Crystallography of the {225}_F martensite transformation in an Fe−Mn−Cr−C alloy

Abstract

This paper reports on a study of the crystallography of the {225}_F * martensite transformation in Fe-3 pct Mn-3 pct Cr-1 pct C for which the habit place was found to be indistinguishable from the (hkh)_F form. The shape strain direction based on analysis of scratch displacements and surface tilts proved to be unique, in contrast to previous work, with a scatter of ≈5 deg about the mean direction. The habit plane was found to be invariant, or at most isotropically distorted by 1/2 pct, and thus the use of a dilatation parameter to explain the {225}_F transformation is not considered to be feasible. The shape strain results clearly indicate the importance of making observations on bulk martensite plates. Nonparallelism of the austenite-martensite close-packed planes and directions for the {225}_F transformation was confirmed by an orientation relationship measurement. The data have been used to test recent crystallographic proposals for the {225}_F transformations and some preliminary calculations suggest the need for either additional considerations or a new theoretical approach.