1. Mechanism of the Bainite Transformation in Steels www.msm.cam.ac.uk/phase-trans IIT Kharagpur

2. Bundy (1965)

3. body-centred cubic cubic close-packed

4. DISPLACIVE RECONSTRUCTIVE

6. 1 µm upper bainite

7. lower bainite

8. Surface 1 Surface 2 Srinivasan & Wayman, 1968 50 µm

9. c r  s 1

14. UPPER BAINITE (High Temperature) LOWER BAINITE (Low Temperature) Carbon supersaturated plate Carbon diffusion into austenite Carbon diffusion into austenite and carbide precipitation in ferrite Carbide precipitation from austenite

15. 500400300 0 1 2 Temperature / °C Decarburisation time / s Fe-0.4C wt%

17. Ae3' T' o x Carbon in austenite Temperature

20. Growth is diffusionless. Strain energy must be accounted for.

22. UPPER BAINITE (High Temperature) LOWER BAINITE (Low Temperature) Carbon supersaturated plate Carbon diffusion into austenite Carbon diffusion into austenite and carbide precipitation in ferrite Carbide precipitation from austenite

24. Oka and Okamoto

25. Ohmori and Honeycombe

26. 1 µm 0.4 C 2 Si 3 Mn wt%

27. Very poor toughness!

28. 50 µm

29. Fe-1C-1.5Si…… wt% periodic cracking stress transfer length Chatterjee & Bhadeshia, 2005

31. Carbide-free alloys wt %

33. 0.4C-3Mn-2Si 0.4C-4Ni -2Si 0.2C-3Mn-2Si Impact Energy 2001000-100-200 0 10 20 30 40 50 60 70 Test temperature / °C Charpy impact / J Temperature / °C

35. 120010008006004002000 Pearlite Martensite Bainite kilocycles to Crack Initiation Yates, Jerath

38. austenite

39. Chang and Bhadeshia 15 mm thick plate, without Mo 550°C for 5 h 0.2C 1.25Si 1.55Mn 0.5Cr 0.15V 0.15Mo wt%

40. U.K.

41. 2500200015001000 20 40 60 80 100 120 140 160 180 Ultimate tensile strength / MPa Fracture toughness / MPa √m 18 wt% Ni maraging steel QT Caballero & Bhadeshia, 2001

42. hexagonal close-packedcubic close-packed Christian, 1951

43. Brooks, Loretto and Smallman, 1979

44. Olson & Cohen, 1976

45. 0 200 400 600 800 00.20.40.60.811.21.4 Carbon / wt% Temperature / K Fe-2Si-3Mn-C wt% B S M S

46. 1.E+00 1.E+04 1.E+08 00.511.5 Carbon / wt% Time / s Fe-2Si-3Mn-C wt% 1 month 1 year

47. 20 nm     

48. excess carbon in solid solution in ferrite !

50. Peet, Babu, Miller, Bhadeshia, 2004