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Advanced High Strength Steels

Formability

Alex A. KoniecznyU. S. Steel Automotive Center

February 19, 2003Great Designs in Steel Seminar

Livonia, MI

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Formability Introduction

σσ22

σσ11

DDS r >> 1DDS r >> 1 DP r = 1DP r = 1

AA

BB

•• FormabilityFormability•• Experimental Forming Limit DiagramsExperimental Forming Limit Diagrams•• BendabilityBendability TestTest•• Other Forming Tests Other Forming Tests

AA

BBComparison of Yield Strength, Tested As Delivered, L-dir.

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2 0.25True Strain

True

Stre

ss

DP800 HSLA340 DDS HSLA550 DP1000 DP600 T600

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Typical Mechanical Properties

Example of Typical Mechanical PropertiesExample of Typical Mechanical Properties

UTS (UTS (MPaMPa)) El (%)El (%)GRADEGRADE YS YS ((MPaMPa)) YPE (%)YPE (%) nn--value value

(10%(10%--UE)UE) nn--value (4value (4--6%)6%)

IFIF 163163 282282 49.049.0 -- 0.2400.240 --

DDSDDS 183183 314314 42.942.9 -- 0.2300.230 --

CMn440CMn440 354354 455455 39.039.0 3.63.6 0.1560.156

HSLA340HSLA340 377377 443443 28.428.4 2.82.8 0.1700.170 --

SF600SF600 490490 615615 28.628.6 3.23.2 0.1480.148 --

HSLA480HSLA480 487487 604604 28.028.0 2.22.2 0.1280.128 --

HSLA550HSLA550 641641 672672 13.513.5 3.33.3 0.040*0.040* --

DP600DP600 340340 602602 29.029.0 -- 0.1700.170 0.2080.208

T600T600 393393 631631 34.034.0 -- 0.2300.230 --

DP800DP800 459459 838838 17.217.2 -- 0.115*0.115* 0.1680.168

T800T800 475475 822822 28.028.0 0.60.6 0.2400.240 --

DP1000DP1000 726726 10031003 10.810.8 -- 0.060*0.060* 0.080.08

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True Stress – Strain Curves

Workhardening of selected materials

0

100

200

300

400

500

600

700

800

0.00 0.05 0.10 0.15 0.20 0.25True Strain

True

Stre

ss [M

Pa]

T600 HSLA340 DP600

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Work Hardening Index

Instantaneous n - value

00.050.1

0.15

0.20.250.3

0 5 10 15 20 25 30

Engineering Strain [%]

n - v

alue

T600 DP600 HSLA340

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Strain Distribution Ability

Instantaneous n - value

00.050.1

0.150.2

0.250.3

0 5 10 15 20 25 30Engineering Strain [%]

n - v

alue

T600 DP600 HSLA340

Comparison of Thinning

-20-15-10

-505

1015202530

0 10 20 30 40

Location #

Thin

ning

(%)

HSLA DP

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Experimental FLDs for Dual Phase Steel

Forming Limit Diagram for DP800 1.2 mm

10

20

30

40

50

60

70

80

90

-30 -20 -10 0 10 20 30

Minor Strain [%]

Maj

or S

train

[%]

TheorExperFailedMarginalSafe

Forming Limit Diagram for DP600 1.2 mm

10

20

30

40

50

60

70

80

90

-30 -20 -10 0 10 20 30Minor Strain [%]

Maj

or S

train

[%]

TheorExperFailedMarginalSafe

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Experimental FLD for T600

Forming Limit Diagram for TRIP T600 1.2 mm

0102030405060708090

100

-30 -20 -10 0 10 20 30 40 50 60 70

Minor Strain [%]

Maj

or S

train

[%]

ExperimentCalculatedFailedMarginalSafe

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FLD Comparison

Forming Limit Curves for T600, DP600, HSLA340, DDS, 1.2mm

10

20

30

40

50

60

70

80

90

100

-30 -20 -10 0 10 20 30 40 50 60Minor Strain [%]

Maj

or S

train

[%]

T600DP600HSLA340DDS

••The FLCThe FLC of T600 is of T600 is comparable to DDS steel comparable to DDS steel in draw forming area, and in draw forming area, and exceeds DDS steel exceeds DDS steel formability up to 10% in formability up to 10% in balanced biaxial formingbalanced biaxial forming

••Influence of strain rate, Influence of strain rate, temperature and stress temperature and stress state on TRIP steels state on TRIP steels formability is different formability is different than for other steelsthan for other steels

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Bendability

BendabilityBendability is needed for dimensional accuracy control is needed for dimensional accuracy control in stampingin stamping

T600-0tT600-0.5t

DP600 HSLA 550

DP800-0.5t

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Cup Drawing Test

Rp0

0.51

1.52

2.5

IFCMn4

40 H

SLA 34

0/440

SF600

HSLA

440/6

00

DP600

DP800

T800

DP1000

Material

Lim

it D

raw

ing

Rat

io

Rp=2mm Rp=6mm Rp=25mm

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Stretch Forming Test

0

5

10

15

20

25

30

IFCMn4

40 HSLA

340/4

40 SF60

0 HSLA

440/6

00DP60

0

DP800

T800

DP1000

Material

Dom

e H

eght

[mm

]

Rp=2mm Rp=6mm Rp=25mm

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Hole Expansion Test

020406080

100120140160180200

IFCMn4

40 HSLA

340/4

40 SF60

0 HSLA

440/6

00

DP600

DP800

T800

DP1000

Material

Hol

e E

xpan

sion

Rat

io [%

]

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T-Channel Drawing Test

T-Chanel Drawing

0

10

20

30

40

50

60

70

80

90

100

IFCMn4

40 HSLA

340/4

40

SF600

HSLA44

0/600

DP600

DP800

T800

DP1000

Material

Hei

ght [

mm

]

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Plane Strain Drawing Test

WWWoWo=48mm=48mm

Delta W = WDelta W = W--WoWo

Rd

010

2030

4050

60

200 400 600 800 1000UTS [MPa]

Del

ta W

[mm

]

R=3mm R =7mm R=10mm

Springback

0

10

20

30

40

50

60

IFCMn4

40 HSLA

340/4

40

SF600

HSLA44

0/600

DP600

DP800

T800

DP1000

Material

Del

ta W

[mm

]

Rd=3mm Rd=7mm Rd=10mm

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Conclusions

•• DP and TRIP steels display excellent formability as DP and TRIP steels display excellent formability as compared to conventional HSS and better capacity to compared to conventional HSS and better capacity to distribute strain over the part surfacedistribute strain over the part surface

•• AHSS display very good AHSS display very good bendabilitybendability•• ASM FLC approximation (KeelerASM FLC approximation (Keeler--Brazier) is applicable for Brazier) is applicable for

DP and TRIP steelsDP and TRIP steels•• Due to excellent combination of strength with formability, Due to excellent combination of strength with formability,

TRIP steel has potential for economic application (possibility TRIP steel has potential for economic application (possibility for reduction of the number of parts in the car)for reduction of the number of parts in the car)

•• A need to understand AHSS unique characteristics to A need to understand AHSS unique characteristics to successfully make partssuccessfully make parts

-- OneOne--forfor--one direct substitution with other HSS may cause issuesone direct substitution with other HSS may cause issues

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References

1.1. KoniecznyKonieczny, A. A., On the Formability of Automotive TRIP Steels, SAE, , A. A., On the Formability of Automotive TRIP Steels, SAE, 20032003--0101--521521

2. 2. KamuraKamura M., M., OmijaOmija Y., Shaw J., Chen M., Formability and Y., Shaw J., Chen M., Formability and SpringbackSpringbackCharacterization of Advanced High Strength Steel, SAE, 2003Characterization of Advanced High Strength Steel, SAE, 2003--0101--522522

3.3. KoniecznyKonieczny, A. A., An Overview of Formability, Technological and , A. A., An Overview of Formability, Technological and MicrostructuralMicrostructural Aspects of the Automotive TRIP Steels, Processing and Aspects of the Automotive TRIP Steels, Processing and Fabrication of Advanced Materials, 11th Int. Symposium 2002, ASMFabrication of Advanced Materials, 11th Int. Symposium 2002, ASM Materials Materials Solution Conference and Exposition, 7Solution Conference and Exposition, 7--10 October, 2002, Columbus, Ohio10 October, 2002, Columbus, Ohio

4.4. KoniecznyKonieczny A. A., On Formability Assessment of the Automotive Dual Phase A. A., On Formability Assessment of the Automotive Dual Phase Steels, IBEC, 2001Steels, IBEC, 2001--0101--30753075

5.5. KoniecznyKonieczny A. A., A. A., HoydickHoydick D. P., An Overview of Formability, Technological and D. P., An Overview of Formability, Technological and MicrostructuralMicrostructural Aspects of the Automotive DualAspects of the Automotive Dual--Phase Steels, Processing Phase Steels, Processing and Fabrication of Advanced Materials, Ninth Int. Symposium 2000and Fabrication of Advanced Materials, Ninth Int. Symposium 2000, ASM , ASM Materials Solution Conference and Exposition, 9Materials Solution Conference and Exposition, 9--12 October, 2000, St. Louis, 12 October, 2000, St. Louis, MissouriMissouri

6.6. Shi M. F., Thomas G. H., Chen X. M., Shi M. F., Thomas G. H., Chen X. M., FeketeFekete J. R., Formability Performance J. R., Formability Performance Comparison between Dual Phase and HSLA SteelsComparison between Dual Phase and HSLA Steels,, Process Symposium 43rd Process Symposium 43rd Mechanical Working and Steel Processing Conference, Iron & SteelMechanical Working and Steel Processing Conference, Iron & Steel Society, Society, 20012001