12 - Advances in AHSS for Automotive Applications

w w w . a u t o s t e e l . o r g

ADVANCES IN HIGH STRENGTH STEELS

FOR AUTOMOTIVE APPLICATIONS

Shrikant P. BhatAutomotive Product Applications

ArcelorMittal Global R&D – East Chicago


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


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)


Automobile Weight Trend - VW


Reasons for Weight Gain


Sheet Steel and the Automobile


Sheet Steel and the Automobile

Design ManufacturingTensile Stress（MPa）

Elon

gatio

n(%

)

200 400 1200600 1000 14008000

10

30

20

40

50

60

UHHSUHHS

Conventional HSS

Mild Steel

Materials

Safety

PerformanceLight Weight

Environment

Cost

Customer Satisfaction


SHEET STEEL AND THE AUTOMOBILE

Dent resistant Ultra-high strengthHigh strength

Forming Grade


Automotive Sheet SteelsE

long

atio

n (%

)

Tensile Strength (MPa)

0

10

20

30

40

50

60

70

0 600 1200

Low StrengthSteels (<270MPa)

Ultra High StrengthSteels (>700MPa)

300 900

High StrengthSteels

1600

DP

AHSS

MARTENSITE

HSLA

IF

MildIF-HS

BHCMn

ISO

Conventional HSS

TWIP

TRIP


Steels – Alloys based on Iron

Fundamentals of Sheet Steel Metallurgy


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


Fe - Fe3C Phase Diagram


Processing of HiTen SteelsTime-Temperature-Transformation (TTT) Diagram

Time

AUSTENITE

BAINITE

PEARLITEFERRITE

MARTENSITE

Tem

pera

ture

Ms

Ar3

MARTENSITE DUALPHASE

TRIP COMPLEXPHASE

BainiteFerrite

AusteniteMartensite

MicrostructureLegend


Sheet Steel Microstructures

Ferrite (F) Martensite (M)

TRIP (F + B/M + RA)Dual Phase (F + M)


Strengthening Mechanisms in Sheet Steels - Summary

Tensile Strength,

MPa

Carbon Level Solid Solution

Hardening

Grain Refinement Precipitation

HardeningPhase

Transformation

270 Low C √ √

340 ULC - L C, Mn, P √ √

440 ULC - L C, Mn, Si √ Nb, Ti, V √

600Low -

Medium C, Mn, Si √Nb, Ti, V,

Mo √

800Low-

Medium C, Mn, Si √Nb, Ti, V,

Mo √

1000 DPLow -

MediumC, Mn, Si,

Mo √Nb, Ti, V,

Mo √

900 – 1500 MMedium -

High C, Mn, Si√ √


Facilities for High Strength Steels

Time (18-36 hrs)

Tem

pera

ture

Soak 600-700°C

Slow coolingSlow

heating

Time (3-4 min)

Tem

pera

ture

Soak >720°C

Overage 200-400°C

Rapid cooling 500-1000 °C/s

T>820o

C

Cooling5 ∼ 10

oC/sec

Coating

Tem

pera

ture

(o C)

4-6 minutes


Sheet Steel Applications

Formability of Sheet SteelsStress – Strain Curves as

Surrogates


PRODUCT CHARACTERISITCSHOT ROLLED STEELS

ENGINEERING STRESS -STRAIN CURVES HR GRADES

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35 40

ENGINEERING STRAIN, %

ENG

INEE

RIN

G S

TRES

S, M

Pa

HSLA 250

HSLA 350

HSLA 550

HSLA 590TS

HSLA 700


PRODUCT CHARACTERISTICSCOLD ROLLED STEELS

ENGINEERING STRESS -STRAIN CURVES CR STEEL GRADES

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25 30 35 40 45 50ENGINEERING STRAIN, %

EN

GIN

EER

ING

STR

ESS,

MPa

270

DIFORM140T (965 MPa TS)

M190 (1300 MPa )

440

590 590DU

980DU


PRODUCT CHARACTERISTICSGALVANNEALED STEELS

100

200

300

400

500

600

700

800

900

1000

1100

0 10 20 30 40 50 60

ENGINNERING STRAIN, %

ENG

INEE

RIN

G S

TRES

S, M

P

2 7 0 E

3 4 0 HR3 4 0 B H

4 4 0

5 9 0 D U5 9 0

9 8 0 D U

ENGINEERING STRESS - STRAIN CURVESGA STEEL GRADES


TYPICAL STRESS STRAIN CURVES FOR 590 MPa FAMILY OF STEELS

0

100

200

300

400

500

600

700

0 5 10 15 20 25 30Engineering Strain, %

Engi

neer

ing

Stre

ss, M

Pa

GA 590TRIP

GA 590 DU

GA 590

GA590

GA 590DU

GA 590TRIP



long

atio

n (%

)


0

10

20

30

40

50

60

70

0 600 1200



300 900

High StrengthSteels

1600

DP

AHSS

MART

HSLA

IF

MildIF-HS

BHCMn

ISO

Conventional HSS

TWIP

USIBOR

USIBOR

TRIP


Typical Hot Stamping Process Steps


Example Parts made with Usibor 1500P

Fuel Tank Guard


Main Properties After Hot Stamping


SHEET STEEL APPLICATION TRENDS



2007 North American Light Vehicle Steel Content for Body, Bumper and Closures

(Extracted from the Ducker 2007 Report)

9,341 Million Pounds of Content for 9.9 Million Vehicles

GM, Ford and DCX- Segmented by Type of Steel -

Foreign Domestics- Segmented by Type of Steel -

4,305 Million Pounds of Content for 5.394 Million Vehicles

56.0%

6.9%

12.0%

2.2%6.2%

16.7%Low Strength (270)

5,234MHSS (340)1,562

CHSS(440)1,122

AHSS(590-980)

644

UHSS (Over 980)203

Bake Hard576

45.3%11.0%

15.0%

1.5%8.9%

18.3%

Low Strength(270)1,952

MHSS (340)472

CHSS (440)646

AHSS (590-980) 787(Includes wheels)

UHSS (Over 980)63

Bake Hard385



51.5%12.4%

36.1%

55.0%9.4%

35.6%59.5%

5.8%34.7%

2007 Body and Closure Steel Content by Type

Mild Steel

HSS

976 Pounds

Advanced HSS

Total Body on Frame

Mild Steel

HSS

763 Pounds

Advanced HSS

Total Unibody Total

842 Pounds

Mild Steel

HSS

Advanced HSS*

*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

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.



2007 North American Light Vehicle Flat Rolled AHSS and UHSS Steel Content

17%

75%

8%

DP 500/600 Including 590R

DP 980

DP 780

665,000 Tons

Dual Phase Steels

31.1%

40.7%28.2%

Boron Steels75,000 tons

Recovery Annealed TRIP and CP Steels

52,000 Tons

Martensitic Steels57,200 Tons

184,200 Tons

Other Steel Grades


Predicted Growth of AHSS Usage - VW


AHSS usage to grow significantly

• 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.

AHSS gathersall MultiPhaseSteels above450MPa Ts

BIW AHSS Usage (%)

05

10152025303540

2000 2006 2012 2020

NaftaJapan EU EM

Source AM Global Auto Marketing Studies



long

atio

n (%

)


0

10

20

30

40

50

60

70

0 600 1200



300 900

High StrengthSteels

1600

DP

AHSS

MART

HSLA

IF

MildIF-HS

BHCMn

ISO

Conventional HSS

TWIP

USIBOR

USIBOR

TRIP


QUESTIONS?

THANK YOU

ADVANCES IN HIGH STRENGTH STEELS

FOR AUTOMOTIVE APPLICATIONS

Documents

12 - Advances in AHSS for Automotive Applications