The effect of S and Mn content on the corrosion behavior of commercially available austenitic stainless steels have been studied electrochemically and metallographically in L-ascorbic acid solutions containing NaCl. According to the results of measurements of the anodic polarization curves, the critical current density for passivation of the specimens decreased for low Mn content even if a large amount of S were present, and decreased for low S content even if a large amount of Mn were present, that is, active dissolution was retarded. Furthermore, pitting potentials of those specimens had a tendency to become noble. For specimens with S contents of not more than about 0.003%, the solutions used, in spite of the immersing of the specimen containing a large amount of Mn, did not degenerate and no smell of H₂S was produced. For specimens containing a large amount of Mn, however, the surface became blackened with only a small increasing in S. For specimens with Mn contents of not more than about 0.5%, on the other hand, no surface blackening occurred even if a large amount of S was present, but the smell of H₂S became pronounced at S contents above about 0.025%. For specimens for which Mn/S ratio was high, MnS inclusions were unstable and easily dissolved, and active dissolution was accelerated by the presence of H₂S which was generated by the dissolving reaction of those inclusions. Corrosion resistance was changed markedly by slight variations in S and Mn content even if the specimens conformed to a single specification, such as SUS 304 or SUS 316.

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When a electrolysis is interrupted in electroplating metallic chromium from a chromic acid bath, granular chromiums are deposited on platelike chromium, and the uniformity of the metallic chromium deteriorates. The nucleation, growth and orientation of the granular chromiums were investigated by means of transmission electron microscopy and electron diffraction, and the conditions necessary for the formation of granular chromiums were determined. Granular chromiums were formed when, after the formation of platelike chromium, electrolysis was interrupted for over 0.3sec. Formation density was affected by the crystallographic orientation of the platelike chromium, but there were no crystallographic relation between the granular and the platelike chromiums. A formation mechanism is proposed for the granular chromiums to explain these results from the standpoint of the oxidation of platelike crystal during the interruption of electrolysis.

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Carbon steel specimens were anodized by a two step procedure, first in a borate solution and second in a borate solution containing 8-hydroxyquinoline [HQ]. The resulting surface inhibits cathodic reactions such as oxygen reduction and hydrogen evolution, and it has good corrosion resistance in aerated chloride media of pH 3-10. The composition and structure of the formed layer were analyzed by UV-VIS-IR reflectance spectroscopy, Auger electron spectroscopy combined with argon ion sputtering, conversion electron Mössbauer spectroscopy, and ellipsometry. The results indicate that the protective layer is composed of two layers: the outer layer is less than 40nm in thickness and consists of condensation products of HQ and HQ derivatives formed by the anodic polarization, and the inner layer is less than 3nm in thickness and consists of Fe-HQ and/or-HQ derivatives complexes. Electrochemical measurements revealed that the inner Fe complex layer is responsible for the corrosion protection in aerated chloride media.

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