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FORMING CHARACTERISTICS OF
ADVANCED HIGH-STRENGTH STEELS
Stuart KeelerInternational Iron and Steel Institute
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PRESENTATIONS
Great Designs in Steel
20042003
2002
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AHSS RESEARCH REPORTS
AISI – DOE Technology Roadmap Program
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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
AHSS RESEARCH
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AHSS RESEARCH
Arcelor BlueScope SteelChina Steel CorusDofasco Iscor (Mittal) SteelIspat Inland (Mittal) JFEKobe Nippon SteelPosco Rautaruukki OyjSalzgitter Severstal NASSAB SumitomoThyssenKrupp Stahl United States SteelUSIMINAS voestalpine Stahl
IISI-AutoCo Steel Companies
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Drivers for data consolidation:
• Production steel availability• Critical mass of data• User demands for information
AHSS RESEARCH
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MERGING WORLDWIDE CONTENT
International Iron and Steel Institute Working Group
Arcelor BlueScope SteelChina Steel CorusDofasco Iscor (Mittal) SteelIspat Inland (Mittal) JFEKobe Nippon SteelPosco Rautaruukki OyjSalzgitter Severstal NASSAB SumitomoThyssenKrupp Stahl United States SteelUSIMINAS 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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Present what is new or different about AHSS.
Do not create a tutorial book.
AHSS WORKING GROUP GOAL
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AHSS
HSLA MILD STEEL
DATA COMPARISONS
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HSLA 450 means:
450 MPa yield strength in Europe and North America
450 MPa tensile strength in Asia
A PROBLEM
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THE SOLUTION
Show steels as: Type YS/TS in MPa
Example of steel comparison for equal YIELD strengths:
HSLA 350/450DP 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 500/600DP 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 1GENERAL DESCRIPTIONS
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SECTION 1GENERAL 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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SECTION 1GENERAL DESCRIPTIONS
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APPLICATION GUIDELINES
Section 2 – Forming• Forming limits• Mechanical properties• Forming modes• Tool design• Springback• Blanking• Press requirements• Multiple stage forming• In-service requirements
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SECTION 2 - FORMING
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
Bend-Unbend
Die
Punch Blank- Holder
a. Draw
Bend-Unbend
Die
Punch
Blank- Holder
b. Form-Draw
BHF
Pad Bend-Unbend
c. Form
Die
Punch
Pad
Die
Punch
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
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SECTION 2 - FORMING
Computerized Forming Process Development
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APPLICATION GUIDELINES
Section 3 – Joining• Welding processes• MIG brazing• Adhesive bonding• Mechanical joining• Hybrid joining• Material issues for weld repair
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APPLICATION GUIDELINES
Section 4 – Glossary•Define metallurgical terms•Use press shop language
Section 5 – ReferencesUseful for looking up originalpapers 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:www.autosteel.org
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Great Designs in Steel is Sponsored by:•AK Steel Corporation•Dofasco Inc.
•Severstal North America Inc.•United States Steel Corporation
•Mittal Steel Company•Nucor Corporation
