FORMING CHARACTERISTICS OF ADVANCED HIGH-STRENGTH STEELS
Stuart Keeler International Iron and Steel Institute
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PRESENTATIONS
Great Designs in Steel
2004
2002
2003
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AHSS RESEARCH REPORTS
AISI – DOE Technology Roadmap Program
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AHSS RESEARCH
Global Steel Industry Projects
UltraLight Steel Auto Body (ULSAB), ULSAC and ULSAB-AVC - led to . . .
• Increased use of HSS and AHSS • Need for AHSS Forming & Joining Application Guidelines
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AHSS RESEARCH
IISI-AutoCo Steel Companies
Arcelor China Steel Dofasco Ispat Inland (Mittal) Kobe Posco Salzgitter SSAB ThyssenKrupp Stahl USIMINAS BlueScope Steel Corus Iscor (Mittal) Steel JFE Nippon Steel Rautaruukki Oyj Severstal NA Sumitomo United States Steel voestalpine Stahl
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AHSS RESEARCH
Drivers for data consolidation:
• Production steel availability • Critical mass of data • User demands for information
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MERGING WORLDWIDE CONTENT
International Iron and Steel Institute Working Group
Arcelor China Steel Dofasco Ispat Inland (Mittal) Kobe Posco Salzgitter SSAB ThyssenKrupp Stahl USIMINAS BlueScope Steel Corus Iscor (Mittal) Steel JFE Nippon Steel Rautaruukki Oyj Severstal NA Sumitomo United States Steel voestalpine Stahl
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AHSS WORKING GROUP GOAL
Assemble information on: • Forming and Joining • Include four current AHSS types:
- Dual Phase (DP) - Transformation Induced Plasticity (TRIP) - Complex Phase (CP) - Martensitic (Mart)
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AHSS WORKING GROUP GOAL
Present what is new or different about AHSS. Do not create a tutorial book.
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DATA COMPARISONS
AHSS
HSLA
MILD STEEL
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A PROBLEM
HSLA 450 means: 450 MPa yield strength in Europe and North America 450 MPa tensile strength in Asia
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THE SOLUTION
Show steels as: Type YS/TS in MPa Example of steel comparison for equal YIELD strengths: HSLA 350/450 DP 350/600
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THE SOLUTION
Show steels as: Type YS/TS in MPa Example of steel comparison for equal TENSILE strengths: HSLA 500/600 DP 350/600
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WORKING GROUP DELIVERABLE
A 100+ page document entitled:
ADVANCED HIGH STRENGTH STEEL (AHSS) APPLICATION GUIDELINES
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APPLICATION GUIDELINES
Section 1: General descriptions • Definitions • Metallurgy • Common steel types
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SECTION 1 GENERAL DESCRIPTIONS
AHSS target two automotive needs: The DP and TRIP steels increase the area under the stress-strain curve. Compared to current HSLA steels, these steels have equal or higher strength levels with improved formability and crash energy absorption
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SECTION 1 GENERAL DESCRIPTIONS
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SECTION 1 GENERAL DESCRIPTIONS
In contrast CP and Mart steels extend the availability of steel in strength ranges above the HSLA grades, while retaining good crush resistance and energy absorption.
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For mild steels and conventional HSS the work hardening exponent (n-value) generally is a continuous inverse function of yield strength
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SECTION 2 - FORMING
Relationship for conventional low and medium strength steels
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SECTION 2 - FORMING
Importance of n-value as a function of strain for AHSS
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SECTION 2 - FORMING
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SECTION 2 - FORMING
• Dome stretching is related to total elongation. • Hole expansion, edge stretch, and bending are related to local elongation measured by a hole expansion test. • For conventional HSS no degradation of local elongation is experienced.
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SECTION 2 - FORMING
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SECTION 2 - FORMING
Required specific steel grade will depend on product and process design.
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SECTION 2 - FORMING
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SECTION 2 - FORMING
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SECTION 2 - FORMING
Steels with equal tensile strength compound the springback problem
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SECTION 2 - FORMING
Interaction between a hat-profile and sidewall curl for different forming processes
Punch BlankHolder BlankHolder
BHF
Punch
Punch
Punch
Die
Die
Die
Die
Bend-Unbend
Bend-Unbend Pad
Bend-Unbend Pad
a. Draw
b. Form-Draw
c. Form
d. Bend
a. Draw
b. Form-Draw
c. Form
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SECTION 2 - FORMING
Increased work hardening creates higher loads on press, tools, lubricant, and other load points
Section 4 – Glossary •Define metallurgical terms •Use press shop language Section 5 – References Useful for looking up original papers for additional study
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FINAL DOCUMENT
Available from member steel companies, IISI, AISI and on-line
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APPLICATION GUIDELINES
Download from:
www.worldautosteel.org
Also linked on:
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w w w . a u t o s t e e l . o r g
Great Designs in Steel is Sponsored by:
•AK Steel Corporation •Dofasco Inc.
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•Mittal Steel Company •Nucor Corporation
•Severstal North America Inc. •United States Steel Corporation