Abstract
The homogeneous microstructure has been utilized preferably for the P/M materials such as machine structural parts required high strength. For the low alloy steels such as AIS14600 produced by Metal Injection Molding (MIM) process, however, the static fracture strength such as tensile strength of mixed elemental powder compacts which showed the fine heterogeneous microstructure was superior to that of homogeneous prealloyed powder compacts in our previous studies. Therefore, the effect of microstructure on the dynamic fracture strength such as fatigue strength of injection molded 4600 steels by MIM process using prealloyed and mixed elemental powders were investigated in this study.
The heat treated compacts using prealloyed powder showed the fine homogeneous tempered martensitic microstructure. On the other hand, the mixed elemental powder compacts heat treated showed the fine heterogeneous microstructure, which consisted of tempered martensitic matrix and retained martensite or austenite phases caused by the segregation of Ni added alloying element. The fatigue strength of the latter were about 100MPa higher than that of the former. Thus the fine heterogeneous microstructure seemed to contribute to improve not only the static but also the dynamic fracture strength. This result indicated that the MIM technique is more effective route for manufacturing high performance low alloy steel compacts using mixed elemental powder.
