Hydrogen induced degradation mechanism of passive film in 2205 duplex stainless steel

The presence of hydrogen poses a significant threat to the integrity of the passive film on duplex stainless steels (DSS), which is crucial for their corrosion resistance. However, a detailed understanding of the persistent, long-term damage after hydrogen removal remains insufficient. This study investigates the degradation mechanism of the passive film on 2205 DSS induced by electrochemical hydrogen charging. Even after 120 h of immersion in 3.5 % NaCl solution, which removed most diffusible hydrogen, the corrosion resistance of pre-charged specimens remained significantly inferior to that of uncharged counterparts. This indicates hydrogen induces lasting, potentially irreversible damage to the passive film. Comprehensive analysis reveals that hydrogen ingress promotes the reduction of Fe 3+ and facilitates the transformation of protective oxides into hydroxides. This compositional shift is directly correlated with a substantial increase in donor density (N D ) and defect density within the film, as determined by Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). The resultant film exhibits lower impedance and higher anodic activity. A degradation mechanism based on the point defect model is discussed, wherein the hydrogen-induced alteration of the passive film structure could potentially facilitate the interaction with aggressive ions such as Cl - .