Statistical characteristics of metastable pitting of 316 stainless steel

The statistical characteristics of the current fluctuations during metastable pitting of 316L stainless steel in NaCl solution were studied by using potentiostatic method. It was found that the growth rates and peak currents of metastable pits follow the log-normal distributions; as potential and chloride concentration increase, both growth rate and peak current of metastable pits increase. The lifetime of metastable pits also follows the log-normal distribution, and is almost not affected by potential. Higher growth rates do not definitely result in larger metastable pits. Besides, it was also found that a certain propagation rate range is beneficial to the micropit to remain growth; and at constant potential, the maximum peak currents in different time intervals during a potentiostatic test followed extreme distribution. The statistical characteristics of metastable pitting may by used to predict the tendency of pitting corrosion.