HEAT-TREATMENT RESPONSE OF SINTERED M3 2 HIGH-SPEED STEEL COMPOSITES CONTAINING ADDITIONS OF MANGANESE SULFIDE, NIOBIUM CARBIDE, AND TITANIUM CARBIDE/

Metal matrix composites based on a sintered M3/2 high speed steel (HSS ) and containing either single additions of TIG, NbC, or MnS particles or combined additions of MnS + TIC or MnS + NbC were sintered to full density and subjected to a conventional hardening heat treatment cycl e of austenitisation, quenching, and double tempering. Relatively poor hardnesses and strengths were obtained in any composites that contain ed MnS particles, principally because of the weakening effects of MnS particles in the structure but also as a result of decarburisation of the steel matrix when oxygen introduced by the MnS particles reacted w ith carbon. Composites that contained TIC were changed in structure so that matrix M(6)C carbides were replaced by the less soluble MC carbi de. They consequently showed slightly reduced hardening response compa red to the baseline M3/2 HSS after heat treatment. Ball milling was ne cessary ill powder mixtures that contained NbC to break up particle ag glomerates. The resultant fine grain sized M3/2 + NbC materials produc ed by sintering and heat treatment gave superior properties to both th e normal M3/2 HSS and the other composites.