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FORMING CHARACTERISTICS
OF
ADVANCED HIGH-STRENGTH STEELS
St uar t K ee ler
International Iron and Steel Institute
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PRESENTATIONS
Great Designs in Steel
2004
2003
2002
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AHSS RESEARCH REPORTS
AISI – DOETechnology
Roadmap Program
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Global Steel Industry ProjectsUltraLight 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 NA
SSAB 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 GroupArcelor BlueScope SteelChina Steel Corus
Dofasco Iscor (Mittal) SteelIspat Inland (Mittal) JFEKobe Nippon SteelPosco Rautaruukki OyjSalzgitter Severstal NA
SSAB SumitomoThyssenKrupp Stahl United States SteelUSIMINAS voestalpine Stahl
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AHSS WORK ING 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 ordifferent about AHSS.
Do not create a tutorial book.
AHSS WORK ING 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 comparisonfor 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 comparisonfor equal TENSILE strengths:
HSLA 500/600DP 350/600
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WORK ING 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 thearea under the stress-strain curve.
Compared to current HSLA steels,
these steels have equal or higherstrength levels with improved
formability and crash energyabsorption
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SECTION 1
GENERAL DESCRIPTIONS
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SECTION 1
GENERAL DESCRIPTIONS
In contrast CP and Mart steelsextend the availability of steel instrength ranges above the HSLA
grades, while retaining goodcrush resistance and energy
absorption.
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SECTION 1
GENERAL 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 workhardening exponent (n-value)
generally is a continuousinverse function of yield
strength
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SECTION 2 - FORMING
Relationship for conventional low andmedium strength steels
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SECTION 2 - FORMING
Importance of n-value as a function ofstrain for AHSS
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SECTION 2 - FORMING
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SECTION 2 - FORMING
• Dome stretching is related to totalelongation.
• Hole expansion, edge stretch, andbending 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 dependon 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 strengthcompound the springback problem
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SECTION 2 - FORMING
Interaction between a hat-profile and sidewallcurl 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 createshigher loads on press, tools,
lubricant, and other load points
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SECTION 2 - FORMING
Computerized Forming ProcessDevelopment
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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 steelcompanies, 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
