POSCO Lectures on Bainite Graduate Institute of Ferrous Technology <ul><li>Microstructure </li></ul><ul><li>Mechanism </li...
http://cml.postech.ac.kr/
To understand bainite, we must consider all other microstructures in steels
Bundy (1965)
Allotropes of iron in three dimensions
Cementite Fe 3 C
Steel: Fe-C ferrite austenite
Fe 3 C
Diffusionless Diffusion
 
 
Allotriomorpic Idiomorphic ferrite
 
 
 
 
 
Pearlite
20 µm
 
 
Jaramillo et al., 2004
 
 
 
Martensite
Ferrite Austenite
 
 
transformation twins (Wayman)
50  m m
 
austenite
Chang and Bhadeshia
 
Bainite
 
1 µm upper bainite
lower bainite
Surface 1  Surface 2 Srinivasan & Wayman, 1968 50 µm
 
 
 
 
50 µm
Bhadeshia and Waugh, 1981
Takahashi and Bhadeshia
Temperature / °C Decarburisation  time  / s  Fe-0.4C wt% 500 400 300 0 1 2
 
 
Bhadeshia & Edmonds, 1979
 
 
TRIP-assisted steel  Fe-0.29C-1.41Si-1.42Mn wt%  (Jacques, 2001)
 
Growth is diffusionless. Strain energy must be accounted for.
Takahashi and Bhadeshia
 
Oka and Okamoto
Ohmori and Honeycombe
The mechanism of transformation is displacive. Transformation temperature higher than martensite. Bainite grows without di...
Think of bainite as martensite which tempers during transformation
 
 
DISPLACIVE RECONSTRUCTIVE
 
 
 
 
 
 
Watson and McDougall, 1973
 
 
 
Mechanism displacive but carbon must partition during growth. Pairs of plates grow together to minimise strain. Summary
Nucleation of martensite, bainite,  Widmanstätten ferrite
  x Gibbs free energy Carbon Thermodynamics  G m x  m   G
 
T h G N
Bhadeshia, 1981 Each point represents a different steel Nucleation function G N
The nucleation of bainite must involve the partitioning of carbon Why does the required free energy vary linearly with T?
hexagonal close-packed cubic close-packed Christian, 1951
Brooks, Loretto and Smallman, 1979
Olson & Cohen, 1976
 
 
 
Nucleation of bainite must involve the partitioning of carbon. Mechanism of nucleation is otherwise identical to that of m...
 
 
 
 
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Posco Bainite 1

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Slide shows on bainite lectures by Prof. H. K. D. H. Bhadeshia

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Posco Bainite 1

  1. 1. POSCO Lectures on Bainite Graduate Institute of Ferrous Technology <ul><li>Microstructure </li></ul><ul><li>Mechanism </li></ul><ul><li>Properties </li></ul><ul><li>Superbainite </li></ul>
  2. 2. http://cml.postech.ac.kr/
  3. 3. To understand bainite, we must consider all other microstructures in steels
  4. 4. Bundy (1965)
  5. 5. Allotropes of iron in three dimensions
  6. 6. Cementite Fe 3 C
  7. 7. Steel: Fe-C ferrite austenite
  8. 8. Fe 3 C
  9. 9. Diffusionless Diffusion
  10. 12. Allotriomorpic Idiomorphic ferrite
  11. 18. Pearlite
  12. 19. 20 µm
  13. 22. Jaramillo et al., 2004
  14. 26. Martensite
  15. 27. Ferrite Austenite
  16. 30. transformation twins (Wayman)
  17. 31. 50 m m
  18. 33. austenite
  19. 34. Chang and Bhadeshia
  20. 36. Bainite
  21. 38. 1 µm upper bainite
  22. 39. lower bainite
  23. 40. Surface 1 Surface 2 Srinivasan & Wayman, 1968 50 µm
  24. 45. 50 µm
  25. 46. Bhadeshia and Waugh, 1981
  26. 47. Takahashi and Bhadeshia
  27. 48. Temperature / °C Decarburisation time / s Fe-0.4C wt% 500 400 300 0 1 2
  28. 51. Bhadeshia & Edmonds, 1979
  29. 54. TRIP-assisted steel Fe-0.29C-1.41Si-1.42Mn wt% (Jacques, 2001)
  30. 56. Growth is diffusionless. Strain energy must be accounted for.
  31. 57. Takahashi and Bhadeshia
  32. 59. Oka and Okamoto
  33. 60. Ohmori and Honeycombe
  34. 61. The mechanism of transformation is displacive. Transformation temperature higher than martensite. Bainite grows without diffusion. But carbon then escapes into the residual austenite. Shape deformation plastically accommodated. Sub-unit mechanism of growth Summary
  35. 62. Think of bainite as martensite which tempers during transformation
  36. 65. DISPLACIVE RECONSTRUCTIVE
  37. 72. Watson and McDougall, 1973
  38. 76. Mechanism displacive but carbon must partition during growth. Pairs of plates grow together to minimise strain. Summary
  39. 77. Nucleation of martensite, bainite, Widmanstätten ferrite
  40. 78.   x Gibbs free energy Carbon Thermodynamics  G m x  m   G
  41. 80. T h G N
  42. 81. Bhadeshia, 1981 Each point represents a different steel Nucleation function G N
  43. 82. The nucleation of bainite must involve the partitioning of carbon Why does the required free energy vary linearly with T?
  44. 83. hexagonal close-packed cubic close-packed Christian, 1951
  45. 84. Brooks, Loretto and Smallman, 1979
  46. 85. Olson & Cohen, 1976
  47. 89. Nucleation of bainite must involve the partitioning of carbon. Mechanism of nucleation is otherwise identical to that of martensite.

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