Potential Dependence of Crack Initiation during Stress Corrosion Cracking of SUS 310S Stainless Steel in Boiling MgCl₂ Solution

Abstract

The crack initiation behaviour during stress corrosion cracking (SCC) of SUS 310S stainless steel in boiling 35% MgCl₂ solution has been studied by the constant potential method.
The constant load type SCC testing apparatus capable of measuring the dissolution current and elongation of the exposed specimens during the test was used in the present study.
The crack initiation morphology during SCC was dependent upon the potential range; pitting and then general corrosion occurred as the potential was shifted to more noble values. The potential dependence of its morphology was in close agreement with the fact that the cracks at open circuit potentials initiated at the bottom of pits. The SCC in the pitting potential range occurred in three steps, i. e., pitting growth, micro-crack growth from the pit-bottom, and macro-crack propagation. These steps were closely related to the time variation of dissolution current during the test.
Based on the results mentioned above, the crack initiation behaviour at the bottom of pits in the pitting potential range was discussed.