Passivation Behaviors of Super Martensitic Stainless Steel in Weak Acidic and Weak Alkaline NaCl Solutions

The passivation behaviors of super martensitic stainless steels (SMSS) were studied by polarization curves at passive potential of −0. 1 V and in various NaCl solutions, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) analysis. Electrochemical test results showed that, in alkaline solutions, passivation region width was wider, passivation current was smaller, and polarization resistance was greater; thus, the passive film of SMSS in alkaline solutions had better passivation behaviors than that in acidic solutions. The polarization curve and EIS of samples SMSS1 and SMSS2 were also used to study which sample had better passivation behaviors. All results demonstrated that passive film structure of SMSS1 sample was more stable, and capacity of passive film was enhanced. The impact of alloying elements on the passive film (SMSS) passivation capability was also discussed by XPS depth profiling, and XPS depth profiling showed that the composition of the passive film was mainly composed of Fe-oxide and Cr-oxide. So the passive film structures were mixed layers of Fe-oxide and Cr-oxide. Fe oxidation product and Cr oxidation product would help to improve the protective property of passive film, which could promote the formation of a passive film structure more stably and densely.