Design of TRIP-Assisted Steels for Automobiles

• Microstructure has been extensively studied

• Microstructure understood: most aspects can be calculated

• Mechanical properties cannot be calculated

• Mechanical properties badly related to microstructure

Bhadeshia & Edmonds, (1980)

Typical composition:

Fe-0.15C-1.5Si-1.5Mn wt%

Bhadeshia & Edmonds, (1980)

b

Swallow & Bhadeshia, 1996

engineering strain

engi

neer

ing

stre

ss /

MP

a

Mizui et al. (1997)

Jacques et al. (2001)

Ro et al. (1994)

transformation-induced plasticity

50 m

s

1

s

1

1

uniaxial dilatation

simple shear

general invariant-plane

strain

s=0.26

=0.03

c

r

s

1

Transformation is a deformation on habit plane

Can be induced by stress

Bhadeshia, 1982

50 m

polycrystalline austenite

Bhadeshia, 1982

sz3

z1

u v

Sakuma et al. (1991)

abso

rbed

ene

rgy

/ kJ

Yoshitake et al. (1996)

Bhadeshia & Edmonds, (1980)

Composite of soft and hard phase

Bhadeshia & Edmonds, (1980)

strain in soft phase

Str

ain

in h

ard

phas

e

Tomota (1976)

Bhadeshia & Edmonds, (1980)

Chester and Bhadeshia, 1997

Chester and Bhadeshia, 1997

Chester and Bhadeshia, 1997

Chester and Bhadeshia, 1997

low silicon high silicon

Jacques et al. (2001)

silicon causes scale

Summary

• Assistance from TRIP is less than 1.4% of total strain

• Emphasis could be shifted from retained austenite to studies of composite deformation

• Low silicon steels can perform well (Jacques)