高温塩化物水溶液中におけるSUS 304ステンレス鋼の孔食

抄録

Pitting behavior of SUS 304 stainless steel at elevated temperatures has been studied in NaCl solution over the temperature range of 25-50°C. Pitting potentials (E_P) and repassivation potentials (E_R) were determined by the stepwise cyclic polarization technique under a deaerated condition. With increasing temperature, E_P and E_R decreased to less noble values up to about 175°C, which meant higher susceptibility to pitting at higher temperature. But, above the temperature of 175°C the trend was reversed and E_P moved to higher potential value, which showed less tendency to pitting. The attack produced by the cyclic polarization exhibited the uniform corrosion under the coarse film at 250°C, contrary to the pitts at other temperature. These results on the effect of temperature were discussed from the point of the hydrolysis of dissolved metal ion and the nature of oxide. The repassivation has been reached easily above 150°C on backscanning of the potential The E_R was not affected by the amounts of corrosion during growth process. These results were considered from the change of current in the potential step and the diffusion of aggressive ions away from the occluded region to the bulk solution.