Abstract

A P/M high speed steel of ASP 30 grade was austenitized, gas quenched and tempered at various conditional. The mechanical properties such as hardness, bend strength and fracture toughness were evaluated after heat treatment. The microstructure and the type and volume fraction of carbides were analyzed by an optical microscope, image analyzer and XRD. The primary carbides after the heat treatment were MC and M_6C type. The volume of the total carbide varied from 10 to 15% depending on the austenitizing and tempering temperature. The tempering temperature for maximum hardness was at around 520°C. But the maximum bend strength was obtained at about 550°C. The fracture toughness was largely affected by the presence of retained austenite after gas quenching and secondary hardening during tempering.