Trapezoidal Potential Fluctuation Observed During the Propagation Stage of Stress Corrosion Cracking Test for SUS304 Stainless Steel in 35 mass% MgCl2 Solution

In the previous paper, the trapezoidal potential fluctuation was observed during the propagation stage of stress corrosion cracking (SCC). However, it had not been examined whether this potential fluctuation had a direct relation to SCC phenomenon. In this paper, the source of the trapezoidal potential fluctuation was investigated. A 35 mass% MgCl2 (353K) solution was employed similarly to the previously reported experiment. Potential fluctuation was measured against an Ag/AgCl reference electrode with a digital voltmeter at a sample frequency of 2.56Hz. The correlation between the elongation rate of the specimen and the potential fluctuation was examined. If the trapezoidal potential fluctuation had a direct relation to the SCC phenomenon, the elongation rate and the potential fluctuation should have a negative correlation. However, these two values correlated positively. The potential fluctuation change by unloading during the experiment was measured. Even after unloading, the trapezoidal potential fluctuation generated continuously. The effect of solution stirring on the corrosion potential fluctuation was also examined. The trapezoidal potential fluctuation disappeared when the solution was stirred. It was estimated that the trapezoidal potential fluctuation was caused by a perturbation of the concentration of dissolved oxygen in the proximity of sample surface. Therefore, it was judged that the fluctuation was not directly related to the SCC phenomenon.