y i d e n t i f i e d
3
be-
cause of i t s f a c e t e d hexagonal appearance and i t s p e r i p h e r a l envelope of ( C a , M n ) S
( 1 5
'
9 4
'
1 4 5
'
2 0 3
'
2 1 0 )
.
The a - A l 0 2
the F e O A ^ O ^ were observed c l o s e r t o the and they were a s s o c i a t e d with
FeO
3
and
additions
(Mn,Fe)S or MnS I I .
The s e r i e s of f i n d i n g s from the c o n t i n u o u s l y CaSi deo x i d i z e d i n g o t s remelted through the CaF -Al 0.j-CaO s l a g 2
i n the 200 mm
2
diameter moulds can be condensed as f o l l o w s .
The s l a g chemical a n a l y s i s have s h o w n — F i g u r e s
(60) and
(61)-^that as the degree o f d e o x i d a t i o n i s i n c r e a s e d
the
CaO content of the s l a g i s i n c r e a s e d w h i l e the A l i s decreased. decrement
Although the f l u o r i n e a n a l y s i s showed a s l i g h t suggesting the formation o f v o l a t i l e
by r e a c t i o n s
fluorides
(8 to 10), the major changes, however, were
189 due to the r e a c t i o n between the d e o x i d i z e r and the s l a g . The "FeO' Content of the s l a g was g r a d u a l l y reduced
as the
1
d e o x i d a t i o n r a t e s were i n c r e a s e d . changes are adequately (FeO) t
[Ca] +
The i n i t i a l
d e s c r i b e d by the f o l l o w i n g r e a c t i o n s :
Fe(1) + (CaO)
2[A1] + 3(FeO) t
(12-v)
3Fe(l) + ( A l 0 ) 2
(12-iv)
3
At t h i s degree of d e o x i d a t i o n of the s l a g i n c l u s i o n s and MnS cipitated. increased observed,
deoxidation
alumina type of
I I were v i r t u a l l y the only phases p r e -
As the l e v e l of d e o x i d a t i o n i n the s l a g
was
Ca-aluminates with i n c r e a s i n g CaO-content were Figures
(58,59) and
(66 ,67). The i n c l u s i o n chem-
i c a l a n a l y s i s r e v e a l e d the f o l l o w i n g p r e c i p i t a t i o n s e quence:
a-Al 0 , 2
3
CaO«6Al 0 , CaO«2Al 0 , CaO«Al 0 2
traces of 12Ca0«7Al 0 2
(^0.2
wt
"FeO").
a t i o n o f segregates
3
3
2
3
2
3
and
a t extreme degrees o f d e o x i d a t i o n
Beyond t h i s d e o x i d a t i o n l e v e l the forme n r i c h e d i n Ca, A l , S i (and Mn)
formation o f ( A l , Ca)S were seen.
These s u l f i d e s showed
(EPMA a n a l y s i s ) t h a t the A l ( A l 0 ) although 2
and the
3
i n very
amounts was p r e f e r e n t i a l l y l o c a t e d i n the i n c l u s i o n
low core.
C o i n c i d e n t a l to the p r e c i p i t a t i o n o f the oxide phases a s u l f i d e phase, which was e n r i c h e d i n c a l c i u m p r o p o r t i o n a l to the amount o f CaO i n the Ca-aluminate phase served.
was
ob-
These a n a l y s i s l e a d to the c o n c l u s i o n t h a t the
mechanism by which the d e o x i d a t i o n - p r e c i p i t a t i o n occurs
is
190 as f o l l o w s : reached
once the l e v e l of the "FeO"
i t s minimum
the t r a n s p o r t of aluminum and
i n t o the l i q u i d p o o l 3[Ca] takes p l a c e .
2
3
2[A1]
+
calcium
(CaO)
(20-c)
Thus, the l e v e l s of d e o x i d a t i o n are
t i o n a l to the amount of A l and to the amount of CaO ratios).
has
by:
(A1 0 ) t
+
i n the s l a g
propor-
S i i n the i n g o t and
i n the i n c l u s i o n phases
also
(i.e.
Ca:Al
Hence the p r e c i p i t a t i o n sequence, i n terms of
the degree of d e o x i d a t i o n
i s as f o l l o w s :
i n the absence
of or a t very low d e o x i d a t i o n r a t e s i n a c o n v e n t i o n a l ( i n dustrial)
C a F - A l 0 - C a O s l a g , the p r e c i p i t a t i o n i s gov2
2
erned
by:
2[A1]
+ 4[0] + Fe
2[A1]
+ 3[0] =
The
3
(24)
(A1 0 ) i n c l u s i o n
(11-ii)
former oxide
(Mn,Fe)S or MnS or MnS
3
=
2
(FeO«Al 0 ) i n c l u s i o n 2
3
(Fe0*Al 0 ) 2
II.
3
i s u s u a l l y a s s o c i a t e d wi th
With the l a t t e r oxide
I I I are u s u a l l y observed.
(a-Al 0 )
The degree of
2
3
MnS
II
(Al) de-
o x i d a t i o n d i c t a t e s the f o r m a t i o n of a s p e c i f i c s u l f i d e .
At
i n t e r m e d i a t e d e o x i d a t i o n l e v e l s the r e a c t i o n (20-c) s t a r t s to operate
a c c o r d i n g to r e a c t i o n (19) or
(19a).
191 T h i s p a r t i c u l a r oxide phase w i t h e i t h e r MnS
I I I or
a d d i t i o n to r e a c t i o n
2
(Ca,Mn)S.
(20-c)
[Ca] + MnS was
(CaO«6Al 0 ) was
commonly
3
observed
Hence suggesting t h a t i n
the f o l l o w i n g r e a c t i o n CaS
t
+
[Mn]
(25)
also taking place. At r e l a t i v e l y h i g h d e o x i d a t i o n l e v e l s , where the r e -
action
(20-c) e n t i r e l y c o n t r o l s the t r a n s p o r t of d e o x i d i z e r s
i n the melt and when very low reached
"FeO"
content i n the s l a g i s
the p r e c i p i t a t i n g phases are C a O « 2 A l 0 2
(CaMn)S or CaS
and C a O « A l 0 2
These l a t t e r two envelope
of CaS.
f i d e s ) suggests aluminates
and
3
3
with
either
12CaO«7Al 0 . 3
3
oxide phases were surrounded
T h i s mixture of phases (oxide and
by
an
sul-
t h a t the c a l c i u m oxide from the c a l c i u m
s t r o n g l y i n t e r a c t s w i t h the s u l f u r and oxygen
i n s o l u t i o n according to: (CaO)* +
[S] =
T h i s r e a c t i o n generated
(CaS)* + a CaS
minimum oxygen content was F i n a l l y , a t extremely CaO:Al 0 2
shifted,
3
[0]
(21)
e n r i c h e d phase wherever the
reached
(^20-30
ppm).
h i g h d e o x i d a t i o n r a t e s where the
r a t i o i n the s l a g i s d r a s t i c a l l y and
suddenly
the f o r m a t i o n of s m a l l segregates e n r i c h e d i n Ca,
A l and S i can o c c u r .
Under these d e o x i d a t i o n c o n d i t i o n s
192 the f o r m a t i o n of Si-phase
(Al,Ca)S and
around the CaS
a p e r i p h e r a l envelope of
(which surrounds the
aluminate) were a l s o observed. w i t h 4 340
and
rotor
calcium
S i m i l a r r e s u l t s were obtained
(Cr-Mo-V) s t e e l s .
This allows
the
f o r m u l a t i o n of a comprehensive mechanism d i s c u s s e d i n the next s e c t i o n . I t i s worthwhile t o mention t h a t while t h e r e are some , . (151,153, 157,214,221,235,236) . . .^ . . advantages • ' • ' • ' ' ' to p r e c i p i t a t i n g aluminates shape and and
e n r i c h e d on c a l c i u m oxide t h e i r CaS
(because of t h e i r
round
envelope) i n s t e a d of the alumina g a l a x i e s
the manganese s u l f i d e s
the c o i n c i d e n t a l t r a n s p o r t of
aluminum i n t o the r e f i n e d i n g o t c o n s t i t u t e s a p o t e n t i a l problem.
T h i s behavior
j e c t i o n processes X[Ca]
+ Y(Al 0 ) 2
This r e a c t i o n
3
can be r e p r e s e n t e d
(210)
i n c l u s
, by: .
o n
ixCaO(Y-f)
as H o l a p p a *
ent to r e a c t i o n (20-c). i s used
as i n the c a l c i u m i n -
2 1 0
^
A l ^ + § X(A1)
has p o i n t e d out
(20-b)
i s equival-
Thus, i f an excess of d e o x i d i z e r
(CaSi)
A l i s i n t r o d u c e d i n the melt and hence the p o t e n t i a l • (221-223)
to reduce the mechanical p r o p e r t i e s i s enhanced
5.3.4
Comprehensive D i s c u s s i o n on the D e o x i d a t i o n When A l or Ca i s added to the ESR-slag as a
i t becomes p a r t of a r e a c t i o n scheme r e p r e s e n t e d
Mechanism deoxidant,
by:
193 [Ca] + 2[A1]
(FeO)
%
Fe(l) +
(CaO)
+ 3(FeO) + F e ( l ) + A l 0 2
3[Ca] +
( A 1 0 ) % 2[Al] 2
3
(12-v) (12-iv)
3
+ 3(CaO)
(20-C)
At high l e v e l s of "FeO", r e a c t i o n s (12-v) and dominate
l e a d i n g to a simple d e o x i d a t i o n scheme
the deoxidant a d d i t i o n appears component. over
(12-iv) w i l l prewhich
as the a p p r o p r i a t e s l a g oxide
At low l e v e l s of "FeO"
(12-v) and
in
reaction
(20-c) w i l l
(12-iv) and i t w i l l be observed
take
t h a t an
ex-
(46 47 change r e a c t i o n
( s i m i l a r to those a l r e a d y r e p o r t e d
'
52 '
'
54) for
S i / A l and T i / A l ) i n which the a l l o y Ca:Al r a t i o i n
the i n g o t w i l l be determined by the CaO:Al20 s l a g low i n s i l i c a ,
( l e s s than 10 wt.
% S i 0 ) , not by the 2
r a t e , form or composition o f the deoxidant. the p o i n t a t which r e a c t i o n s (12-v) and way
r a t i o i n the
3
In determining
(12-iv) w i l l g i v e
t o (20-c) i n the sense of producing i n g o t composition,
the l e v e l of s l a g F e O - a c t i v i t y i s e v i d e n t l y of prime ance.
I t i s more important than the i n t r i n s i c
e l e c t r o d e chemical composition. slag
import-
s l a g and
the
At low F e O - a c t i v i t y i n the
i f l a r g e q u a n t i t i e s of Ca are added as a d e o x i d i z e r ,
the r e s u l t
i n a c o n v e n t i o n a l ESR-slag composition
be a c o r r e s p o n d i n g i n c r e a s e i n the a l l o y A l l e v e l , reaction
(20-c).
will through
194 In order to i l l u s t r a t e the r o l e o f r e a c t i o n s (12-v) to
(12-iv) the r e s u l t s o b t a i n e d from the 4 340
selected
i n g o t were
as the p r o t o t y p e o f the g e n e r a l behavior
approach t h i s d i s c u s s i o n .
to
The d e o x i d a t i o n sequence
in
terms o f the chemical composition of the i n g o t and the s l a g are shown i n F i g u r e s (70) and (71). A p p l y i n g a mass balance to t h i s i n g o t and the s l a g , i t i s apparent addition
(from the d e o x i d i z e r ) , appears
t h a t the s i l i c o n
almost q u a n t i t a t -
i v e l y i n the i n g o t
with very l i t t l e
I t i s a l s o observed
t h a t the c o n c e n t r a t i o n o f A ^ O ^ i n
the s l a g decreases
w h i l e the CaO content
p a r t o f the t o t a l Ca content) data
o f S i C ^ t o the s l a g .
increases.
(represented as a Utilizing
this
i n c o n j u n c t i o n with the i n c r e a s e d A l assay o f the
i n g o t l e a d s to an e x c e l l e n t c l o s u r e o f a mass balance drawn on the system u s i n g equation
(20-c).
In consequence, i f
the f o l l o w i n g s t o i c h i o m e t r i c r e l a t i o n s h i p *
^
2 1 0
which r e -
l a t e s the r e d u c t i o n o f alumina by Ca i n the chemical
comp-
o s i t i o n o f the i n c l u s i o n s , X[Ca]
+ Y(Al 0,). , t z J inclusion o
XCaO-(Y - *-) A l 0 , + \ X[A1] J z 6 s o
(20-b) is u t i l i z e d
t o perform the balance, e q u i v a l e n t r e s u l t s and
a very c l o s e p r e d i c t i o n o f the i n c l u s i o n chemical i s obtained.
composition
These r e s u l t s are taken as a s t r o n g evidence
t h a t the c a l c i u m component o f the CaSi a l l o y a d d i t i o n has r e duced A ^ O ^
from
s l a g , f o l l o w i n g (20C) producing A l i n the
195 i n g o t and l e a d i n g to a CaO
i n c r e a s e i n the s l a g .
d u c t i o n i s s t o i c h i o m e t r i c , as would be 210
expected'
4 7
'
1 4 8 ,
216) '
from an e q u i l i b r i u m a n a l y s i s of
process of r e f i n i n g , as expected ' ' l e v e l i n the s l a g remained 0.1
This re-
- 0.2
wt.
2 7
'
3 8
(20) .
'^ ' 7
8 2
During
^
a t low but f i n i t e
the
the
"FeO"
l e v e l of
%, F i g u r e (73).
These r e s u l t s l e a d to the c o n c l u s i o n t h a t a t an 'FeO" a c t i v i t y c o r r e s p o n d i n g to approximately 0.1 in t h i s slag
(50/30/20),
- 0.2
the r e a c t i o n of A l 0 2
wt.
%
to g i v e an
3
i n c r e a s e i n the i n g o t w i l l take p l a c e i f c a l c i u m i s used as a deoxidant.
When e i t h e r A l or aluminum s i l i c o n
used as deoxidant at e q u i v a l e n t r a t e s , i t was the s l a g "FeO"concentration was Figures
(39, 40) and
was
observed
again h e l d a t low
that
levels—
(45,46) and Tables XII and X I I I
(a-c)
— a n d t h a t both A l and S i were q u a n t i t a t i v e l y t r a n s f e r r e d to ... . . . , . ,(147, 148,210,216) the i n g o t .
T h i s r e s u l t i s to be expected
from r e a c t i o n
'
'
(20-C) as o n l y a very s l i g h t degree of alum-
inum r e d u c t i o n of Ca from CaO would a r i s e from
reaction
(20-C), producing composition changes not d e t e c t a b l e w i t h i n the accuracy o f t h i s mass balance. c l u s i o n compositions
The behavior of the i n -
i s a more s e n s i t i v e guide than the
mass balance i n r e l a t i o n to the Ca/Al exchange r e a c t i o n i n the s l a g .
The Ca:Al r a t i o i n the oxide phase and
the
p a r t i a l s u b s t i t u t i o n of Mn by Ca i n the s u l f i d e phase i n i n c l u s i o n s i n A l - d e o x i d i z e d i n g o t s — F i g u r e s (43,44) and 52)--as w e l l as the Ca:Al r a t i o i n the oxide
(51,
(inclusion)
196 phases and t h e i r p r o p o r t i o n a l amounts of CaS
i n the CaSi
and i n the A l - S i based d e o x i d i z e d i n g o t s — F i g u r e s (66,67),
(71,75) and F i g u r e
( 7 6 ) — i n d e e d monitor
(58,59),
the magni-
tude and d i r e c t i o n of the e q u i l i b r i u m d i c t a t e d by r e a c t i o n s (20-b,c). F i g u r e 4340 i n g o t
(74)
which shows the behavior of the
shows t h a t the Ca:Al r a t i o i n the oxide i n -
c l u s i o n s r i s e s r a p i d l y to a c o n s t a n t value which i s a p p r o x i mately may
equal t o a composition CaD'A^O^.
These r e s u l t s
be compared to those r e p o r t e d f o r c a l c i u m i n j e c t i o n
processes
(144
'
148
'
154
'
steelmaking p r o c e s s '
157) 4 0 , 2 0 6
and f o r the b a s i c e l e c t r i c arc ^
p a r t i c u l a r l y those shown i n
(178) Figure
(78)
where an e q u i v a l e n t l y l o w - s u l f u r s t e e l shows
the same b e h a v i o r .
F a u l r i n g and R a m a l i n g a m * ^ 21
s t u d i e d the r e l a t i o n s beween CaO oxide i n c l u s i o n s i n t h i s system. r e p r e s e n t e d by the p r e c i p i t a t i o n shown i n F i g u r e (11).
and A^O^
have
i n generating
T h e i r c o n c l u s i o n s are ( e q u i l i b r i u m ) phase diagram
When the Ca a c t i v i t y i s estimated
i n the ESR s l a g / m e t a l system f o l l o w i n g r e a c t i o n (20-c), (234 ) (19 8) u s i n g the data of Rein e t a l . and S p o n s e l l e r and F l i n n and assuming t h a t C a F v i t y of h
(_a
= 6.7
2
x 10
a c t s as an i n e r t d i l u e n t , an —8
a t 0.1
wt.%
acti-
A l i s obtained.
This
c o n c l u s i o n would i n d i c a t e from F a u l r i n g ' s data, F i g u r e (11), t h a t one
should observe an i n c l u s i o n composition c l o s e t o
CaO-A^O^/ which i s indeed the case.
I t i s c l e a r , there-
f o r e , t h a t i n s p i t e of an e x c e s s i v e l y h i g h a d d i t i o n of
197
calcium
('vlO kg/ton)
, the i n c l u s i o n composition i s
c o n t r o l l e d e n t i r e l y by r e a c t i o n
(20-c) and t h a t i n c l u s i o n
c a l c i u m contents w i l l not r i s e above those p e r m i t t e d by reaction
( 2 0 - c ) , d e s p i t e the c a l c i u m a d d i t i o n .
teresting dition,
It i s i n -
to note a l s o t h a t a t t h i s l e v e l o f c a l c i u m ad-
the s u l f i d e i n c l u s i o n
surrounding the c a l c i u m a l -
uminates were e x c l u s i v e l y composed of CaS not MnS.
This
f i n d i n g can a l s o be compared t o those r e p o r t e d i n (Ca,CaO) i n j e c t i o n p r o c e s s e s i n A l d e o x i d i z e d melts of r e l a t i v e l y low oxygen a c t i v i t y , where the p r e c i p i t a t i o n
o f e i t h e r MnS
c i p i t a t i o n o f aluminates ls
, ,
ui
p h e r a l double 19 7
i n c i p i e n t amounts o f Ca induce o
4-
r
n e
pre-
(low i n CaO content) with a p e r i -
/„
sulfide,
m ' ^ " ' ^ ^
„ ^ ( 1 4 0 , 144, 146,153, 159, 160,
(Mn,Ca)S
'
212)
'
'.
T h i s t r a n s i t i o n i s o b v i o u s l y d i c t a t e d by: MnS
and i t i s expected
+ [Ca]
.
•
(25)
t o occur when the Ca i n the melt i s ap-
p r o x i m a t e l y 5-10 ppm. N
CaS + [Mn]
t
At h i g h e r l e v e l s of Ca, the s u l -
. ,(140, 144, 146,147, 153,157,211,216)
f i d e phase i s expected
•
'
•
'
'
'
•
.
to
be r u l e d by: * CaO
* + [S]
and hence p r e c i p i t a t i n g or pure CaS. the observed
t
CaS
+ [0]
a p e r i p h e r a l s u l f i d e , namely
(21)
(Mn,Ca)S
In the case o f d e o x i d a t i o n with the A l S i
alloy,
changes i n s l a g composition were almost e q u i -
198
v a l e n t t o the C a S i , the o n l y change being a s l i g h t i n c r e a s e i n both S i C ^ and Al^O^ a t low "FeO" Table
(XII).
The observed
of Ca-aluminates about 5-7%
l e v e l s i n the
i n c l u s i o n composition was
c o n t a i n i n g approximately
S as CaS
slag, that
20-30% CaO
and
i n t h e i r p e r i p h e r y , F i g u r e (76).
These
f i n d i n g s i n d i c a t e t h a t s i n c e the e q u i l i b r i u m p o s i t i o n of reaction
(20-c) r e s u l t s i n r e d u c t i o n of CaO
by A l , the
t o t a l mass of Ca c a r r i e d i n t o the metal by t h i s means w i t h the A I S i a l l o y i s s i m i l a r t o t h a t i n the CaSi and " h y p e r c a l " case, F i g u r e (76).
the
The e q u i l i b r i u m r a t i o s of
Ca:Al r e p o r t e d by F a u l r i n g and R a m a l i n g a m ^ ^
hence are
2 l
r
a t t a i n e d by the C a S i , " h y p e r c a l " and the A I S i a l l o y .
The
chemical r e s u l t of d e o x i d a t i o n by A I S i and the " h y p e r c a l " a l l o y i n r e s p e c t of i n g o t composition i s t h e r e f o r e v i r t u a l l y i d e n t i c a l w i t h t h a t o b t a i n e d by c o n v e n t i o n a l CaSi d e o x i d a t i o n a t about the same r a t e .
It i s interest-
i n g t o note t h a t aluminum d e o x i d a t i o n f o l l o w s a p a t t e r n f a m i l i a r from e l e c t r i c furnace p r a c t i c e . aluminum d e o x i d a t i o n a t the p r e s e n t l e v e l s
In the case of (10 k g / t o n ) , a
range of A l content i s achieved i n the i n g o t as shown i n Figure
(71).
The
corresponding l i q u i d and s o l i d i n g o t
oxygen a n a l y s i s are shown i n F i g u r e (72 a-b)
where i t can
be seen t h a t the minimum oxygen content i s a t 0.1 wt% A l .
T h i s minimum i s a t the composition (175
Figure 2
(10) J
expected,
177) '
, from a c o n s i d e r a t i o n of
[Al] + 3 [0] t
1
approximately
1
J
(Al 0-,) . i . ' 2 3 inclusion o
(11-ii)
199 u s i n g the compiled
i n f o r m a t i o n by G u s t a f f s o n and
Melberg
(175)
Al Figure
(10), f o r e
proximately
a t an e q u i l i b r i u m temperature of
Q
ap-
1600°C.
I t can t h e r e f o r e , be assumed t h a t the d e o x i d a t i o n p r e c i p i t a t i o n of i n c l u s i o n s are c l o s e l y e q u i v a l e n t to e s t a b l i s h e d i n the e l e c t r i c 5.3.5
furnace'
4 0 , 2 0 6
and
those
^.
F i n a l Remarks I t i s important
to emphasize t h a t an inadequate
o x i d a t i o n o f a ESR-melt w i t h A l or Ca-bearing becomes very important properly adjusted.
de-
deoxidants
where ever the aluminate-CaS i s not
The A l d e o x i d a t i o n or the l a c k of
CaSi d e o x i d a t i o n seen as generators
of alumina g a l a x i e s or as
(133) i n d u c e r s of "burning"
or the excess
a l l o y s , because of the excess through r e a c t i o n (15 a-b)
of A l , A l S i or CaSi
of A l i n i n g o t s i n t r o d u c e d
c o n s t i t u t e a p o t e n t i a l source of
sul-
f i d e s and n i t r i d e s and hence to a d e g r a d a t i o n of mechanical (221-223) properties
of the r e f i n e d i n g o t s .
Hence, the f i n a l remarks, the l a t t e r s e t of q u e s t i o n s i)
ESR-deoxidation
which at the same time answer
to be drawn a r e :
w i t h Ca w i l l f o l l o w the r e a c t i o n
(20-c) a t low oxygen p o t e n t i a l s , i . e . below 0.2 ii)
s l a g "FeO"
contents
wt.%; At i n t e r m e d i a t e oxygen p o t e n t i a l s
( s l a g "FeO"
ranging between 0.4-0.6 wt,%), the d e o x i d a t i o n process e i t h e r A l or Ca i s e q u i v a l e n t and
content using
serves o n l y to c o n t r o l
the s l a g composition.
This l a t t e r
f a c t o r w i l l t h e r e f o r e de-
termine the c h o i c e o f deoxidant; iii)
Deoxidation
w i t h A l w i l l a l s o f o l l o w the r e a c t i o n
(20-c) but w i l l not reach the p r e d i c t e d i n g o t Ca:Al due
t o unfavorable
a carrier
k i n e t i c f a c t o r s , unless
ratio
S i i s added as
f o r Ca;
i v ) The maximum S i C ^ content
i n the s l a g f o r e f f i c i e n t
d e o x i d a t i o n through r e a c t i o n ( 1 2 - v ) , ( 1 2 - i v ) , and ( 2 0 - c ) ; i s l e s s than
10 wt. %;
v) The chemistry r o l e i n the d e o x i d a t i o n (low)
o f the e l e c t r o d e does not p l a y a ( r e a c t i o n ) scheme u n l e s s
d e o x i d a t i o n r a t e s a r e used, i . e .
inappropriate
sacrificial
elect-
rode d e o x i d a t i o n which leads t o change the ESR s l a g or i n g o t composition; v i ) E x c e s s i v e and/or abrupt
d e o x i d a t i o n can l e a d t o
d e l e t e r i o u s mechanical p r o p e r t i e s , i . e . h i g h l e v e l s o f A l or d e o x i d i z e r s
i n i n t r o d u c t i o n of
(as s m a l l segregates) i n
the ESR i n g o t ; and v i i ) The shape o f i n c l u s i o n s depends upon the type and degree o f d e o x i d a t i o n :
1) i n A l d e o x i d i z e d i n g o t s s p h e r i c a l
s i n g l e o r c l u s t e r s o f alumina phases
( a - A l ^ ^ and FeO'A^O^)
a s s o c i a t e d w i t h manganese s u l f i d e s are found a t r e l a t i v e l y low deoxidation inates
l e v e l s and f a c e t e d aluminates
and low c a l c i u m alum-
(CaO-eA^O-j) as s i n g l e o r c l u s t e r s a t r e l a t i v e l y
deoxidation rates.
2) i n C a S i ,
high
"hypercal" or AISi deoxidized
201 ingots, faceted calcium
(a-Al 0 2
3
and C a O 6 A l 0 ) and s i n g l e s p h e r i c a l 2
3
aluminates ( C a O * 2 A l 0 , C a O « A l 0 2
3
2
3
and
12CaO«7Al 0 )
w i t h p e r i p h e r a l s u l f i d e s are found at r e l a t i v e l y low and deoxidation
rates respectively.
2
3
high
202 5.4
F i n d i n g s and D i s c u s s i o n Related t o the T h i r d Question
5.4.1
D e s c r i p t i o n of Experimental
5.4.1.1
The I n c l u s i o n Mean Diameter Tables
Results
(XIV a-b) show the standard i n f o r m a t i o n drawn
from the i n c l u s i o n
(EPMA) a n a l y s i s .
As p r e v i o u s l y d e s c r i b e d ,
a minimum o f twenty and a maximum o f 40 s i n g l e analyses were performed i n each sample.
S o l i d i n g o t samples 2.5 x 2.5 cm
i n area and l i q u i d p o o l samples approximately
2
75% o f t h i s
area were s y s t e m a t i c a l l y analyzed. Analyses were performed i n l o n g i t u d i n a l and t r a n s v e r s a l d i r e c t i o n s i n both
types
of samples. The mean i n c l u s i o n diameter Figures The
was s t a t i s t i c a l l y
obtained.
(79 a,b) show an example o f each type of sample.
linearity
shown i n these graphs c l e a r l y i n d i c a t e s t h a t
the s i z e o f i n c l u s i o n s i s r e p r e s e n t e d by a normal d i s t r i b u t i o n . The
c o r r e l a t i o n c o e f f i c i e n t s ranged from 0.97 t o 0.99 which
are e x c e l l e n t f o r the p a r t i c l e s i z e found. information
Based on t h i s
p l o t s o f mean i n c l u s i o n diameter,
50% o f the cumulative
frequency,
given as the
a g a i n s t i n g o t h e i g h t (or
d e o x i d a t i o n l e v e l s ) were o b t a i n e d .
To c o r r e l a t e t h i s
inform-
a t i o n to the d e o x i d a t i o n b e h a v i o r , these f i n d i n g s are a l s o p l o t t e d along w i t h the t o t a l oxygen a n a l y s i s from both of
samples.
types
203 5.4.1.2
F i n d i n g s from I n d i v i d u a l Experiments The
as RII-W
Figure
( 36 ) which corresponds t o i n g o t
labelled
i n which the CaSi was d i s c r e t e l y added, shows t h a t
the i n c l u s i o n average s i z e depends s t r o n g l y on the d e o x i d a t i o n practice.
T h i s p l o t c l e a r l y shows t h a t c o i n c i d e n t a l to the
l a r g e s t Ca:Al r a t i o s i n i n c l u s i o n s
the s m a l l e s t mean i n -
c l u s i o n s i z e i s found. The Figure with
behavior
corresponding
t o R I I - I l i s shown i n
(41). T h i s shows t h a t the mean i n c l u s i o n s i z e v a r i e s
the t o t a l oxygen content.
a t low d e o x i d a t i o n
T h i s graph a l s o shows t h a t
r a t e s (3.60 and 6.1 kg ton ^ ) , the i n -
c l u s i o n s i z e of samples from the l i q u i d p o o l are s m a l l e r the ones from the i n g o t .
At moderate and high
l e v e l s , however, the opposite
behavior
deoxidation
i s observed.
ference i n average s i z e i s approximately 1 pm.
(43)—also
behavior.
Findings
from
RII-I2 a r e shown i n F i g u r e (42).
Since t h i s i n g o t was d e o x i d i z e d than R I I - I l
The d i f -
Vari-
a t i o n s i n the Ca:Al r a t i o s i n i n c l u s i o n s — F i g u r e reflect this
than
by lower A l - a d d i t i o n r a t e s
the mean i n c l u s i o n diameter i n samples from
i n g o t and l i q u i d p o o l were almost e q u i v a l e n t .
The average
Ca:Al r a t i o s o f i n c l u s i o n s i n t h i s i n g o t a l s o changed i n an e q u i v a l e n t manner, F i g u r e (44). The
i n g o t i d e n t i f i e d as R I I I - I l , which was CaSi de-
oxidized,
i n some r e s p e c t behaved as RII-I2.
Variations in
the Ca:Al r a t i o s i n i n c l u s i o n s and oxygen contents are a l s o r e f l e c t e d i n the mean s i z e o f i n c l u s i o n s .
It i s
important t o note t h a t the CaSi a d d i t i o n r a t e s were almost e q u i v a l e n t from one t o the other and g r a d u a l l y i n c r e a s e d during r e f i n i n g , Figures
(56 a-b) and
(58).
RIII-I2 used an e q u i v a l e n t d e o x i d a t i o n procedure to RIII-Il.
R I I I - I 2 , however, was r e f i n e d under d i f f e r e n t de-
o x i d a t i o n regimes.
The three lowest CaSi a d d i t i o n s were
added i n s h o r t e r p e r i o d s o f time a t the bottom o f RIII-I2, w h i l e the f o u r t h l e v e l of a d d i t i o n s (22.4 4 kg t o n ^) was much longer than i n R I I I - I l . unmistakenly
In t h i s experiment,
i t is
shown t h a t i n c l u s i o n s from l i q u i d p o o l , a t
moderate and h i g h e r CaSi a d d i t i o n s , a r e l a r g e r i n s i z e the ones from the i n g o t .
The Ca:Al r a t i o s , the t o t a l oxygen
content as w e l l as the mean i n c l u s i o n
diameters behaved i n
e x a c t l y the same way as R I I - I l , F i g u r e s 57(a-b) and Finally,
than
(59).
Ingot 4340 which was CaSi d e o x i d i z e d shows
the same p a t t e r n , i n terms o f t o t a l oxygen a n a l y s i s , r a t i o s and p a r t i c l e s i z e s , as RII-I2 (72 a,b) and (74a,b).
Ca:Al
and R I I I - I l , F i g u r e s
205 5.4.1.3
Complementary S t u d i e s To gain a b e t t e r understanding about i n c l u s i o n
a t i o n and growth and
to e l u c i d a t e whether the
mechanism operates
under the ESR-conditions
of experiments was
performed.
form-
flotation one more s e t
Samples were sucked
from
the l i q u i d p o o l i n t o s i l i c a tubes which contained e i t h e r a mishmetal or Zr w i r e .
R e f i n i n g was
and at a constant d e o x i d a t i o n r a t e A I S i or C a S i ) . of i n c l u s i o n s
c a r r i e d out under argon (10 kg/ton of e i t h e r
Three major areas, i n terms of the were i d e n t i f i e d
i n these samples.
composition Regions
where i n c l u s i o n s were mainly c o n s t i t u t e d by e i t h e r r a r e e a r t h or z i r c o n i u m e n r i c h e d phases.
A r e g i o n where the Zr o r the
r a r e e a r t h phases were mixed w i t h complex C a - A l - s i l i c a t e s and a r e g i o n where a mixture few
of pure Ca-aluminates and
very
i n c l u s i o n s with p e r i p h e r a l r a r e e a r t h or z i r c o n i u m
s u l f i d e phases were i d e n t i f i e d . c l u s i o n s i s shown i n F i g u r e s
T h i s l a t t e r type of i n -
(80,81) and
(82,83) where
the composition maps f o r A l , Ca,Ce, La, S and i s very important as much as 7-10%
Zr are g i v e n .
to emphasize t h a t t h i s type accounted of the t o t a l amount of i n c l u s i o n s
for
analyzed
(40-50) i n each sample. M e t a l l o g r a p h i c a n a l y s i s on specimens o b t a i n e d from l i q u i d pools
(1020
and 4340)show t h a t a c o n s i d e r a b l e amount
It
of i n c l u s i o n s was found c l o s e t o the w a l l of the s i l i c a
206 tube.
Most of them, however, were l o c a t e d i n i n t e r d e n d r i t i c r e g i o n s and o n l y approximately 5-7% were trapped by primary d e n d r i t e s , Figures
(85) and (86).
207 5.4.1.4
Summary of Experimental F i n d i n g s
In o r d e r to approach
the answer
q u e s t i o n a summary of f i n d i n g s , size,
( d i s c u s s i o n ) to t h i s
i n terms of 1) i n c l u s i o n mean
2) i n c l u s i o n composition and 3) t o t a l oxygen a n a l y s i s ,
i s presented. 1)
-
I n c l u s i o n s i z e d i s t r i b u t i o n s obey the normal bution 0.96
(the c o r r e l a t i o n c o e f f i c i e n t ranged
distri-
from
- 0.99) .
The mean i n c l u s i o n diameter was The average
approximately 6-8
ym.
i n c l u s i o n s i z e i n c r e a s e s approximately
1 ym i n diameter i n both types of samples
(ingot
and l i q u i d pool) as the d e o x i d a t i o n r a t e i s i n creased. In i n g o t heads (CaSi d e o x i d i z e d ) some i n c l u s i o n s were seen as l a r g e as 30 ym i n samples e x t r a c t e d from l i q u i d p o o l s and t h i s s i z e was
very r a r e l y seen i n
the i n g o t . The
i n c l u s i o n d e n s i t y , number of i n c l u s i o n s per a r e a ,
i s g r a d u a l l y i n c r e a s e d from the c e n t e r t o the mould wall.
T h i s f a c t was
accentuated i n CaSi d e o x i d i z e d
ingots. 2)
-
Calcium aluminates were almost always observed to c o n t a i n a core e n r i c h e d i n alumina
( i . e . A l by EPMA).
208 The
Ca:Al r a t i o s i n i n c l u s i o n s i s almost always smaller
i n samples e x t r a c t e d from l i q u i d p o o l s than from i n g o t s The p e r i p h e r a l S content
as CaS
i s p r o p o r t i o n a l to
the Ca:Al r a t i o s i n the c a l c i u m e n r i c h e d
aluminate
phases. At r e l a t i v e l y l a r g e d e o x i d a t i o n r a t e s the formation of segregates ( A l , Ca and
Si) was
enriched i n deoxidizers
observed.
r e c a l l t h a t these segregates
(^10-12 kg/ton)
I t i s important
to
were commonly seen i n
samples e x t r a c t e d from the l i q u i d p o o l and very in ingots.
3)
-
The
They a l s o contained
some
mately 20
5.4.2
Mn.
average d i f f e r e n c e i n t o t a l oxygen content
samples e x t r a c t e d from l i q u i d p o o l and
rarely
between
ingot i s approxi-
ppm.
P r e c i p i t a t i o n of I n c l u s i o n s i n the Fe-Al-Ca-O-S(Mn) System By using F a u l r i n g ' s and
Tables
(IV) to
Ramalingham's d a t a ^
2 1
^
given i n
f
(VI), to c o n s t r u c t the Fe-Al-Ca-0 p r e c i p i -
t a t i o n diagram, c o n j o i n t l y with o b s e r v a t i o n s
of other
investi-
g a t o r s , p r e v i o u s l y d e s c r i b e d i n s e c t i o n s 2.3.5, 2.3.7.2 and 5.3.4, the p r e d i c t i o n of the p r e c i p i t a t i o n of the Ca-aluminate/ C a - s u l f i d e phases can be pursued a l i t t l e Fe-Al-Ca-0 system i s now
approached by
further.
I f the
superimposing
the
(CaS)
[0]
+
CaO
t
e q u i l i b r i u m to the Fe-Al-Ca-0 system,
+
(21)
[S]
system, as the Fe-Al-Ca-O-S
and care i s taken to c o n s i d e r the phase r u l e , a
diagram r e p r e s e n t i n g the p r e c i p i t a t i o n of
Ca-aluminates
and t h e i r corresponding s u l f i d e phases was c o n s t r u c t e d . The procedure used et a l . (
239
^
was
e q u i v a l e n t to t h a t used by Wilson
and F a u l r i n g e t a l .
efficients
.
The a c t i v i t y
[CaO-Al 0
f o r CaS i n e q u i l i b r i u m w i t h l i q u i d
( l i q u i d ) - C a S ( l i q u i d ) ] and
2
[CaO-CaS]solid were estimated N
(240
from Sharma's and R i c h a r d s o n s s i n v e s t i g a t i o n s (XV).
T h i s diagram based on Henrian a c t i v i t i e s i s
= 0.001,
A l
,
(1550° C) and was developed f o r l e v e l s of A l
isothermal (h
241) '
1
Table
co-
0.01 and 0.1)
i n the range of major i n t e r e s t .
The data generated from these e q u i l i b r i a i s summarized i n Table
(XV). The major r e a c t i o n s are g i v e n i n Appendix ( I ) .
Although the Fe-Al-Ca-O-S system was
exclusively
veloped as a four f o l d component e q u i l i b r i a , the MnS e q u i l i b r i u m with A^O^
• 4- •
•
n
-A
and the double ••'
u t i o n of Mn by Ca i n the MnS
in
[(Ca,Mn)S] s u l f i d e i s
-,(140,146,210)
i n t r i n s i c a l l y considered
de-
, .
,
.
The g r a d u a l s u b s t i t -
phase i s governed by the
fol-
lowing e q u i l i b r i u m : (MnS)*+ [Ca] t
(CaS)*+
[Mn ]
(25)
The presence of Ca i n s o l u t i o n i n the melt generates s e v e r a l transitions.
I n c i p i e n t amounts of Ca
o r i g i n a t e the
210 t r a n s i t i o n of MnS
I I to
(91
MnS
92
R e l a t i v e l y h i g h e r Ca contents double s u l f i d e s , e.g.
(Ca,Mn)S.
duced i n the melt i s i n c r e a s e d CaS
and MnS
appears' * ^. 4
between the f o r m a t i o n The
144)
i n the melt induce
I f the amount of Ca a m i s c i b i l i t y gap
This t r a n s i t i o n occurs
5
of the C a O ' e A ^ O ^ and
the
the
intro-
between the somewhere
CaO^A^O^.
s u l f i d e phase, as r e p o r t e d by s e v e r a l r e s e a r c h e r s
heterogeneously described)
and
Ca(Al)
is
p r e c i p i t a t e d on the oxide phases ( p r e v i o u s l y i t i s very dependent on the a c t i v i t y of the A l .
In p r e v i o u s d i s c u s s i o n s i t was
CaO
140
acknowledged t h a t as
d e o x i d a t i o n l e v e l i s i n c r e a s e d , the amount of Ca
i n the Ca-aluminate phase i s i n c r e a s e d by r e a c t i o n
and hence the amount of CaS and/or
(26).
The
produce pure CaS
phase i n c r e a s e s by
f a c t t h a t the i n j e c t i o n of CaO i s also considered.
the
as (20)
reactions
(25)
s l a g s do
As Saxena and
not
cowork-
(147 148 214) •' ' have r e p o r t e d , t h i s t r a n s i t i o n w i l l take p l a c e (144 153 a f t e r Ca-aluminates have formed. As s e v e r a l r e s e a r c h e r s ' ' 154,156 .185,197.211) . _ . . . .. . _ _ • • • ' work suggest, the p r e c i p i t a t i o n of pure CaS
ers
i s expected to occur once the Ca-content i n the melt oxygen l e v e l i s approximately
10-40
o s i t i o n i n the double s u l f i d e , to 50.0
wt.
(or the
ppm)
i s such t h a t a comp-
(Mn,Ca)S
i s g r e a t e r than 4 3.0
% (140,146)^
T h i s t r a n s i t i o n i s reached once the (202) CaO-A^O^ s t o i c h i o m e t r i c phase i s formed . O t o t a n i ' s and Kataura's r e s u l t s * ^ c o n f i r m K i e s s l i n g s and Westman s* ^^ 2 1 5
S a l t e r and
1
(140) Pickering's
r e p o r t a "pure" CaS
v /
and
Church's
phase a f t e r the
(159) ' findings.
" A l 0 " content 2
3
14
They
i n the
Ca-aluminates i s reduced by Ca to approximately i s also r e p o r t e d ' ^
t h a t once t h i s p e r c e n t
1
i s reached a sharp increment i n the CaS
40.0%.
of CaO
It
(40.0%)
i s noted.
A schematic r e p r e s e n t a t i o n of the above d e s c r i p t i o n i s shown i n F i g u r e thermal
(87).
(1823K) and
This Figure
prehensive h ^ A
(h
g
= h
A l
manner the h ^ t h ^
= 0.001, 0.01
and
I I - I I I , the Ca-aluminates 2
3
and
0.1)
(88) and
(89). A^O^/ and
5.4.3.1
N u c l e a t i o n , Growth and
Results F l o t a t i o n of
d i f f e r e n c e i n the mean diameter
from l i q u i d p o o l and
(1-3
Inclusions ym)
of i n c l u s i o n s
from i n g o t s i n d i c a t e s t h a t the
mechanism i n the ESR-conditions under which t h i s behavior was
operate.
The
d i s p l a y e d were:
flotation
conditions a) when the
d i f f e r e n c e i n t o t a l oxygen content between the l i q u i d i n g o t s i s g r e a t e r than 20 ppm
g r a d u a l and c l u s i o n s and
the
CaO/CaS e q u i l i b r i a .
D i s c u s s i o n of
and
the
i n a com-
of the
(C•6A,C•2A)/(Mn,Ca)S
5.4.3
The
To
r a t i o s are p l o t t e d a g a i n s t e i t h e r
(88,89) summarize the behavior
CaO-Al 0 (liq)
= 0.1.
f t l
composite phases over
or hg i n l o g a r i t h m i c s c a l e s i n F i g u r e s
These F i g u r e s MnS
i s necessarily iso-
at a f i x e d A l a c t i v i t y , h
r e p r e s e n t the s t a b i l i t y of these ranges of i n t e r e s t
(87)
and
pool
b) Where smooth,
e q u i v a l e n t changes i n the Ca:Al r a t i o s of i n i n the t o t a l oxygen content
l i q u i d p o o l and
i n g o t were observed.
i n samples from
Case (a) was
speci-
212 f i c a l l y observed i n the A l - d e o x i d i z e d and
p a r t i a l l y i n RII-I2.
ference
i n oxygen content
r a t e with A l
was
These two
ingots, i . e .
ingots e x h i b i t t h i s
when the h i g h e s t
applied.
RII-Il dif-
deoxidation
I t i s important to note t h a t
because of the changes i n oxygen a n a l y s i s i n the l i q u i d and
ingot
(RII-I2), a d i f f e r e n c e g r e a t e r than 20
i s observed i n t o t a l oxygen.
T h i s behavior
i n the Ca:Al r a t i o s i n i n c l u s i o n s .
Case
ppm
i s also reflected
(b) i s found i n R I I I -
12 and p a r t i a l l y i n R I I - I l where the d e o x i d a t i o n given by the behavior
sequence,
of the t o t a l oxygen content
A l r a t i o s i n i n c l u s i o n s , Figures
pool
(57,59) and
and
the
Ca:
(43,44), shows
smooth and p a r a l l e l changes. The
s o l i d i f i c a t i o n c o n d i t i o n s i n samples from i n g o t s
(center p a r t )
are l e s s d r a s t i c than i n samples e x t r a c t e d from
l i q u i d pool.
The
secondary d e n d r i t e arm
i n g o t s where the samples were o b t a i n e d
spacing
was
(DAS
about
1 1
, as acknowledged i n the l i t e r a t u r e " '
provides
(
In s p i t e o f . t h i s
ym
A larger '
1 0 3 - 1 0 6
>
more advantageous c o n d i t i o n s f o r the n u c l e a t i o n
growth o f i n c l u s i o n s . extracted
1 0 1
) in
250-300
w h i l s t i n samples from the l i q u i d p o o l 30-50 ym. DAS
1 1
the
and
i n c l u s i o n s i n samples
from the l i q u i d p o o l , under the d e s c r i b e d
conditions,
showed a l a r g e r mean diameter. I t i s a l s o important to note t h a t the d i f f e r e n c e i n i n c l u s i o n mean s i z e was
1 ym,
above
where
the
faceted
(a-A^O^)
al-
213
umina
was
observed.
i r o n aluminates
At lower c o n c e n t r a t i o n s o f aluminum round
(FeO'A^O^) were i d e n t i f i e d whereas at
higher d e o x i d a t i o n r a t e s the aluminates and
some angular
with some c a l c i u m
alumina were i d e n t i f i e d .
These f i n d i n g s (99
s t r o n g l y agree with T u r p i n ' s and E l l i o t ' s and o t h e r s 184) (99) observations.
These r e s e a r c h e r s
who
the n u c l e a t i o n phenomenon under sub-cooled suggested
t h a t the angular
sub^-liquidus temperatures.
'
have s t u d i e d
c o n d i t i o n s , have
alumina phase was
the melt a t e q u i l i b r i u m temperature and
183 '
nucleated i n
i t simply grew at
C o i n c i d e n t a l l y to t h i s
ob-
(99) servation
, i t was
a l s o r e p o r t e d t h a t i n very e a r l y stages
o f s u b - c o o l i n g a scum was Thus,
formed on the s u r f a c e of t h e i r
i n d i c a t i n g t h a t a t the beginning
i n c l u s i o n s simply
melts.
of s u b - c o o l i n g some
f l o a t e d to the s u r f a c e .
To determine the e x t e n t a t which the f l o t a t i o n mechanism i s allowed
i n the E S R - l i q u i d p o o l a more e l a b o r a t e
(SEM
and
EPMA) study, through the e x t r a c t e d samples c o n t a i n i n g e i t h e r RE o r Zr, was
c a r r i e d out.
The p e r i p h e r a l RE and
Zr as o x i -
s u l f i d e s e n c l o s i n g the Ca-aluminates have c l e a r l y r e v e a l e d t h a t the l a t t e r phases were a l r e a d y p r e s e n t i n the pool.
These experiments a l s o suggest
a liquid-solid
state
( 9 2
'
9 4
'
l 2 l )
liquid
t h a t i n c l u s i o n s are i n
, Figures
(80) to
r e s u l t s which are a l s o i n agreement with the
(84).
These
metallography
o b s e r v a t i o n s , show t h a t the f l o t a t i o n of i n c l u s i o n s can
occur
214
i n as much as 7-10% i n the i n g o t . resent
of
the
total
These r e s u l t s , however,
inclusion do
not
content
rep-
the amount o f i n c l u s i o n s removed from the s o l i d i f y i n g
ingot. one
out
I f an a n a l y s i s o f F i g u r e s
(79a) and (79b) i s made
can see t h a t i n o r d e r t o account f o r the d i f f e r e n c e i n
size
(1.0 - 1.5 ym i n diameter) a d i s p l a c e m e n t i n t h e cumul-
a t i v e frequency from 50 t o 70% produces the expected ence.
This
differ-
i n d i c a t e s t h a t an e l i m i n a t i o n o f i n c l u s i o n s o f
a p p r o x i m a t e l y 20% i s c a r r i e d o u t by f l o t a t i o n . A l t h o u g h these experiments do not c l e a r l y r e v e a l the nature of s a t u r a t i o n , the
i t i s believed
three mechanisms' ^ 00
o x i d i z e r s and d u r i n g of d e o x i d a t i o n
t h a t i t i s r e a c h e d by
namely by c o o l i n g ,
solidification.
additions
The h i g h e s t
o f de-
degrees
which r e s u l t from the i n t r o d u c t i o n o f l a r g e
amounts o f A l i n t h e melt e i t h e r from the d e o x i d i z e r o r through r e a c t i o n
(20a-c)
and the h i g h c r y s t a l l i n e c h a r a c t e r
o f the alumina phase l e a d t o the b e l i e f t h a t t h i s phase is uniformly the
n u c l e a t e d i n e a r l y stages o f u n d e r c o o l i n g a t
beginning of s o l i d i f i c a t i o n .
enriched ingot
i n deoxidizers
a l s o suggest t h a t
The presence o f s e g r e g a t e s
i n some samples from l i q u i d p o o l and " l o c a l supersaturation"
(by a d d i t i o n s )
can be a c h i e v e d . It i s i n f e r r e d that
i f growth o f i n c l u s i o n s r e s u l t s from
a mechanism o t h e r than d i f f u s i o n and p r e c i p i t a t i o n , s p e c i f i c a l l y growth due t o c o l l i s i o n c o a l e s c e n c e between i n c l u s i o n s o f d i f f e r e n t s i z e s and t h e r e i s
s u b s t a n t i a l con-
215 v e c t i v e mixing
i n the i n g o t p o o l then t h i s phenomena should
be r e f l e c t e d i n i n c l u s i o n s i n the ESR-ingot.
The
and arrangement of i n c l u s i o n s e x t r a c t e d by the acetate-methanol i n Figures
(91)
s i z e , shape
iodine-methyl
method from A l d e o x i d i z e d i n g o t s i s shown and
(92).
These
that the growth by c o l l i s i o n and
(SEM)
photographs r e v e a l
coalescence
of A^O^
and
CaC"6Al2C>2 i n the l i q u i d p o o l indeed has taken p l a c e . As
4. A u
suggested
i
u
by s e v e r a l r e s e a r c h e r s
(38, 121,242,243) '
,
s i n c e there i s not a complete a s s i m i l a t i o n of i n c l u s i o n s by the s l a g some i n c l u s i o n s are c a r r i e d back i n t o the ingot.
The
type of i n c l u s i o n s , c l u s t e r s of
solidifying
aluminates,
i d e n t i f i e d i n t h i s r e s e a r c h very much resemble those i n conventional mechanically,
,,
cally
..
,
s t i r r e d melts
t h e r m a l l y , or
(38,120,183, 189,193-195) ' ' ' ' .
reported
electromagnetiThus,
. ..
.
although
the growth o f i n c l u s i o n s i n ESR-ingots can be accounted f o r by the simultaneous
d i f f u s i o n - p r e c i p i t a t i o n mechanism, the
d i f f e r e n c e i n s i z e found
i n l i q u i d p o o l and
i n g o t cannot be
e x p l a i n e d by a mechanism other than the f l o t a t i o n . also r e a l i s t i c
to suggest
It i s
t h a t the i n c l u s i o n s i z e d i s t r i b u t i o n
seen by the s o l i d i f y i n g i n t e r f a c e i s not s t r i c t l y simply by buoyance c o n s i d e r a t i o n s but i n s t e a d by
controlled overall
(244 ) bath hydrodynamics as suggested
by Engh and
Lmskog
(245) and L i n d e r
.
From t h i s d i s c u s s i o n , i t i s e v i d e n t t h a t
the i n c l u s i o n f l o t a t i o n mechanism cannot be approached by
216 s t r a i g h t Stokes t h i s equation The that 0.1
1
Law
u n l e s s the a p p r o p r i a t e c o r r e c t i o n s to
(13) are c o n s i d e r e d , Table ( I ) .
second important
c o n c l u s i o n from these r e s u l t s i s
at d e o x i d a t i o n r a t e s which produce an A l content - 0.15
wt.
% i n (ESR)
i n g o t s , i n c l u s i o n s are e x c l u s i v e l y
n u c l e a t e d and grown i n i n t e r d e n d r i t i c spaces d u r i n g fication.
of
solidi-
These f i n d i n g s i n agreement with A l d e o x i d i z e d
4. • 4 . - n 4. i , • (90, 172,183-187) ingots i n conventional steelmakmg p r a c t i c e indicate levels
t h a t the n u c l e a t i o n phenomenon at these
deoxidation
i s c o n t r o l l e d by the formation of the F e O « A l 0 2
c l u s i o n phase, e.g. fication.
l o c a l supersaturation during
Recent s t u d i e s *
i n g o t s d e o x i d i z e d w i t h 0.1
2 4 6
2.0
% Al
in-
solidi-
^ in unidirectionally
and
3
solidified
which c l o s e l y r e -
semble the Al(ESR) d e o x i d i z e d i n g o t s , have shown t h a t the FeO«Al 0 2
3
phase i s p r e c i p i t a t e d at a s o l i d f r a c t i o n of
i n the low A l (0.1%) content and a t 0.89 r e s u l t s suggest
t h a t the F e O « A l 0
phase p r e c i p i t a t e d and searchers
2
3
i n the o t h e r .
i s the i n c l u s i o n
t h e r e f o r e as suggested
( 1 8 3 , 1 8 4 , 1 8 6 _ 1 8 8 )
umina as the s o l i d i f i c a t i o n
These
first
by other r e -
t h i s phase i s transformed proceeds.
0.65
to a l -
217 5.4.3.2
Comparison Between T h e o r e t i c a l and
Experimental
Results The and
t o t a l oxygen content of samples from the l i q u i d
ingot
Figures
pool
under an a p p r o p r i a t e d e o x i d a t i o n sequence,
(41) and
(57), have c l e a r l y shown t h a t there i s a
d i f f e r e n c e between the samples of approximately
20 ppm.
This
(63)
behavior Figure both
i s expected
(10).
The
from an e q u i l i b r i u m s i t u a t i o n i n
average Ca:Al r a t i o s i n i n c l u s i o n s from
types of samples
( l i q u i d p o o l and
ingot) a l s o i n d i c a t e
t h a t under a g r a d u a l d e o x i d a t i o n sequence with e i t h e r
an
A l S i , CaSi o r h y p e r c a l a l l o y the c a l c i u m which remains i n s o l u t i o n p r e c i p i t a t e s on c a l c i u m aluminates fication.
during
solidi-
T h i s , a c t s to r a i s e the Ca:Al r a t i o s by a l l o w i n g
the r e a c t i o n (CaO)*+ [S] X ,
,
(CaS)*+ [0] , ,.
to take p l a c e i n the forward
^.
(18)
(147,148)
direction
'
o r t a n t to emphasize t h a t d e s p i t e the 20 ppm
^ .
.
I t i s imp-
of oxygen i n
s o l u t i o n i n the l i q u i d p o o l , the e q u i l i b r i u m i s achieved i n the d i r e c t i o n i n d i c a t e d by the r e a c t i o n (18). temperature decreases
a-c)
sulfide, i.e.
t r a n s i t i o n of these phases i s presented * where the CaS/CaO
T h i s behavior
the
the c a l c i u m , oxygen and s u l f u r . p r e -
c i p i t a t e as p e r i p h e r a l oxide and The
As
CaS. (92
revealed.
when the l e v e l of "FeO"
i s such t h a t the c a l c i u m aluminates
and
i n Figures
interphase i s c l e a r l y
i s observed
CaO
i n the
are e i t h e r CaO«2Al O_ n
slag
218 or
12CaO«7Al 0_. 2 3
At higher l e v e l s of "FeO"
where the A l 0 _ 2 3
3
o
i s transformed to CaO-GA^O^, the r e a c t i o n which c o n t r o l s the p r e c i p i t a t i o n of s u l f i d e i s : MnS
+
[Ca] t
CaS +
[Mn]
(19)
T h i s r e a c t i o n enables the p r e c i p i t a t i o n of double i.e.
(Ca,Mn)S, F i g u r e s (51) and
sulfides,
(52).
The most important f a c t to p o i n t out i s t h a t the secondary p r e c i p i t a t i o n strictly
which i s heterogeneous
i n nature
c o n t r o l l e d by the Ca:Al r a t i o i n the i n c l u s i o n
The e f f e c t o f the temperature on the p r e c i p i t a t i o n particularly CaO
is phases.
sequence,
i n the Ca:Al r a t i o s where aluminates e n r i c h e d i n
are i n e q u i l i b r i u m
i s e q u i v a l e n t to an increment i n the
aluminum c o n t e n t i n the melt i n the Ca-Al-0 system, F i g u r e
(11)
T h i s b e h a v i o r i s a l s o expected from the Ca0-Al 0.j pseudo 2
b i n a r y e q u i l i b r i u m diagram.
T h i s i n d i c a t e s t h a t as the
CaO
c o n t e n t i n c r e a s e s i n the aluminates t h e i r s t a b i l i t y i n terms of
temperature
decreases and a more s t a b l e compound i s formed.
The completion of the s u l f i d e p r e c i p i t a t i o n r e a c t i o n s and
(19) i s e x p e c t e d ' ^ 4
(18)
to occur a t approximately 1000°C
where the m i s c i b i l i t y gap i n the MnS-CaS b i n a r y diagram appears.
I t i s a l s o important to mention
f i c a t i o n some i r o n or Cr
can
be
in
dis-
that during s o l i d i -
solution
with
the
. (92, 140,159) s u l f i d e phase ' ' Another p o i n t to be c o n s i d e r e d i n t h i s a n a l y s i s i s t h a t where the aluminate phase
(A^O^
or CaO'GA^O^) i s s t a b l e
the s u l f i d e phase i n e q u i l i b r i u m with i t i s o n l y the MnS
in
219 any
of i t s shapes, i . e .
MnS
I, I I or I I I which are
dependent on the chemistry of the melt. h a v i o r of the a l u m i n a t e - s u l f i d e ures
Figure
of "pure" CaS
(87)
also
The o v e r a l l be-
t r a n s i t i o n i s condensed i n F i g -
(88,89) which are an e x t e n s i o n
(87).
also
of r e s u l t s shown i n F i g u r e
indicates
cannot occur unless
that
the
precipitation
lower oxygen p o t e n t i a l s ,
than those r e q u i r e d to p r e c i p i t a t e C a O i A ^ O ^ and
12CaO • 7AI2O.J
are reached. If
these f i n d i n g s are compared a g a i n s t s t u d i e s on
i n j e c t i o n p r o c e s s e s then i t can be ous
seen that the
simultane-
d e o x i d a t i o n - d e s u l f u r i z a t i o n mechanism i s a l s o r e f l e c t e d
• 4.1. ^ 4.i n the d e o x i d a t i o n
J 4. (140,147,148,153,197, 211,214) products ' ' ' ' ' . (14 7
T h i s diagram i n agreement w i t h Saxena et a l . ' s work 148
in
'
214) '
CaO
Ca-
c l e a r l y r e v e a l s t h a t Ca does not d i r e c t l y
i n c l u s i o n s unless
e i t h e r as a C a S i or
as
c o n t r i b u t e to the CaS p r e c i p i t a t e
the alumina i s f i r s t transformed i n t o
Ca-aluminates. While c a l c i u m
aluminates w i t h p e r i p h e r a l Zr or
oxides s u l f i d e s , i n the samples e x t r a c t e d
from the
RE liquid
p o o l by the s i l i c a tube c o n t a i n i n g e i t h e r Zr or mischmetal, were not commonly found, a l l of the i n c l u s i o n s which cont a i n e d these elements
(Zr o r Ce and
La) homogeneously d i s -
t r i b u t e d were p r e f e r e n t i a l l y composed of phases e n r i c h e d calcium.
I n c l u s i o n s g e n e r a l l y show t h a t among the
in
elements
220 t r a c e d by the X-ray spectrum and
S i as o x i d e - s u l f i d e and
of the main c o n s t i t u e n t s taken as one
in iron
contributes reaction
analysis
of these phases.
'
. i s gradually
and
3
hence i t by
(20-C).
Reaction
to 12CaO«7Al 0 . 2
(20-C) and
The
3
sulfide transition, i.e. Figures
(87)
g i v e n i n Tables
and
(XVI)
MnS
(88) and
t h a t the p r e c i p i -
the r e a c t i o n scheme (19)
(21)
above ones
II
MnS
dictate
and
the
(25),
determine
III
the
(Ca,Mn)S
r e v e a l t h i s behavior.
(XVII)
(12-iv),
the gradual t r a n s i t i o n
reactions
which occur s i m u l t a n e o u s l y t o the
CaS.
solu-
( s e c t i o n 5.4.1.4,
established
chemistry o f the oxide phase, i . e . 2
to i t s low
as the s o l i d i f i c a t i o n p r o g r e s s e s .
t a t i o n o f i n c l u s i o n s i s r u l e d by
of A 1 0
one
This f i n d i n g i s
the Ca:Al r a t i o i n i n c l u s i o n s ,
5.4.3.1), i t was
(12-v), and
calcium i s
r e j e c t e d and
In p r e v i o u s d i s c u s s i o n of r e s u l t s 5.4.2
Ca
199)
to i n c r e a s e
(18)
( A l , Zr,
almost pure CaS)
more evidence that c a l c i u m , due (198
bility
(SEM)
-»-
Results
t o a c e r t a i n e x t e n t des-
c r i b e these r e s u l t s . The (XVI)
equilibrium,
isothermal
c a l c u l a t i o n s shown i n
were performed by assuming constant
i n t e r a c t i o n c o e f f i c i e n t s f o r Al-O, used were - 5 . 2 5
( 1 7 5 )
, -62.0
l a s t value f o r the Ca-S the
was
f r e e energy of the CaO
( 1 7 5 )
Ca-0
and
-40
Table
( f i r s t order)
and
Ca-S.
The
respectively.
assumed on the b a s i s t h a t i s approximately 1 1/3
values The since
l a r g e r than
t h a t f o r CaS,
Table
(XV), then the r a t i o of t h e i r
first
order i n t e r a c t i o n parameters c o u l d be e q u i v a l e n t . if
S-analyses
from the 1020
M.S.
the s t a r t i n g p o i n t i n e a r l y
Hence,
e l e c t r o d e are taken
(low) d e o x i d a t i o n stages
and they are compared a g a i n s t those g i v e n i n Table for in
as
(XVI)
the A l 0 - C a O « 6 A l 0 - C a S e q u i l i b r i u m , i t i s noted t h a t 2
3
2
3
terms of s u l f u r , very good agreement i s observed.
these v a l u e s are compared
i n terms of Ca- and S-
and t h e i r r e s p e c t i v e oxide phases
If
contents
a g a i n s t those r e p o r t e d
(144) by H i l t y and Popp
given
agreement i s found.
in
F i g u r e (78),
good
On the o t h e r hand, p r e d i c t e d values f o r
oxygen are overestimated, F i g u r e (72). Since, Gustafsson and M e l b e r g ' ^ ?
suggest the use of
7
v a r i a b l e f i r s t order i n t e r a c t i o n c o e f f i c i e n t s then a set
of c a l c u l a t i o n s was
performed.
r e s u l t s shown i n Table
second
Under these c o n d i t i o n s ,
(XVII) were computed.
The
first
order i n t e r a c t i o n c o e f f i c i e n t s w e r e ; - 5 3 5 " ^ , -400, -350 for
and -200 Ca-S,
CaS,
f o r the Ca-O,
-62.0
( 1 7 5 )
-300,
f o r A l - 0 and -110
( 2 1 1 )
f o r the A l 0 - C a O • 6 A l 0 ~ C a S , C a O • 6 A l 0 ~ C a 0 • 2 A l 0 2
3
2
3
2
3
2
CaO«2Al 0 -CaO«Al 0 -CaS, CaO'Al^-CaO + A l ^ - C a S 2
3
and Ca0^ y - CaO s
Table
(XV).
2
3
+ A l 0 ~ C a S e q u i l i b r i a , Figure
While
2
3
Regarding
and
the Ca, A l and 0 are p r e d i c t a b l e by
lowing t h i s approach the s u l f u r i s underestimated
(87)
(10
6
i s not.
The
sulfur
fol-
content
- 10 ^ wt.%).
the independence of r e a c t i o n
(20-C) on
the
3
222 oxygen p o t e n t i a l
t h i s i s c l e a r l y r e v e a l e d through these
c a l c u l a t i o n s . Table (XVII). ranges between 10-40
ppm
The oxygen content i n the melt
r e g a r d l e s s of the amount of A l
and Ca i n s o l u t i o n . I t i s a l s o important to note t h a t the p r e d i c t i o n s in section ition are
5.3.4
i n terms of the expected i n c l u s i o n compos-
which were based on F a u l r i n g s
also
stated
et a l . ' s ^
2 l 6
^
findings
i n agreement with the r e s u l t s presented i n F i g u r e
(88) . F i n a l l y , two important f a c t s are worthwhile t o mention: First,
the Ca-0
i n t e r a c t i o n parameters are very important i n
the Al-Ca-O-S p r e c i p i t a t i o n and second a c o n f i d e n t
prediction
of the p r e c i p i t a t i o n sequence cannot be f u l l y r e l i a b l e u n l e s s the
interaction
appropriately
( f i r s t and second order) c o e f f i c i e n t s are
determined.
223
CHAPTER VI THE
RADIAL DISTRIBUTION OF
INCLUSIONS IN CaSi AND
Al
DE-
OXIDIZED INGOTS
6.1
Experimental D e t a i l s and The
Techniques
l a s t p a r t of t h i s i n v e s t i g a t i o n was
e l u c i d a t e how
i n c l u s i o n s are d i s t r i b u t e d , i n terms of
t i c a l l y determined s i z e s , i n i n g o t s . s e r i e s of samples from s e v e r a l 1020 ESR
ingots
radially
undertaken to
deoxidized
w i t h A l and
For t h i s purpose a M. S.
and
l e v e l s and
s l i g h t l y etched on four and
f i v e of t h e i r f a c e s .
one
4340
the CaSi a l l o y , were
s l i c e d at known d e o x i d a t i o n
were p o l i s h e d and
statis-
samples
sometimes
P r i o r to performing measurements,
microprobe a n a l y s i s and
X-ray spectrum a n a l y s i s were c a r -
r i e d out to i d e n t i f y the major i n c l u s i o n phases. Measurements of mean diameter ary d e n d r i t e
arm
spacing
of i n c l u s i o n s or second-
were performed almost i n v a r i a b l y
a t every h a l f centimeter on each f a c e . A l deoxidized
i n g o t s were very
small and
Since
inclusions in
complex i n shape
(alumina g a l a x i e s a s s o c i a t e d w i t h manganese s u l f i d e s ) , s e v e r a l approaches to determine the mean s i z e o f i n c l u s i o n s were f o l l o w e d ,
i.e.
normal d i s t r i b u t i o n s and
l a r g e s t i n c l u s i o n s technique."
"the
five
224
6.2
Experimental
Findings
R e s u l t s of t h i s r e s e a r c h are shown i n F i g u r e s
(9 3) t o
(95) and (96) t o (99) f o r secondary d e n d r i t e arm spacing and i n c l u s i o n mean s i z e s r e s p e c t i v e l y . i n g o t s , as p r e v i o u s l y d e s c r i b e d and manganese s u l f i d e .
The A l d e o x i d i z e d
showed alumina g a l a x i e s
Only t r a c e s o f c a l c i u m were found.
The morphology o f i n c l u s i o n s i n the 1020 M.S. A l d e o x i d i z e d i n g o t s v a r i e d from g l o b u l a r s i n g l e and double phase
( s p h e r i c a l aluminates
and manganese s u l f i d e ) a t the
i n g o t core, t o elongated with double phase manganese s u l f i d e ) a t midradius
(aluminates and
and almost e x c l u s i v e l y
s m a l l alumina g a l a x i e s a s s o c i a t e d with manganese
sulfide
at the mould w a l l . The
1020 M.S. CaSi d e o x i d i z e d i n g o t s showed c a l c i u m a l -
uminates and s i n g l e and double c a l c i u m s u l f i d e s , i . e . , CaS and
(Ca,Mn)S.
aluminates
The d e o x i d a t i o n l e v e l was such t h a t c a l c i u m
o f the type C a O « 6 A l 0 2
3
as the p r i n c i p a l i n c l u s i o n phases. c l o s e d the oxide phase. showed v i r t u a l l y
and C a O • 2 A l 0 2
3
were
found
The s u l f i d e phase en-
The 4340 CaSi d e o x i d i z e d i n g o t
the same types o f i n c l u s i o n phases as the
1020 M.S. i n g o t s d e o x i d i z e d with the CaSi a l l o y .
I t i s im-
p o r t a n t t o mention t h a t the amount o f the p e r i p h e r a l CaS phase was p r o p o r t i o n a l t o the Ca:Al r a t i o i n the oxide phase and
i t was not n e c e s s a r i l y dependent on the s i z e of the i n -
clusions.
F i n a l l y , the i n c l u s i o n d e n s i t y
(number o f i n -
e l u s i o n s / p e r u n i t area) i n a l l of the i n g o t s was c o n s i d e r a b l y with
6.3
increased
the r a d i u s .
D i s c u s s i o n of
Results
In the d i s c u s s i o n of the p r e v i o u s
r e s u l t s , i t has
been
emphasized t h a t some f l o t a t i o n of i n c l u s i o n s (about 10-20%) w i l l take p l a c e .
T h i s was
determined to o r i g i n a t e during
s o l i d i f i c a t i o n i n e a r l y stages
of c o o l i n g .
T h i s statement, however, i s t r u e only when the
required
s u p e r s a t u r a t i o n r a t i o f o r the p r e c i p i t a t i o n o f aluminates i s achieved,
i.e.
The
d i s c u s s i o n has
previous
above 0.1
to 0.15
wt.
% A l i n the i n g o t .
also established that i n -
c l u s i o n s i n samples from l i q u i d p o o l were l a r g e r i n d i a meter ingots
(under an a p p r o p r i a t e
deoxidation
sequence) than i n
although the s o l i d i f i c a t i o n c o n d i t i o n s
t h e i r corresponding former samples.
secondary DAS)
by
were more d r a s t i c i n the
Consequently, i t was
i n c l u s i o n growth was
(given
concluded t h a t
the
almost e n t i r e l y c o n t r o l l e d by the
f u s i o n - p r e c i p i t a t i o n of s o l u t e s on p r e n u c l e a t e d On the other hand, r e s u l t s obtained
dif-
phases.
from the r a d i a l i n -
c l u s i o n s i z e d i s t r i b u t i o n s show that- the p r e c i p i t a t i o n i n i n g o t s i s e s s e n t i a l l y c a r r i e d out d u r i n g
solidification.
Hence, i t i s very dependent on the l o c a l thermodynamic ,... (99,100,101,104,10 5,10 6,121,143,184,186,189) conditions ' ' ' ' ' ' • ' ' •
Since the i n c l u s i o n mean s i z e ranges r a d i a l l y from 6.0 5.0
ym i n the i n g o t c e n t r e l i n e t o 3.0
w a l l and the secondary DAS
- 2.0
ym i n the mould
e q u i v a l e n t l y v a r i e s from 20 0-250
to 60-100 ym then the p r e c i p i t a t i o n of i n c l u s i o n s , c u l a r l y i n i n g o t s d e o x i d i z e d w i t h the CaSi a l l o y e n t i r e l y c o n t r o l l e d by the r e j e c t i o n of 121
-
partii s almost
solutes'
0
1
,
1
0
2
-
1
0
6
'
243) '
, e.g.
by the l o c a l thermodynamic
c o n d i t i o n s o f the
i n t e r d e n d r i t i c m i c r o p o o l s formed as the s o l i d i f i c a t i o n p r o ceeds . Thus, although the l o c a l s o l i d i f i c a t i o n time g i v e n DAS
X 1
*
= a t£
= b(GR)"
n
= 707.946 ( G R ) " ' 0
(65 i s very s h o r t , about (1-1.5 cm)
5-30
seconds
1
=
i n locations
close
1 0 0
'
1 0 6
'
up to even
1 1 5
^,
by the
larger
secondary d e n d r i t e arm spacing, i n ym
a and b =
constants
n
=
exponent which ranges from 1/2
t^
=
l o c a l s o l i d i f i c a t i o n time, i n seconds
GR
=
product o f qrowth r a t e by the thermal g r a d i e n t , in
°C/min.
^:
(26)
3 8 2 5
to the ESR-mould w a l l ; t h i s i s s u f f i c i e n t to grow
d i f f u s i o n - p r e c i p i t a t i o n mechanism 1
4 7
225) '
i n c l u s i o n s on p r e n u c l e a t e d p h a s e s ^ " '
* DAS
by'
to
1/3
sizes'
^.
2 1
Thus, the c o n t r o l l i n g steps are e i t h e r the
n u c l e a t i o n of i n c l u s i o n s where the s u p e r s a t u r a t i o n .
-
.
,
-
, .
i s not reached i n e a r l y stages of c o o l i n g the r e j e c t i o n o f s o l u t e s o
^
(oxygen and
ratio
(99,100,101)
d e o x i d i z e r s ) which are
-i • ^ • •
o.u
or
(102-106,
g r a d u a l l y b u i l d i n g up as the s o l i d i f i c a t i o n
progresses
121,185,121,227,243)
I t i s a l s o important
to emphasize t h a t the growth of i n -
c l u s i o n s d u r i n g c o o l i n g i s very dependent on the d e n s i t y andJ
• i, s i•z e of* ^the o r i•g i•n a l-i phases p r e s e n t 4- ( 9 1 , 1 0 1 , 1 2 1 ) . I f
T + T
5
these parameters are 1 0
7
-
10
inclusions/cm
2
i n r a d i u s , as expected i n ESR-melts, o n l y a very should be e x p e c t e d
( 1 0 1
'
1 2 1 , 2 4 3 )
,
Table
1 - 1 0 um
and
s l i g h t growth
(XVIII).
I t can a l s o be e l u c i d a t e d t h a t s i n c e "oxygen
segregation"
does not take p l a c e along r a d i a l d i r e c t i o n s i n i n d u s t r i a l ingots'
4 8
2 5
°)
f
i t i s expected to observe a gradual change i n
the i n c l u s i o n d e n s i t y , a f a c t which agrees with the in t h i s research. should be
size
Hence the i n c l u s i o n r a d i a l s i z e
observations distribution
i n v e r s e l y p r o p o r t i o n a l to the i n c l u s i o n d e n s i t y .
228 CHAPTER V I I * 7.0 7.1
Conclusions I n c l u s i o n s from the e l e c t r o d e a r e p h y s i c a l l y and chemic a l l y transformed i n the e l e c t r o d e t i p by the thermal gradients.
I n c l u s i o n s are c h e m i c a l l y
a l t e r e d by the
presence o f the l i q u i d s l a g a t the l i q u i d f i l m and they are almost e n t i r e l y removed
(by d i s s o l u t i o n -
r e a c t i o n s ) when the d r o p l e t i s completely
formed.
Thus, e l e c t r o d e i n c l u s i o n s only p l a y a r o l e i n the f i n a l ESR i n g o t i n s o f a r as t h e i r s o l u t i o n product e n t e r s i n t o the slag-metal during 7.2
reactions
experienced
processing.
I n c l u s i o n s i n ESR-ingots are more s t r o n g l y i n f l u e n c e d by the d e o x i d a t i o n p r a c t i c e than by the e l e c t r o d e composition SiC^ slags.
and/or the s l a g system used i n low I t i s important t o comment, however,
t h a t under low d e o x i d a t i o n chemistry
r a t e s the i n t r i n s i c
o f the s l a g predominates, i . e .
a t high
s l a g oxygen p o t e n t i a l s . 7.3
As a consequence of the above c o n c l u s i o n , i t has been confirmed t h a t the p r e c i p i t a t i o n o f complex silicate
i n c l u s i o n s i s p r e d i c t a b l e i n high
Al-Casilica
s l a g s where t h e i r o r i g i n i s s t r i c t l y given by the s l a g chemistry,
i.e.
i f wt. % SiO„ > 10.0.
For ease of r e f e r e n c e , the nomenclature o f r e a c t i o n s i n p r e v i o u s t e x t s a r e r e w r i t t e n i n t h i s chapter.
229 7.4
The most a p p r o p r i a t e s l a g system i n which t o perform an e f f i c i e n t d e o x i d a t i o n i s the CaF2~CaO-Al20
3
system a t 50, 30 and 20 wt. % r e s p e c t i v e l y , i . e . the h i g h e s t Ca:Al r a t i o i n i n c l u s i o n s i n the absence of d e o x i d a t i o n . 7.5
The i n c l u s i o n c h e m i s t r y s l a g system
expected, from the most common
(CaF -CaO-Al 0 ) 2
2
used i n the ESR-process,
3
i s c o n t r o l l e d by the f o l l o w i n g 2[A1] + 3(FeO) [Ca] + (FeO) t
t
3
(CaO) + Fe
(7.5.i)
( A ^ O ^ + 3Fe
( A 1 0 ) + 3[Ca] t 2
equilibria:
(7.5.ii)
3(CaO) + 2 [ A l ]
(7.5.iii)
T h i s r e a c t i o n scheme depends on the type and degree of deoxidation.
Hence the p r e c i p i t a t i o n o f i n -
c l u s i o n s i s d i c t a t e d by: mCaO + n ( A l 0 ) J mCaO-nA^O.^ 2
(7.5.iv)
3
or more a p p r o p r i a t e l y by: X[Ca] + Y(Al 0-.) *• i n c l u s i o n o
J
?
'XCaO'(Y - *-) A l 0 _ J
A
J
o
J
+ \ X[A1]
(7.5.v) 7.6
From the above e q u i l i b r i a ,
i t can be seen t h a t i f
an excess o f d e o x i d i z e r i s added t o the s l a g ( i n the forward d i r e c t i o n o f r e a c t i o n s 7 . 5 . i i i or 7.5.v)
230
u n d e s i r a b l e composition high A l c o n t e n t s ,
w i l l r e s u l t i n the i n g o t , i . e .
i n which case
there e x i s t s a
p o t e n t i a l problem of p r e c i p i t a t i n g A l n i t r i d e s or sulfides. 7.7
D e o x i d a t i o n of s l a g s d u r i n g r e f i n i n g by u s i n g C a S i , C a A l S i and CaSiBaAl
a l l o y s i s more e f f i c i e n t
than by u s i n g A l p e l l e t s alone. of the above a l l o y s system
The
silicon in a l l
under the a p p r o p r i a t e
slag
(7.3), a c t s e x c l u s i v e l y as a c a r r i e r of
deoxidant 7.8
AlSi,
the
i n t o the metal l i q u i d p o o l .
A l and A l S i a l l o y are e f f i c i e n t d e o x i d i z e r s , however, they do not c o n t r o l the shape of the d e o x i d a t i o n ucts, i . e . Although aluminate
A l generates
alumina g a l a x i e s and MnS
II.
the A l S i a l l o y does produce s p h e r i c a l Cai n c l u s i o n s i t does not so s t r o n g l y
the p r e c i p i t a t i o n of CaS The
prod-
induce
at the p e r i p h e r y of the
C a S i , C a A l S i and CaSiBaAl
i n c l u s i o n shape c o n t r o l l e r s .
a l l o y s are very
oxides.
strong
At low CaSi or h i g h
A l or A l S i d e o x i d a t i o n r a t e s MnS
I I - I I I or
(Ca,Mn)S
are formed. 7.9
I n c l u s i o n p r e c i p i t a t i o n can be e x p l a i n e d by a d e t a i l e d H e n r i a n - p r e c i p i t a t i o n diagram i n which the r e a c t i o n :
superimposing
231
(CaO)* + [S] t on
the p r e v i o u s l y
reported
(CaS)* + [0]
(7.5.vi)
(Ca-Al-0) diagram and
u s i n g i n t e r a c t i o n c o e f f i c i e n t s from the l i t e r a t u r e a realistic prediction
can be made.
intrinsically
the t r a n s i t i o n s o f s u l f i d e s ,
includes
T h i s diagram
r u l e d by: [Ca] 7.10
+ (MnS)
F l o t a t i o n of inclusions
*
[Mn]
+ (CaS)
to some e x t e n t
o c c u r s i n moderate or h i g h l y
*
(10-20%)
d e o x i d i z e d melts.
At low d e o x i d a t i o n r a t e s , as expected from 7 . 5 . i i and
7.5.v
dendritic 7.11
uniform n u c l e a t i o n
spaces d u r i n g s o l i d i f i c a t i o n takes p l a c e .
I f electrode inclusions, and
of inclusions i n
deoxidation rates
s l a g system, deoxidant
are known, by u s i n g a
s i m p l i f i e d t e r n a r y - Si02, (Ca,M)0
and A^O^-
diagram, the f i n a l i n c l u s i o n composition can be estimated. 7.12
Inclusion function
s i z e , as expected from
(7.10)
o f the l o c a l s o l i d i f i c a t i o n time
hence on the l o c a l ( i n t e r d e n d r i t i c ) conditions.
isa and
thermochemical
232 SUGGESTIONS FOR FUTURE WORK
Based on r e s e a r c h c a r r i e d out i n the p a s t , i n terms of i n c l u s i o n s i n c o n v e n t i o n a l steelmaking and i n ESR and the type o f r e a c t i o n s s t u d i e d i n t h i s r e s e a r c h , s e v e r a l immediate r e s e a r c h p r o p o s a l s a r e suggested: 1.
To determine
with a higher degree o f accuracy the
t r a n s i t i o n p o i n t between r e a c t i o n s which i n v o l v e the oxygen p o t e n t i a l i n the s l a g - l i q u i d metal 2[A1]
+ 3 (FeO) t
such a s :
( A l ^ ) + Fe
and [Ca] + (FeO) 1 (CaO) + Fe and the exchange r e a c t i o n s (between two l i q u i d s ) , 3[Ca] 2. termine
such a s :
+ ( A 1 0 ) X 3(CaO) + 2[A1] 2
3
With e x a c t l y the same purpose as above, t o dethe s e r i e s o f t r a n s i t i o n s i n the s u l f i d e
inclusion
phases: MnS I I
-y
MnS I I I
by d e s i g n i n g s p e c i f i c experiments ials
(Ca,Mn)S
CaS
where v a r i o u s oxygen p o t e n t -
( s e v e r a l amounts o f A l and Ca) i n the melt should be
involved.
233 3.
As an e x t e n s i o n o f the r e s u l t s found through
this
r e s e a r c h , i t i s suggested t o perform experiments w i t h exa c t l y the same techniques and purposes i.e.
t o determine
as i n t h i s work
the p o s s i b l e d e o x i d a t i o n and s l a g b e s t
combination i n terms o f the f o l l o w i n g r e a c t i o n schemes t ( S i 0 ) + Fe
[Si] + 2 (FeO) [Ca] + FeO t
2
(CaO) + Fe
and [Si] + 2(CaO) Z
s
i
0
t
+ 2
C a
l
and [Mn] + (FeO) % MnO + Fe and [Si] + 2(FeO) J S i 0
+ Fe
2
or [Ca] + (FeO) J CaO + Fe and
either [Si] + 2(MnO) t
s
i
0
2
+
2
[
M
n
J
or [Ca] + (MnO) t
2(CaO) + [Mn]
These r e a c t i o n s can be compared t o those a l r e a d y r e p o r t e d for A l 0 / A l / S i / S i 0 2
2
2
and f o r T i 0 / T i 2
.
I t i s worthwhile
to study these r e a c t i o n s s i n c e the excess o f A l i n i n g o t s can cause d e l e t e r i o u s mechanical
properties.
234 4. in point
I t becomes obvious t h a t the t r a n s i t i o n s s p e c i f i e d (1) w i l l be a l s o necessary f o r any other
s e t of
e q u i l i b r i a i n p r o p o s a l (3). 5.
I t a l s o becomes apparent t h a t once these c o n d i t i o n s
are f u l l y c o n t r o l l e d the best s l a g / d e o x i d a t i o n the most a p p r o p r i a t e
mechanical p r o p e r t i e s ,
of the i n g o t and i n c l u s i o n c h e m i s t r i e s
and hence as a r e s u l t
can be s e l e c t e d .
Thus, t h e i r e v a l u a t i o n i n terms o f mechanical and
chemical
r e s i s t a n c e as a f u n c t i o n o f these parameters should be evaluated. 6.
I t i s a l s o very
i n t e r e s t i n g t o note t h a t s i n c e the
Ca and the A l a c t i v i t i e s are c o n t r o l l i n g parameters, i n a Al and eo which have
8
been r e p o r t e d with a g r e a t d e a l o f s c a t t e r should be once and
f o r a l l a p p r o p r i a t e l y determined. 7.
Experimental and t h e o r e t i c a l work along
l i n e s as those proposed i n p o i n t s formed; i n t h i s case,
(1) and (2) c o u l d be per-
i t i s suggested t o use Ce as (RE)
d e o x i d i z e r i n the presence o f a CaO-CaF enriched
slag.
the same
2
(A^O^) o r a RE-
The r e a c t i o n scheme might be as f o l l o w s :
[RE] + (FeO) t
RE-O + Fe
and/or Ca + (FeO) t
(CaO) + Fe
235 L I S T OF REFERENCES
1.
Kay, D.A.R.: Proc. o f the F i r s t I n t e r n a t i o n a l Symposium on ESR and C a s t i n g Technology. P i t t s b u r g h , Pa, 1967, P a r t I I .
2.
Myzetsky, V . L . , e t a l . : Proc. I n t . Symp. on E l e c t r o m e t a l l u r g y , Kiev , 1972, 119.
3.
Klyueb, M.M. and Mironov, June, 1967, 6, 480-483.
4.
K u s l i t s k y , A.B., e t a l . : i b i d . , 85.
5.
Volkov, S.E.: i b i d . , 12.
6.
M i t c h e l l , A., J o s h i S. and Cameron J . : 2, February 1971, 561-567.
7.
E l l i o t , J . F . , and Maulvault, M.A.: P r o c , AIME, 1970, 2%_, 13.
8.
Mendrykowski, J . e t a l . , Met. Trans., ASM-AIME, 1972, 3, 1761.
9.
Tacke, K.H., and Schwerdtfeger, 1981, 52^, 4, 137-142.
M. Yu:
Stal i n English,
Met. Trans.
E l e c t . Furn. Conf.
K.: Arch.
Eisenhuttenwes,
10.
M i t c h e l l , A., and J o s h i J . ; Met. Trans. 1973, 4_, 631.
11.
F r e d r i k s s o n , H. and J a r l e b o r g , 0.: 2_3, 9, 32-40.
12.
Kay, D.A.R. and Pomfret, 962-964.
13.
Chan, J.C.F., e t a l . : IB, 135-141.
Met. Trans. B., March 1976,
14.
Wadier, J.F., e t a l . : 127-136.
T o o l A l l o y S t e e l s , A p r i l 1978,
15.
M i t c h e l l , A.: Ironmaking 1974, 3, 172-179.
16.
H a j r a , J.P. and Ratnam, U.: Trans o f the Indian I n s t , of M e t a l s . 31_, 1, Feb. 1978, 20-23.
J . M e t a l s , 1971,
R.J.: J . I . S . I . , 1971, 209
and Steelmaking
(Quarterly)
236 17.
Medovar, B . I . e t a l . : P r o c . o f t h e 5 t h S o v i e t - J a p a n e s e Symp. o n P h y s i c a l - C h e m i c a l B a s i s o f M e t a l l u r g i c a l P r o c e s s e s , 1975.
18.
M i t c h e l l , A.: P r o c . o f t h e 1 s t I n t . Symp. on ESR, P a r t I I I , M e l l o n I n s t . , P i t t s . , P a . , A u g u s t 1967.
19.
Roshchin, 679-681.
E. e t a l . :
Steel
20.
Roshchin,
E. e t a l . :
ibid.,
21.
B u r e l , B. a n d M i t c h e l l , 2253.
22.
P a t o n , B.E. e t a l . : P r o c . 5 t h I n t . Symp. o n ESR and O t h e r S p e c i a l M e l t i n g T e c h n o l o g i e s , P i t t s b u r g h , Pa., 1974, P a r t I , 433-448.
23.
Z h e n g b a n g , L i , Wenhiu, Z. a n d Y i d a L i ; V o l . 15, No. 1, J a n u a r y 1980, 20-26.
24.
J i e , Fu: Acta M e t a l l u r g i c a S i n i c a , Dec. 1979, 526-539.
25.
Wadier, J . F . , e t a l . : 127-136.
26.
M i t c h e l l , A. and Beynon B.: 3333-3345.
27.
Mitchell, Bulletin
28.
Schwerdtfeger, K.: Proc. M u n i c h , 1976, 133-141.
29.
Beynon, B., Ph.D. t h e s i s , D e p t .
30.
M i t c h e l l , A.: "Electroslag P r o c e s s e s , " t o be p u b l i s h e d m a k i n g , AIME p u b l i c a t i o n .
31.
P e o v e r , M.;
32.
Maximovitch,
i n t h e USSR, D e c . 1978,
F e b . 1980, 80-81.
A.: Met. T r a n s .
Tool Alloy
1970, 3^,
I r o n and S t e e l
V o l . 15, No. 4,
Steels,
Met. T r a n s .
A p r i l 1978,
2L, 1971,
A.: "The E l e c t r o s l a g R e m e l t i n c Process," 669, U.S. B u r e a u o f M i n e s , 1976, 15-19. 5th I n t l .
C o n f . V a c . Met.,
o f M e t . , U.B.C., 1973.
and Vacuum A r c R e m e l t i n g i n E l e c t r i c Furnace S t e e l -
J . I n s t . Met. 1972, 100, 97-106. B.I.;
Avtom.
Svarka,
19 61,
8, 86-88.
237 33.
Hawkins, R.J. e t a l . : Proc. Conf. i n E l e c t r o s l a g R e f i n i n g , S h e f f i e l d , Jan. 1973, 21-34.
34.
Holzgruber, W.: Proc. o f the 1st I n t l . Symp. on ESR M e l l o n I n s t . P i t t s , Pa., August 1967, P a r t I I .
35.
Klyguev, M.M. e t a l . : 168-171.
36.
M i t c h e l l , A.: Proc. 1st I n t l . Symp. on ESR, M e l l o n I n s t . , P i t t s , Pa., Aug. 1967, P a r t I I .
37.
Buzek, Z. and Hlineny, A.: Prob. S p e c i a l E l e c t r o m e t a l l u r g y . Naukova Dumak, Kiev 1972, P a r t I. (Sbornik Vedeck. Prac. Vys. Skol b.v.s. V o l . 11, 3, 1965, 483-487) .
38.
Miska, H. and Wahlster, M.: 44, (1), 1973, 19-25.
39.
T o b i a s , J.B., and Bhat, G.K.: Proc. o f the 1 s t I n t l . Symp. on ESR., M e l l o n I n s t . , P i t t s . , Pa., August, 19 76.
40.
Schwerdtfeger, K. and K l e i n , K.: Proc. o f the 4th I n t l . Symp. on ESR, Tokyo, Iron and S t e e l I n s t i t u t e of Japan, June, 1973, 81-90.
41.
M i t c h e l l , A.: 112.
42.
P o v o l o t s k i i , D.Y., e t a l . : Izv. Vyssh. Zared Chem. M e t a l l . 1977, 2, 40-42.
43.
Zhmoidin, G.I.: 1971, 6, 46-52.
44.
Choudhury, A.: 1012-1018.
45.
M i t c h e l l , A.: 1418.
46.
P a t e i s k y , G.: Prob. S p e c i a l E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 19 72, P a r t I I .
S t a l i n E n g l i s h , Feb.
1969,
Archiv. f u r Eissen,
Can. Met. Quart.,
1981, V o l . 20, 101Ucheban.
Izv. Abad. Nauk. CCCP M e t a l l y , S t a h l und E i s e n , 1980, 100, No. 17,
Trans. Farad. S o c , 1967, 6_3, 1408-
238 47.
P a t e i s k y , G. e t a l . : 1972, 9, 1318-1326.
J o u r n a l of Va. S c i . Technol.
48.
Kay, D.A.R.: Prob. Spec. E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 1972. P a r t I I .
49.
Kopoywuy, B.: Problemy S p e t s i a l ' n a i E l e c t r o m e t a l l u r g y , V o l . 13, 1980, 12-23.
50.
Korousiv, B. Berg-und Htlttenmannische Monatshefte 122, Jahrgang, J u l y 1977, Heft 7, 287-291.
51.
Ko ro usid, B. and Holzgruber, W.: i b i d . , January 1978, Heft 1, 17-22.
52.
K r u c i n s k i , M.:
53.
A l l i b e r t , M. e t a l . : Iron Making and Steelmaking, 1978, No. 5, 211-216.
54.
Wadier, J.F. e t a l . : Mem. S c i . M e t a l l . , Feb. 61-78.
55.
K a j i o k a , H., e t a l . : Proc. o f the 4th I n t . Symp. on ESR, Tokyo, Iron and S t e e l I n s t i t u t e o f Japan, June 1973, 102-114.
56.
F r a s e r , M.E.:
57.
Wei, Chi-ho and M i t c h e l l , A.: Proc. I n t l . Conf. on Process M o d e l l i n g , AIME, P i t t s b u r g h , 1982, t o be published.
58.
Knights, C.F., and P e r k i n s R.: Proc. of a Conference on ESR, S h e f f i e l d , The Iron and S t e e l I n s t . , Jan. 1973, 35-40.
59.
Kusamichi, H. e t a l . : Proc. o f the 1st I n t l . Symp. on ESR, P a r t I I I , M e l l o n I n s t . , P i t t s b u r g h , August, 1967.
60.
K r i c h e v e c , M.I. e t a l . : Prob. S p e c i a l E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev 1972, P a r t I, 61-72. (Neue Hdtt. Sept.-Oct. 1971, 16, (9-10), 614-618).
61.
P a t c h e t t , B.M. and M i l n e r , D.R.: Welding Research Supplement, (Paper presented a t the AWS 53rd Annual Meeting i n D e t r o i t , A p r i l , 1972), 491-505(s).
123, Jahrgang,
Hutnik, Rok 1974, Nr. 11, 539-548.
1978,
Ph.D. t h e s i s , Dept. o f Met. , U.B.C., 1970.
239
62.
M i t c h e l l , A.: Ironmaking 1974, 3, 172-179.
and Steelmaking
(quarterly)
63.
Boucher, A.: Prob. Spec. E l e c t r o m e t a l . Naukova Dumka, Kiev 1972, P a r t I I , 47-62.
64.
Cooper, C K . e t a l . : Trans. AIME, E l e c t . Furn. Conf. Proceedings, 1970, 26_, 8.
65.
B a l l a n t y n e , A.S.:
66.
M i t c h e l l , A. e t a l . : Proc. o f a Conference i n ESR. S h e f f i e l d , Iron and S t e e l I n s t . , 1973, 3-15.
67.
B a l l a n t y n e , A.S. and M i t c h e l l , A.: Steelmaking, 1977, 4_, 222-239.
68.
Wahlster, M.: Proc. o f the 5th I n t l . Conf. on ESR and Other S p e c i a l M e l t i n g T e c h n o l o g i e s , M e l l o n I n s t . , P i t t s b u r g h , Pa., P a r t I, October 1974, 40-61.
69.
R e t e l s d o r f , J.H., and Winterhager, H.: Prob. Spec. E l e c t r o m e t a l l u r g y , Naukova Dumka, Kiev, 1972, P a r t I I , 122-135.
70.
Pho, P. and E c k s t e i n , F. H.-J.: Sept. 1980, 342-244.
71.
M i t c h e l l , A.: Prob. Spec. E l e c t r o m e t a l l . , Naukova Dumka, K i e v , 1972, P a r t I I , 95-109.
72.
Holzgruber, W. and Peterson, K.: Prob. Spec. E l e c t o m e t a l l . , 1970, Naukova Dumka, Kiev, 4_, 90.
73.
Hozgruber., 6, 190.
74.
Holzgruber, W. : Proc. o f the 1st I n t l . Symp. on ESR and C a s t i n g Technology, M e l l o n I n s t . P i t t s b u r g h , Pa., P a r t I I , 1967.
75.
Rohde, L.E., Choudhury, A.U., Wahlster: 42, 1971, 165-174.
76.
Holzgruber, W. and P l o c k i n g e r , E.: 88, 1968, Nr. 12, 13 J u n i .
Steel
Ph.D. t h e s i s , Dept. o f Met., U.B.C., 1977.
W. and Peterson, K. :
Ironmaking and
Neue Hutte., H e f t 9.
i b i d . , 1973,
Arch.Eisen.
S t a h l und E i s e n ,
240
77.
Kusamichi, H. e t a l . : Proc. of the 1st. I n t l . Symp. on ESR and C a s t i n g Technology, Mellon I n s t . , Aug. 10, 1967, P a r t I I .
78.
Choudhury, A., Jauch, R. und V O l k l i n g e n , F.T.: S t a h l und E i s e n , 100, 1980, Nr. 17, 25 August.
79.
Jager, H. and Kdhnelt, G. : Berg und Htlttenmannische, Monatsheft, V o l . 190, Nr. 9, 1975, 423-429.
80.
Kamardin, V.A. e t a l . : 4, 1974, 59-63.
81.
O p r a v i l , 0.: Proc. Conf. "Metal-Slag-Gas-Reactions," E l e c t r o c h e m i c a l Soc. Toronto, 1975, 923-931.
82.
Kay, D.A.R., M i t c h e l l , A., and Ram, M.: S t e e l I n s t i t u t e , Feb. 1970, 141-146.
83.
Rehak, B. e t a l . : Proc. o f the 5th I n t l . Conf. on Vacuum M e t a l l u r g y and ESR Processes, Munich, Oct. 19 76, 147-152.
84.
Iodkovskiy, S.A. and Panin, V.V.: I z v e s t , Akad. Nauk. SSSR, M e t a l l y , Marz-Apr., (2), 1968, 115-121.
85.
Nakamura, Y. e t a l . : 623-627.
86.
M a r a k h o r s k i i , I.S. e t a l . : S t a l , 1968, 1, 277-279.
87.
Tokumitsu, N., Nakamura, Y., e t a l . : ' Proc. 6th I n t l . Vac. Met. Conf.) on S p e c i a l M e l t i n g , San Diego, Ca. A p r i l 19 79.
88.
S o m e r v i l l e , J . and Kay, D.A.R.: 2, 1727.
89.
C h a i , C.S. and Eagar, T.W.: W i l d i n g Research Supplement of the AWS, 1982, 229-S. (Paper presented a t the 62nd Annual Meeting i n C l e v e l a n d , Ohio, A p r i l 1981.)
90.
Sims, C.E.: The 1959 Howe Memorial l e c t u r e : "The Non-Metallic Constituents of S t e e l , " Trans, o f the Met. Soc. o f AIME, 215, June 1959, 367-393.
Russian M e t a l l u r g y (Metally)
J . Iron and
Trans. I S I J . , V o l . 16,
1976,
F i z . Khim. Osn. P r o i s v o d .
M e t a l l , Trans., 1971,
241
91.
K i e s s l i n g , R. and Lange, N. "Non-Metallic I n c l u s i o n s i n S t e e l , " , 2nd E d i t i o n . P u b l i s h e d by the Metals SocietyLondon, 1978.
92.
P i c k e r i n g , F.B.: " I n c l u s i o n s " , the I n s t i t u t i o n of M e t a l l u r g i s t s , Monograph No. 3, 1979.
93.
" S u l f i d e I n c l u s i o n s i n S t e e l , " Proc. of an I n t l . Symp. Nov. 1974. Port Chester, N.Y. Ed. J . B a r b a d i l l o and E. Snape, ASM, N.6.
94.
"Swedish Symposium on N o n - M e t a l l i c I n c l u s i o n s i n S t e e l " , arranged by Uddeholm Research Found. Swedish I n s t , f o r Met. Research, Apr. 1981.
95.
Van Vlack, L.H.: 1977, 187-228.
96.
S c a n i n j e c t . , I n t l . Conf. on I n j e c t i o n M e t a l l u r g y , Lule.a Sweden. June 9-10, 1977.
97.
S c a n i n j e c t I I . , Second. I n t l . Conf. on I n j e c t i o n M e t a l l u r g y , L u l e a , Sweden, June 12-13, 1980.
98.
Holappa, L.E.K.: "Ladle I n j e c t i o n M e t a l l u r g y , " Metals Reviews, 1982, V o l . 27, No. 2, 53-76.
99.
T u r p i n , M.L.
100.
Forward, G. 1967.
101.
Turkdogan, E.T.:
102.
Sigworth, G.K. and 1973, 105-113.
103.
Malm, S.: 137.
Scand. J o u r n a l of M e t a l l u r g y
5_, 1976,
104.
Malm, S.:
Scand. J o u r n a l of M e t a l l u r g y ,
5, 1976,
105.
Yarwood, J.C., Fleming, M.C. and E l l i o t , Trans., V o l . 2, Sept. 1971, 2573-2581.
106.
E l l i o t , J.F. and J.K. Wright.: 1972, V o l . 11, 574-584.
107.
F r e d r i k s s o n , H. and Hammar, 0.: Sept. 1980, 383-408.
:
and and
I n t e r n a t i o n a l Metals Reviews, Sept.
Elliot, Elliot,
J.F.: J.F.:
J I S I , 204, Elliot,
J I S I , 204,
1966,
J o u r n a l of Metals, 1966,
J.F.:
Intl. 217-225. 54,
914-919. Met.
Can. Met.
Trans 4_,
J.F.:
Jan. 134248-257. Met.
M e t a l l . Quart. Trans. B.,
Vol.
11B,
242 108.
Volmer, N. and Weber, A.: 1926, 277.
Z. Physik Chem. 119,
109.
Becker, R., Doring W.:
110.
Popel, S.I.:
Izv. VUZ Chem. Met 4, 1962, 5-13.
111.
Chipman, J . :
Trans. AIME, 224, 1962, 1288.
112.
McLean, A. and Ward, R.G.: 526.
113.
Kim, C M . and McLean, A.: Proc. Conf. "Metal-Slag-Gas Reactions," E l e c t r o c h e m i c a l S o c , Toronto, 19 75, 284-299.
114.
Von Bodgandy, L. e t a l . : Nr. 7. 1961, 451-460.
115.
Lindon, P.H. and B i l l i n g t o n , J . C : 340-347.
116.
Shewmon, P.G.: Diffusion i n Solids, New York. 1963, 19.
117.
Lindborg, U. and T o r s e l l , K.: 94-102.
118.
Wert, C. and Zener, C. :
119.
M i y a s h i t a , Y. :
120.
T o r s e l l , K. and O l e t t e , M.: 814-822.
121.
Iyengar, R.K.: D. of Ph., Department o f M e t a l l u r g y , C.M.U., P i t t s b u r g h , Pa., 1970.
122.
Mathew, M.P. e t a l . : Arch. Eisenhtlt. , 4_6, J u n i 1975, Nr. 6 ( i b i d . 45_, Sept. 1974 , Nr. 9, 569-573.)
123.
Jacobs, J . E . : Open Heart S t e e l Conf., AIME, Proc. 40, 1957, 315-318.
124.
Hartman, F. :
125.
Kawawa, T. e t a l . :
Ann. Physik., 2£, 1935, 719.
J . o f Metals, 2/7/ 1965,
A r c h i v . E i s s e n h u t . , 32,
J I S I , 207, 1969, McGraw-Hill
Co.,
Trans-TMS, AIME, 1968,
J . Appl. Phys. 21_ , 1950, 5.
Trans. I S I J , 1_, 1967, 1-8. Rev. de Met., Dec. 1969,
S t a h l und E i s e n , 65_, Nr. 3-4, 1945, 29-36. Trans. I S I J , 8, 1968, 203-219.
243 126.
Fuchs, N.A.: N.Y., 1964.
The Mechanics o f A e r o s o l s .
127.
Korber, F. : 1349-1355.
128.
Urban, S.F. and Chipman,J.: 1935, 645-671.
129.
C r a f t s , W. and H i l t y , D.C.: E l e c t r i c Furnace S t e e l Conf. P r o c , AIME, V o l . 11, 1953, 121-145.
130.
Van V l a c k , L.H., e t a l . : Trans o f the Met. Soc. o f AIME, V o l . 221, A p r i l 1961, 220-228.
131.
Weinberg, F.: 219-227.
Met. Trans B,, V o l . 10B, June 1979,
132.
Weinberg, F.:
i b i d . , Dec. 1979, 513-522.
133.
Boldy, N.D., e t a l . : MIT, t e c h n i c a l r e p o r t , Jan. DAAG-46-78-C-32; AMMRC-TR^-81-4.
134.
Sims, C E . and Dahle, F.B.: Ass. 46, 1938, 65-132.
135.
Dahl, W. e t a l . :
136.
F r e d r i k s s o n , H. and H i l l e r t , M.: l u r g y 2, 1973, 125-145.
137.
Mohla, P.P. and Beech, J . : J o u r n a l o f the Iron and S t e e l I n s t i t u t e , Feb. 1969, 177-180.
138.
Takada, H. e t a l . : 573.
139.
I t o , Y. e t a l . :
140.
S a l t e r , W.J.M. and P i c k e r i n g , F.B.: 992-1002.
141.
Wilson, G.W. and McLean A.: " D e s u l f u r i z a t i o n o f Iron and S t e e l and S u l f i d e Shape c o n t r o l , " ISS of AIME, pub. 1980, 1-40.
142.
Baker, T . J . and C h a r l e s , 706.
S t a h l und E i s e n ,
Pergamon
Press.
19 37, V o l . 57, 19 37, Trans, ASM. V o l .
27,
1981.
Trans. Am. Foundrymen s
S t a h l und E i s e n ,
1
1966, 86_, 796. Scand. J . o f M e t a l -
Trans. I S I J , V o l , 18, 1978, 564-
i b i d . , V o l . 21, 1981, 477-573. J I S I , J u l y 1969,
J.A.: J I S I , Sept. 1972, 702-
244 143.
Steinmetz, E. e t a l . : Arch. E i s e n h t l t t . 4_7, Feb. 1976, 71-76 ( i b i d . 47, Sept. 1976, 521-524).
144.
H i l t y , D.C. and Popp, V.T.: AIME E l e c t . Furn. Conf. Proc. 1969, V o l . 7, 1952, 56-66.
145.
T a h t i n e n , K. e t a l . : S c a n i n j e c t Conf. June 1980, paper 24. L u l e a , Sweden, ( r e f . 97).
146.
K i e s s l i n g , R. and Westman, C.: 669-670.
147.
Saxena, S.K. and coworkers: Scand. J . o f M e t a l s , V o l . 5, 1976, 105-112. ( i b i d . , V o l . 4, 1975, 42-48).
148.
Saxena, S.K. e t a l . : Proc. o f a Conf. i n Steelmaking, Chicago, 1978, V o l . 61, 561-573.
149.
Wilson, A.D.:
150.
Kobayashi, 260-269.
151.
Uemura, T. e t a l . : V o l . 59, 457-478.
152.
F O r s t e r , E. e t a l . : S t a h l und E i s e n , 23 Mai, 474-485.
153.
Nashiwa, H. e t a l . : S p e c i a l Rep. I S I J . , 1977, (6th Japan-USSR-Joint Symp. Phys. Chem. M e t a l l . Processes, 81-94.
154.
Takenouchi, T. and Suzuki, K.: 1978, 344-351.
155.
O e l s c h l a g e l , D. e t a l . : Dec. 1981, 332-330.
156.
Folmo, G. e t a l . : 99-104.
Scand. J . o f M e t a l l . , 9, 1980,
157.
Haida, O. e t a l . :
Tsetsu-to-Hagane,
158.
Haida, 0. e t a l . : Proc. o f the 8th, Japan-USSR J o i n t Symp. on Phys. Chem. of M e t a l l u r g i c a l Processes., June 19 81, Tokyo, 56-6 7.
J I S I , J u l y 1970,
Metal P r o g r e s s , A p r i l
S. e t a l . :
Steel
1982, 41-46.
Trans. I S I J . , V o l . 11, 1971,
AIME, Proc. Open Heart Comm., 1976 94, 1974, Nr. 11
Trans. I S I J . V o l . 18,
Iron and S t e e l
International,
1980, 6_6, 3, 48-56.
245 159.
Church, C P . e t a l . : 62-78.
J o u r n a l o f Metals., Jan.
1966,
160.
Eklund, G. : Jerkont A n n a l i , V o l . 154 , 1970, 321-325.
161.
Rosenqvist, T., and Dunicz, B.L.: V o l . 194, 604-608.
162.
Turkdogan, E.T.: 546-563.
163.
H i l t y , D.C and C r a f t s , W.: 1307-1312.
164.
Turkdogan, E.T. e t a l . : 1561-1570.
165.
Kor, G.J.W. and Turkdogan, E.K.: i b i d . , V o l . 2, June 1971, 1571-1578.
166.
Kor, G.J.W. and Turkdogan, E.K.: i b i d . , V o l . 3, May 1972, 1269-1278.
167.
H i l t y , D.C. and C r a f t , W.: 1954, 959-967.
168.
H i l t y , D.C. and F a r r e l l , 17-27.
169.
Silverman, E.N.: Trans, o f the Met. Soc. o f AIME, V o l . 221, June 1961, 512-517.
170.
Hilty, 414 .
17.1.
D'Entremont, J.C. e t a l . : ( i b i d . , 1967, 239^, 123) .
172.
Wentrap, H. e t a l . :
Arch. E i s e n , 13_, 1939, 15.
173.
Gokcen, N.A. e t a l . :
J . o f Metals, 1953, 173.
174.
McLean, H. and B e l l , H.B.:
175.
G u s t a f s s o n , S. and Melberg, P-O.: Scand. J . o f M e t a l l u r g y , V o l . 9, 1980, N. 3, 111-116.
176.
Janke, D. and F i s h e r , W.A. : 195-197.
177.
Fruehan, R.I.:
Trans AIME, 1952,
Trans. TMS-AIME, 1961, V o l .
221,
J . o f M e t a l s , Dec.
1952,
Met. Trans., V o l . 2, June 1971,
Journal o f Metals,
J.W.:
D.C. and C r a f t s , W.:
Sept.
I . and S.M., May 1975,
Trans. AIME, 188,
1950,
Trans. AIME, 1963, 227,
14
J I S I , 203, 123.
Arch. E i s e n 4_7, 1976,
Met. Trans. 1, 1970, 3403-3410.
246
178.
Rohde, L.W. p. 1966.
et a l . :
179.
Ototani,
180.
M i y a s h i t a , Y. e t a l . : 1969-1975.
181.
Kobayashi, S. e t a l :
182.
Kusakawa, R. e t a l : 1976, paper 21.
183.
Watanabe, S. e t a l . : 683-688.
184.
Steinmetz, E. e t a l . : Arch. E i s e n . 4_7, 1976, Nr. 4, A p r i l , ( i b i d . , Arch. E i s e n 4_8, 1977, Nr. 11, November 569-574.
185.
H i l t y , D.C. and F a r r e l , J.W.: 13th Annual Conf. of M e t a l l u r g y , Toronto. Aug. 27, 19 74.
186.
Hammar, 0.: "Progress Through Research Sandvik." S t e e l Research Centre Lab. Sandviken-Sweden.
187.
Waudby, P.E. and S a l t e r , W.J.M.: 518-522.
188.
Morgan, E.L. e t a l :
189.
Cremer, P. and D r i o l e , J . : Met. Trans. B., 13B., March 1982, 45-51.
190.
P l o c k i n g e r , E.: S t a h l E i s e n , 1956, 76, 810 1957, 7 7 / 701, i b i d . , 1960, 8_0, 656).
191.
Straube, H. e t a l . : Arch. Eisenhtlt. J u l y 1967, 509 ( i b i d . , 1967/ 38, 607).
192.
Sloman, H.A.
193.
Braun, T.B., E l l i o t , J.F. and Flemings, M.C.: Trans. B.,1979, V o l . 10B., 171-184.
194.
Okohira, K. e t a l . : 102-109.
195.
O o i , H. e t a l . :
T. e t a l . :
A f d . E i s e n h i i t t . , £2, 1971, Trans. I S I J . 16, 1976, 275-282. Tetsu-to-Hagane',
5_7, 1971,
Trans. I S I J . , 11, 1971, 260-269. Japan S c i . Assn. 19th Committee, Trans I S I J . , V o l . 19_, 1979,
J I S I , J u l y 1971,
J I S I , 1968, 206, 987.
and Evans, E.L.:
(ibid.,
J I S I , 165, 1950, 81. Metall..
Trans. I S I J . , V o l . 14, 1974,
Trans. I S I J . , V o l . 15, 1975, 371-379.
247
19 6.
Waudby, P.E. a n d W i l s o n , F.G.: P r o c . I n t l . Symp. C h e m i c a l M e t a l l u r g y o f I r o n and S t e e l , S h e f f i e l d , J u l y 1971, 195-197.
197.
Gatellier, 275-283.
198.
S p o n s e l l e r , D.L. 1964, 876.
199.
Shurmann, E.B. e t a l . : J u l i 1974, 433-436.
C. e t a l . :
ABM.
3_3 , No.
and F l i n n , R . A . :
Arch.
ibid.,
46, N r .
10, O k t o b e r
ibid.,
46, N r .
8, A u g u s t
ibid.,
4_5, N r . 6, J u n i
ibid.,
46, N r .
Trans.
Eisenhtltt.
1975,
1975,
1974 ,
234 , M a i o ,
AIME,
1977,
230,
45_, N r .
7,
619-622.
473-476.
336-371.
12, D e z . 1975,
767-771.
200.
K e p k a , M. : 645-652,
Neue H t l t t e , V o l . 2 1 ( 1 1 ) ,
201.
L i n d o n , P.H. 340-347.
202.
J a e g e r , H. and H o l z g r u b e r , W. : P r o c . I n t l . Symp. C h e m i c a l M e t a l l u r g y o f I r o n and S t e e l , S h e f f i e l d , J u l y 1971, 195-197.
203.
Boris, M.J. : 28, 89.
204.
Dunn,
205.
K o c h , W.:
206.
P i c k e r i n g , F.B.: P r o d u c t i o n and A p p l i c a t i o n C l e a n S t e e l , 1972, L o n d o n , 75-95.
207.
B r u c h , J..: M i k r o c h i m . A c t a , S u p l . 5., J a n . 1974, S p r i n g e r V e r l a g , 137-146. ( B r u c h , J . e t a l . : A r c h i v . E i s e n h t l t t , H e l f t 11, Nov. 1965, 799-807) .
208.
L i n d o n , P.H. 340-347.
E.J.:
and B i l l i n g t o n ,
AIME, E l e c .
ibid.,
Stahl
1971,
J.C
Furn.
29,
1976,
JISI,
March
Steel
Conf.
1969,
Proc,
1970,
117.
und E i s e n , 8 1 ,
and B i l l i n g t o n ,
:
Nov.
1961,
J.C:
1592.
JISI,
of
March
1969,
248
209.
F a u l r i n g , G.M. e t a l . : 14-20.
210.
Holappa, L.E.K.
211.
Sanbongi, K.:
Iron and S t e e l Maker, 1980,
( r e f . 94), 19-34. Trans. I S I J . , V o l . 19, 1979, 1-10.
(Emi, T., Sanbongi, K., e t a l . : 1978, 64 (10), 1538-1547) .
Tetsu-to-Hagane,
(Kobayashi, S., Sanbongi, K., e t a l . : 1961, 198, 260-269.)
Trans.
ISIJ.
212.
R i k a t a l l i o , P.:
Paper 13, Ref. 97, S c a n i n j e c t I .
213.
U s u i , T.:
214.
Saxena, S.K.: Ironmaking and Steelmaking, 1982, V o l . 9, No. 2, 50-57.
215.
O t o t a n i , T. and Kataura, Y.: 1972, 334-342.
216.
F a u l r i n g , G.M. and Ramalingam, S.: 11B, March 1980, 125-130.
Met. Trans. B.
217.
F a u l r i n g , G.M. and Ramalingam, S.: 10A, Nov. 1979, 1781-1787.
Met. Trans. A.
218.
B e l l , M.M.: M.A. Sc. t h e s i s , Department o f M e t a l l u r g y , U.B.C., 1971.
219.
M i t c h e l l , A. and B e l l , M.M. : 1972, 363-369.
220.
B u r e l , B.: M.A. Sc. t h e s i s , Department o f M e t a l l u r g y , U.B.C., 1969.
221.
V a c c a r i , J.A.:
222.
Viswanathan, R. and Beck, G.: Nov. 1975, 1997-2003.
Met. Trans. A., 6A,
223.
R a t l i f f , J . L . and Brown, R.M.: V. 60, 176.
Trans. ASM. 1967,
224.
K e l l y , T.N. e t a l . , Proc. o f the 3rd I n t l . Conf. on ESR and o t h e r Spec. M e l t i n g , Techs., M e l l o n I n s t . P i t t s burgh, Pa., June 1971* 125-140.
Paper 12, Ref. 98, S c a n i n j e c t I I .
Trans. I S I J , V o l . 12,
Can. Met. Quart.
2,
Design Engineer, May 1980, 57-60.
249
225.
B a l l a n t y n e , A.S. and M i t c h e l l , A.: Proc. of an I n t l . Conf. on S o l i d i f i c a t i o n . S h e f f i e l d M e t a l l , and E g. Assn. and U. of S h e f f i e l d . J u l y 1977, 363-370.
226.
E t i e n n e , M.: Ph.D. t h e s i s , Dept. of M e t a l l u r g y , U.B.C., 1971.
227.
S i d l a , G. and M i t c h e l l , A.: "The Design, C o n s t r u c t i o n and O p e r a t i o n of an ESR Furnace I n s t a l l a t i o n , " Special Report to DREP/DSS, June 1980.
228.
R i d a l , K.A. e t a l . :
229.
Malm, S.:
230.
Colby, J.W.: Company r e p o r t , B e l l Telephone Inc., Allentown, Penn. 1971.
231.
Rooney, T.E. and S t a p l e t o n , A.G.: 1935, 249-254.
232.
Y u l e , J.W. and Swanson, G.A.: l e t t e r , 8, 1969, 30.
233.
Ingamels, C O . :
234.
Rein, R.H. and Chipman, J . : Trans, o f the Met. Soc. of AIME, V o l . 233, Feb. 19 65, 418.
235.
K l i s i e w i c s , Z.. e t a l . :
Hutnik 1980, 47 (2), 56-60.
236 .
Kuo C-K. and Yen T-S. : 381.
A c t a Chim. S i n i c a ,
237.
Nakai, Y. e t a l . : 410.
238.
B e r c i k , P., Hutnicke, L i s t y , : 867-872.
239.
Wilson, W.G., Kay, D.A.R. and Va hed A.; J . of Metals, 1974, 26, 14-23.
240.
Sharma, R.A. and Richardson, F.D.: 386-390.
241.
Sharma, R.A. and Richardson, F.D.: Trans, of the Met. Soc. of AIME, Aug. 1965, V o l . 233, 1586-1592.
J I S I , Oct. 1965, 995-1003.
Scand. J . o f M e t a l l u r g y , 4_, 1975, 231-237. Labs.
J I S I , V o l . 131.
A t . A b s o r p t i o n News-
A n a l . Chim. Acta' 5_2, 1970, 323.
30_, 1964,
Trans. I S I J . , V o l . 19, 1979, 401V o l . 31, No. 12, 1976,
J I S I , Aug. 1961,
250
242.
Iyengar, R.K. and P h i l b r o o k , W.O.: J u l y 1972, 1823-1830.
243.
Lindskog, L. and Sanberg, H.: 1973, 2, 71-78.
244.
Engh, T.A.
245.
L i n d e r , S.:
246.
A r i t o m i , N. and Gungi, K.: Trans of the Japan I n s t , of M e t a l s , V o l . 22, No. 1, 1981, 43-56.
247.
Suzuki, A. e t a l . : Nippon Kinzoku Gakkai Shuho, 32, 1968. (see Brutcher T r a n s l . 7804 (1969).
248.
Choudhury A. e t a l . : S t a h l u. E i s e n 96, 946-951.
249.
Mochizuki, T. e t a l . : 4th I n t l . Symp. on ESR, I S I J , Tokyo, Japan, 260.
250.
Kadose, M. e t a l . : i b i d .
and Lindskog, N.: ibid.,
1974,
Met.
Trans. V o l . 3
Scand. J . M e t a l l u r g y , ibid.
1975,
4, 49-58.
5, 137-150.
246.
1976,
Nr. June
20, 1973
251
F i g u r e ( 1 ) - S c h e m a t i c i l l u s t r a t i o n o f an ESR
system.
252
Axial length (cm)
Figure
(2) - P r e d i c t e d and measured temperature p r o f i l e s f o r a 1018 M.S. e l e c t r o d e , 25 mm i n diameter.
253
Figure
(3) - Manganese content of the metal f o r u n i v a r i a n t e q u i l i b r i u m gamma i r o n + "MnO" + "MnS" + l i q u i d (1) f o r the Fe-Mn-S-0 system and u n i v a r i a n t e q u i l i b r i u m gamma iron + "MnS" + l i q u i d s u l f i d e f o r Fe-Mn-S system.
800
1000
1200
Temperature
Figure
(4)
1400
1600
(°C)
U n i v a r i a n t e q u i l i b r i a i n Fe-Mn-S-0 system the presence o f gamma i r o n and Mn(Fe) 0 (164) phases
255
>i
•P > •H
4 > O
<
—
CD CO
|Fe-Mn-0
CD (0 CO .£ CD ft
c
C i—I (0 O S co
ToFe-5-0'S> 1100
1300
1500
1700
Temperature (°C) —•>•
actual conditions
(cooling)
equilibrium conditions starting ~ —
(cooling)
composition
heating conditions f 16 6> )
F i g u r e (5) - U n i v a r i a n t e q u i l i b r i a i n v o l v i n g s o l i d metal and Mn(Fe)0 i n Fe-Mn-S-0 system bonded w i t h t e r n a r y Fe-Mn-0 and Fe-S-0 terminal-phase f i e l d s ; (e) 6, 'O', 1 ; (p) f S , l , 1 ; (f) 6, 'o', ; (n) 6, ' o \ 1 , 1 ; (g) 6, y, 'o'; 1 ^ 2
1
2
(h) # Y
1
'o'; 'MnS', 1
1
.
2
2
256
MiS
.MO-&0,
(a) MiS
MnO
Figure
(7)*
1 6 6
)-
E q u i l i b r i u m phases i n three planes o f the FeO-MnO-MnS-Si0 s y s t e m , a) MnS-FeO-2MnSiOj 2
b)
MnS-2FeO'Si0 -2MnO«Si0 2
2
and c)
MnS-FeO-MnO,
257
(95) Figure
(8)
a) MnO-Si0 b i n a r y phase d i a g r (T-Mn_SiO. and R-MnSiO-.) 2
b) Schematic i l l u s t r a t i o n of l i q u i d versus Mn/Si/O r a t i o s .
compositions
(b) i s a s e c t i o n of the Fe-Mn-Si-S-0 system. ABC are s i m p l i f i e d l i q u i d compositions. A'B'C* are l i q u i d compositions s a t u r a t e d with s o l i d s u l f i d e a t 1315°C.
258
gure
(9) - Schematic i l l u s t r a t i o n o f changes i n i n c l u s i o n composition (enriched i n S i and Mn) i n a 1020 MS electrode.
260
Figure
(11) - I s o t h e r m a l . activities)
Fe-Al-Ca-0 p r e c i p i t a t i o n diagram' *^. 1
(Henrian
to
263
Figure
(14) - Schematic i l l u s t r a t i o n of the ESR used i n t h i s i n v e s t i g a t i o n .
arrangement
I
II & 01
IV
Figure (15) - Schematic illustration of the "inclusion extractor".
265
Figure
(16) -
I n c l u s i o n s from 1 0 2 0 - s t e e l used as l i g h t microscope. 4 30 X. Spectrum X-ray a n a l y s i s are a i v e n 17 (a-b) .
electrode i n Figure
X-ray energy
Figure
(17)
Deformed i n c l u s i o n (a) S p e c t r u m X - r a y (b) S p e c t r u m X - r a y
(KeV)
i n a 1020 M.S. a n a l y s e s of dark phase. a n a l y s e s o f l i g h t phase.
267
Figure
(18) - M a c r o s t r u c t u r e o f a 1 0 2 0 - e l e c t r o d e t i p . (a) u n e t c h e d s u r f a c e (125X). (b) m a c r o s t r u c t u r e where l i q u i d f i l m , s e m i l i q u i d r e g i o n and y - g r a i n g r o w t h , a r e a s a r e shown.
268
(c) Figure
(d)
(19) - M a c r o s t r u c t u r e s from a 4340-electrode t i p . (a), ( c ) , and (d) show the l i q u i d f i l m , p a r t i a l l y l i q u i d r e g i o n and the f u l l y and p a r t i a l l y a u s t e n i t i z e d zones( b ) , (c) and (e) 30X. (a) shows a d r o p l e t i n process o f forming (b) 6.6 X.
269
270
Figure
(21)
S c h e m a t i c i l l u s t r a t i o n o f a 1020 e l e c t r o d e t i p s u b j e c t e d t o ESR t h e r m a l g r a d i e n t s .
271
Figure
(22)
- M u l t i p h a s e ( r e l a t i v e l y grown) i n c l u s i o n s i n a 1 0 2 0 e l e c t r o d e . 400 X.
272
Figure
( 2 3 ) - S i n g l e phase i n c l u s i o n s i n p a r t i a l l y and f u l l y molten r e g i o n s i n a 10 20 e l e c t r o d e t i p . (a) 45 X and (b) 400 X.
Figure
(24)
-
C o m p l e x ( C a , A l , S i , Mn) i n c l u s i o n s f o u n d in t h e l i q u i d f i l m a n d d r o p l e t s o f 1020 e l e c t r o d e s (a), (c), ( d ) - 1 . 8 x 1 0 X a n d (b) 3 . 6 x 1 0 X. 2
2
274
X-ray energy (KeV)
Figure
(25) -
(a) T y p i c a l in
complex
the l i q u i d
film
(2.4 x 1 0 X ) (b) S p e c t r u m X - r a y
(Ca, A l , S i , Mn) and d r o p l e t
3
analysis.
inclusion
o f 1020
electrodes
275
Composition i n a t . %
Figure
(26) - Changes i n i n c l u s i o n chemical composition i n a 4340(1) e l e c t r o d e t i p s u b j e c t e d to (ESR) thermal g r a d i e n t s .
276
Figure
(27)
- Changes i n i n c l u s i o n chemical composition i n a 4340 e l e c t r o d e t i p with strong r e c r y s t a l l i z a t i o n .
277
• A! ACa
E
o & • Mn
12000 •H
fr,
spherodization of sulfide inclusions
•a
cr •rl
8000
£ O 4-1
CD U
•f 4000
C
solidus
fO
w
•H
— i 20
40
Composition
Figure
" -|- 285Cym
Liquid-solid region
4J
Q
5500iim
Incipient heat affected zone
60
$- 350Mm
80
liqiidus
( a t . % x)
(28) - B e h a v i o r o f o x i d e i n c l u s i o n s i n an e l e c t r o d e t i p of a r o t o r s t e e l s u b j e c t e d t o ESR-thermal g r a d i ents.
Figure
(29) - A l - s i l i c a t e i n c l u s i o n s i n a 4340 ESR i n g o t , 75 mm i n d i a m e t e r . Deep e t c h e d sample by i o d i n e m e t h y l a c e t a t e m e t h a n o l ( I n g o t 3) (a) 1000 X and (b) 2000 X.
279
RIII-W
20
40
60
T o t a l Oxygen Content
Figure
80 (ppm)
(30) - I n f l u e n c e o f C a S i and FeO i n t e r m i t t e n t a d d i t i o n s on the oxygen c o n t e n t i n a 1020 M.S.
100
280
RII-W
25
Ca,
20
g
3
15
FeO, 2 nd add. 'Ca', 1st add.
4->
2
2ndaddJ
io
o Ul c
FeO,
1st add.
40
60 Total
Figure
Oxygen C o n t e n t
80
100
(ppm)
(31) - Changes i n t o t a l o x y g e n c o n t e n t r e s u l t i n g i n C a S i and FeO i n t e r m i t t e n t a d d i t i o n s d u r i n g r e f i n i n g o f a 1020 M s t e e l .
281
Figure
(32) - Changes i n s l a g chemical composition i n a 1020 (RIII-W) s t e e l r e s u l t i n g from CaSi and FeO i n t e r m i t t e n t a d d i t i o n s .
282
RII-W
01 0
1
1 0.2
(wt.% Mn)
Figure
1
U 0.4
I 2
| 3
(wt.% Fe X 10
| 4
)
(33a) - Changes i n s l a g chemical composition as a r e s u l t of i n t e r m i t t e n t a d d i t i o n s of CaSi and FeO i n s l a g d u r i n g r e f i n i n g .
L 5
283
RII-W
Slag Chemical Composition
Figure
(wt.%)
(33 b) - Changes i n S i , A l and Ca as a r e s u l t of d i s c r e t e a d d i t i o n s of CaSi and FeO i n the s l a g during r e f i n i n g .
284
RIII-W
1
i—i—i—i—I
06
I—i—i—i—I
0 . 7 5 0 B 5 0.1 02 Ingot
Figure
i—I—I
Chemical
I—I—i—i—I—r
I
i
i
i
i
i
|
I
•
.
.
001 0.03 0 0 5 0 0 7 0 2 0 0 2 4 Composition
.
I
0.28
(wt.%)
( 3 4 ) - Changes i n i n g o t c h e m i c a l c o m p o s i t i o n a s a r e s u l t o f C a S i and FeO a d d i t i o n s i n s l a g .
285
Figure
(35) - E f f e c t of CaSi and FeO a d d i t i o n s i n the s l a g on the chemical composition of a 1020 MS ESR-ingot.
286
RIII-W
~i
i
1
r
1
o inclusion size x 10>m
251
power off
20 15
2nd Ca-addition 2nd FeO addition
+J
x:
Cn •H
10
(1)
BC JJ O Cn C
5h
20
40
60
80
a t . % Ca at.% A l
Figure
(36) a,b
100
1 n X
1
120
140
160
4
0
- Changes i n i n c l u s i o n c o m p o s i t i o n (a) and mean s i z e (b) i n a 1020 MS i n g o t as a r e s u l t o f i n t e r m i t t e n t o x i d a t i o n and d e o x i d a t i o n o f t h e s l a g .
287
Figure
(37)
- Chemical a n a l y s i s of s l a g samples i n
RI-H
288
0.1
0.2
0.1
Ingot Composition
Figure
0.6
0.2
(wt.
0.7
0.8
%)
(38) - Ingot chemical a n a l y s i s i n R l - I l . as a r e f e r e n c e ) .
(Ingot used
289
RII-Il
Slag Composition
Figure
(39) - Slag chemical a n a l y s i s
(wt. %)
(wt.%) i n R I I - I l .
290
4-> tn •H cu
K 4-1
o Cn c
H
0.2
0.6
1.0
28
30
Slag Composition
Figure
(40) - Slag chemical a n a l y s i s
(wt. % X)
(wt.%) i n RII-I2.
291
RII-Il
i—I—r
i—r
30h
\
V
25h
o i l i I i o
1 —
•
Solid
O
Liquid
20
o I t
15
o
V
10
A J
P
2 3 4 5 6 7 8 9
I n c l u s i o n Mean (ym)
(41) -
Diameter
60 Total
st add. i I00
80 Oxygen C o n t e n t
I n c l u s i o n mean d i a m e t e r and t o t a l content i n R I I - I l .
3rd add. 2nd add.J
L
I
Figure
1
4th add.
(ppm)
oxygen
292
30
1
T
r
T
r
()
25
5 th odd
-i 20 x: tn
•H
4th add
oi:
4-»
15
~o—-~
0)
3rd odd
K
4->
o
tn CJ
10 r
V
o Liquid pool •Solid / ingot I
2Qd.Qq!d
\ Ca
addition
*
\
o
r
2
j
/
4 6 8
30
I n c l u s i o n Mean Diameter (ym)
Figure
(4 2)
1 *A
40
L
50
\
° Liquid pool
1
• Solid ingot 1st add. * Calculated total oxygen content from extracted inclusions 70 80 90 100 t
60
T o t a l Oxygen Content (ppm)
- T o t a l oxygen content and i n c l u s i o n mean d i a meter i n RII-I2.
293
T
,* 10
1
1
20 20
1
40 30
40
1
1
, 6 0 50
60
,at.% Ca, 'at.% A1
1
1
,89 70
1
r
liguidpod, 80
ingot
1 Q 2
J
Figure
(4 3) - I n c l u s i o n chemical composition (at.%) as a f u n c t i o n of c o n t i n u o u s l y i n c r e a s i n g deoxida t i o n r a t e s (ingot height) i n i n g o t R I I - I l .
294
30
—3»0
25
o-=^-~
r-
/
20 o e
£ 15
/
o'
4-1
Cn
i
10
4-1
o in H
5
^
Ca addition
^
/
o u
g j_ ^ /
«/
.
, 50
Figure
(44)
•
solid ingot
°
liquid pool
, 100
I n c l u s i o n chemical composition as a f u n c t i o n of the i n g o t h e i g h t (or c o n t i n u o u s l y i n c r e a s i n g d e o x i d a t i o n r a t e s ) i n RII-I2.
295
RII-Il
Ingot Chemical Composition
Figure
(wt.%)
(45) - Ingot chemical composition a g a i n s t i n g o t h e i g h t (or d e o x i d a t i o n r a t e ) .
296
Ingot Composition
Figure
(46)
(wt.%)
- Ingot chemical composition v s . i n g o t h e i g h t (or d e o x i d a t i o n r a t e ) i n R I I - I 2 .
2 9 7
298
(c)
Figure
(d)
(4 8) - "Alumina g a l a x i e s * a s s o c i a t e d w i t h MnS I I i n an A l d e o x i d i z e d i n g o t , ( R I I - I l ) . 2000 X. (a) BE photograph, (b) A l (c) Mn and (d) S maps.
299
X-ray
Figure
(49)
- a-Al^O^
(corundum)
Energy
inclusions
in
(KeV)
Al
deoxidized
ingots. (a) u n e t c h e d s u r f a c e , ^ 1 0 0 0 X; (b) a n d ( c ) a r e d e e p ( i o d i n e m e t h y l a c e t a t e ) e t c h e d s a m p l e s , * 3 0 0 0 X; (d) s p e c t r u m a n a l y s i s o f (a) a n d (b) r e s p e c t i v e l y ; •v 2 0 0 0 counts.
300
(c) Figure
(d)
(50) - Calcium-aluminate i n c l u s i o n from a h e a v i l y A l deoxidized ingot. (a) b a c k s c a t t e r e d e l e c t r o n photograph taken a t 4000 X. Reverse p o l a r i t y . (b) , ( c ) , and (d) are A l , Ca and S maps. RIIII2-S8-SLD.
301 RII-Il
1-••
1
—"1
1
o o
S - Stoichiometry Ratio
8
6h
X
to u < 0\° 0\°
• -p
f0
/ /
•/
s
•
/
/
/
/
// —
4
c
+J
/
/
'
/
/
/
/«»
•
•
/ /
/
/
r
/*! ' 0.4
i
0.6
i
i i
i
0.8
1.0
1.2
.at. at.
Mn"
L
Figure
(51) - C o m p o s i t i o n dependence Ca-aluminate i n c l u s i o n
1.4
1.6
o f s u l f i d e p h a s e s on t h e phases i n R I I - I l .
Figure
(52) - Composition dependence o f s u l f i d e phases the Ca-aluminate i n c l u s i o n phases i n RII
'igure
(a)
(b)
(c)
(d)
(53)
- Segregated m a t e r i a l i n an A l - d e o x i d i z e d ingot, (a), (b) , (c) and (d) are A l , Ca, S i and Mn maps. -v 1 0 0 0 X.
3 0 4
Figure
(54) - Dependence of "FeO"
content
on the
r a t i o i n slag i n a continuously mgot, (RII-H). y
(—^3, CaO Al-deoxidized ueoxiaizea
305
u
1.3
1.2 A
Figure
(55)
1
1.1
2°3
Al 0 - Dependence of the "FeO" on the ( — - ) ratio , CsO i n s l a g i n a c o n t i n u o u s l y A l - d e o x i d i z e d incrot. (RII-I2).
y
'
306
RIII-Il
Figure
(56) - T o t a l oxygen content and i n c l u s i o n mean diameter i n a CaSi-deoxidized ingot (RIII-Il) .
307
RIII-I2
T—i—i—i—I
0
4
8
|
1
30
40
Inclusion Mean Diameter (ym)
Figure
'
1
60
1
1
80
T o t a l Oxygen Content
(57) - I n c l u s i o n mean diameter content i n RIII-I2.
r
(ppm)
and t o t a l oxygen
308
025
0.5
r a.t • L
Figure
(58)
at.
0.75
% Ca i % A1 J
- I n c l u s i o n chemical composition (at. % ) , as a f u n c t i o n o f d e o x i d a t i o n r a t e s i n RIII-Il.
309
Figure
(59) - I n c l u s i o n chemical composition as a f u n c t i o n of d e o x i d a t i o n r a t e s i n R I I I - I 2 .
310 RIII-Il
Figure
(60)
- Changes i n t h e s l a g c o m p o s i t i o n i n a c o n t i n u ously Ca-Si deoxidized ingot ( R I I I - I l ) .
RIII-I2
r
1
T
1
r
1
30 ^ 25 •
J
6 th addition
r
\ "
t t
20
-P
si
tn
•H
CD
15
-P O
tn
C
H
10
\
c/3rd
add..
/ \
2nd
add. Fe J
•
/
0.2
^
\
<
J
I
0.6
o Si \ 1st add.
I
'
I
1.0
A
Al\
L
1.4
II
13 15
Slag Composition
Figure
(wt. %)
(61) - Changes i n s l a g composition i n a c o n t i n u o u s l y (CaSi) d e o x i d i z e d i n g o t , (RIII-I2)
312
Figure
(62)
- Changes i n A l and S i i n ingot deoxidation i s increased.
( R I I I - I l ) as CaSi
313
RIII-I2
r~o—i
T
o Si
r
1
7 I _i/
r
6th addition 5 th addition
4th
add.
3rd
add.
2nd
add.
1st
add.
_o
1
6 0.2
0.6
0.7
0.8
)
i 1
i
i
i
2
3
4
Wt.% X (Al,Mn,Si) i n i n g o t
Figure
(63) - Changes i n chemical composition i n a c o n t i n u o u s l y CaSi d e o x i d i z e d i n g o t , ( R I I I - I 2 ) .
314
RIII-Il
Figure
(64) - Dependence of "FeO" contents i n the s l a g on deoxidation rates i n R I I I - I l .
the
315
R HI 0.8
I
2.5
1 2
,
3.0
3.5
Wt. % Co ] . s l a g Wt. % Al
Figure
(65) - Dependence of "FeO" contents i n the the d e o x i d a t i o n r a t e i n RIII-I2.
slag
316
RIII-Il
Figure
(66) - S u l f u r content i n i n c l u s i o n s as a f u n c t i o n of the Ca:Al r a t i o i n the Ca-aluminate phases (RIII-Il).
317
R1I-I2 (Ca-Si ~i
deoxidized ingot) r-
r~w
1
( A t % S ).
,
.
inclusion
Figure
(67) - I n c l u s i o n composition i n samples from liquid p o o l and i n g o t as d e o x i d a t i o n r a t e i s i n c r e a s e d .
0
Ingot
Height
(cm)
ro
ro cn
o
o -I—
cn ro O H
C
P-
3
\
o
3 rt
n
0) I
0 3
01
O
OJ
ro
o
ao i- g c t> go H-
'
cn
*
o
OD
zr
a.
a a.
a.
a
o a. a.
o a. a.
Q.
a. a.
o.
•
V
2
_1_
O
01
~~ 01
Q
o
• 1 —
cr
— 3
01
At. At.
m Ul
» c H (-• M M I M
% Ca % Al
1
0
0
i
n
s
a
m
p i e s
from
liquid
pool
oo
cn
ro
rr
ort\
1
>>.
& (t O X H"
01
>
r
r
*\ \
a
a
—
01 3
a
0
^
\ *s
o
R
\
— \ \
\
\
cn x
0)
ro
o
8T£
1
1
J
\ X
\
-v. —1
319
Figure
(69)
- Segregate enriched (c) S i and (d) Mn.
i n (a) A l , * 5000 X.
(b)
Ca,
320 R-4340(1)
35
30 25
~
20
^7t
F
T—r
5. L
/
I.. ...
/
...
4J
15
fI
10
M 5h o
Fe Mn J
0
Si
A
L
01 02 03
-I
I
1
I
u
0.7 OS 11 13 15 17
%
Slag Composition
Figure
(70)
16
(wt.
38
AO
%)
- Slag chemical a n a l y s i s of a 4340 i n g o t c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y ([R-4340 ( 1 ) ] .
321
Figure
(71) - Ingot chemical composition of a 4340-ingot c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y . [R-4340 ( 1 ) ] .
322
Figure
(72) a - V a r i a t i o n i n mean i n c l u s i o n
size.
b - Oxygen a n a l y s i s i n a 4340-ingot c o n t i n u o u s l y d e o x i d i z e d with a CaSi a l l o y , [R-4340(1)].
323
0.1
25
26 (
Figure
2.7
2.8
wt.
% Al
29 }
S l a
3.0
3.1
^
(73) - Changes i n s l a g composition as a r e s u l t of c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s , R-4340 (1).
324
Figure
(74)
- I n c l u s i o n chemical composition, i n (a) i n g o t and (b) l i q u i d p o o l , as a r e s u l t of c o n t i n u o u s l y i n c r e a s i n g CaSi d e o x i d a t i o n r a t e s i n a 4340 ingot R-4340(1).
325
R-4340 liquid pool
140
120
100
|At.%Caxl00 At.% Al
80
ingot
1-700 600
h500 /
400 /
60
(I)
300
40
/ / / 200 /
20
.00//
/
/
/
/
o'
,o
/
/
p
/
/
/
/
/
/
/ /
10
o
LIQUID POOL
•
SOLID
20
(At. % S )
Figure
(75) - I n c l u s i o n composition i n terms o f the Ca:Al r a t i o and s u l f u r content (as CaS) i n R-4340(1).
326
0.8 10
c o
CO r—I
u c
0.6
•H CO
U
-P cd
0.4
0.2
•
(§)
Ca-Si, solid and liquid
*
®
Hypercal,
(§)
Al-Si,
2.0
4.0
6.0
'»
»»
80
»«
10.0
12.0
S u l f u r Composition i n I n c l u s i o n s
Figure
(76)
(at.
S)
- I n c l u s i o n chemical composition (oxide and s u l f i d e phases) i n a r o t o r s t e e l d e o x i d i z e d with three d e o x i d i z e r s ; R-RS-I, R-RS-II and R-RS-III.
327
(c)
Figure
(77)
-
(d)
S e g r e g a t e e n r i c h e d i n A l (40 a t . % ) , C a (41 a t . %), S i (17 a t . % ) a n d Mn ( b a l a n c e ) i n t h e r o t o r steel deoxidized w i t h Al-65 wt. % S i . (a) A l , (b) C a , ( c ) S i a n d (d) M n , 250 X. t
328
401—i—i—i—i—i—i—i—i—r—r
Calcium conlent of steel ppm
Figure
(78)
- I n c l u s i o n " p r e c i p i t a t i o n sequence"in a s t e e l c o n t a i n i n g two l e v e l s of s u l f u r .
329
Figure
(79)
S t a t i s t i c a l determination of the mean i n c l u s i o n diameter (ym). (a) sample from an i n g o t , (b) sample from l i q u i d p o o l .
330
Ca
Al
Ce
Figure
(80) - A l , Ca and Ce d i s t r i b u t i o n i n an i n c l u s i o n o f a sample e x t r a c t e d from the l i q u i d p o o l by a q u a r t z tube c o n t a i n i n g a RE-wire. (a) BE photograph, 4000 X (b) A l , Ca and Ce d i s t r i b u t i o n a c r o s s the inclusion.
331
Figure
(81) - (a) - BE photograph = 6COO X, and A l , Ca, Ce and La d i s t r i b u t i o n s i n a l i q u i d p o o l CaSi d e o x i d i z e d . La and Ce come from a RE-wire p r e v i o u s l y l o c a t e d i n the s i l i c a t e tube.
332
Figure
(82)
-
(a) - BE photograph, 4000 X and A l Ca and Zr d i s t r i b u t i o n s i n an i n c l u s i o n of a sample e x t r a c t e d from a l i q u i d p o o l d e o x i d i z e d with "hypercal". The Zr was p r e v i o u s l y l o c a t e d i n the s i l i c a tube.
333
Figure
(83)
- Composition p r o f i l e s and maps of an
inclusion
i n a sample e x t r a c t e d from a
(ESR)
d e o x i d i z e d with
"hypercal".
(b), ( c ) , (d)
(e) are A l , Ca,
S, and
Zr.
liquid
pool and
334
(e) Figure
(84)
(f)
- BE photograph (a) * 4000 X and composition maps from an i n c l u s i o n e x t r a c t e d from a l i q u i d p o o l d e o x i d i z e d with " h y p e r c a l " ; (b) Ca, (c) A l , (d) S, (e) S i and (f) Zr.
335
Figure
(85) - I n c l u s i o n d i s t r i b u t i o n i n a d e n d r i t i c s t r u c t u r e o f 1 0 2 0 - s t e e l samples t a k e n from l i q u i d p o o l during r e f i n i n g . ( a ) , (b) and (c) show commonly f o u n d i n c l u s i o n s i n a n A l - d e o x i d i z e d ingot. (a) 50 X, (b) and (c) 170 X.
336
337
Figure
(87) - Isothermal (1823°K) p r e c i p i t a t i o n (Fe-Al-Ca-O-S) diagram at 0.1 a c t i v i t y of aluminum.
338
Figure
(88, - E f f e c t o f the a c t i v i t y o f A l (h
=
0.001
Symbols: A
- A1 0
S C-6A
- MnS (11,111) - CaO-6Al 0
C-2A
I ?a"2A? 0 ^ " ' "2 3
C-A
- CaO.Al 0
C
- CaO
A
(l)
2
3
2
2
-
A 1
2°
( 1 3
)
3
3
(
C
a
'
M
n
)
S
°
r
C
a
S
339
Figure
(89)
- E f f e c t of the a c t i v i t y of S (h
= 0.1,
0.01
0.001) on the " p r e c i p i t a t i o n sequence" of c a l c i u m aluminates. Symbols are d e f i n e d i n F i g u r e
(88).
and
340
(b) Figure
(90) - I n c l u s i o n s e x t r a c t e d from a C a - S i - d e o x i d i z e d i n g o t by the Iodine-Methyl Acetate-methyl a l c o h o l method. (RIII-Il-Sl-SLD). Photographs were taken a t : (a) 3000; ( a ) and (b) 8000 X. 1
341
(a)
(b)
(c) Figure
(91) - I n c l u s i o n s e x t r a c t e d from a C a - S i - d e o x i d i z e d i n g o t by the Iodine-methyl a c e t a t e - m e t h y l alcohol"method. (RIII-I1-S3-SLD). (a) and (b) 4000 X and (c) ^ 1000 X. (calcium aluminates)
342
Figure
(92a)
- Calcium aluminate/calcium s u l f i d e i n t e r f a c e s of inclusions i n CaSi deoxidized ingots, (a) and (b) a r e SEM and EPMA p h o t o g r a p h s 1.2 x 1 0 and 6.0 x 1 0 X. (b) a l s o includes Ca and S a n a l y s i s . (c) a r e t y p i c a l compo s i t i o n s o f c o r e and p e r i p h e r y o f i n c l u s i o n s , respectively. 3
3
343
Figure
(92b) :
S p h e r i c a l c a l c i u m aluminate (core) v/ith ( p e r i p h e r a l ) s u l f i d e phases i n CaSi d e o x i d i z e d i n g o t s (a) and (b) EPMA photographs. ( c ) , (d) and (e) are A l , Ca and S maps, r e s p e c t i v e l y .
344
RII-I2
Figure ( 9 3 )
- Secondary d e n d r i t e arm spacing i n a round 1 0 2 0 MS — ESR i n g o t .
345
RIII-Il
ingot
Figure
(94) - S e c o n d a r y in
radius
dendrite
d i a m e t e r ) ESR
arm
ingot.
(cm)
spacing 1020
m
°
U
l
d
W
a
l
1
i n a round MS.
(200
346
R-4340 (1)
wall
Ingot Radius (cm)'
(95) - Secondary d e n d r i t e arm spacing i n a round i n diameter) ESR-ingot (4340)'.
(200mm
347
RII-I2
8 Ingot r a d i u s
Figure
9
mold wall
(cm)
(96) - R a d i a l s i z e d i s t r i b u t i o n of i n c l u s i o n s i n an A l deoxidized ingot.
348
RIII-Il
u
cn
-u
0)
e
3
o o R
(0 •H Q C O
•H tfi i H CJ
c
o o
o o
o
o
o o
o
o o
8 §
o o
8
A 3 measurements same points • average large dia. inclusions measurements o average value from one picture 1
I
i
i
i
4
i
'
5
6
Ingot Radius
Figure (97) - Radial i n c l u s i o n deoxidized ingot
(cm)
-I
8
I
9 mould w a l l
s i z e d i s t r i b u t i o n i n a low Ca(1020 MS).
349
RIII-Il
Figure
(98)
- Radial inclusion size distribution ESR i n g o t . ('5-biggest i n c l u s i o n s
i n a 200 mm technique')
350
R 4340
->
(1)
r
5.0
CD
4.0
+J
CD
E nJ
•H
Q
3.0
C O -H
CO
H U C
CD tn rd S-i CD >
2.0
1.0
8 Ingot
Figure
Radius
mold wall
(cm)
(99) - R a d i a l i n c l u s i o n s i z e d i s t r i b u t i o n i n a 4340 i n g o t (200 mm i n d i a m e t e r ) d e o x i d i z e d w i t h Ca-65% S i A l l o y .
351
TABLE Modification
Ideal
to Stokes'
condition
Correction wall
due
Law
I for Deviation
U
to
crucible
=
2
no
9
—
u = u
Ideality
2
9
(1
s t
from
=
r
U
s t
bJL)
+
distance of p a r t i c l e from w a l l b
Presence
of
other
particles
s 0. 5 t o
U = U
2
. / (1 + st
K*
/,) 3
* = concentration by v o l u m e K =
Inertial
effect
U = U Re
Liquid
particle
Presence agents
of on
1.3
s t
to
/(1
surface active liquid particle
^ st
+
I
particle-fluid
3
number
+
2-j
v
+
u'
st
2u
+
3p
Br + of
particle
3p'
of
coeff.
E
of
viscosity
. st
D
particles
Re)
= retardation
S l i p at the interface
of
1.9
= Reynolds
U = 0
center
liquid
particle
+ 1
Y +
n
3y.
coefficient
2L
;
sliding
friction
• st<li-H' U
= =
6 ' ( e x p ' a ' S (W slip
factor
k
- K
)/kT)-l)
Non-spherical
particles
9 r ^
X
v
= equivalent
g
X = dynamic
R
eq
r
=
, 7
X
radius
shape
factor
J sed
R
, = sedimentation sea
radius
x = f(x ) B
X
Slightly
deformed
inclusion
v
= coef.
S
=
of
2 Ap_ 3 u
sphericity
g r g
;
1 3
( 3 + | Re + j i -
We)
2rp Re = R e y n o l d s number 2rp,U We = Weber number * o r
= inclusion
radius
= density
of l i q u i d
o = surface
tension
U
J
metal
TABLE I I - A Data f o r I n v a r i a n t
Equilibria
i n Fe-S-0 System
-RT Invariant
Equilibria
pO^i
atm
P S 2 / atm
I.
560°C
Iron, wustite magnetite, p y r r h o t i t e , gas
4.8
X 10~
2 7
II.
915°C
Iron, wustite pyrrhotite, l i q u i d ( 1 ) , gas
3.2 X 1 0 ~
1 7
III.
942°C
Wustite, magnetite, pyrrhotite, l i q u i d (1), gas
1.1 X l o " " *
Composition of
a t 915°C:
C o m p o s i t i o n of l j a t 942°C:
5.5
N^ N
e
F e
-
1
2.2 X l o "
8
5.4
1
X lO
"
X 10~ * 6
in p0 kcal
2
-RT i n p kcal 2 g
100.3
50.5
89.6
41.6
77.6
29.3
= 0.50,
N
Q
= 0.19,
N
g
=
0.31.
= 0.49,
N
Q
= 0.19,
N
g
=
0.32.
a
Fe =
0.09.
LO
354
TABLE I I - B Estimated
Data
f o r Invariant Equilibria
Fe-Mn-S
a n d Mn-S-0 T e r n a r y
Fe-Mn-0 t e r n a r y
1527°C
Solid Liquid
system
800
iron:
a
oxide: oxide:
a
=0.65
FeO
FeO
- ° -
ternary
= 0.35
o
3
0.27 MnO
Solid
(Fe) s u l f i d e :
a
FeS
Solid
(Mn) s u l f i d e :
a
MnS
sulfide:
Solid
oxide:
Solid
sulfide:
Liquid
oxysulfide:
ppm S
1
°'
3
7
= 30 w t . p e t . S
= 1.0 X 10~ atm 7
system
Traces *MnO
o f S and 0 ° -
S
>MnS ~'
9
8
° '
9
8
3 0 % Mn, s 3 5 % S , s 351 0
E
p„
Gas:
£
2 1 w t . p e t . Mn p„
manganese:
83
15 ppm Mn
Mn-S-0 t e r n a r y
1230°C
MnO
system
iron:
Gas :
B
7
a
9
Gamma
Liquid
ppm 0
1130
1.2 X 10 ~ atm
Fe-Mn-S
Liquid
52 ppm 0
ppm Mn
Gas :
980°C
Systems
5 80 ppm Mn
6-iron: Liquid
i n Fe-Mn-0,
= 7.6 X
10
_ 2 0
atm
p_ b
"2
= 1.5 X 10" 2
atm Solid Liquid 1225°C
manganese: manganese:
Traces
o f S and O
Traces
o f S and 0
Solid
oxide:
MnO
Solid
sulfide:
MnS
s 0.98 = 0.98
= 5.8 X 1 0
Gas: w
2
atm
_ 2 0
atm,
p
= 1.2 X 10
_i
2
TABLE I I I E s t i m a t e d Data f o r I n v a r i a n t E q u i l i b r i a i n Fe-Mn-S-0 Q u a t e r n a r y System y-iron Solid =900°C
Solid
= 10 ppm. (Mn) s u l f i d e :
a
(Fe) s u l f i d e :
MnS FeS
= 0.4
M
s
1
g 0.5
a
a ^
Liquid
s 26 p e t . FeO, 54 p e t . FeS, 15 p e t . MnS and 5 p e t . MnO by w e i g h t
Solid
(1) o x y s u l f i d e :
p0
Fe/Mn:
"MnS" =1225°C
> 1 ppm. 0
Fe(Mn)0 o x i d e :
Gas:
II.
a
Mn
"MnO" Liquid (1): Liquid (2):
2
s 3.8 X 1 0
F
_ 1 8
atm,
pS
2
= 1.4 X 1 0 "
8
g
0
= 0.5
atm
90 p e t . Mn MnS MnO
s 1 = 1
s 0.1 p e t . FeO, 0.3 p e t . FeS, 65.2 p e t . Mns and 34.4 p e t . MnO by w e i g h t (pet.
O/pct. S) f o r 1
2
(metallic)
< ( p e t . O/pct. S) f o r l j ( o x y s u l f i d e )
Ul
356
TABLE Calculated for
and
Fe-O-Ca-Al
Published Free
Energy
System
K
Equation
Ca(g)
=
Al(l)
1/2
2 Al + C a +
372
1/2
2 Al + Ca
%)
0 , ( g ) = 0 ( 1 wt.
0
0
2
=
%)
-1
2°3
2°3
CaO = CaO-Al 0
CaO
+ Al °
3
CaO
+
2
M
2
CaO
+
6
A1 0
2
2
0 2
3
3
Data
(1550°c/
2 1 6
Atom
'
Ref.
50 (-39
574 .68 481 . 52 +
49.4T)
-114 (-63
137 . 1 220 .68
27.93T)
-122 (- 1 1 7
= CaO
2
3 0 = Al
+ 0 =
A 1
a t 1823
J/kg
C a ( l w t . %)
= A l (1 w t .
IV
Sigworth"''
Sigworth''' -
498 .9 230 .4 -•
Elliott
085
230 . 1
JANAF
3
-437
996, .22
JANAF
3
-489
480. .46
-366
081. .65
-45
845 ..46
3
= Ca0'2
A1 0
3
-50
869 .,62
Kireev^
3
= CaO-6
A1 0
3
-60
708. ,60
Taylor
CaO-Al 0
3
-901
407 .,57
-1
395
9 1 2 . 20
-3
363
6 7 3 . 03
Ca
+ 2 Al + 4 0 =
Ca
+ 4 Al +
Ca
+
12 A l + :19 0
Ca
+
S =
2
2
2
7 0 = CaO-2
A1 0 2
= CaO-6
3
A1 0 2
3
CaS
-257
1.
G.K.
Sigworth
and J . F . E l l i o t t :
2.
J . F . E l l i o t t a n d M. A d d i s o n - W e s l e y Pub.
3.
JANAF T h e r m o c h e m i c a l E d i t i o n , 1971.
4.
V.A. K i r e e v : p p 3-18.
5.
J . Taylor:
Sb. T r . Mosk.
Proc.
Brit.
Met•
S c i . , 1 9 7 4 , v o l . 8, p p .
Inzh-Stroit,
Soc,
298-310.
f o r Steelmaking,
2nd e d . , N a t i o n a l S t a n d a r d
Ceram.
5
659 . 0
Gleiser: Thermochemistry Co., 1960. Tables,
2
2.89T)
Inst.,
Ref.
1971, v o l . 69,
1 9 6 7 , v o l . 8, p p .
115-23.
TABLE V E q u i l i b r i u m Constants
Compound
A c t i v i t y Product
CaO
1
2
l / ( h 3
CaO-2 A 1 0
3
CaO-6 A 1 0
3
2
2
2
(
h C
CaO-Al 0
A1 0
/
1
1
h
/(
h
1 / ( h 3
Ca
/(
X
h
0
X
h
Al
a
C
a
C
a
Al
(216) Reactions
f o r Deoxidation
)
X
X
h
Al
X
X
h
Al
X
X
h
0
K (1823 K)
)
X
h
0
h
0
)
^
>
}
6
,
3
-
0 5
X
4
6
X
1
l o l
q
2
°
5
9.46 X 1 0 )
2
'
1 3
1
'
X
0 4
1
X
q
1
9
q
3 9
6
1
4
TABLE Equations
of Lines
Al 0 -CaO-6Al 0 2
3
2
C
X h
a
A l
3
X
2
/ h
3
2
h
C
h
2
3
3
X
C
=
O
h
=
3
X h
a
h• , { Al
2 / 3
2
3
a
X
h„
Q
Y h X h„ 0 h
/h { 2
3
CaO-Al 0 (solid)^030(42 3
h
h
h
CaO
10~
X
10"
1 3
5
8
2
1.59
,
0
1
X
X
1
0
10"
"
1 2
5
=
7.90
X
10"
=
2.24
X
10"
=
1.90
X
10
=
1.18
X
10"
8
-OaO-Al^ h
2
2.13
X
= 2.82 X l O "
Q
/h {
a
6.01
3
2
C
=
3
X h
a
A l
h
CaO-2Al 0
O
h
CaO-6Al 0 -CaO-2Al 0
=
Q
Ca l(
h
the I n d i c a t e d Phases
3
h
h
Between
VI
C
A l
h
h
3
X
/h {
a
A l
3
X
h
/h { 2
c
a
=
pet.) + A 1 0 2
0 3
1.89
=
=
7
X
10 10"
(liquid)
1 2
5
X lO"
7
(42.6 p e t . )
3
5
X
1.20
=
Q
5
(58 p e t . )
3
2.27
=
3
X h
a
=
Q
(57.4
C
2
0
h
2
C
( s o l i d ) -CaO h
X h
a
pet.) + A 1 0
1 2
3.29
-
7
7
X
5.70
X
1
0
10
~
-
1
6
X lO"
6
(liquid) 1
TABLE
VII
Chemical A n a l y s i s of E l e c t r o d e s Electrode 1020 M S t e e l (1)
Used i n t h i s
Research:
Chemical Composition i n wt.% Rotor S t e e l
4340 -
Steels
(1)
(2)
(1)
(2)
c
0 . 19
0 . 415
0.422
0.213
0 . 202
p
0 . 099
0 . 014
0.014
0 . 007
0.007
s
0.026
0.016
0.015
0.005
0 .006
Mn
0 . 709
0.697
0.696
0.673
0 . 673
Cu
-
0.094
0.091
0 .049
0.048
Ni
-
1.882
0 . 184
0 .357
0.0362
Cr
-
0 . 873
0. 867
1. 151
1.1150
Si
0 . 25
0.357
0.353
0 . 246
0 . 244
V
-
0. 005
0 .005
0 . 246
0 . 244
Mo
-
0. 189
0.188
0.940*
0.940*
Al
-
0 . 029
0.029
0.006
0 .006
0.005
0 .005
0.005**
0.005*
Sn
where and
(*) stands f o r more than 0.940 wt.%
(**) i n d i c a t e s l e s s than 0.005 wt.%.
TABLE V I I I
Run No.
1
Type o f Electrode
4340(I)
2
•'
3
••
Electrode D i a m e t e r (mm)
5
••
8
••
3
2
30
20
-
55
15
15
15
40
20
20
20
40
22
23
5
55
15
22
8
31
0
46
23
50
30
20
-
"
55
15
15
15
50
30
20
-
55
15
15
114.3
49
16
17
76. 2
70
0
30
114 ,3
70
15
15
"
70
0
30
••
50
20
30
76 . 2
50
30
20
9
4340(II)
44 .75
10
4340 ( I I )
"
11
rotor
steel
2
50
6 7
2
"
»
List
I n i t i a l Slag Composition CaF /Al O /CaO/SiO /Mg0
31.75
4
-
of
Type o f Deoxidizer
-
Nil
-
Al
-
Experiments
No.
of Additions Rates
-
-
Al
along
remelting
Type o f A d d i t i o n (deox.)
Deoxidation (kg t o n
-
- 1
rates )
2.3
constant
kg t o n
_i
"
-
Ca-Si
15
-
Ca-Si
12
6
Al
"
-
Al
"
-
Al
-
Al
Ca-Si
2
-
Ca-Si
2
Nil
-
Al
4
Al
5
constant
^
0.0 2 k g t o n
M.S.
76.2
70
30
-
M.S.
76.2
50
30
20
-
50
30
20
-
-
»
50
30
20
-
-
••
60
36
4
-
-
Ca-Si
4. 5
'•
50
30
20
-
-
Ca-Si
6
5.61,11.23,16.83,2; 28.05 and 56.10 .
88.9
50
30
20
-
-
Ca-Si
6
4.17,8.35,12.5,16. 20.85,41.7, and 20
114 . 3
50
30
20
R-RSII
50
30
20
-
R-RSI 11
50
30
20
-
12
1020
13
rotor
M.S. steel
14 15 RII-W RIII-W RI-Il
" 1020 1020 1020
M.S.
RII-Il RII-I2 RIII-Il
"
RIII-I2 R-4340
4340
R-RSI
rotor
steel
-
Al
Ca-Si Al-Si Hyperca1
" "
II
II
"
"
a long remelting
intermittent
continuously increasing
50 g r a m s
(each)
50 g r a m s
(each)
-
3.63, 6.1 a n d 3 7.6 k g t o n 1.21, 2.42, 3.6' 4.85,6.06 and 12.1/
"
constant
5.61,11.23,16.83,2; and p a r t i a l l y 28.0J
36.0 kg t o n
constant
33.0
constant
36.0
- 1
oo
o
361
TABLE Chemical
IX
Composition
of Deoxidizers
Calcium-Silicon
Hypercal
Al-Si
Calcium
29 .. 50
10,.50
-
Silicon
6 2 . . 50
39,.00
65
Iron
4 ,. 50
18,.00
-
Barium
0. . 50
1 0 , . 30
-
Aluminum
1.. 20
20 ,. 00
35
Manganese
0 ,. 2 5
0 .. 30
Carbon
0 .. 55
0 ,. 50
Chromium
0 .. 10
0 ,. 0 3
Copper
0 ,. 0 1
0 .. 03
Nitrogen
0 .. 0 3
0 ,. 0 5
Nickel
0 .. 0 1
0 ,. 0 2
Oxygen
0 .. 50
0 ,. 7 0
Phosphorous
0 .. 0 1
0 ,. 0 2
Sulfur
o ,. 0 5 5
0 ,. 12
Titanium
0 ,. 0 8
0 ,. 06
Bulk
Density
110 l b . / c u .
f t . 95 l b . / c u . f t .
TABLE X Inclusion
Chemical
Deoxidizer
a
No.
)
Inclusion
Nominal
CaF
2
Slag
A1 0 2
3
i n 4340
Chemical
System
CaO
Composition
1
50
30
20
-
2
55
15
15
3-
40
20
4
40
5
6
Atom
Al
2
diameter)
Composition
(wt.%)
Si0
(small
as a F u n c t i o n o f S l a g and ESR
Ingots
as a F u n c t i o n of Slag
Percent
Ca
Types
System
of Inclusions
Si
96.1
3.733
15
75.86
1.8470
22.28
20
20
85.33
2.470
13.160
22
33
5
99.20
0.19
0.60
"Alumina", sulfides
55
15
22
8
96.27
3.462
0.265
"Alumina" and Caaluminates, "Fayalite"
31
0
46
23
84.88
4.38
b)
Slag-Deoxidant
wt. %
Effect
(X)
0.170
10.74
on F i n a l
at. %
Calcium aluminates, Manganese s u l f i d e s Alumino-Silicates, Manganese s u l f i d e s , and "Fayalite."* Calcium, Aluminums i l i c a t e s , Manganese s u l f i d e s and " F a y a l i t e " * Manganese
Calcium-alumino silicates. Manganese s u l f i d e s and "fayalite".*
Inclusion
Chemistry
(X)
+ No.
CaF
CaO
Si0
7
50
30
20
-
Al
92.42
7.11
0.170
Calcium Calcium
8
55
15
15
15
Al
89.20
7.85
2.940
Aluminates, Calcium Aluminum s i l i c a t e s and "Fayalite".*
9
50
30
20
- Ca-Si (*)
91.00
7.20
1-80
Calcium aluminates, Manganese s u l f i d e s
10
55
15
15
15 C a - S i (*)
2
A1 0 2
3
2
Deox.
Al
Ca
76.217 2.143
Si
21.64
aluminatessulfides
Aluminum c a l c i u m s i l i c a t e s , f a y a l i t e * and Manganese sulfides
c)
Inclusion
Chemistry
E l e c t r o d e s f o r 1 t o 8 (31.75 im)
Al 89.00
E l e c t r o d e s ! * ) f o r 9 and 10 (44.75 nm)
81.08
of Electrodes
Ca Si 10.00 balance 5.237
Calcium Aluminates calcium sulfides 13.685 A l u m i n u m C a l c i u m silicates and
Remarks:
1. 3.
Manganese
sulfides
Melting rates 1.2 - 1.5 Kg m i n . , 2. d e o x i d a t i o n r a t e " ^ 2 . 3 Kg t o n F a y a l i t e * was not always observed t o f o l l o w the t h e o r e t i c a l s t o i c h i o m e t r y . - 1
- 1
TABLE Chemical
Effect
of
(Extension
Slag of
and
R e s u l t s Found 1020
Ingot
Electrode
Type
Nominal
CaF
2
CaO
Electrode
A 1
Steels
Slag
2°3
XI
S u r f a c e P r e p a r a t i o n on
i n 4340
to a
Small
Cr-V-Mo
Rotor
Composition
s
i
0
2
M
g
and
Large
Inclusion
Composition
ESR-ingots,
and
Steel*
Inclusion
Type
and
Shape
0
* 11
rotor
steel
49
16
17
12
12
rotor
steel
70
15
15
-
6
A l - C a s i l i c a t e s and a l u m i n a t e s . Semiround types; they were o c c a s i o n a l l y seen w i t h p e r i p h e r a l MnS. Mg t r a c e s w e r e a l s o d e tected . -
Aluminates A1 0 . 2
and
3
of
the
Round,
clusters
type
Fe0-Al 0
elongated
and
angular
2
and
3
(FeO-Al 0 ) 2
3
A1 0 . 2
3
* 13
rotor
steel
14
rotor
steel
70
30
-
-
A l u m i n a t e s , s i n g l e r o u n d and c l u s t e r s . I r o n o x i d e s a n d some i r o n s u l f i d e s w e r e also observed.
*
15
1020
50
20
30
-
70
-
30
-
-
A l u m i n a t e s , s i n g l e r o u n d and c l u s t e r s a minor amount o f r o u n d C a - a l u m i n a t e s MnS I I . -
Aluminates
generally
as
clusters
and
and and
MnS
II.
Remarks 1. 2. 3.
T h e s e E S R - i n g o t s w e r e s l i g h t l y d e o x i d i z e d w i t h A l a t a c o n s t a n t r a t e , 0.02 Kg t o n ^. E l e c t r o d e s 11, 12, 13 a n d 14 w e r e s u r f a c e g r o u n d a n d c o a t e d w i t h a n A l - M g s p i n e l p a i n t i n g p r e v e n t s c a l e ("FeO") o x i d e f o r m a t i o n d u r i n g r e m e l t i n g . E l e c t r o d e and E S R - i n g o t c o m p o s i t i o n a r e g i v e n i n T a b l e s ( V I I ) and (VIII).
4.
Refining 1 Kg
min
conditions
were
equivalent
f o r a l l experiment,
Ar-atmosphere
and
melting rates
to
about
TABLE Slag
Chemical
Analysis
from
XII
(Ni-Cr-Mo) R o t o r
Deoxidized with CaSi, A l S i
and CaF
Nominal
(initial)
Hypercal*
slag
CaO
A1 0 2
3
Si0
"FeO"
2
20
30
CaSi**
47.33
20.15
32.2
0.175
AlSi
43.32
18.27
38.11
0.141
43.51
18.19
37.88
0.25
Si alloy)
(wt.%)
2
50
(Ca, A l , Ba,
composition
ESR-ingots * Ca-Al-Ba-Si Alloys
0.14 .
0.147 0.165
* * Remarks:
D e o x i d a t i o n r a t e u s e d i n t h i s e x p e r i m e n t was s l i g h t l y l o w e r t h a n i n t h e o t h e r two e x p e r i m e n t s , i . e . ^ 33 grams/min and ^ 36 grams/min respectively. R e m e l t i n g c o n d i t i o n s were a p p r o x i m a t e l y c o n s t a n t f o r t h e a b o v e r u n s , i . e . , m e l t i n g r a t e s were ^ Kg/min. E x p e r i m e n t s were c a r r i e d o u t u n d e r a p r o t e c t i v e atmosphere (argon).
cn
TABLE XIII - A Chemical
A n a l y s i s (wt.%) o f a Cr-Mo-Mn-Ni-V-Steel Deoxidized
w i t h Al-65.0 wt. % S i
C
P
s
1
0, . 261
0 .008 .
0 .003
0 .707 .
0.,050
0 ., 353
1. 176
0 ,594 .
2
0 . 252
0 .007 .
0.,003
0., 700
0..051
0,. 369
1. 165
3
0 . 255
0..007
0..003
0 .695 .
0 .050 .
0 . 350
4
0.. 253
0..007
0..003
0..695
0.,050
5
0.. 251 '
0 .007 .
0..003
.0.,689
6
0 .249
0..007
0..003
7
0 . 255
0,.007
8
0 . 250
9 10
Mn
Cu
Ni
Cr
Si
V
Mo
Al
0 .239
.94 +0 ,
+ 0 .250
-0 .005
0., 536
0 .246
+ 0,.94
+ 0,.250
-0 .005
1., 160
0., 532
0 .242
+ 0 .94
+ 0 .250
-0.005
0 . 348
1. 160
0.. 536
0. 242
+0 .94
+ 0 .250
-0.005
0..051
0 . 362
1.. 147
0 . 536
0 .245
+ 0 .94
+ 0 .250
-0 .005
0,.691
0..049
0 . 355
1.. 155
0 .534 ,
0 .241
+ 0 .94
+ 0 .250
-0.005
0,.003
0 .693
0,.051
0 . 354
1.. 155
1 0 ., 538
0 .243
+ 0 .94
+ 0 .250
-0.005
0 .007
0 .003
0 .695
0,.051
0 . 359
1.. 160
0 . 538
0 .243
+ 0 .94
+ 0 .250
-.0.05
0 . 260
0 .008
0 .003
0 .701
0,.052
0 . 361
1,. 161
0 . 539
0. 245
+ 0 .94
+ 0 .250
-0 .005
0 .254
0 .007
0 .003
0 . 694
0 .052
0 .361
1 . 154
• 0 . 543
0 .246
+ 0 .94
+ 0 .250
-0 .005
Sn
TABLE Chemical
Analysis
(wt.%)
Deoxidized C
P
c
1
0 . 262
0 .007
0..002
2
0 .271
0..007
3
0 .242
4
pie
No.
Mn
XIII
- B
o f a Cr-Mo-Mn-Hi-V
with
a Ca-Si
Steel
Alloy
Cu
Ni
Cr
Si
0,.691
0 .049
0 .337
1.103
0 .627
0 . 247
+0 .94
0.. 157
-0 .005
0 .002
0 .696
0 .048
0 . 334
1. 116
0 .674
0 . 236
+ 0,.94
0.. 150
-0 .005
0 .007
0 .002
0,. 673
0 .046
0 . 321
1.091
0 .646
0 . 235
+ 0..94
0.. 147
-0 .005
0 . 258
0,.007
0,.002
0,.688
0 .045
0 . 324
1.118
0 .650
0 .235
+0,.94
0 .117 .
-0 .005
5
0 .266
0..007
0..002
0..691
0 .04 8
0 . 343
1.115
0 .648
0 .244
+ 0..94
0 . .126
-0 .005
6
0 . 226
0,.007
0..002
0..690
0 .047
0 . 340
1. 119
0 .654
0 . 242
+0..94
0 . 126
-0 .005
7
0 . 273
0..007
0..002
0 . 687
0 .047
0 .341
1. 116
0 .652
0 .652
+ 0..94
0 . .125
-0 .005
8
0 .264
0..007
0..002
0.. 680
0 .046
0 . 337
1. 1031
0 . 645
0 . 240
+ 0..94
, 121 0 .
-0 .005
9
0 . 273
0.,007
0 .002 .
0.. 685
0 .048
0 .351
1. 114
0 .660
0 . 246
+ 0 .94 .
0., 121
-0 .005
10
0 . 276
0..007
0..002
0., 687
0 .047
0 .332
1. 118
0 . 652
0 . 241
+ 0..94
0 ., 119
-0 .005
11
0 . 228
0..007
0..002
0., 700
0 .049
0 . 355
1. 125
0 . 665
0 . 245
+ 0..94
, 122 0 .
-0 .005
(+) - m o r e
than
a certain
calibration
(-)
than
a certain
calibration
- less
V
Mo
Al
Sn
cn
TABLE
XIII-C
Chemical A n a l y s i s of a
Cr-Mo-Mn-Ni-V-Steel
Deoxidized with a Ca-Si-Al-Ba
%C
9
p
%s
%Mn
%Cu
? Ni
%Cr
Alloy
Si
V
%Mo
%Al
Sn
1
0 . 253 0 008
0. 004
0.706
0.056
0 366
1. 126
0 815
0 229
+0 .94
+ 0 .250
-0 005
2
0. 255
0 007
0. 003
0.702
0.053
0 366
1. 146
0 772
0 241
+ 0 94
+ 0 250
-0 005
3
0. 253
0 008
0. 004
0. 704
0.051
0 34 7
1. 160
0 757
0 234
+ 0 94
+ 0 250
-0 005
4
0. 267
0 008
0. 004
0.718
0.052
0 356
1. 174
0 774
0 236
+ 0 25
+ 0 250
-0 005
5
0.263
0 008
0. 003
0.714
0. 056
0 382
1. 164
0 793
0. 248
+ 0 94
+ 0 250
-0 005
Ul CTi
TABLE
Example
Sample No.
of inclusion
Inclusion No.
size
XIV-A
distribution
Shape
i n Rlll-Il-LQD-Sample
Florescence under the e l e c t r o n beam
1.
Diameter i n pm
1
round
blue
4. 5
2
elongated
blue
5.0
3
semiround
blue
6.0
4
elongated
blue
7.0
5
round
blue
4.5
6
S-shape
blue
6.0
7
round
blue-green
6.0
8
angular
blue
4. 5
9
duplex-round
2-blue
5.0
10
round
blue
4.0
11
triangle
blue
5.5
12
duplex
blue
8.5
13
elongated
blue
5.5
14
elongated
blue
5.5
15
triangle
blue
5.5
16
angular
blue
4.5
17
elongated
blue
6.5
18
round
light-blue
8.0
19
duplex
2-blue
8.0
20
irregular
blue
6 . 0
21
round
blue
8.0
22
round
blue
6.0
369
TABLE Example
Sample No.
of
Inclusion
Lusion No.
Size
XIV-B
Distribution
Shape
i n RIII-Il-SLD-Sl
Fluorescence
Diameter i n ym
1
semi-round
blue
4.0
2
elongated
blue
6.0
3
round
violet
5.5
4
elongated
blue
4 . 5
5
round
blue
4. 5
6
irregular
blue
5.5
7
elongated
blue
5.5
8
round
blue^
8.0
9
irregular
blue
6.0
10
elongated
blue
5.0
11
round
blue
6.0
12
in a clusterround
blue-green
5.5
13
in a clusterround
blue
6.5
14
elongated
blue
5.0
15
round
blue
5.0
16
half-moon shape
blue
7.5
17
elongatedirregular
blue
5 .0
18
elongated
blue
5.0
19
elongated
blue
4 .0
20
elongated
blue
5 .0
TABLE Data
of Plot
Equilibria
V
Al 0 /CaO-6Al 0 /CaS 2
3
2
1.4155
3
6Al 0 -CaO/CaO-2Al 0 /CaS 2
3
2
1.995
3
CaO-2Al O /Ca0-Al 0 /CaS 2
3
2
3
+ CaO-Al 0 /(CaO)* 2
+
+
C
*
s o l i d
0
t +
+
a
+
Slag 3
a
CaS CaS
CaS
+
3
/
(
C
a
0
)
t
( A l ^ W C a S
(Al 0 ) /Cas
+
compositions = ° =
0
3
" ,
*
°- *8 9
~
3
according A
l
2
-1.0,
o
a
A
l
Ca
x 10'
x 10~
0.758 x 10 -3
3.360
x 10
4 x 10~
6.87
3
1.35 x 10"
a, CaO
^
suggest
a
0.8
CaO
(238,239) f r o m Sharma a n d R i c h a r d s o n @
Y
This
i s also
/ J
an average v a l u e
=
Y
x
1.4228
7.85
- !
2.5 -8
^
h
x 10
x 10~
1.2457
9
1.35 x 10
4
x 10
x 10"
-4
-3
K
h
x
10
!-567
x
10"
1-0
-3
@ 1650°C
X
CaS
0
568 '
Y
x
9-61
%
X = 1 x 6.3
x
10 10
3
x
(1550°C)
- 2 x 10~ . 3
and
a
v r
CaS(1650°C)
=
'
l
x lo"
65
CaS(solid)
-5
2-014
1.2156
3
3.84 x 10
Al O
- 0.9 = 0
a
and
C a S ( l ii q u i d )
since
x 10~
9
S
0.0625
0.1,
v /< CaS(solid)
Al
p s e u d o - b i n a r y d i a g r a m a t 1827°
C
They
S
x 10 -10
2.3155
x 10"
U
a
(87 - 8 9 )
S
to the C a O - A l ^ 2 3
0.7,
3
Figures
1.83
^
+
2
h
XV
l^fifl i
b
6
B
0
-
5
5
5
10~
6
371
TABLE
and
e
e^
=-5.25,
A 1
a
XVI
= -62,
%Ca Equilibrium (invariant)
«? = -
%0
(1)
1 x
10"
(2)
2.5
(3)
.5 x
(4)
8 x
10"
(5)
1 x
10"
x
and
2.65
3
10~ 10~
3
2.6
x x
%A1 10~ 10~
2
2
%S
2.35
x
5 x
10~
2
5.35
x
10
10~
2
3.95
x
10
2.75
x
10
1.56
x
10'
2.35
x
10~
2
1 x
3
2.27
x
10"
2
1.2
2
2.15
x
10"
2
1.89
3
4 0
x
10"
10~ x
3
2
10"
2
7.4
x
10" 2 2 -2 2
TABLE XVII Computed Compositions by Using Data i n Table XV
Interaction Parameter e£ Equilibrium (invariant)
Composition
a
Ca
Al
(ppm) 0
(i)
-535
10
15
20
(2)
-400
25
38
32
(3)
-300
65
97
34
ti
(4)
-250
80
120
36
ii
(5)
-200
100
150
42
II
The i n t e r a c t i o n parameter f o r the C a - 0 was assumed v a r i a b l e and the A l - 0 and Ca-S were: e = -62 A l
and -110
TABLE
Effect
of Initial
Growth
During
XVIII
Number
Cooling
of Inclusions of Liquid
on
Metal
Number o f Inclusions Initially
Initial Radius
Final Radius
10 /cc
1 ym
40
72
2
40
72
268. 0
5
40
75
238 . 9
9
40
87
208 . 3
10
40
92
201. 7
1
18
90
5 7 . 37
2
18
91
5 2 . 79
5
19
02
4 2 . 40
"
9
19
56
32. 87
"
10
19
79
30. 98
1
8 78
1 1 . 23
2
8 81
9 .58
5
9 28
6 .38
3
»
10 /cc 4
10 /cc 5
10 /cc 6
"
Growth Time (Lowe r Limi
um
279. 5
9
11
2
4 .15
10
11
88
3. 79
1
4 09
2. 02
2
4 23
1. 5
5
5 77
0. 76
9
9 27
0 .44
22
0. 39
10
10
10 /cc
1
1 98
0. 31
It
2
2 45
0. 19
9
9 03
0. 04
7
"
10
10
02
sees
0. 0 3 9 7
374
APPENDIX Thermodynamic faces
relationships
of s t a b i l i t y
1(1):
(I):
2°3
6 A 1
AG°
l f
2
2
1
4
7
'
1
4
'
8
2
2
C
a
3
0
1
'
6
2
+
o
G
^
[
+
6Al 0 -CaO
a
(
2
3
2
'
2
3
8
'
2
3
9
data
>.
S
]
3
6 A l 0 - C a O + CaS + [0]
=
2
A
the sur-
Al 0 /CaO/6Al 0 -CaO/CaS
+
=
to generate
f o r t h e Fe-Ca-Al-O-S system, u s i n g
from the l i t e r a t u r e
Equilibria
developed
G
O
A
B
=
S
~ "CaS"
3
A
G
-
~ Al 0
a
3
7.082 X 10
A
3
a
~ CaO
a
2
2 A G °
-
^
~
a
3
= RTlnK
Q
I ( 1 )
1
0 = -RT l n [ ^ ] S h
h
l
n
h
1(2):
I(l)
K
1
-
9
5
5
= 1.4155 X 1 0
Q
6 A 1
"
=
2°3
+
2
f
C
a
^
K
h
_ 1
+
i ( l )
h
=
4
-
6
3
2
7
x
h
Ca O S
=
7
'
5
9
4
2
x
h
h
C a
h
h
s
1
0
iO"
= 2.316 X 1 0 "
t
h
2 1
/
1 0
h
O
S
= 6 A l 0 - C a O + CaS 2
]
3
= -1.6781 X 1 0
5
Ca O S h
h
1
I(2)
-1 = —•
10
A - I (1)
[S]
+
x
g
= -RT l n [ - 5 - ^
-RT InK
l n K
i^iss
=
u
s
b
Y
K
i(2)
=
1
-
?n 3
1
substituting
6
8
x
1
0
A-I(l)
A-I(2)
375
1(3):
12 [ A l ] + 18[0] + CaO +
-7.8183 X 1 0
5
[S] = 6 A l 0 « C a O 2
= -RT l n K
-> l n K
l ( 3 )
+ CaS
3
I ( 3 )
= 2.158 X 1 0
2
93 K
I(3)
=
h
Al O
=
h
Equilibria
11(1):
5.46657 X 10
2
'
0
(II):
1
4
X
1
0
and by
AG°
=
6Al 0 •CaO/CaO/2Al 0 «CaO/CaS 2
3
2
3
AG°
AG°
+
[S] = 2 A l 0 « C a O 2
- |(AG°
A S
3
)
A 0
±
f
a
CaS
- |(AG
D
a
CA
"
0
a
CaO
"
a
CA
2
K
0 yh s
I I
II(D
^ j
= 1.4257 X 1 0
1
=
1
'
c
"
1
O
9
5
3
h
thus
) =
I I ( 1 )
"
-RTlnK
+ CaS + [0]
3
2 -RTknK
A-I(2)
A-I(3)
5
| ( 6 A 1 0 - C a O ) + y(CaO) + 2
substituting
= 1.953 X 10
X
-2
1
0
~
4
+ l n K ^ ^ j
=
- 3.9359
3
A-II(I)
11(2):
j(6Al 0 -CaO) 2
2A1 0 2
+ |[Ca] + |[0] +
3
[S] =
«CaO + CaS
3
-RTlnK
3.629
= 1. 3146 X 1 0
I l ( 2 )
X
10
-»• l n K
5
by
II(2)
=
substituting
h
11(3):
Ca S h
£
1
,
1
1
6
0
8
2
x
X
h
Equilbria
2
Al O h
1
q
1
*
5
2
)
2
ca O S h
h
=
-
2
3
1
9
5
x
iO"
1
6
1
0
=
8
~
A-IK2)
9
[Ca] +
[S] = 2Al <D -CaO 2
'
6
0
8
X
l
o
1
5
•* n ( 3 ) K
3
+ CaS
-+
=
2
- 324 4
X
10
3 7
A-II(1)
=
1
(III):
-
7
0
4
X
1
0
~
3
A-IK3)
5
2Al 0 -CaO/CaO/Al 0 •CaO/CaS 2
3
1 3 ( 2 A 1 0 - C a O ) + j CaO + 2
h
= - 3.11824 X 1 0
( l I ( 3 )
II(3)
substituting
III(l):
3
4[A1] + 6 [ 0 ] +
l n K
(
A-II(l)
-RTlnK
by
-
4
l
1
5 K
I
2
3
[S] = A l ^ - C a O
+ CaS +
[O]
377 AG°
=
AG°
-RTlnK
l
f
a
=
S
| ( A G °
~~ C A
a
A
2
~
a
= 1.67697
I I l ( 1 )
= 9.758
-
)
§(AG°
a 0
)
=
X 1 0 " h
2
X 1 0
a
4
CaO
+
L
N
"
1
= -4.63
K I
I
I
(
1
)
A-III(l)
3
g
y ( 2 A l 0 - C a O ) + |(CaO) + [Ca] + [S] = A l ^ - C a O + CaS 2
3
-RTlnK
by s u b s t i t u t i n g
h
Ca S h
=
= 7.0675 X 1 0
I I l ( 2 )
1.95111 X 1 0
111(3):
a
" CaS
3
Q
C
I I I ( 1 )
= RTlnK
h
AG
+
Al 0 .CaO 2
111(2):
A
-»• K
1
I I I ( 2
)
lnK
4
=
I I l ( 2 )
= 2.97546 X 1 0
8
A-III(l)
3
,
3
6
X
1 0
~
A-IIK2)
9
2[A1] + 3[0] + [Ca] +
[ s ] + CaO = A l ^ - C a O + CaS 5
-RTlnK
I I I ( 3 )
5.346 X 1 0
1
= -1.9366 X 10
K I I I (
3)
^
lnK
= 1-6568 X 1 0
I I l ( 3 )
2 3
=
378
by s u b s t i t u t i n g
A-III
(2)
2 h
Al O h
i -
=
Equilibria (IV)
2
1
5
6
!0~
x
A-III
5
:
A 1 0 - C a O / C a O ( 4 2 .0 wt.%) + A1 C> 2
(3)
3
2
58.0 wt. %
3
(liquid)/CaS
IV(1):
2CaO + A l 0 2
-RTlnK
l n K
u
a
0
CaO
=
a
CaO
a.
then
h
2
9
5
8
+
6
K I V
->
4
(1)
=
"5.18915 X 1 0 ~
2
a
S
f
" -
+ CaS + [0]
2
h~
l
=
[S] = C a O - A l ^
= 1.06873 x 1 0
I V ( 1 )
IV(l)
+
3
Q
C a S
CaS
a
A
1
X 5.18915 X l O
0
2
0.0355
= 4.0 X 1 0 ~
2
3
- 0.0625(
=
-
3
2 1 6
'
( 2 3 8
h
2 3 2
'
g
),
2 3 3
a
5
- 0.7
( 2 3 2 )
and
>
A - I V (1)
IV(2):
2 [ C a ] + 2[A1] + 4 [0] +
-RTlnK
K
by
IV(2)
[S] = C a O - A l ^
= -2.8111 X 1 0
=
5
'
0
5
3
3
a
substituting
4
x
1
q
3
+ CaS
->
5
3
= 0.0355
(
2
3
8
'
2 3 9
^
and
A - I V (1)
(-3 O
h
IV(3):
Al O h
f
1
X
1
0
5
A
CaO + 2 [ A l ] + 3 [ 0 ] +
AG
i
=
a
t° =
CaO
=
A G
A l
K ,,>
CA
+
2°3
A G
=
CaS
"
A G
[Ca] +
CaO
-
= 1.65287 X 1 0 —
substituting
-
a
, a L3b
h
Ca S h
=
6
,
8
7
R T l n K
( )
V
[S] = C a O - A l ^
2 3
=
C
X
a
2
+ CaS
IV(3)
[
S
-
a
by
I
1
"
IV(3)
TT7
=
_
CaO
i
.3. T~Al O Ca S 2
h
h
h
h
and A - I V (2) (_,civj
1
0
_
9
A
-
I
V
(
3
)
E q u i l i b r i a (V): CaO
/
C
a
S
( s )
/CaO(57.4
(s)
wt.%)
+ A
l
^ (42.6 wt.%)
(liquid)
380
±
f
a
CaS
0.988 - 1 . 0
B
and a _ s 0.8 CaO n
h
C a
h
s
h
Al O
h
Ca O
h
h
h
S
0
( 2 3 8
.9
s
1.35 X 10
=
9.6 X 10
3.29 X 10
= 2.35 X 10" h
s
2 3 9 )
( 2 1 6
'
,
a
A l O ,
,
=
0.1
( 2 3 2 )
2 3 2 )
A-V (1)
A-V (2)
6
3
Q
8
'
1
1
A-V (3)
A-V (4)
Sponsor Documents
Recommended
No recommend documents