Effect of boron on dissolution and repairing behavior of passive film on S31254 super-austenitic stainless steel immersed in H2SO4 solution

The impact of boron on the dissolution and repairing behavior of passive films formed on S31254 super-austenitic stainless steel (SASS) was investigated. SASS was immersed in 0.5 mol/L of H2SO4 for 0, 2, 6, 10, and 14 days to explore the evolution of the passive film. The electrochemical impedance spectroscope (EIS), the Mott–Schottky analysis, and X-ray photoelectron spectroscope were utilized to analyze the semiconductor properties and compositions of the passive films. EIS showed a decrease and consequent increase over 14 days; the same pattern was observed for Cr2O3 and Cr/Fe. However, the defect density of the passive film exhibited a reverse trend. The variation in film thicknesses indicated that the passive films possessed dissolution and repairing behavior. SASS passive film had a double-layer structure; the outer layer was found to be rich in Fe3+ and Cr(OH)3, but low on Mo6+, while the inner layer was rich in Cr2O3 and low in Mo4+. The addition of boron increased the corrosion resistance and could promote the efficiency of the passive film repair, likely by promoting the migration of Mox+, which promoted the repairing of the passive film.