The Effects of Prior Transformation and Prestrain on the Habit Planes of Acicular Iron-Nickel Martensite

Abstract

The habit planes of martensite in two iron-based alloys containing 31.7 and 32.8 wt.-% nickel have been measured by two-surface trace analysis after both prior transformation and prestrain of the austenite. The habit plane in strain-free austenite was close to {3, 10, 15}, the plane predicted by the simple crystallographic theories of martensite formation. The habit planes of plates forming after the initial plates displayed a considerable deviation from {3, 10, 15}. It has been shown that the previously reported scatter of the habit plane, which is not due to experimental error, can be attributed to the large strains introduced into the austenite by the growing martensite plate and cannot be accounted for by the current multiple-shear latticeinvariant deformation theories of the crystallography of martensite. Some evidence is presented indicating that the lattice-invariant plane-strain condition on the habit plane must be relaxed in order to explain the habit planes in strained austenite.