matlock distribution aisi workshop (feb2012pdf) | nist

David K. Matlock, John G. Speer, and Emmanuel De Moor

Advanced Steel Processing and Products Research Center*Colorado School of Mines

Golden, Colorado

Recent AHSS Developments for Automotive Applications:

Processing, Microstructures, and Properties

*ASPPRC: An NSF Industry/University Cooperative Research Center - Est. 1984

http://aspprc.mines.edu/

Workshop : Addressing Key Technology Gaps in ImplementingAdvanced High-Strength Steels for Automotive Lightw eighting

February 9 - 10, 2012USCAR Offices, Southfield, MI

Scope of Today ’s Presentation

• AHSS historical perspective – very brief

• Status of recent AHSS developments

• Identify opportunities• Enhanced first generation AHSS• New Third generation processing routes

• Observations and suggestions

DP Developments – 1970 ’s to ……

• 1960’s – 1970’s: HSLA steel• Thermomechancial processing +

microalloy additions

• 1970”s – 1980’s: Dual-phase steel• Fundamentals identified• Basis for AHSS developments

• 1990’s --- TRIP (Transformation I nduced Plasticity) and other AHSS developments, leading to “3 rd Generation AHSS ”

Dual-Phase Steels: “The Early Days ”

Significant Parallel Research Activities

•Nippon Steel• 1975: S. Hayami and

T. Furukawa, Microalloying ‘75

•GM• 1976: M.S. Rashid,

SAE + others

•Ford• 1978: R.G. Davies,

Met. Trans. + others

M.S. Rashid,SAE, (1977)

Time

Tem

pera

ture

"Dual Phase"

Ferrite +Martensite

A1

A3

Overage/Galvanize

DP Steel Processing

• Initially conceived based on “simple”processing routes for hot and cold rolled steels

• Microstructures more complex than simply ferrite + martensite and contained retained austenite + ??

0 1 2 3 4 5 6Retained Austenite (pct)

8

12

16

20

24

28

32

Elo

ngat

ion

(pct

)

0.10C - 1.32Mn - 0.54Si - 0.11V0.12C - 1.50Mn - 0.61Si - 0.055V

(a)

0 4 8 12 16 20 24Uniform Strain (pct)

0

1

2

3

4

5

6

Ret

aine

dA

uste

nite

(pct

) 0.12C - 1.50Mn - 0.61Si - 0.055V

(b)

“… the ductility could be further improved by increasi ng the amount of retained austenite …” A. Marder (1977)

…Lessons Learned from “Early ” DP Steels

A. Marder, “Factors Affecting the Ductility of Dual -Phase Alloys,” TMS, (1979)

• Processed as dual-phase steel• Observed microstructures more complex than

ferrite + martensite

However, in a different study: “… retained austenite did not have a measureable effect” due in part “to the fact that the first few percent pla stic strain eliminated … austenite from the microstructure.” Eldis, TMS, (1979)

0 0.1 0.2 0.3 0.4True Strain

0

0.2

0.4

0.6

0.8

1

Vo

lum

e F

ract

ion

Mar

ten

site

A

D

C

B

AusteniteStability

Condition

Schematic Austenite Stability Comparison*


Time

Tem

pera

ture

Ferrite-Bainite-Austenite

"TRIP"

"Dual Phase"Ferrite +Martensite

A1

A3

TRIP Steel Processing – “modified DP ”

• Isothermally transform or control cool

• Austenite in high strength matrix (e.g. fine grain ferrite, martensite, bainite, …)

• Strength = f(MVF , ferrite grain size)

• Basic TRIP steel requirements identified

• Control amount of retained austenite at room temperature.

• Control austenite mechanical stability

• Microstructures are “complex”

• “First Generation AHSS ”


σσσσT = Vfσσσσf + VMσσσσM

Microstructural Classes:1st Generation AHSS

Elo

ngat

ion

(%)

Tensile Strength (MPa)

0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

HSLA

IF

MildIF-HS

BHCMn

ISO

Elo

ngat

ion

(%)

600

-Conventional HSS

First Generation AHSSISO

Mild Steels

AISI: www.steel.org (2006)

1800

1600

1400

1200

1000

800

600

400

200

00.20.1 0.3 0.4

Tru

e S

tres

s (M

Pa)

True Strain0

Martensite

HSLA320

TRIP800

DP590

DP980

IF

Compiled from:Huang 1989Bruce 2003

Cornette 2005Säglitz 2008

Elo

ngat

ion

(%)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

HSLA

IF

MildIF-HS

BHCMn

ISO

Elo

ngat

ion

(%)

600

-

TWIP

AUST. SS

L-IP

ISO

Third Generation AHSS:

Affordable Multiphase Steels:

Unique Microstructures**Goal: Formable steels with

Increased strength and ductility

Future Opportunities for AHSS**Predicted to contain:

• High strength constituent• Retained austenite with controlled stability


Processing Opportunities for AHSSE

long

atio

n (%

)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

IF

MildIF-HS

BHCMn

ISO

-

BH

TWIP

AUST. SS

L-IP

Future Opportunity

Third Generation AHSSHSLA

$$Enhanced TRIP with Modified γ

“Q&P”

B-Modified Hot Formed

TWIP with Lower $$

EnhancedDP

D.K. Matlock and J.G. Speer, “Third Generation of A HSS: Microstructure Design Concepts,” Microstructur e and Texture in Steels and Other Materials, ed. by A. Haldar, S. Su was, and D. Bhattacharjee, Springer, London, 2009, pp. 185-205.

Enhanced Dual-Phase Steels

Example approaches:• Control heating rate

• Thermal cycling to refine grain size

• Alter ferrite strength to control ferrite/martensite strength ratio

• …other….

D. Mumford, G. Fourlaris, A. Smith, and N. Silk, “T he Interaction of Recrystallization and Transformation during the Rehe ating of Multiphase Steels,” AISTech, 2008.

Heating Rate: CMnSiCr DP600 Steel

Heating Rate = 2 oC/s Heating Rate = 200 oC/s

20 µm

Heated to 800 oC; Soak for 30 s; Quenched

20 µm

UFG DP

Process Control: Ultra -Fine Grain DP Steels

Martensite TemperedMartensite

Steel: 0.17C, 0.74Mn

H. Azizi-Alizamini, M. Militzer, W.J. Poole, Procee dings AHSS Conf., AIST Orlando (2008)

UFG DPSteel: 0.17C, 0.74Mn

ND

RD

5 µµµµm



UFG DP

ND

RD

5 µµµµm



Steel: 0.17C, 0.74Mn

ND

RD5 µµµµm

MVF = 0.42Island size ≈ 2 µm

Advanced DP Steels - Optimization

• Processing for higher strength & enhanced performance

• High volume fraction of martensite uniformly dispersed as fine particles

• May need to control martensite strength

• Fine grain ferrite

• Modified to control martensite to ferrite strength ratio

• Minimize banding

• However, Third Generation AHSS not achievableby enhanced DP steels!!!

Multi-phase Modelingto Design “Third Generation AHSS ”

(1) Constituent volume fractions(2) Constituent properties(3) Austenite Stability

Approaches:• Ideal Composite Model• Micromechanical Models

• FEA Based• …other…

Application of Composite Model to IdentifyNew Multiphase AHSS Steels (2006)

True Strain

Tru

e S

tres

s Composite

Component 2

Component 1

εU2εU1 εU-C

CompositeInstability

REF: “The Tensile Strength and Ductility of Contin uous Fibre Composites” S.T. Mileiko, J. Mat. Sci., (1969)

• Assume each “constituent” described by flow curve:

σσσσ = Kεεεεnεεεεm

• Apply rule of mixtures for composites (assumes “Isostrain ”) σσσσT = σσσσ1V1 + σσσσ2V2 + ….

• At InstabilityUd

d σσσσ====εεεεσσσσ

Increase MVF

Constituent propertiesfrom the literature

• High Mn Austenite(assumed stable )• Martensite

Constituent UTS (MPa)

Uniform True

Strain

Ferrite 300 0.3

Martensite 2000 0.08

Austenite 640 0.6

200 400 600 800 1000 1200 1400 1600Ultimate Tensile Strength (MPa)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Un

ifo

rm E

ng

inee

rin

g S

trai

n

Ferrite + Martensite

Austenite + Martensite

50%

30%

40%

60%

% MVF

Property Assessment: Stable Austenite (2006)

D.K. Matlock and J.G. Speer, “Design Considerations for the Next Generation of Advanced High Strength Sheet Steels,” Proceedings of the 3 rd Int. Conf. on Structural Steels , ed. by H.C. Lee, The Korean Institute of Metals and Materials, Seoul, Korea, 2006, pp. 774-781.

Comparison to “3 rd Generation ” AHSS (2006) E

long

atio

n (%

)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

IF

MildIF-HS

BHCMn

ISO

-

BH

TWIP

AUST. SS

L-IP

Future Opportunity



Ferrite + MartensiteFerrite + Martensite

50% MVF

Stable Austenite+ Martensite

UPostUTotal eee −−−−++++====

D.K. Matlock and J.G. Speer, “Design Considerations for the Next Generation of Advanced High Strength Sheet Steels,” Proceedings of the 3 rd Int. Conf. on Structural Steels , ed. by H.C. Lee, The Korean Institute of Metals and Materials, Seoul, Korea, 2006, pp. 77 4-781.

Initial Microstructure: Ferrite + AusteniteInitial Metastable Austenite = 0 to 85 %

Property Assessment: Metastable Austenite


Uniform True

Strain

Uniform Engineering

Stain

Ferrite 300 0.3 0.35

Austenite 640 0.6 0.82

Martensite 2000 0.08 0.08

Calculation Approach

• Assume austenite stability described by saturation function

• Assume function depends on alloying, microstructure, T, etc.

• Consider only “static hardening”

• Vary initial austenite content in ferrite-austenite composite

Saturation function reference: e.g. G.B. Olson, in Deformation, Processing, and Structure , ed. by G. Krauss, ASM, Metals Park, OH, 1984, pp. 391-425.

0 0.1 0.2 0.3 0.4True Strain

0

0.2

0.4

0.6

0.8

1

Vo

lum

e F

ract

ion

Mar

ten

site

A

D

C

B

AusteniteStability

Condition

D.K. Matlock and J.G. Speer: [presented at ICASS-2 006, Korea, August, 2006 and MATS 2008, Jamshedpur, India, Febr uary, 2008]; published as “Third Generation of AHSS: Mic rostructure Design Concepts,” Microstructure and Texture in Stee ls and Other Materials, ed. by A. Haldar, S. Suwas, and D. Bhattacharjee, Springer, London, 2009, pp. 185-205.

Initial Microstructure: Ferrite + AusteniteInitial Metastable Austenite = 0 to 85 %


Uniform True

Strain

Uniform Engineering

Stain

Ferrite 300 0.3 0.35

Austenite 640 0.6 0.82

Martensite 2000 0.08 0.08

Elo

ngat

ion

(%)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

IF

MildIF-HS

BHCMn

ISO

-

BH

TWIP

AUST. SS

L-IP

Future Opportunity


A

B

CD

A

C

D

B

Elo

ngat

ion

(%)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

IF

MildIF-HS

BHCMn

ISO

-

BH

TWIP

AUST. SS

L-IP

Future Opportunity


A

B

CD

A

C

D

B

10%25%

40%

0 0.1 0.2 0.3 0.4True Strain

0

0.2

0.4

0.6

0.8

1

Vo

lum

e F

ract

ion

Mar

ten

site

A

D

C

B

AusteniteStability

Condition

Austenite Amount

Property Assessment: Metastable Austenite

D.K. Matlock and J.G. Speer: [presented at ICASS-2 006, August, 2006 and MATS 2008, Jamshedpur, India, February, 20 08]; published as “Third Generation of AHSS: Microstruc ture Design Concepts,” Microstructure and Texture in Steels and Other Materials, ed. by A. Haldar, S. Suwas, and D. Bhatt acharjee, Springer, London, 2009, pp. 185-205.

H.N. Han, C.S. Oh, G. Kim, O. Kwon, “Design method for TRIP-aided multiphase steel based on a microstr ucture-based modeling for transformation-induced plasticity and mechanically induced martensitic transformation,” Ma terials Science and Engineering A, 499 (2009) 462–468.

Micromechanical Modeling: Korea (2009)• Assumed TRIP, multi-phase steel – varied vol. fracti ons• Applied a general kinetic model for the mechanically

induced transformation of austenite to martensite

K.S. Choi, A. Soulami, W.N. Liu, X. Sun. M.A. Khale el, “Influence of various material design parameter s on deformation behaviors of TRIP steels,” Computational Materials S cience 50 (2010) 720–730.

14 % Austenite

14 % Austenite

44 % Austenite 44 % Austenite

Micromechanical Modeling: PNNL (2010)• FEA Model - utilize “Representative Volume Element”

(RVE) to describe TRIP Steel microstructure

• RVE based on actualmicrostructures

Summary of Model Predictions

• “Big -Picture” predictions independent of modeling approach

• New (e.g.“3 rd Generation ”) AHSS will require:• High strength constituents

e.g. Martensite, fine grained ferrite, bainite…

• Austenite with controlled stability• e.g. transformation to martensite

• Additional Predictions: Steels with improved resistance to localized fracture obtained by• Refined microstructures• Minimized property gradients

Advances in Steel Processing

New 3rd Generation AHSS

Processing Examples

(1) “Enhanced ” TRIP Steels with high austenite volume fractions

(2) Q&P Steels produced by Advanced Processing = f (T, t)

Design Approach:

• Add alloying elements• Mn or N or C or …. to stabilize austenite

• Increase ferrite strength• Decrease Ferrite Grain Size by TMCP

(Thermomechanical processing)

• Increase austenite volume fraction > 20%• Fine and uniformly distributed

•Acknowledge: NSF, CMMI Grant # 0729114

Mn-Modified TRIP Steels

P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, “Austenite Stability Effects on Tensile Behavior of Manganese Enriched Austenite TRIP Steel,” Met. and Mat. Trans., vol. 42 , (2011), pp. 3691-3702.

Experimental Approach

wt pctC Mn Si

0.099 7.09 0.13

Mn

C

Si

P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, Met. and Mat. Trans., vol. 42 (2011) pp. 3691-3702.

•Material – 7.1 Mn

•Partition Mn:long-time intercritical heat treatments

•Predict heat treatments•Use ThermoCalc: TCFE2 Data (1999)

•Austenite composition•Austenite fraction

Step 1

Microstructure

• Heat treat for 1 week• 575 to 675 oC

• Retained austenite measured by neutron diffraction (Lujan Center at the Los Alamos National Laboratory)

Prediction


Tensile Properties – Room Temperature

(33 %)

(26%)

(40%)

(43.5%)

(< 2%)•Constant engineering strain rate

•ASTM E-8 sub-sized samples•32 mm reduced section

•Initial austenite contents in (%)


Strain -dependent Austenite Transformation


(33 %)

(26%)

(40%)

(43.5%)(< 2%)

(33 %)

(26%)

(40%)

(43.5%)(< 2%)

• Intercritical annealing:• Enhances Mn partitioning• Increases austenite stability

• Cost efficient ways to enhance partitioning need to be identified

• ….Research is ongoing ……..

• Acknowledge: NSF, CMMI Grant # 0729114

Ferrite -Austenite: Mn -Modified TRIP Steels

Quenching and Partitioning“Q&P ”

Time

Tem

pera

ture

Ferrite-Bainite-Austenite

"TRIP"

"Dual Phase"Ferrite +Martensite

A1

A3

TRIP Steel Processing

• Isothermally transform or control cool

• Austenite in high strength matrix (e.g. fine grain ferrite, martensite, bainite, …)

Interrupted Cooling: The “Q&P ” Process

J.G. Speer, et al. ASPPRC, Colorado School of Mines, ( 2003 - 2011)Time

Tem

pera

ture A1

A3

MS

MF

` 2-Step Q&P

1-Step Q&P

• Novel method to produce high strength material with significant amounts of retained austenite

• Processing path to 3 rd Generation AHSS

Quenching and Partitioning (Q&P)

J.G. Speer, D.K. Matlock, B.C. De Cooman, and J.G. Schroth, “Carbon Partitioning Into Austenite after Martensite Transformation,” Acta Materialia , vol. 51, 2003, pp. 2611-2622.

• Fundamentally new approach developed by Prof. John G. Speer at ASPPRC/CSM with automotive collaborators

• Designed to produce enhanced AHSS with retained austenite in controlled martensite/ferrite matrix

(1) Annealing temperature controls amount of initial ferrite

(2) Quench temperature (QT): controls amount of ini tial martensite

(3) Alloying controls carbide stability(4) Partitioning temperature and time: control aust enite

stability(5) Result: unique combinations of martensite + aus tenite

+ ferrite + ..other..

MF

Ac 3

QTTem

per

atu

re

C = CA3γ

MS

Ac 1

γγγγγ

γγγγαααα

Time TimeTime

MF

Ac 3

QTTem

per

atu

re

C = CA3γ

MS

Ac 1

γγγγγ

γγγγαααα

Time TimeTime

Q&P: Unique Designed Microstructures

J.G. Speer, D.K. Matlock, B.C. De Cooman, and J.G. Schroth, “Carbon Partitioning Into Austenite after Martensite Transformation,” Acta Materialia , vol. 51, 2003, pp. 2611-2622.

“Q&P ” Alloying and Processing• Alloying: e.g. Mn Si Al C Mo

• … to control critical temperatures: M s Mf …..

• … to suppress cementite formation

1 10 100 1000Partitioning Time (s)

0

0.05

0.1

0.15

0.2

0.25V

olu

me

Fra

ctio

n R

etai

ned

Au

sten

ite

High Si1.54 wt pct

Low Si0.45 wt pct

Steel: 0.2C, 3.5Mn QT = 240 oC PT = 350 oC

M.J. Santofimia, et al., “Experimental Investigatio n of Q&P on Two Low-Carbon Steels with Different Silicon Contents,” Proc. Int. Conf. on New Developme nts in AHSS , ed. by J.G. Speer, B. Nelson, and R. Pradhan, AIST, Warrendale, PA, 2008.

400 800 1200 1600Ultimate Tensile Strength, MPa

0

20

40

60

To

tal E

lon

gat

ion

, %

TRIP (ULSAB)A

TRIP (GM)A

Conventional TRIPB

1-Step Q&PB

2-Step Q&PB

M (ULSAB)A

M (GM)A

M (Ispat-Inland)C

DP (ULSAB)A

DP (GM)A

DP (Ispat-Inland)C

7500C,180 s + WQB

8200C,180 s + WQB

9000C,180 s + WQB

TRIP, Austemper

DualPhase

Martensitic

Q&P

Note A: 80 mm gauge lengthNote B: 25.4 mm gauge length Note C: Gauge length unspecified

Properties of Q&PSummary and Comparison with AHSS

A.M. Streicher, J.G. Speer, D.K. Matlock, and B.C. De Cooman, Int. Conf. on AHSS for Automotive Applications Proc. , ed. by J.G. Speer, AIST, Warrendale, PA, 2004, pp . 51-62.

International Interest in the “Q&P ” Process

• Initially conceived, 2003

• Ongoing R&D at:

• Universities

• 21 in 13 countries

• Research Institutes


• Companies


Current Status of

AHSS Developments

Elo

ngat

ion

(%)


0

10

20

30

40

50

60

70

0 600 1200300 900 1600

DP, CP

TRIP

MART

IF

MildIF-HS

BHCMn

ISO

-

BH

TWIP

AUST. SS

L-IP

Future Opportunity



Ferrite + MartensiteFerrite + Martensite

Stable Austenite+ Martensite

Example representative property combinations for automotive market

1000 MPa30%

1500 MPa20%


AHSS Property Targets

D.K. Matlock and J.G. Speer, “Design Considerations for the Next Generation of Advanced High Strength Sheet Steels,” Proceedings of the 3 rd Int. Conf. on Structural Steels , ed. by H.C. Lee, The Korean Institute of Metals and Materials, Seoul, Ko rea, 2006, pp. 774-781.

De Moor, Gibbs, Speer, Matlock, and Schroth, “Strat egies for Third-Generation Advanced High-Strength Steel Development”, AIST Transactions , Iron & Steel Tech. Nov. 2010.

AHSS Development StatusEnhanced DP

Ultrafine DP27

Modified TRIP

Matsumura29,30

M icro-alloyed TRIP31

TRIP Type Bainite34

TRIP-DUAL35

Interrupted Quench36

Bainite

Bhadeshia-Edmonds47,48

M iihkinen-Edmonds49,50

Caballero37,38,44

Garcia-Mateo46

Quenching & Partitioning

Jun-Fonstein35

Streicher52

De Moor54,55,56,57

Li 58

W ang - ind. trial59

Rapid Heating and Cooling

flash process60,61,62

Lower Mn TW IP/TRIP

Frommeyer67

Dastur-Leslie68

M erwin69,70,71,72

800 1000 1200 1400 1600 1800 2000 2400

5

10

15

20

25

30

35

40

45

50T

otal

Elo

ngat

ion,

%

Tensile Strength, MPa

1000 MPa30%

1500 MPa20%

Ductility data adjusted to represent standard ASTM E-8 geometry

De Moor, Gibbs, Speer, Matlock, and Schroth, “Strat egies for Third-Generation Advanced High-Strength Steel Development”, AIST Transactions , Iron & Steel Tech. Nov. 2010.

AHSS Development StatusEnhanced DP

Ultrafine DP27

Modified TRIP

Matsumura29,30

M icro-alloyed TRIP31

TRIP Type Bainite34

TRIP-DUAL35

Interrupted Quench36

Bainite

Bhadeshia-Edmonds47,48

M iihkinen-Edmonds49,50

Caballero37,38,44

Garcia-Mateo46

Quenching & Partitioning

Jun-Fonstein35

Streicher52

De Moor54,55,56,57

Li 58

W ang - ind. trial59

Rapid Heating and Cooling

flash process60,61,62

Lower Mn TW IP/TRIP

Frommeyer67

Dastur-Leslie68

M erwin69,70,71,72

Ductility data adjusted to represent standard ASTM E-8 geometry

800 1000 1200 1400 1600 1800 2000 2400

5

10

15

20

25

30

35

40

45

50T

otal

Elo

ngat

ion,

%

Tensile Strength, MPa

Matsumura et al. (1987, 1992)0.39C, 1.2Mn, 1.2-1.5Si

Q&PDe Moor et al.(2008, 2009)

Mn PartitionedGibbs et al. (2011)Merwin (2006)

Flexible Processing Linesand the Production of New AHSS

�DP�TRIP�Mart�Q&P

��DPDP��TRIPTRIP��MartMart��Q&PQ&P

Tem

pera

ture

Time

0 2 4 6 8 10 12 14 16 18 20 22 24 26200

400

600

800

1000

1200

1400

1600

HC1200/1500MS

HC950/1180MS

HC700/980MS

HC550/980DP

HC500/780DPHC420/780DP

Str

ess(

MP

a)

Strain(%)L. Wang, X. Jin, and H. Qian, “Recent Development o f Galvanizing Sheet Steels in Baosteel,” Proceedings Galvatech 2011 .

Baosteel's Special Flexible HSS Line

• Opened March 2009• Multi-purpose processing

• CR and GI• Flexible heating/cooling

Li Wang and Weijun Feng, “Development and Applicatio n of Q&P Sheet Steels,”Advanced Steels, Y. Weng et al. (eds), Springer-Verl ag, Berlin, (2011) .

Q&P1000: Composition (wt pct)0.2C, 1.5 Si, 1.8 Mn

Baosteel: Q&P from New Line

B pillar Trial

Formability Limited by Fracture

Tensile Properties … NOT the Whole Story …

Formability Limited by Fracture Edge Cracking

Shear Fracture

Hole Expansion Test Sample

Images Courtesy of Jim Fekete, GM (2006)

www.autosteel.org

Dünckelmeyer et al.,Slovika (2009)

Tensile Properties … NOT the Whole Story …

Banding: DP980

A. Hudgins, et al. ASPPRC 2010

10 µm

Void Nucleation: DP 740 MPa

Steel(780 MPa)

Tensile Elong.

Stretch-flangeability

(HER)

DP 19 % 60 %

TRIP 30 % 40 %

Lee et al. ASPPRC/Posco 2005after Cho, Pusan Nat. U., 200

SampleSampleSample

2 mm

Hole Expansion

Shear FractureTest

Shear FractureTest

FullyAustenitized

Hole Expansion Tests: Summary

• Hole Expansion Ratio (HER) = f(microstructure)• Improved microstructural homogeneity = higher HER

E. De Moor, C. Föjer, J. Penning and J.G. Speer, Proc. of IIDDRG 2009 Conference , ed. by B.S. Levy, D.K. Matlock and C.J. Van Tyne, Colorado Scho ol of Mines, Golden, CO, 2009, pp.413-424.

1.0 mm DP600

1.0 mm 2.5 mm 3.2 mm 5.0 mm 6.4 mm 12.7 mm

2.5 cm

Microstructural Effects on AHSS Fracture

Bending Under TensionFBACK

VPull , FFront

Increase Radius

Alex W. Hudgins, “Shear Failures in Bending of Advanced High Strength Steels,” PhD Thesis, Colorado School of Mines, Golden, CO, 2010.

0 2 4 6 8 10 12 14R/t

400

600

800

1000

Pea

k F

ron

t S

tres

s (M

Pa)

1.0 mm DP780

Commercial Steel Matrix

Bending Under Tension Data

(R/t)crit = measure of formability

(R/t)crit = formability (i.e. susceptibility to shear )

A.W. Hudgins, D.K. Matlock, J.G. Speer, J.R. Fekete, and M.S. Walp, “The Susceptibility to Shear Fracture in Bending of Advanced High Strength Sheet Steels,” Proceedings of Steel Properties and Applications Conference, edited by L.C. Oldham, AIST, Warrendale, PA, 2007, pp. 145-157.

Application of Nanoindentation Techniques

Dis

tanc

e (m

icro

ns)

5

10• 0.1C-1.0Mn-0.3Si DP

• Vary intercritical T

• Vary MVF and martensite hardness

• Determine “hardness ratio”

• Result: R/t critical decreases with a decrease in the martensite to ferrite hardness ratio

A.W. Hudgins, D.K. Matlock, J.G. Speer, J.R. Fekete , and M.S. Walp, “The Susceptibility to Shear Fracture in Bending of Advanced High Strength Sheet Steels,” Proceedings of Steel Properties and Applications Conference, edited by L.C. Oldham, AIST, Warrendale, PA, 2007, pp. 145-157.

•Formability (as measured by R/t) increased with a decrease in hardness ratio between martensite and ferrite.

•Other variables evaluated

• Martensite morphology (limited effect)

• Banding (effect orientation dependent)

Summary: Shear Fracture Susceptibility

A.W. Hudgins, D.K. Matlock, J.G. Speer, J.R. Fekete , and M.S. Walp, “The Susceptibility to Shear Fracture in Bending of Advanced High Strength Sheet Steels,” Proceedings of Steel Properties and Applications Conference, edited by L.C. Oldham, AIST, Warrendale, PA, 2007, pp. 145-157.

Alternate Processing Routes:

Press Hardening

Time

Tem

pera

ture A1

A3

MS

MF

` Press Hardened

Deform Austenite

Press Hardened Steels (PHS)

• Production of high strength (1500 MPa) parts• Martensitic microstructures; boron alloys

http://www.interlaken.com/hotstamping (2011)

T. Altan, 2007www.stampingjournal.com


kam-stampingguru.blogspot.com/2011www.cartype.com/pics/6272 (2011)

http://www.batz.com/stamping-dies/press-hardening.php (2011)

Heated Blank Blank in Die

PHS for High StrengthStructural Components


Press Hardening

• Enhanced press hardening steels still maturing

• Cost (e.g. heating, etc) and surface finish continue to be issues for consideration

• Steel developments leading to alternate processing routes for similar strength parts are of significant interest

• e.g. Q&P, bainitic , …• Cold or warm forming

AHSS Closing Comments

• Approaches to potentially produce Third Generation AHSS have been identified

• Need optimized production routes to control:

• Constituent volume fractions, size, distribution

• Constituent mechanical properties• Austenite stability• …other

• Possibility for national research processing facility???

• AHSS: Additional Important Points• Welding and Joining• Formability – Springback• Surface Finish• Coating• Hydrogen effects• ……..• TWIP steels???

• Significant government funding in Germany and Korea


• AHSS developments need to optimize time to implementation!!!

• …DP Steels, 35 years + ….• “ Most Important ” AHSS

• …TRIP Steels, >20 years• …Q&P ≈ 7+ years • ………

• …The Competition Continues …


AHSS -- “Beyond Automotive ”

• Multiple inquires received at ASPPRC -Examples:

• Lightweight military vehicles• DOD/DOE workshop

Detroit, July 2011

• Blast resistant surfacing – US Army

• Metal storage cabinets (shipping costs!)

• Personal hand tools

• ….others …..

Steel ProducersAK SteelArcelorMittal SteelBaosteelEssar Steel Algoma Inc.Evraz Inc., N.A.GerdauNucor Steel Co.POSCOSABICSeverstal NA Inc.SSAB Enterprises, LLCTata Steel EuropeThe Timken Co.United States Steelvoestalpine Stahl GmbH

Heavy Equipment Mfg.Caterpillar Inc.Deere & Co.Automotive ManufacturesChrysler Group LLC General Motors Co.ToyotaSuppliersBekaertJohnson ControlsTube Investments of IndiaOtherEast Metals N. Amer. (Vanadium)Los Alamos National LabPrecision Cast Parts Corp.Reference Metals (Niobium)

The support of the Advanced Steel Processing and Products Research Center corporate partners,

listed below, is gratefully acknowledged .

http://aspprc.mines.edu /

matlock distribution aisi workshop (feb2012pdf) | nist

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