1. Retained Austenite in TRIP-Assisted Steels role of transformation plasticity China Steel

2. Shape deformations due to transformations

3. Fe-30.5Ni-0.32C wt% Forsik, 2004 Invariant-plane strain

4.  s 1 s 1  1 uniaxial dilatation simple shear general invariant-plane strain s=0.26  =0.03

5. 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

6. body-centred cubic cubic close-packed

7. (a) BAIN STRAIN (c) Body-centered tetragonal austenite (d) Body-centered cubic martensite a a a 1 2 3 b 3 b 1 b 2 (b)

8. [100] [001] o a a' b b' o b a,a' (a) (b)

9. 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 wz y x w z y x wz y P 1 2

10. Bhadeshia & Edmonds, (1980) Typical composition: Fe-0.15C-1.5Si- 1.5Mn wt% polycrystalline

11. Bhadeshia & Edmonds, (1980)   b

12. Is the shear important in a polycrystalline sample?

13. How can we bias the microstructure? By transforming under the influence of stress.

14.  s 1 s 1  1 uniaxial dilatation simple shear general invariant-plane strain s=0.26  =0.03

18.  50  m polycrystalline austenite Bhadeshia, 1982

19. What is the maximum tensile strain obtained from TRIP? ……in a fully austenitic sample which transforms completely into martensite.

20.  s z3z3 z1z1

21. u v

22. Sakuma et al. (1991)

23. absorbed energy / kJ Yoshitake et al. (1996)

24. Retained Austenite in TRIP-Assisted Steels Slide 1 …..very small contribution to elongation.

25. Bhadeshia & Edmonds, (1980) Composite of soft and hard phase

26. Bhadeshia & Edmonds, (1980) strain in soft phase Strain in hard phase

27. Tomota (1976)

28. Bhadeshia & Edmonds, (1980)

29. low silicon high silicon Jacques et al. (2001) silicon causes scale

30. 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)

37. Sherif et al. 2003