Sinterability Study of PM M2 and T15 High Speed Steels Reinforced with Tungsten and Titanium Carbides

Sintered high speed steels (HSSs) are assuming an increasingly important role as wear resistant and cutting tool materials, areas in which they are in competition with cemented carbides. Research on HSSs has taken three basic approaches: use of advanced technologies such as hot isostatic pressing to produce full density materials; assessment of their sinterability under industrial conditions (nitrogen-hydrogen atmospheres, low sintering temperatures, continuous furnaces, etc.); and reinforcement with hard materials such as ceramics and carbides to increase cutting or wear performance. In the present work, which combines the last two approaches, additions of tungsten carbide and titanium carbide were made, singly and in combination, to M2 and T15 steels. Microstructures, densification, and transverse rupture strength were compared after sintering in vacuo and under a nitrogen-hydrogen atmosphere. Addition of 10 wt-% of a 90WC–10Co powder mixture to the base steels produced a marked increase in sinterability at low temperatures, resulting in better flexural strengths, but, because of its lower reactivity, titanium carbide produced little effect on densification; addition of both carbides together produced intermediate results. Acceptable levels of flexural strength can be obtained by sintering in N₂–20 vol.-%H₂ atmospheres at temperatures below 1250°C, but vacuum sintering was found to be the most efficient method of producing HSSs reinforced with cemented carbides. PM/0608