Properties of AISI M3:2 high speed steels produced by conventional casting and by powder metallurgy techniques

Abstract

The aim of this study was to determine the properties of AISI M3:2 high speed steels produced by conventional metallurgy and by other powder metallurgy routes. PM Sinter 23 produced by hot isostatic pressing of gas atomized powders, M3:2 produced by axial cold compaction and vacuum sintering of green compacts obtained from water atomized powders and VWM3C manufactured by a conventional metallurgical route were investigated in this work. Specimens of Sinter 23 and VWM3C were taken in the longitudinal and transverse direction of hot forging. Transverse rupture strength (TRS) specimens of the five M3:2 high speed steels were manufactured as per the ASTM B 528-99 standard, heat treated by austenitizing and air quenched at 1140, 1160, 1180 and 1200 °C followed by triple tempering at 540, 560 and 580 °C. These specimens were fractured in three point bending tests with a bending rate of 2.5 mm/minute. TRS and hardness (Vickers and Rockwell C) of the high speed steels were determined. Scanning electron microscopy was used to study the microstructures of specimens that had undergone the different hardening treatments and the sizes of the primary carbides were measured at 1000 X on polished and etched specimens. The Quantikov image analyzing software was used to determine primary carbide distribution and at least six micrographs of the specimens in each condition were used. Correlation between TRS and size of the primary M6C and MC type carbides was found.