SINTERED STABILITY AND MACHINABILITY OF P/M STEEL USING MODIFIED MNS ADDITIONS

摘要

MnS is well-known and widely used additive for enhancing machinability but presents the problems of extreme sensitivity to reaction with moisture and thermal decomposition during sintering. In this study, MnS and xMnS(x=Cu, Fe, Mo) were poduced by Mechano-Chemical process and its hygroscopic property and thermal stability together with powder properties were evaluated. The mixtures of Fe-4Ni-l.5Cu-0.5Mo base powder, 0.5wt% graphite and 0.8wt% stearic acid with 0.5wt%MnS and xMnS(x=6wt%) additions, or no addition were used for the comparison of powder and sintered properties as well as machinability test through the subsequent P/M processes. Results showed that xMnS formed the solid solutions of transition metals, x substituted for Mn in the MnS matrix. This study revealed that MnS containing Mo had the best resistance to environmental degradation and thermal stability with better machinability than other versions of xMnS and MnS. This study also shows that xMnS, similar to MnS, had little effect on powder and sintered properties.