Abnormal Corrosion of Carbon Steels Caused by Cathodic Polarization

We have observed the cathodically polarized specimen surface of S25C and S50C carbon steels, SUS304 stainless steel and pure platinum by using scanning electron microscope. The carbon steel specimens were heat-treated at 100～900℃ after cold-rolling. When these carbon steel specimens were polarized cathodically in an aqueous solution of 0.5kmol/m3 H2SO4, needle-shaped deposits were observed on the specimen surface regardless of heat-treatment temperature. In the specimen of SUS304 stainless steel, slight corrosion was observed, but the deposits were not observed. In the specimen of platinum, a change of the specimen surface was not observed. These experimental results indicate that the deposits observed in the carbon steel specimens are corrosion products, and less noble metals corrode even when they are polarized cathodically