Shape Deformation
The formation of bainite causes a deformation (Fig. 5) which is an invariant–plane strain
with a shear component of about 0.26 and a dilatational strain normal to the habit plane of
about 0.03. This is consistent with a displacive mechanism of transformation.
Bainite forms at a relatively high temperature when compared with martensite. The
parent austenite is weaker at high temperatures and cannot accommodate the large shape
deformation elastically. It therefore relaxes by plastic deformation in the region adjacent to
the bainite. This is evident in Fig. 5, but is also presented as a height scan in Fig. 6. The effect
of this plastic deformation is to stifle the growth of bainite plates before they hit any obstacle.
This is why each bainite plate grows to a size which is often smaller than the austenite grain
size and then comes to a halt. Further transformation happens by the formation of a new plate
and this is why the sheaf morphology arises.