Martensite in Steels

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Martensite in Steels

• cml.postech.ac.kr/teaching.html
• Graduate Institute of Ferrous Technology (GIFT)

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http//cml.postech.ac.kr/
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Materials, transformation temperatures strength
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Olson and Hartman, 1982
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Olson and Hartman, 1982
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Olson and Hartman, 1982
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Diffusionless transformation?
Martensite can form at very low
temperatures. Martensite can grow very
rapidly. No composition change during
transformation.
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Shape of martensite ?
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Irrational why?
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Orientation relationships irrational
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athermal transformation
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Creation of a bi-crystal
cut and rotate by angle q about axis normal to
diagram
q
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Glissile interface
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Glissile interface cannot contain more than one
set of dislocations. Martensitic transformation
only possible if the deformation which changes
the parent into the product leaves one line
undistorted and unrotated, i.e. an
invariant-line. Deformation is an invariant-line
strain.
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s
d
c
r
1
Christian, 1957
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body-centred cubic
cubic close-packed
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b
a
3
3
a
2
b
b
2
1
a
1
(a)
(b)
BAIN
STRAIN
(d)
(c)
Body-centered
Body-centered
cubic martensite
tetragonal
austenite
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001
b
b'
100
o
a'
a
b
(a)
o
b'
(b)
a,a'
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transformation twins (Wayman)
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hexagonal close-packed
cubic close-packed
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Brooks, Loretto and Smallman, 1979
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a
g
Free Energy
a
ag
ga
x
x
x
Carbon Concentration
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