MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF HEAT-TREATED ULTRAHIGH CARBON-STEELS

The mechanical properties of submicron grain size plain carbon steels (1.3 and 1.6% C) have been studied after heat treatment. It has been shown that such steels can be austenitized and quenched to high hardness (Rc = 67), high compression fracture strength (4345 MPa (about 630 klbf in-2)), and good compression ductility (about 10%). These unusual and desirable characteristics are achieved by austenitizing at low temperature, where a fine austenite grain size exists, prior to quenching. In contrast, austenitizing at high temperature leads to a decrease in fracture strength because of a coarsening of the transformation products. Microscopic studies of samples quenched from low austenitizing temperatures revealed the presence of optically unresolvable martensite and fine undissolved cementite. Transmission electron microscope studies showed a structure consisting mostly of submicron lath martensite, some very fine twin martensite regions and undissolved cementite particles. © 1979.