Tungsten Carbide as an Addition to High Speed Steel Based Composites

Abstract

Design criteria for high strength tool materials have to include wear resistance of the abrasive particle, high hardness and adequate toughness. Cold compaction and vacuum sintering of PM high speed steels (HSSs) to full density is now a well established technique [1-3]. In recent years, work has been undertaken to sinter metal matrix composites that contain ceramic particles in HSSs by the same route. Most studies have focused on sintering with additions of hard ceramics such as Al203, VC, NbC, TiC, WC and TiN with the aim of producing a more wear resistant HSS type material [4-18]. These composite materials have been developed for wear resistance applications as attractive alternative to the more expensive cemented carbides. Compared with high strength steels, these composite materials have higher hardness, wear resistance and elastic modulus. However, depending on size and distribution, the addition of brittle ceramic particles may cause degradation of bend strength and toughness owing to the initiation of cracks at or near the reinforcing particles. In order to ensure good bonding at the ceramic/matrix interfaces, the ceramic particles must exhibit some reactivity with the matrix. In contrast to Al2O3, which presents no interface reactions with the iron matrix, the diffusion of iron from the matrix into the MC carbide particles establishes a good cohesion across the ceramic/matrix interface. Besides, these carbides are stable in contact with iron during sintering and do not dissolve extensively. Therefore, MC particles were chosen as the reinforcement. A cheap and easy route to develop high speed steels reinforced with MC carbides consists of mixing powders of commercial high speed steel powders with the carbides.