  One of the important characteristics of solid-state phase transformations in
steels is the choreography of atoms as they traverse the frontier between the
parent and the product phases. Some transformations involve a chaotic motion of
atoms consistent with long-range diffusion, and hence are closer to equilibrium
than those that where a disciplined transfer occurs. Since the pattern of atoms
changes during transformation, a disciplined motion of atoms necessarily leads
to a change in the shape of the transformed region, and like any deformation,
such changes cause strains in the surrounding material. These displacive
transformations are therefore strain dominated, with the morphology, chemical
composition and thermodynamic framework sensitive to the strain energy due to
the shape change. Here we consider the published data that have been
accumulated on the displacements associated with `bainite', a phase
transformation product in steels that forms the basis of the world's first bulk
nanocrystalline metal.
