Complete theory for martensitic transformations

Unlock the intricate world of martensitic transformations with in-depth insights into the Bain strain, lattice-invariant deformation, transformation twins, athermal transformation, and more. Dive into the fundamentals of martensite and austenite structures, encompassing observations of macroscopic shapes, correct structures, and the suppression of martensitic transformations by rapid cooling. Unravel the complexities surrounding martensite start temperature and the contributions of influential figures in the field.

• Martensitic Transformations
• Bain Strain
• Transformation Twins
• Athermal Transformation
• Martensite Start Temperature

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1. Complete theory for martensitic transformations www.msm.cam.ac.uk/phase-trans Adolf Martens memorial lecture

2. Bain, Toriano, Wechsler, Liebermann, Reed, Bowles, MacKenzie, Nishiyama, Tamura, Shimizu, Kurdjumov, Roitburd, Khandros, Cohen, Patel, Krauss, Olson, Wayman, Zackay, Wasserman, Christian, Bilby, Hornbogen, Speich, Magee, Koistinen, Marburger, Loretto, Ko

7. The Bain strain

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

9. RB z w w z w z P Observed shape, wrong structure P2 1 Martensite (wrong shape) Austenite y x x y x y (a) (b) (c) LATTICE -INVARIANT DEFORMATION w w z z Twin Boundary x y x y Twinned Martensite Slipped Martensite Correct macroscopic shape, correct structure

11. transformation twins (Wayman)

12. Martensite start temperature

13. athermal transformation

14. Brooks, Loretto and Smallman, 1979

15. However, martensitic transformation can be suppressed by rapid cooling to 4 K Ullako et al. 1990

18. Fe-0.1C wt% Influence of tensile stress

19. Bhadeshia, 1982

20. polycrystalline austenite 50 m Bhadeshia, 1982

21. Texture prediction

22. No method calculates INTENSITY, only POSITIONS of poles

23. TRIP steels that are fully austenitic are expensive How do we produce cheap austenite?

24. TRIP-Assisted Steels austenite is expensive carbon can be cheap too much carbon is bad Jae Hoon Jang, In Gee Kim

25. Typical composition Fe-0.15C-1.5Si-1.5Mn wt%

28. Cracking of brittle martensite tensile stress in fibre enclosed by matrix

29. Chatterjee & Bhadeshia, 2006

30. plates become finer than stress-transfer length, and hence do not crack

31. Austenite grain size effects plates stopped by austenite grain boundary total volume transformed reduced when grain size small detection limit leads to reduction in start temperature

32. Yang & Bhadeshia, 2009

33. Plastic strain: grain shape

34. Plastic strain: stabilisation Shipway & Bhadeshia 1995

35. Plastic strain: stabilisation Chatterjee & Bhadeshia

36. Classic TRIP-assisted steel stress or strain-induced?

37. Classic TRIP-assisted steel calculations of austenite stability

38. Crystallography Interfacial structure Atomic structure Texture Chemical composition Thermodynamics Magnetic Stress Kinetics Plastic strain Critical mechanical properties

40. Standard thermodynamic databases fail for epsilon martensite

41. analysis limited to cases where

42. Pure iron CALPHAD First principles Fe-5Mn-2-Si-2Cr First principles

44. empirical method

45. non-linear: neural networks