compensation of residual stress in welds using phase transformation
Post on 22-Dec-2015
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Compensation of residual stress in welds using phase transformation
How to reduce residual stress
Temperature
Stress
+ve
-ve0
Reduce transformation temperature
Why martensite?
To achieve minimum transformation temperature.
Martensite transformation causes deformation.
Under stress plates are aligned in favoured direction.
Alloy Design
Neural net analysis
Residual stress measurements using neutron diffraction
Real time phase transformations using synchrotron X-rays
Scanning electron microscopy
Electron backscattered diffraction
Final chemistry
Synchrotron Study
Synchrotron study
Effect of external stress on transformation temperature and kinetics.
Variant selection during martensite transformation.
Nature of stress in various phases.
Synchrotron results
Crystallography Model
(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)
(F B F)
(F J F)
(F S F)=(F B F) (F J F)
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)
[u v w] = ( J ) [1 0 0]
24 variants of martensite
( J ) Coordinate transformation matrix
Single crystal of austenite, <0 0 1> poles of martensite
100
010
Poly crystal
1
2
Relationship between two grains: (1 J 2)
[u v w]= (1 J 2)[1 0 0]
Future work
Construction of pole figure in polycrystalline material
Effect of stress on the pole figures
Thank you …