Abstract

For the purpose of investigating the effect of sintering atmosphere and carbon addition on sintered density and microstructural characteristics, the M3/2 grade high speed steel powders with the addition of carbon are sintered in vacuum and 20%H_2/79%N_2/l%CH_4 gas atmosphere. With the addition of 0 wt%C, 0.45wt%C and 1.15 wt%C the optimum sintering temperatures decrease down to 1260°C, 1210°C and 1150°C respectively for the vacuum sintered specimen, and also decrease down to 1130°C, 1120°C and 1115°C for the gas sintered specimen. The threshold temperatures for full densification decrease steeply with increasing carbon content of the sintered specimen, while this temperatures are slowly decreased at high carbon content. The vacuum sintered specimen shows the primary carbides of MC and M_6C type at the optimum sintering temperature, and eutectic carbides of M_2C and Fe-Cr type are produced in the oversintered specimen. The gas sintered specimen exhibits M6C and Fe-Cr type primary carbides at the optimum sintering temperature. The eutectic carbides of M_6C and Fe-Cr type and MX type carbonitride are shown for the oversintered specimen in the gas atmosphere. The hardness of gas sintered specimen shows high value of 830-860 Hv due to the increment of carbide precipitation.