Crystallography and interface boundary structure of pearlite with M 7C 3 carbide lamellae

Abstract

The crystallography of pearlite with M 7C 3 carbide lamellae and the atomic structure at the ferrite/carbide interface have been examined by means of transmission electron microscopy in an Fe–8.2Cr–0.96C alloy. Two orientation relationships with the corresponding habit planes were determined: OR-I and OR-II. Variants of these orientation relationships have been frequently observed. Microscopic steps at the ferrite/carbide interfaces accommodate the curvature of the habit planes. Each of these orientation relationships provides a small misorientation between the {110} b close packed planes of ferrite and the coincident planes of M 7C 3 carbide, and the atomic planes are perfectly matched through the interface. The orientation relationship between the parent austenite and M 7C 3 carbide was also deduced assuming the ferrite/austenite orientation relationship so far obtained.