On the Main Factors Contributing to Improvement of Fatigue Strength of Induction Hardened Steel

Abstract

In the previous study the influence of induction hardened steel on its fatigue strength was investigated with respect to the hardened depth and residual stress. It is hard, however, to explain, on the bases of hardness and residual stress alone, the increase of endurance limit due to induction hardening. In the present paper it is intended to find out main factors that will contribute to improvement of fatigue strength.
It is found that all the specimens tested have shown a linear relation existing between the endurance limit and the integral width of X-ray refraction line, regardless of the hardening methods, whether by progressive hardening or by static quenching. The specimen obtained from the integral width according to Hall's analysis has also shown a linear relation existing between its micro strain and particle size and the endurance limit. It is this micro strain and particle size evidently rather than the residual stress that have influence on the endurance limit of induction hardened steel.