Abstract
In a previous paper, mechanical properties of the injection moulded and sintered 304 stainless steels having different Mn/Si ratio were studied. As the result, the tensile strength was hardly affected by the Mn/Si ratio, but the fatigue strength changed considerably by the Mn/Si ratio. It was suggested that the shape and distribution of pores influenced the fatigue behavior.
In this paper, two kinds of sintered specimens which have unlike shape of pores were produced by the same process as mentioned previously, and the effects of pore shape and distribution on fatigue crack initiation and crack propagation were studied in detail.
The main results obtained are summarized as follows;
(1) The pore shape of sintered stainless steel changed with the Mn/Si ratio of SUS304 powder. The steel with a high Mn/Si ratio contained a lot of sharpened pores which have a large aspect ratio. However, the steel with a low Mn/Si ratio contained many spherical pores. On the other hand, the pore distribution was independent of the Mn/Si ratio.
(2) Fatigue crack propagation behaviors of injection moulded and sintered stainless steels were hardly affected by the Mn/Si ratio.
(3) Although the chemical compositions of the steels were almost the same except Mn, the smooth specimen made of steel with a high Mn/Si ratio showed the fatigue limit lower than that of the steel with a low Mn/Si ratio, because the presence of sharpened pores in the former accelerate the fatigue crack initiation.
