Crystallography of the martensite transformation in Fe−Al−C alloys

Crystallographic measurements on highly tetragonal bct martensite in two Fe?Al?C steels have been made and the results have been interpreted in terms of the phenomenological crystallographic theory of martensite formation. Agreement between theory and experiment was found to be excellent. Of particular interest is the high martensite tetragonality (c/a→1.14) in aluminum-steels compared to others. Because of this the principal distortions of the Bain deformation are substantially smaller and consequently the magnitudes of the shape and lattice invariant deformations are reduced considerably. Measurements of the dilatation parameter δ indicate that the shape deformation is not significantly different from an invariant plane strain.