Role of Molybdenum in Promoting Densification During Vacuum Sintering of T1 Grade High Speed Steel Powders

Abstract

It is shown that densification during vacuum sintering of T1 type high speed steel powders is due to the presence of a liquid phase and that sinter-ability is influenced by the molybdenum content of the T1 powder, with 0·5 wt-% being essential for satisfactory sintering behaviour. The results of differential thermal analysis, sintering trials, and microstructural studies carried out on three batches of T1 powder containing <0·02, 0·26, and 0·51 wt-%Mo are discussed with reference to phase diagrams. Sintering behaviour and sintered microstructures can be correlated with phase diagram predictions. For sintering to full density to occur, the solidus temperature must be exceeded. Optimal sintering occurs within the austenite + carbide + liquid region. The amount of liquid is also important. Increasing the molybdenum content changes the position of the solidus, promoting sintering through the formation of a larger volume fraction of liquid at the sintering temperature. PM/0491