William Kepler Whiteford Professor and Director, Basic Metals

Processing Research Institute, Department of Mechanical Engineering

and Materials Science, University of Pittsburgh, USA

and

Finland Distinguished Professor, Department of Mechanical

Engineering, University of Oulu, Oulu, Finland

Anthony J. DeArdo

Future Challenges and Opportunities for Steel and Steel Research

Key to Producing Improved, High

Strength Steels: Better Control

of Hot Rolling(CCR) and

Accelerated Cooling(IAC/IDQ)

Examples:

a) CGL

b) Plate mill (or HSM ROT)

c) Bar mill/Forging Press

d) Metallographic Techniques

Outline

Sheet Steel (Zn coated sheets with high strength and good ductility)

Plate Steel (CCR and IDQ with good properties, weldability and acceptable flatness)

Bar Steel (Improving strength and toughness using CCR and IAC)

Rail Steel

Stainless Steels (Improving stretch forming in ferritic SS)

Yield Strength, MPa

Norm

aliz

ed

Ma

ss

0

1

0.378

0.408

0.446

0.5

0.577

0.707

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800

Mass-vs-Constant Resistance to Yielding in Bending

21

213

oC

Fblm

Ashby & Jones, 1993

Weight reduction with higher strength steels

30% Lighter

Why & How Weight / Mass

Reduction?

Why?

Fuel Efficiency

Environment

How?

Developing DP 780, 980 & 1180 grades to

substitute for older 450 MPa and lower grades

(1000 kg = 2205 lb)

(1000 lb = 454 kg)(1 metric tonne = 2205 lbs)

Safety,

Crashworthiness

Role of High Strength steels:

Crash energy:

(i) directed away from passenger

compartment

(ii) consumed as deformation energy

Thinner = Danger?

Passenger compartment axial and vertical crush

protection using High-Strength DP Steels.

Note curvatures and spot welds

Evolution of AHS

Steels

Banana Diagram

0 300 600 900 1200 1600

MART

ISO

BH

IF-HS

IF

Mild

70

60

50

40

30

20

10

0

Tensile Strength, MPa

Elo

ng

ati

on

,%

MART

ISO

BH

IF

Mild

Difficult

Easy

Raising Strength Easy

Increasing

Ductility/Formability

Difficult

Microstructural Control on the CG Line

ZnZn

460ºC

Time

Te

mp

era

ture

αIC + γIC ; Cγ

γIC + αIC + αNEW (??)

D-P

TRIP

M90 D-P

BS

TRIP

Ac1

Ac3

γIC→ αB + γRICH (??) TRIP

γIC→ γRICH + αNEW (??) D-P

M90 TRIPRT

Critical Issues in CGL Processing

Current Joint Research

Topics-CASR & BAMPRI

1. New Process - (Q to below 460OC & induction heating

to 460OC)

2. Improve temper resistance during short holds at

460OC(GI) and 520OC(GA)

3. Role of Al

450

550

650

750

850

950

1050

1150

200 250 300 350 400 450 500

First hold temperature C

UT

S (

MP

a)

0

10

20

30

40

50

60

Elo

ng

.(%

)

BDP5-UTS

BDP-2-UTS

BDP1-UTSDP5BI-UTS

DP2BI-UTS

DP1BI-UTS

DP5AI-UTS

DP2AI-UTS

DP1AI-UTSBDP5-elong

BDP2-elong

BDP1-elong.

DP5BI-Elong

DP2BI-Elong

DP1BI-elongDP5AI-Elong

DP2AI-Elong.

DP1AI-ELong

Linear (BDP5-elong)

Linear (BDP2-elong)

Linear (BDP1-elong.)Linear (BDP5-UTS)

Linear (BDP-2-UTS)

Linear (BDP1-UTS)

Trendline

A1:460Cx0s-460x15s--ACRT

B1:350Cx0s-460x15s--ACRT

C1:300Cx0s-460x15s--ACRT

D1:250Cx0s-460x15s--ACRT

1DPXBI:350Cx15s-460x60s-ACRT

First tensile test

Effect of the quench temperatures (Ti) on the mechanical properties of DP steels

460 C520 C

IATx t1

Time(s)

TºC

t2t3

Ti C

3 3

UTS

Elongation

yBDP5-1 = -0.014x + 30.474

R2 = 0.0673

yBDP5-2 = -0.0325x + 45.88

R2 = 0.4432

12

13

14

15

16

17

18

19

20

21

22

850 900 950 1000

UTS (MPa)

Elo

ng

. (%

)

BDP5-1 BDP5-2

BDP:Second tensile test data,70%reduction

A1:460Cx15s--ACRT

B1:350Cx15s-460x15s--ACRT

C1:300Cx15s-460x15s--ACRT

D1:250Cx15s-460x15s--ACRTTrendline

A2:460Cx15s--520Cx60s--ACRT

B2:350Cx15s-460x15s--520Cx60s--ACRT

C2:300Cx15s-460x15s--520Cx60s--ACRT

D2:250Cx15s-460x15s--520Cx60s--ACRT

1 2

yBDP2-2 = -0.0379x + 52.172

R2 = 0.5779

yBDP2-1 = -0.0386x + 54.365

R2 = 0.9027

12

13

14

15

16

17

18

19

20

21

22

850 900 950 1000

UTS (MPa)

Elo

ng

. (%

)

BDP2-1 BDP-2-2

BDP:Second tensile test data,70%reduction

A1:460Cx15s--ACRT

B1:350Cx15s-460x15s--ACRT

C1:300Cx15s-460x15s--ACRT

D1:250Cx15s-460x15s--ACRT

Trendline

A2:460Cx15s--520Cx60s--ACRT

B2:350Cx15s-460x15s--520Cx60s--ACRT

C2:300Cx15s-460x15s--520Cx60s--ACRT

D2:250Cx15s-460x15s--520Cx60s--ACRT

1 2

yBDP1-1 = -0.0262x + 40.756

R2 = 0.809

yBDP1-2 = -0.0179x + 33.097

R2 = 0.4468

12

13

14

15

16

17

18

19

20

21

22

850 900 950 1000

UTS (MPa)

Elo

ng

. (%

)

BDP1-1 BDP1-2

BDP:Second tensile test data,70%reduction

A1:460Cx15s--ACRT

B1:350Cx15s-460x15s--ACRT

C1:300Cx15s-460x15s--ACRT

D1:250Cx15s-460x15s--ACRTTrendline

A2:460Cx15s--520Cx60s--ACRT

B2:350Cx15s-460x15s--520Cx60s--ACRT

C2:300Cx15s-460x15s--520Cx60s--ACRT

D2:250Cx15s-460x15s--520Cx60s--ACRT

1 2

EBSD (IMAGE QUALITY) ANALYSIS of experimental TRIP steels

ALLOY 0.05%Al-550

TIA=750 C, 60s, 15C/sec to 450C, Quench

ALLOY 1%Al-550

TIA=770 C, 60s, 15C/sec to 450C, Quench

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50 60 70 80 90 100 110

IQ

Fre

qu

en

cy

EBSD Data without GB Contribution

RXD Ferrite Ferrite

Non-RXD Ferrite

Martensite

Sum of all simulated contributions

37.17

36.2826.55

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 10 20 30 40 50 60 70 80 90 100 110

IQP

op

ula

tio

n

EBSD Data without GB Contribution

RXDl Ferrite

Non-RXD Ferrite

Martensite

Retained Austenitee

Sum of all simulated contributions

50.97%

29.13%

16.38%3.52%

Austenite (Martensite) = 16.38%

Recrystallized Ferrite= 50.97%

Non-RXD + New Ferrite= 29.13%

New Ferrite = 29.13-16.9= 12.23%

Retained Austenite=3.52%

Austenite (Martensite) = 26.55%

Recrystallized Ferrite= 37.17%

Non-RXD + New Ferrite= 36.28%

New Ferrite = 36.28-27.78= 8.5%

Retained Austenite= 0%

CLOSURE

Formability of high-strength DP Steels

can be improved by:

(i) Presence of the optimum γRET with

the proper stability, not too high or

low.

(ii) High levels of recrystallized ferrite

coming from the intercrit. anneal.

(iii) Exciting new process being

developed

Duquesne Incline

taken by Norman W. Schumm

Weight

and cost

reduction

by using

HSLA

steels

Stress analysis in thin-walled cylindrical pressure vessels

= PD/2t

xx = PD/4t

AP

I-G

rad

e

X90

X80

X70

X60Ferrite + Pearlite

(~30% Pearlite)

Ferrite + Pearlite

(~15% Pearlite)

Ferrite + Bainite

Bainite

TM-MACOS

Hot rolled and normalized

TM-treated

Toughness

Increasing

grain refinement

& decreasing

transformation T

Evolution of plate steel for large diam. linepipe:

microstructure and mechanical properties

F1 History

Evolution of linepipe technology

(The Future is Now!)

(ksi/0.145 = MPa)

Through Thickness Variations and Flatness Problems

HSLA steel development shown in the Graville diagram

Cold Cracking Tendency

Dependence of

CTOD value of

simulated HAZ on

area fraction of

high carbon

martensitic

islands.

Haze & Achara,

1988

HSLA Controlled Rolling

Thermomechanical rolling plus in line cooling of HSLA steels

Deformation stage Transformation stage

Thank you