EFFECT OF MEAN STRESS ON FATIGUE STRENGTH OF A RAPID HEAT TREATED STEEL.

The effect of metallurgical factors and the effect of residual stress, respectively on the fatigue strength of an induction hardened machine component were investigated. The specimens, salt bath quenched in the similar heat cycle to that on the surface of an induction hardened component, were used. On the basis of the assumption that the effect of mechanical mean stress and the effect of residual stress on the fatigue strength were equivalent, the following results were obtained. The effect of increasing the hardness on the fatigue strength of the material without residual stress is not quite so great. On the other hand, when the hardness increases, the effect of mean stress on the fatigue strength of the material becomes greater. Thus, it is important to use this kind of hardened materials under compressive residual stress or mechanical compressive mean stress.