Abstract
Completely reversed plane bending fatigue tests were carried out using sintered iron compacts made from five different iron powders. The fatigue specimens with sintered densities in the range of 6.2-7.0g/cm3 were prepared by single compacting and sintering at 1200°C for 1 hr in hydrogen. The fatigue limits of various specimens were measured, and the fatigue microcracks were observed by optical microscopy.
The patterns of fractured surfaces were also investigated in a scanning electron microscope.
Results were summarized as follows;
1) The type of S-N curves for sintered irons showed no difference between iron powders, snd the endurance limits of them increased with increasing sintered densities.
In comparison with the same sintered densities of them, the fatigue strengths of electrolytic and reduced ore iron powder compacts were higher than that of atomized powder. The fatigue ratios were found to be in the range of 0.40-0.47.
2) Fatigue microcracks were initiated at the edge of the specimen, small pores or non-metallic inclusions with porosity of the specimen surface, and then the main fatigue crack for final failure was formed and grew from pore to pore in mixed transgranular-intergranular mode.
3) At the early period of fatigue life, the pattern was partly the grain boundary fracture, and at the final period, it was mainly the ductile dimple pattern by the shearing fracture.
