DEPTH-COMPOSITION PROFILES OF IRON-BASE ALLOY SURFCES ANODICALLY OXIDIZED IN CONCENTRATED NaOH SOLUTION.

The depth-composition profiles of Fe-30Cr alloy, a seris of fe-Ni alloys SUS 304 and 316 austenitic stainless steels anodically oxidized at room temperatue in deaerated 10. 7 mol multiplied by (times) lg** minus **1 NaOH etching techniques. Chromium is enriched in the passive film formed on the alaloy. A rather thick film (9-28 nm) with a chromium-depletion zone extending to the substrate grows on fe-30Cr alloy during short polarization time (5-15 min) in the transpassive region where chromium dissolves into solution. Nickel-enrichment ranging from the uppermost surface to the alloy substrate was always observed for a series of Fe-Ni alloys anodically oxidized in the passive, transpassive ro secondary passive potential region of nickel. The addition of nickel suppresses the transpassive dissolution of chromium and contributes to the improvement of corrosion resistances of the austenitic stainless steels inconcentrated NaOH solution.