Corrosion Behavior of Stainless Steels in Crevice under Wet-Dry Exposure in Chloride-Containing Environments

－Effect of Steel Species－

Abstract

Cyclic corrosion tests, consisting of 0.86 kmol･m^－3 NaCl solution spraying, drying, and wetting process, were conducted using a crevice-structured spot-weld specimen of some stainless steels in order to clarify the relation between corrosion behavior and the amount of chloride accumulated into the crevice. The component of chlorides accumulated into the crevice was mainly sodium chloride, although far less amount of metallic chlorides were also contained. When the amount of chloride was reached at about 20 mmol･m^－2 and the total amount of iron and chromium was reached at about 0.5 mmol･m^－2 in crevice, the maximum corrosion depth in crevice of SUS436L and SUS444 increased as cycle number increased. In case of SUS304 and SUS316L, sodium chloride and metallic chloride that enough to be increased the maximum corrosion depth as cycle number increased were not accumulated into the crevice. It is necessary that chlorides which contains specific amount of metallic chlorides accumulate into the crevice for corrosion to proceed in the depth direction. The corrosion form in this study was pitting. It is considered that the crevice have a role of accelerating the accumulation of chloride.