Electrochemical analysis on the potential decay behavior of Fe-20Cr stainless steels in sulfuric acid solution

Potential decay behavior of Fe-20Cr alloy was examined by potential decay test, X-ray photoelectron spectroscopy, and Mott-Schottky analysis. The potential decay behaviors characterized by a short plateau followed by 1st decay and a long plateau followed by 2nd decay to an active state were closely associated with the duplex layer structure of passive film. We demonstrate that the short plateau followed by 1st decay is due to rapid dissolution of outer non protective Fe(III) enriched (Fe, Cr) oxide/Cr(III) hydroxide layer, whereas the long plateau followed by 2nd decay is attributed to slow dissolution of inner protective Cr(III) enriched (Fe, Cr) oxide layer. •We identify the cause of the characteristic potential decay behavior of stainless steels.•Characteristic potential decay behavior is due to the duplex layer structure of passive film.•Each potential drop results from a dissolution of outer and inner oxide layer respectively.