Forming Characteristics of Advanced High-strength Steels

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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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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 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

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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 – 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:
www.autosteel.org
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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

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