High performance sintered 4600 steels were obtained by Metal Injection Molding (MIM) process in our previous studies. This seemed to be due to the fine heterogeneous microstructure which were consisted of martensite surrounded by a network of tempered martensite through the segregation of Ni added as alloying element. Consequently, Ni has great effects in the heterogeneous microstructure of like this low alloy sintered steels. For example, the mechanical properties may largely change by the amount and distribution of Ni content.
In this study, the effects of Ni content (2, 4, 6 and 8mass% Ni) on the static strength and microstructures of sintered and heat-treated 4600 steels has been investigated using the conventional powder metallurgy (P/M) process. The hardness and tensile strength of sintered steels were improved with increasing Ni content. However, tensile strength of heat-treated steels were decreased by the addition of 8mass% Ni. This was seemed to be due to the appearance of retained austenite. Optimum combinaion of strength (1450MPa), elongation (2%) and hardness (40HRC) was obtained by the addition of 6mass% Ni.