4. upper bainite
1 µm

5. lower bainite

6. Surface Surface 2
50 µm
Srinivasan & Wayman, 1968

7. s d c r 1

10. 50 µm

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

13. 1 2
Fe-0.4C wt%
Decarburisation
time / s
500
400
300
Temperature / °C

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

17. Summary 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

18. DISPLACIVE
RECONSTRUCTIVE

24. Watson and McDougall, 1973

28. Summary Mechanism displacive but carbon must partition during growth.
Pairs of plates grow together to minimise strain.