Structure of lath martensite and occurrence of retained austenite in as-quenched Fe-V-C low-alloy steels

Abstract

A detailed examination by transmission electron microscopy has been made of the as-quenched martensitic microstructures in Fe-C-V low-alloy steels. The morphological characteristics of the martensitic laths and the occurrence of autotempered cementite have been classified. Thin films of retained austenite have been shown to exist between martensitic laths and at martensite packet boundaries; the austenite can be unambiguously identified and differentiated from other similar microstructural features by selected-area diffraction and dark-field imaging techniques of conventional 100 kV transmission electron microscopy. The retained austenite is used as an orientation memory of the parent austenite in order to define the austenite/martensite phase crystallography. Some adjacent laths and groups of laths were found to be twin-related. Finally, some observations are made on the stability of the martensitic lath structure at elevated temperatures, and of the interlath retained austenite with respect to refrigeration and deformation.