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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