Abstract

An investigation was performed to apply the M3/2 grade high speed steel for metal injection molding using both prealloyed and elementally blended powders. The injected samples were subjected to a debinding step in H_2/N_2 gas atmosphere at a ratio that affected the carbon content of the material. The carbon content ranged from 1.4wt.% to 1.43wt%. with increasing H_2 content up to 80% H_2 in H_2/N_2 atmosphere for the prealloyed powders. The carbon contents of the elementally blended powders exhibited 1.44wt.% and 1.62wt.% at 10% H_2/N_2 and 20% H_2/N_2 gas, respectively. This level decreased to 0.17wt.% upon increasing the H_2 content. The sintered density of both powders increased rapidly as the temperature reached the liquid phase forming temperature. After forming the liquid phase, the density rapidly increased to the optimum sintering temperature for the prealloyed powders, whereas the density of mixed elemental powders goes up slowly to the optimum sintering temperature. The optimum sintering temperature and density are 1260°C and 97.3% for the prealloyed powders and 1280°C and 96.9% for the elementally blended powders, respectively. The microstructure of the specimen at the optimum sintering temperature consisted of fine grains with primary carbides of MC and M_6C type for the prealloyed powders. The elementally blended powders exhibited coarse grains with eutectic carbides of MC, M_2C and M_6C type.