The Effect of Residual Stress on the Fatigue Strength of Case Hardened Steel

Abstract

It is well-known that the enormous increase in fatigue strength of case hardened steel is due to the high compressive residual stress in the material and to the doubled hardness caused by heat treatment, and that the effect of the residual stress on the endurance limit can be accounted for by taking it as the mean stress.In this paper the fatigue test results which were obtained of the carburized and induction hardened steel, have been re-examined from the viewpoint of crack propagation process. It appears that the fatigue strength of case hardened steel can be regarded as resistance against fatigue crack propagation in the specimen having minute flaw, because, in highly hardened material, the micro inclusions and metallurgical discontinuity can be taken as the origins of fatigue cracks.