Effect of Core Hardness and Notch Shape on the Rotating Bending Fatigue Limit of Induction Surface Hardened S45C Steel

Abstract

This report revealed the effects of preheat treatment, core hardness and notch shape on the rotating bending fatigue limit of induction surface hardened S45C steel. In addition, the effect of fracture mode on it was discussed. The results obtained are as follows;
1) Fatigue limit of test specimens with gentle notch (stress concentration factor α=1.46) is higher than that of smooth. This reason will be that, the crack initiation of the notch specimen is at specimen surface, but that of the smooth specimen is at fish eye. Therefore, in the case of the fracture starting from fish eye in smooth specimens, the fatigue limit can be increased by the method of making a gentle notch on the smooth specimen.
2) In the case of the effective depth of about 1.1 mm and 1.5 mm (diameter of the test specimen : 8 mm), the fracture mode starting from surface occurred when the core hardness was more than about HV 260, but the fracture mode starting from fish eye occurred when the core hardness was less than about HV 260. The fatigue limit decreased with the decrease of the core hardness.