Compensation of residual stress in welds using phase transformation.
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Transcript of Compensation of residual stress in welds using phase transformation.
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Compensation of residual stress in welds using phase transformation
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How to reduce residual stress
Temperature
Stress
+ve
-ve0
Reduce transformation temperature
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Why martensite?
To achieve minimum transformation temperature.
Martensite transformation causes deformation.
Under stress plates are aligned in favoured direction.
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Alloy Design
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Neural net analysis
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Residual stress measurements using neutron diffraction
Real time phase transformations using synchrotron X-rays
Scanning electron microscopy
Electron backscattered diffraction
Final chemistry
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Synchrotron Study
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Synchrotron study
Effect of external stress on transformation temperature and kinetics.
Variant selection during martensite transformation.
Nature of stress in various phases.
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Synchrotron results
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Crystallography Model
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(a)
BAIN STRAIN
(c) Body-centered
tetragonal austenite
(d) Body-centered
cubic martensite
a
a
a1
2
3 b3
b1 b2
(b)
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[100]
[001]
o
aa'
b
b'
o b'
b
a,a'
(a)
(b)
(F B F)
(F J F)
(F S F)=(F B F) (F J F)
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Austenite
(a)
w
x
y
z
Twinned Martensite
Twin Boundary
Correct macroscopic shape, correct structure
x
w z
y
z
Slipped Martensite
LATTICE -INVARIANT DEFORMATION
x
w
y
Observed shape, wrong structure
P
(b)
w
x
z
y
1
(F P F)RB
(c)
x
w z
y
P2 Martensite (wrong shape) (F J F)
(F S F)=(F P F)(F J F)
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[u v w] = ( J ) [1 0 0]
24 variants of martensite
( J ) Coordinate transformation matrix
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Single crystal of austenite, <0 0 1> poles of martensite
100
010
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Poly crystal
1
2
Relationship between two grains: (1 J 2)
[u v w]= (1 J 2)[1 0 0]
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Future work
Construction of pole figure in polycrystalline material
Effect of stress on the pole figures
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Thank you …