  A mathematical framework is proposed to predict the features of the (5 5 7)
lath transformation in low-carbon steels based on energy minimisation. This
theory generates a one-parameter family of possible habit planes and a
selection mechanism then identifies the (5 5 7) normals as those arising from a
deformation with small atomic movement and maximal compatibility. While the
calculations bear some resemblance to those of double shear theories, the
assumptions and conclusions are different. Interestingly, the predicted
microstructure morphology resembles that of plate martensite, in the sense that
a type of twinning mechanism is involved.
