18-8ステンレス鋼の耐孔食性に及ぼす鋼中SおよびMn量の影響

抄録

The effects of S and Mn contents on pitting corrosion behavior of 18-8 stainless steel have been studied by means of anodic polarization and immersion test in chloride media. The main results obtained are summarized as follows:
In 3% NaCl solution at 0 and 30°C, pitting potential (V'c₁₀₀) had tendency to become less noble with the increase in S content. This tendency, however, could not be found for the specimens containing S above about 0.01%. On the other hand, V'c₁₀₀ continuously became less noble with the increase in Mn content. In 3% NaCl solution at 70°C or 3% NaCl acidic (HGl) solution at 30°C, V'c₁₀₀ depended on S and Mn contents, and it became noble with the decrease in those elements. In 10% FeCl₃·6H₂O solution at 25°C, the frequency of occurrence or the density of pits increased with the increase of the quantity of sulfide inclusions. On the other hand, the growth tendency of pits depended on the Mn/S ratio, and anodic reaction of specimen was retarded with decrease of the ratio. In all of the specimens, the pit initiation site, was sulfide inclusion/metal interface in the pitting potential region in NaCl and FeCl₃·6H₂O solution, and pit grew preferentially into the metal matrix.