Electrochemical and microstructural characterization of a precipitation hardened 17-4 steel in different environments

In this study, an in-depth electrochemical characterization of a precipitation hardened 17-4 stainless steel (SS17-4PH) was carried out in combined acidic, alkaline, and chloride environments. The characterizations were carried out through polarization-EIS analysis, Mott-Schottky analysis to characterize the semiconducting properties of the thin oxide films, and a post-mortem scanning electron microscopy (SEM-EDX) analysis to reveal the morphologies after anodic polarization. The electrochemical measurements revealed that the corrosion rate of SS17-4PH samples in acidic-chloride solutions is higher than the sample polarized in only NaCl or NaOH solution. From the Mott Schottky results, the straight lines with a positive slope obtained for the steel samples in different test media show that there is no change in the semi-conducting properties of the passive film. For samples polarized in acidic-chloride medium, the microstructural examination revealed the formation of a foot-like pit and zig-zag degradation structure. This was attributed to the presence of acid in the test media, and the deposition of corrosion products on the sample surface.