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 …