Gas Nitriding and Ferritic Nitrocarburizing - Nitriding Solutions

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Gas Nitriding and Ferritic Nitrocarburizing - Nitriding Solutions

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http://www.nitrex.com/english/technologies_modern.htm

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Nitreg® Potential-Controlled Gas Nitriding

Nitreg®-C Potential-Controlled Gas Nitrocarburizing (FNC process)
ONC® In-process Post-Nitriding/Nitrocarburizing Oxidation
Nitreg®-S Potential-Controlled Nitriding of Stainless Steel
Nano-STM Potential-Controlled Nitriding of Stainless Steel with better
corrosion resistance - New
Nitreg®-Ti Potential-Controlled Nitriding of Titanium Alloys
Plasma (Ion) Nitriding
Vacuum Carburizing
Vacuum Carbonitriding
Corr-Check® Corrosion Protective Treatment
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Gas Nitriding and Ferritic Nitrocarburizing - Nitriding Solutions

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Nitreg®: Potential-Controlled Nitriding

The main objective of nitriding is to increase the hardness of the
component’s surface by enriching it with nitrogen. Of the three traditional
methods Nitrex does not employ salt bath techniques due to their
environmental and safety risks. Plasma nitriding is described later in this
section and traditional gas nitriding is gradually being phased out thanks
to the development of the Nitreg® family of processes.
General principles of the various nitriding methods and an explanation of
potential-controlled techniques are described in more detail in an extension
of this page, accessible by clicking here. This will open a separate viewing
window and you will be able to return back here by simply closing it.
Nitreg® is a modern process, capable of meeting the metallurgical
requirements of all nitriding specifications that may have been originally
written for salt bath, plasma or traditional gas nitriding. The ability to
control the concentration of nitrogen in the surface allows the user to
control the growth of the compound layer virtually independently from
developing a desirable diffusion zone. This approach facilitates not only
meeting any specification requirements but it also makes it possible to
improve on them by allowing tighter tolerances to be satisfied, particularly
with regard to the thickness and properties of the compound layer.
Summary of Benefits:

control of the thickness of the compound (white) layer and its
properties
elimination of closed nitride networks within the diffusion zone
control of case depth
control of surface hardness
no distortion
family of derivative and related processes.

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Nitreg®-C: Potential-Controlled Nitrocarburizing
A shorter cycle time of the Nitreg® process carried out predominantly on
carbon and low alloy materials.
Its objective is to reliably produce a nitrided case with typically increased
WL content and a particular nitrided phase configuration in the WL.
Nitreg®–C is a controlled version of ferritic nitrocarburizing. It allows for
precise Kn control during the process. The additions of carbon bearing

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gases to the nitriding atmosphere help to increase the relative content of
the epsilon phase.
The advantage of a Kn controlled technology is best evidenced when
increased wear and/or corrosion resistance is sought. Such properties of
the nitrided case are not only influenced by the thickness and relative
phase composition of the WL. They also strongly depend on the relative
level of porosity developed in the WL.
The Kn control is essential in producing the desired WL configuration
Example of various porosity levels achieved through Kn control are shown
below.

Benefits:
Increased wear/corrosion resistance on selected alloys
No distortion
No brittleness
Excellent process reliability
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ONC®: In-process Post-Nitriding/Nitrocarburizing Oxidation
When resistance to atmospheric corrosion and an attractive black finish are
the predominant requirements, ONC® is the appropriate process.
Its objective is to transform the very top portion of the WL obtained with
either Nitreg® or Nitreg®-C technologies into a complex spinel type
structure consisting mostly of Fe3O4 type of iron oxide.
Such a post-nitriding oxidation treatment has a net effect of enhancing the
corrosion resistance of an already nitrided component. This integrated
process (i.e. Nitreg® + ONC® or Nitreg®-C + ONC®) simultaneously
enhances corrosion and wear resistance of steel, while giving the surface
an attractive dark or black appearance, expressly desired by many
customers.

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ONC®, applied in combination with the Nitreg® potential-controlled
nitriding process or the Nitreg®-C potential-controlled nitrocarburizing
process, is a clean technology that in many instances can replace chrome
plating and salt bath nitriding with their inherent problems of pollution and
cost.
Depending on the type of steel, parts treated in the Nitreg®-ONC process
can easily pass well over 200 hours of salt-spray test per ASTM B117 before
the first corrosion spot appears. Fig. 2 shows a comparison of metallurgical
and corrosion test results obtained on three materials treated by the
Nitreg®-ONC process.
Benefits:
Improved corrosion resistance
Attractive black surface finish
Inherent wear resistance
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Nitreg®-S: Potential-Controlled Nitriding of Stainless Steel
The rules applying to nitriding of stainless steel or refractory alloys are no
different than those for the other groups of steels, with one exception.
The exception is the proprietary de-passivation stage that allows for a
removal of oxides of alloying elements such as Cr, Ni and others which, if
not removed, will effectively block the nitriding process. The same way they
block the rust formation on the stainless steel surface.
All types of stainless steel can be nitrided. The martensitic, austenitic or PH
materials inclusive.
Example of a nitrided stainless steel part.
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Nano-STM: Potential-Controlled Nitriding of Stainless Steel
NANO-STM is a surface hardening process that improves the wear and
galling resistance of stainless steel components without affecting the
inherent corrosion resistance.

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Benefits:
Attains excellent wear resistance
Improves fatigue strength
Retains intrinsic corrosion properties
Prevents galling
Does not alter chemical composition of alloy
Has no effect on the steel’s non-magnetic nature
No change in the color, shape or size
Uniformly hardened even small bores, tight grooves and sharp edges
Green technology, no waste pollution
Treatable Materials:
Austenitic Stainless Steels
Martensitic Stainless Steels
A286
Custom 465
Duplex Stainless Steel
Hastelloy C22 and C276
Inconel 625 and 718
Inquire about other materials
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Nitreg®-Ti: Potential-Controlled Nitriding of Titanium Alloys
Titanium alloys, used mostly in the aerospace and defense industries can
also be successfully gas nitrided leading to an increased wear resistance
and providing an attractive golden finish.
The technology is not widely known since the applications involved are
also very specific. For best results consult with our engineers who will
advise you on certain unique aspects of the manufacturing sequence of
operations.
Example of a nitrided titanium alloy part.
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Plasma (Ion) Nitriding
As an alternative to gas nitriding, nitriding plasma (ion) nitriding process
has been developed to overcome the shortcomings of the earlier traditional
uncontrolled gas nitriding processes and to offer certain operational
advantages that gas nitriding does not have.
Plasma is essentially a gas nitriding treatment in which the method of
delivering nitrogen atoms to the surface of nitrided components is quite
different from the standard gas nitriding processes. It occurs at a very low
pressure and under high voltage.
From the metallurgical, tribological and mechanical properties standpoint
the properties of nitrided case obtained with Nitreg® and well controlled
plasma technology are comparable.
Plasma offers certain distinct advantages such as:
The ease of masking the component surface where nitriding is to be
avoided.
Ability to nitride low density powder metallurgy parts
Ask us for an advice about which nitriding method is better suited to your
situation.
If your drawing calls for "ion" or "plasma" nitriding we are at your service.
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Vacuum Carburizing
Vacuum carburizing is a state-of-the-art thermal process where carburizing
is effected under very low pressures. First the parts are heated in vacuum
to above the transformation temperature of the alloy. Then they are exposed
to carbon-carrying gas, or gas mixtures, under partial pressure. Nitrex has
developed a revolutionary process called "Pulse- Pressure", a method
quickly becoming the industry standard.
Relative to conventional carburizing, the main advantages of the method
are:
repeatable results to within ±0.001" (±25µm),
significantly reduced size changes and distortion,
improved fatigue strength,
better control of the surface layer chemistry,
the process is environmentally friendly.
The basic aspects or carburizing in general are described in the

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Conventional Carburizing section.
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Vacuum Carbonitriding

It is a thermal process of simultaneously diffusing both carbon and
nitrogen into ferrous alloys under partial pressure. This leads to an
extremely hard and wear resistant surface. Vacuum carbonitriding is a
significant improvement over conventional gas carbonitriding. The process
contains all of the inherent benefits of vacuum carburizing, but also has the
additional benefit of precise computer control of surface ammonia content.
Furthermore, this process does not require any additional refractory
burn-outs so not only is the end product of higher quality, but it is often
less expensive than with competing conventional gas processes.
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Corr-Check®: Corrosion Protective Treatment

Ferrous alloys suffer from corrosion to some extent. Surface treatments will
weaken or enhance the corrosion resistance of the treated surface, as an
intentional design objective or a side effect. Nitriding or Nitrocarburizing
are of particular interest because in most cases such surface treatments will
be the last manufacturing operation. The nitrided/nitrocarburized
component as a finished product may require additional protection.
Corr-Check® has been developed with that end in mind. It is a light, non-oil
based corrosion inhibitor, applied to enhance the corrosion resistance of
the surface, both in service as well as simply to increase the component’s
shelf life.
Corrosion resistance of non-stainless alloys is enhanced somewhat by
nitriding or nitrocarburizing due to the compound layer created on the
surface. However, the improvement is relatively small and a Corr-Check®
treatment is frequently added as an inexpensive means of improving the
component’s resistance to corrosion by an order of magnitude. In as much
as a nitrided surface may show rust spots in a corrosion test even before 24
hours, Corr-Check® will in most cases move that point to well over 96
hours, a traditional cut-off limit for many applications. If additional
corrosion resistance is required, the ONC® process should be considered.
The treatment is equally applicable to stainless steels, which tend to lose

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some of their inherent corrosion resistance in a nitriding process.
Summary of Advantages:
Easy and safe treatment,
Non-sticky surface when the surface has dried off,
Significant enhancement of corrosion resistance.
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