12 - Advances in AHSS for Automotive Applications

ADVANCES IN HIGH STRENGTH STEELS FOR AUTOMOTIVE APPLICATIONS Shrikant P. Bhat Automotive Product Applications ArcelorMittal Global R&D – East Chicago

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Presentation Outline • Introduction - Material Choice in Automobiles • Sheet Steel and the Automobile – General Introduction • Fundamentals of Sheet Steel Metallurgy • Product Characteristics and Application Trends • Hot Rolled Products • Cold Rolled Products • Coated Products Hot Stamping • Q&A www.autosteel.org

Steel – Material of Choice for Modern Living • “Most Large Metal Structures are made of Carbon Steel – the World’s Most Useful Structural Material” – Kennedy Space Center website • Integral Material for modern buildings, medicine, homeland security, food packaging, transportation and infrastructure. • In today’s cars, Steel makes up about 62% weight - Steel is the Backbone of the entire vehicle (Protect occupants, Provide positive driving experience, React to road loads, Provide comfort, and attachment points to other components of the vehicle)

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Automobile Weight Trend - VW

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Reasons for Weight Gain

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Sheet Steel and the Automobile

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Sheet Steel and the Automobile 60

Elongation(%)

50

Mild Steel

40

Conventional HSS

30 20

UHHS

10 0

200

400

600

800

1000

1200

1400

Tensile Stress（MPa）

Materials

Design Safety

Environment

Customer Satisfaction Cost Performance

Light Weight

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Manufacturing

SHEET STEEL AND THE AUTOMOBILE Dent resistant

High strength

Ultra-high strength

Forming Grade

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Automotive Sheet Steels Low Strength Steels (700MPa)

TWIP

Conventional HSS

IF

IF-HS

40

Mild ISO BH

30 20

AHSS CM

TRIP n

HSL A

10

DP MARTENSITE

0

0

300

900 600 Tensile Strength (MPa)

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1200

1600

Steels – Alloys based on Iron

Fundamentals of Sheet Steel Metallurgy

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Strengthening Mechanisms

• • • • •

Work Hardening (Dislocation Strengthening) Solid Solution Strengthening Grain Refinement Precipitation Strengthening Phase Transformations Strength/Ductility in Steel obtained by a combination of strengthening mechanisms

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Fe - Fe3C Phase Diagram

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Processing of HiTen Steels Time-Temperature-Transformation (TTT) Diagram

AUSTENITE

Temperature

Ar3

FERRITE PEARLITE BAINITE

Ms

MARTENSITE Time

MARTENSITE

DUAL PHASE

TRIP

COMPLEX PHASE

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Microstructure Legend Austenite Martensite Ferrite Bainite

Sheet Steel Microstructures

Ferrite (F)

Martensite (M)

Dual Phase (F + M)

TRIP (F + B/M + RA)

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Strengthening Mechanisms in Sheet Steels - Summary Tensile Strength, MPa

Carbon Level

270

Low

C

√

√

340

ULC - L

C, Mn, P

√

√

440

ULC - L

C, Mn, Si

√

Nb, Ti, V

√

600

Low Medium

√

Nb, Ti, V, Mo

√

800

LowMedium

C, Mn, Si

√

Nb, Ti, V, Mo

√

1000 DP

Low Medium

C, Mn, Si, Mo

√

Nb, Ti, V, Mo

√

900 – 1500 M

Medium High

Solid Solution Hardening

C, Mn, Si

Grain Refinement

Precipitation Hardening

√ C, Mn, Si

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Phase Transformation

√

Facilities for High Strength Steels

Slow cooling

Slow heating

Rapid cooling 500-1000 °C/s

o ( C)

o T>820 C

Overage 200-400°C

Time (18-36 hrs)

Cooling o 5 ∼ 10 C/sec

Temperature

Soak 600-700°C

Temperature

Temperature

Soak >720°C

Coating

4-6 minutes

Time (3-4 min)

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Sheet Steel Applications

Formability of Sheet Steels Stress – Strain Curves as Surrogates

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PRODUCT CHARACTERISITCS HOT ROLLED STEELS 800

ENGINEERING STRESS -STRAIN CURVES HR GRADES

HSLA 700 HSLA 550

ENGINEERING STRESS, MPa

700

HSLA 590TS

600

500 HSLA 350

400

300 HSLA 250

200

100 0

5

10

15

20

25

ENGINEERING STRAIN, %

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30

35

40

PRODUCT CHARACTERISTICS COLD ROLLED STEELS 1400

ENGINEERING STRESS -STRAIN CURVES CR STEEL GRADES

ENGINEERING STRESS, MPa

1200

M190 (1300 MPa )

1000

980DU DIFORM140T (965 MPa TS)

800

600

590DU

590

400

200

440

270

0 0

5

10

15

20

25

30

35

ENGINEERING STRAIN, %

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40

45

50

PRODUCT CHARACTERISTICS GALVANNEALED STEELS 1100

ENGINEERING STRESS - STRAIN CURVES GA STEEL GRADES

ENGINEERING STRESS, MP

1000

980DU

900 800 700 600

590

590DU

500 440

400 300

340HR 340BH

200

270E

100 0

10

20

30

40

ENGINNERING STRAIN, %

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50

60

TYPICAL STRESS STRAIN CURVES FOR 590 MPa FAMILY OF STEELS 700

Engineering Stress, MPa

600 500 400

GA590

300

GA 590DU GA 590TRIP

GA 590TRIP

200

GA 590 DU GA 590

100 0 0

5

10

15

20

Engineering Strain, %

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25

30

Automotive Sheet Steels

Low Strength Steels (700MPa)

DP

USIBOR

MART

0

300

900 600 Tensile Strength (MPa)

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1200

1600

Typical Hot Stamping Process Steps

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Example Parts made with Usibor 1500P

Fuel Tank Guard

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Main Properties After Hot Stamping

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SHEET STEEL APPLICATION TRENDS

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SHEET STEEL APPLICATION TRENDS 2007 North American Light Vehicle Steel Content for Body, Bumper and Closures (Extracted from the Ducker 2007 Report)

GM, Ford and DCX

Foreign Domestics

- Segmented by Type of Steel -

- Segmented by Type of Steel -

Bake Hard 576 AHSS 6.2% (590-980) 6.9% 644 CHSS 12.0% (440) 1,122

16.7% MHSS (340) 1,562

UHSS (Over 980) 203 2.2%

Bake Hard 8.9% 385

UHSS (Over 980) 63 1.5%

MHSS (340) 11.0% 472

56.0% Low Strength (270) 5,234

9,341 Million Pounds of Content for 9.9 Million Vehicles

15.0% CHSS (440) 18.3% 646 AHSS (590-980) 787 (Includes wheels)

45.3% Low Strength (270) 1,952

4,305 Million Pounds of Content for 5.394 Million Vehicles

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SHEET STEEL APPLICATION TRENDS There is a significant difference between the percent of AHSS in vehicles using a body on frame type architecture versus vehicles using a unibody type architecture.

Total Body on Frame

Total Unibody

Total

2007 Body and Closure Steel Content by Type Advanced HSS HSS

Advanced HSS*

Advanced HSS

5.8%

12.4%

34.7%

51.5%

Mild Steel

HSS

36.1% 59.5%

9.4%

Mild Steel

35.6%

HSS

Mild Steel

976 Pounds

763 Pounds

842 Pounds

*AHSS is 73.6 pounds of Dual Phase , 5.8 pounds of martensitic, boron, complex phase, recovery annealed steels and TRIP steel not including door intrusion or bumper beams

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55.0%

SHEET STEEL APPLICATION TRENDS 2007 North American Light Vehicle Flat Rolled AHSS and UHSS Steel Content

Other Steel Grades

Dual Phase Steels

Recovery Annealed TRIP and CP Steels 52,000 Tons

DP 780

8%

28.2%

17%

Boron Steels 75,000 tons

40.7%

DP 980

75% DP 500/600 Including 590R

665,000 Tons

31.1%

Martensitic Steels 57,200 Tons

184,200 Tons

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Predicted Growth of AHSS Usage - VW

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AHSS usage to grow significantly 40 35 30 25 20 15 10 5 0

Nafta

BIW AHSS Usage (% )

Japan EU EM

Source AM Global Auto Marketing Studies

2000

2006

2012

AHSS gathers all MultiPhase Steels above 450MPa Ts

2020

• Advance of Japanese OEMs in AHSS implementation • AHSS Growth currently limited by transformation constraints • Future Emerging markets needs calculated as if required AHSS were available.

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Automotive Sheet Steels Low Strength Steels (700MPa)

DP

USIBOR

MART

0

300

900 600 Tensile Strength (MPa)

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1200

1600

ADVANCES IN HIGH STRENGTH STEELS FOR AUTOMOTIVE APPLICATIONS QUESTIONS? THANK YOU

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