Properties of AISI M3 Class 2 High-Speed Steels Produced by Conventional Casting and Powder Metallurgy Techniques

The aim of this study was to evaluate the mechanical properties, specifically transverse rupture strength (TRS) and hardness, of AISI M3 Class 2 high-speed steels produced by different manufacturing processes. The materials investigated were: the commercial powder metallurgy (PM) steel Sinter 23, produced by hot isostatic pressing (HIP); the conventional cast and wrought steel VWM3C; and an AISI M3-2 steel produced by a PM route involving cold uniaxial compaction of water-atomized powders (with a 0.3 wt.% graphite addition) followed by liquid-phase vacuum sintering. Specimens for transverse rupture strength (TRS) testing were prepared according to the ASTM B528-99 standard. They were heat-treated by austenitizing at 1140, 1160, 1180, and 1200 °C in salt baths, followed by quenching and triple tempering at 540, 560, and 580 °C. The TRS and hardness (Vickers and Rockwell C) of the steels were determined. The microstructures of the hardened specimens were characterized using scanning electron microscopy (SEM), and the primary carbide sizes were measured. A correlation was established between the TRS, the microstructure, and the size of the primary M6C and MC carbides.