Influences of non-metallic inclusion and carbide on high-cycle fatigue strength of tool steels

Abstract

Rotating bending, high-cycle fatigue properties of tool steels JIS SKD61 and SKD11 were discussed from viewpoints of the effects of non-metallic inclusion and carbide on the fatigue crack initiation and on the relationship between fatigue strength and hardness. Fatigue cracks initiated mostly from non-metallic inclusions or carbides depending on materials and heats. As the results, the fatigue strength at 108 cycles decreased compared with that estimated from the relationship between fatigue strength σwb and hardness HV for steels without any defect or with hardness less than HV400. In the case of inclusions being the crack initiation site, the value of σwb/HV decreased with increasing the weighted value of inclusions and with increasing hardness.