CRYSTALLOGRAPHY AND INTERFACE BOUNDARY STRUCTURE OF PEARLITE WITH M7C3 CARBIDE LAMELLAE

摘要

The crystallography of pearlite with M_7C_3 carbide lamellae and the atomic structure at the fer- rite/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 deterapined: OR-I: (251)_b//(1120)_hex —habit Plane, (113)_b//(1100)_hex' (311)_b ≈ //(0001)_hex' OR-II: (251)_b//(1100)_hex —habit plane, (113)_b//(1120)_hex' (311)_b ≈ //(0001)_hex' Variants of these orientation relationships have been fre- quently 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 per- fectly 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.