Microstructure evolution during sintering of injection molded M2 high speed steel

Production of precision engineering components with powder metallurgy (P/M) technology is greatly influenced by a number of critical manufacturing fac tors. The outcome of microstructure in a P/M part is a sum function of corr ect processing parameters and accurate diagnostic of the mechanisms governi ng particle packing, compaction and bonding. in the present work, sintering densification kinetics, microstructure evolution and fracture morphology o f powder injection molded M2 high speed steel were investigated. Results sh ow that the specimens densified rapidly via supersolidus liquid phase sinte ring mechanism. When vacuum sintering was employed, a near full density was obtained at 1210 degrees C after 60-min holding. Sintering above the criti cal temperature of 1210 degrees C and prolonged isothermal sintering in the presence of liquid species result in rapid growth in the grain size, and c oarsening of Mo, W rich M6C carbides. Fracture morphologies revealed that c racks originated from the carbides or carbide films on the grain boundaries with concomitant property decrements. For vacuum sintering, the sintering window is from 1210 degrees C to less than 1220 degrees C. When nitrogen si ntering was utilized, rapid densification shifted to a temperature range 12 50-1270 degrees C. Carbonitrides and fine carbides on the grain boundaries hindered the growth of the grain size. Near full density without microstruc ture coarsening was obtained at a sintering temperature range 1270-1290 deg rees C. Thus, the sintering window was 20 degrees C, an increase of more th an 10 degrees C over that of vacuum sintering. (C) 2000 Elsevier Science S. A. All rights reserved.