Analysis of Potential Fluctuation for an Embryonic Stage of SCC of Sensitized SUS304 Stainless Steel in a Chloride Solution

摘要

Corrosion potential of sensitized type 304 stainless steel has been monitored in a 0.35 percent chloride solution at 313 approx 353 K in order to analyze the embryonic stage of stress corrosion cracking (SCC) using a U-bend specimen. The drops in corrosion potential indicated ruptures of passive films and they recovered sooner or later. The cathodic process was analyzed based on a simple RC parallel equivalent circuit model, where R is resistance for the electron transfer (Faradic process) and C an apparent capacitance for the cathodic electrode (non-Faradic process). The values of R and C were determined experimentally as a function of electrode potential so that the local anodic currents could be estimated for every event of potential drop. The histograms of the amount of electricity for each event showed that the distribution shifted to larger values with increase of temperature. Among the apparent parameters of potential drop, such as drop duration (DELTA t), drop depth (DELTA E) and bottom potential (E_R), DELTA t showed the closest correlation with the amount of electricity.