Effect of Crystal Structure of Compound Layer on Bending Fatigue Strength of Nitrided Medium Carbon Steel

Abstract

The effect of the crystal structure of the compound layer on the plane bending fatigue strength of nitrided carbon steel S45C was evaluated. When the compound layer consisted mainly of ε phase, the plane bending fatigue limit was higher than that of γ’ phase. The fatigue failure originated from the surface of the ε-phase at high stresses, but all other conditions resulted in an internal origin. The fatigue limit was affected by the internal properties of the specimen. The local fatigue limit of the diffusion layer calculated from hardness and residual stress was higher for the ε phase than for the γ’ phase, which was consistent with the experimental results.