Retained Austenite in TRIP-Assisted
Steelsrole of transformation plasticity
China Steel
Shape deformations due to transformations
Fe-30.5Ni-0.32C wt%
Forsik, 2004
Invariant-plane strain
s
1
s
1
1
uniaxial dilatation
simple shear
general invariant-plane
strain
s=0.26
=0.03
Minimum requirement for martensitic transformation
• there must exist an invariant-line at interface
• i.e., one set of dislocations which can glide conservatively
• can be more than one invariant-line
body-centred cubic
cubic close-packed
(a)
BAIN STRAIN
(c) Body-centered
tetragonal austenite
(d) Body-centered
cubic martensite
a
a
a1
2
3 b3
b1 b2
(b)
[100]
[001]
o
aa'
b
b'
o b'
b
a,a'
(a)
(b)
Austenite Martensite (wrong shape)
Twinned Martensite
Slipped Martensite
Twin Boundary
Observed shape, wrong structure
RB
P
LATTICE -INVARIANT DEFORMATION
Correct macroscopic shape, correct structure
(a) (b) (c)
w
x
y
z
w
x
z
y x
w z
y
x
w z
y x
w z
y
P1 2
Bhadeshia & Edmonds, (1980)
Typical composition:
Fe-0.15C-1.5Si-1.5Mn wt%
polycrystalline
Bhadeshia & Edmonds, (1980)
b
Is the shear important in a polycrystalline sample?
How can we bias the microstructure?
By transforming under the influence of stress.
s
1
s
1
1
uniaxial dilatation
simple shear
general invariant-plane
strain
s=0.26
=0.03
50 m
polycrystalline austenite
Bhadeshia, 1982
What is the maximum tensile strain obtained from TRIP?
……in a fully austenitic sample which transforms completely into martensite.
sz3
z1
u v
Sakuma et al. (1991)
abso
rbed
ene
rgy
/ kJ
Yoshitake et al. (1996)
Retained Austenite in TRIP-Assisted
SteelsSlide 1Slide 1…..very small
contribution to elongation.
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)
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)
Sherif et al. 2003
Sherif et al. 2003
Sherif et al. 2003
Sherif et al. 2003
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