The first theory invokes a diffusion-controlled transformation, describing the growth of bainite via the propagation
of ‘ledges’ — a series of steps on the transformation interface. The second interpretation favours a
displacive, diffusionless transformation. Bainite growth occurs via the autocatalytic nucleation and growth
of successive sub-units or platelets. Over time, a wealth of techniques has been implemented in order to increase
the understanding of the mechanism by which bainite forms. From the early approaches that involved
thermodynamic and kinetic considerations; through detailed work on the crystallography of the transformation;
to studies involving advanced characterisation techniques that focused on the distribution of atoms, etc.
Some of the theories have been progressively adapted to new evidence and new concepts as they emerge. For
example: the concepts of the T0 curve and of paraequilibrium transformation.