HSLA steel

8/10/2019 HSLA steel

1/5

Institut fr Eisenhttenkunde

der RWTH achen

Case Study:HSLA steel

Prof. Dr.-Ing. Wolfgang Bleck

Outline

Case Study: HSLA steel Introduction Strengthening mechanisms in HSLA steels Strip processing Automotive application Conclusions

Outline


1975 1995199019851980 20052000

post-rolled steels isotropic steels

microalloyed steels

P-alloyed steels

DP-steels

BH-steels

IF-steels

TRIP steels

SULC steels

TWIP steels

Al-alloyed steels

Material design

Process development

Chronological development ofhigh strength steels for car bodies

European consumption of hot and coldrolled high strength steels

0

1.000

2.000

3.000

4.000

5.000

6.000

7.000

1990 1995 2000 2005 2010 Year

C o n s u m p t i o n ,

1 03

t

HSLACMnBoronDPCP, Mart, TRIP

HSLA

CMn

CP, Mart,TRIP

DP

Boron

0

1.000

2.000

3.000

4.000

5.000

6.000

7.000

1990 1995 2000 2005 2010 Year

HSLABH, PHSIF, IsotropicDPCP, Mart, TRIP

HSLA

BH, P

HSIF,isotropic

DP

CP, Mart,

TRIP

HotHot RolledRolled ColdCold RolledRolled

Automotive share 2001: 41%2006: 45%

Automotive share 2001: 92%2006: 93%

urce: Leitner, E.: Hot & Cold Rolled High Strength Steels in Western Europe, Pariser & Leitner, Wien, 2002

Outline



2/5

Characteristics ofmicroalloying elements

very low concentration: 10 -3.10 -1 %

interaction with C, N and S

precipitation of secondary phases

strong influence on microstructure

control of solution and precipitationby process management

Microstructural impact of microalloying elements

IF-status of matrixinfluence on recristallisationtexture developmentgrain boundary reinforcement

Grain refinementPrecipitation hardening

Hbond during enamelling

influence on diffusion during hot dipgalvanizing

influence on sulfide shape

grain refinement

precipitation hardening

toughness improvement in the heataffected zone of welds

increase of hardenability

Cold rolled stripHot rolled strip

Influence of precipitation temperatureon precipitate size

coarseca. 50 nm

fineca. 10 nm

grain refinement

medium strengthgood toughness

precipitation hardening

high strengthmedium toughness

Acceleration of Transformation

20

200

10080

60

40

1000800 1200Precipitation temperature, C

AlNNb(C,N)

A v e r a g e p r e c

i p i t a

t e s

i z e ,

n m

very coarseca. 100 nm

Outline


Coldrolling

Tandemmill

Hot rollingheat treatment

Compactstrip mill

Hot strip

mill

CastedStrip

Thin Slab

Slab

Hot rolledstrip

Cold rolledstrip

CAL

HDG

HDG

CAL

HDG : Hot Dip Galvanizing LineCAL: Continuous Annealing Line

Process routes of HSLA steels Effect of Nb, Ti, V on the austeniteNo-Rex-Temperature

r o l l i n g

t e m p e r a

t u r e

i n C

mass contents of Nb, Ti or V in %

area of recristallisation

area of strongly delayed or inhibited recristallisation

Nb

Ti

V

0 0,060,040,02 0,08 0,10 0 ,12 0,14 0,16750

1000

950

900

850

800


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Effects of soluble and precipitated MAEon austenite recrystallisation

R e c r y s

t a l l i s e

d s

t r u c

t u r e

f r a c

t i o n

i n %

Interpass time in s

10 -1 10 2 10 3 10 41 100

20

40

60

80

100

[Nb] Nb C

0.002 % C0 % Nb

0.002 % C0.10 % Nb

0.020 % C0.10 % Nb

Interaction of MAEduring hot strip processing

Cooling

NbC,V(C,N)

Coiling

NbC,TiC,V(C,N)

Finishing

NbC,TiC

Roughing

TiN

[M]In solution

coarseparticles100nm

fine,deform. inducedparticles10nm

fine,in rows arrangedparticles10nm

extreme fineparticles


4/5

fullyrecrystallized

partially recrystallized

reduction of precipitationhardening

c o l d r o l l i n g

r e d u c t i o n A n n e a

l i n g

t e m p e r a

t u r e ,

C

600

650

700

750

800

850

600

0 0,01 0,030,02 0,050,04

Nb-content,%

Annealing limits for HSLA steels Influences on themicrostructure development

metallurgicalprocessesin the material

as castmicrostructure

Hot stripmicrostructure

Cold stripmicrostructure

Reheating

Hot Rolling

Coiling

Cold rolling and annealing

process parameters

transformationgrain growthprecipitation

precipitation

precipitationtransformation

grain growth

grain growthprecipitation

dynamic and staticrecristallisation

static Rex.

static Rex.

cooling rate

temperature-time-cycle

temperature-time-cycledeformation degree and deformation rate

cooling ratecoiling temperature

cold deform. degreeannealing cycle

pass sequence

Outline


Available Product forms of differenthigh-strength steels

HSS

H o

t r o

l l e d

s t r i p

E l e c t r o g a l -

v a n

i s e

d

h o

t r o

l l e

d

s t r i p

H o

t d i p

g a l v a n

i s e

d

s t r i p

C o

l d r o

l l e d

s t r i p

E l e c t r o g a l -

v a n

i s e

d

c o l d s t r i p

H o

t d i p

g a l v a n

i s e

d

c o l d s t r i p

BH IF-HS

P IS

HSLA DP

TRIP CP/PM

Automotive parts madefrom HSLA steels

0.00

200

400

600

800

1000

1200

0.00 0.05 0.10True strain

0.15 0.20 0.25

DDQDDQDC04, DC06

AHSSAHSSPM1000, PM800, TRIP700Z, HT500X

HSSHSSHT340LA, H260P, H260YD,

H260B, H250G1, H180B

T r u e s

t r e s s ,

M P a

New steels for automobile applications

Source :


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Flow curves of cold-rolled sheet steelsDistribution of steel grades in a

modern car

Conclusions

Microalloying is a well-developed method to increase strength bymaintaining good formability.

HSLA steels are used widely for automotive applications due totheir attractive properties balance.

HSLA steels have been developed for many different productforms and process routes.

HSLA steels are easy handling materials both from theprocessing and from the application point of view.

Documents

HSLA steel