Effect of Precipitation Hardening on the Fatigue Strength

Abstract

Effect of precipitation hardening on the rotary bending fatigue strength of an austenitic heat resisting steel was investigated at room temperature. It was concluded that strengthening processes such as precipitation hardening were effective only when fatigue cracks formed were associated with slip bands, but in the presence of structural inhomogeneity such as twin boundaries the stress concentrated readily there and the fatigue strength decreased in spite of a hardness increase. In this case the work hardened layer had an important role of making the structure homogeneous at surface and it could prevent a decrease in fatigue strength. In order to improve the fatigue strength it was most important to reduce the structural inhomogeneity as well as to harden.