It is well-known that the high performance sintered alloys were obtained by a Metal Injection Molding (MIM) process. Although assessment of the dynamic properties such as fatigue strength is important to design a reliable structural sintered steels, especially for the high strength steels, there are very few reports about the dynamic properties of MIM steels at the present time. In this study, the behavior of fatigue properties for high strength 4600 steels (Fe-1.8%Ni-0.5%Mo-0.2%Mn) produced by the MIM process using mixed elemental powders were investigated taking the microstructure into account.
Sintered and heat treated steels showed the fine heterogeneous microstructures with the segregation of Niadded as one of the alloying elements. The fatigue strength of heat treated MIM 4600 steels were higher than that of the conventional P/M steels because of the near full-densification and the spheroidization of pores. Additionally, the regions of a high nickel concentration, which were hard martensite or retained austenite and were uniformly distributed within the tempered martensitic matrix, were also effective against the crack propagation. This result indicated that it is possible to attain high performance structural steels combined with high static and dynamic strength by MIM techniques.