Crystallography of lath martensite and lower bainite in alloy steels

Abstract

The crystallographic features of lath martensite and lower bainite were investigated using precise transmission electron microscopy proposed by the authors. It was found that the martensite laths related to each other by a relative rotation of about 60° around the normal to their common close-packed planes {1 1 1} A{1 1 0} M, thus resulting in an approximate pseudo-{1 1 2} M twin relationship between two adjacent laths, that all parallel martensite laths formed in a single packet kept a unique G–T orientation relationship (OR) with the austenite matrix, and that the habit plane of the lath martensite was close to {3 3 5} A. A {3 3 5} f martensite was thus revealed. Furthermore, crystallographic features similar those of lath martensite were also observed in lower bainite formed in the same steel, thus confirming a crystallographic similarity between the lath martensite and lower bainite.