The Fatigue Crack Retardation of a Low Alloy Steel in Saltwater

Abstract

Fatigue crack retardation behaviour was investigated in saltwater using two materials of a low alloy steel, SCM435, whose strength or susceptibility to hydrogen was changed by heat treatment, and was compared with the data in laboratory air. The results show that there exists a significant difference between the overload affected zone sizes in saltwater and in air, depending on both the strength of the material and the baseline stress intensity level. The decreased overload affected zone size in lower strength material is related to a rapid resumption of the crack propagation rate after the minima, due to hydrogen embrittlement (HE) and corrosive dissolution. In higher strength material, in addition to a rapid resumption of the crack propagation rate due to the extreme HE, the overload affected zone size is also affected by the existence of SCC crack propagation caused by the overload application because of overload stress intensities above the K_{I SCC} value of this material.