Corrosion fatigue test of Type 403 stainless steel was performed under constant frequency of 5 Hz in pure water at room temperature in order to evaluate the effect of loading and MnS inclusion on the initiation of corrosion pits. Corrosion pits initiation which is the initial phenomenon of corrosion fatigue damage occurs on the MnS inclusion which appears on the specimen, and crack initiation depends on the shape, size and distribution of MnS inclusion in the matrix. Therefore it was clarified that fatigue strength can be improved by suppressing the formation of MnS inclusion which reduces the fatigue strength. And applied loading will act on the dissolution of MnS inclusion. Therefore, it was considered that corrosion pits initiated even in the pure water due to the change of water chemistry near the MnS inclusions for their dissolution.
