Mechanisms of Sintering in High Speed Steels with Phosphorus Alloying Additions

Abstract

Cu–P alloy powder additions to M3 class 2 high speed steels reduce the sintering temperature required to produce near full density by ∼100 K. Densification was found to occur in distinct stages, due to the successive formation of a series of liquid phases at various sintering temperatures. These phases, each of which gave rise to an identifiable change in densification rate, were identified as the ferrite-carbide-phosphide eutectic at ∼1050°C, melting of residual copper at 1090°C, and an austenite-carbide eutectic at 1150°C. An activated sintering model for densification by the formation of a phosphide rich grain boundary liquid was developed. This concluded that sintering occurs by rapid grain boundary migration due to solutionprecipitation across an unstable grain boundary liquid film. PM/0512