Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr–7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/_Ag/AgCl, and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/_Ag/AgCl.

钝化度决定了高合金不锈钢的耐腐蚀性和稳定性，并且通常认为由于Cr（VI）物种的形成和溶解，钝化击穿在固定电位下发生。在这项工作中，对在1 M NaCl溶液中的25Cr-7Ni超级双相不锈钢的研究表明，钝化击穿是钝化膜在电位范围内的连续降解进程，与快速Cr溶解和去除之前的Fe溶解增强有关。的氧化物。击穿涉及钝化膜和下面的合金表面层的结构和组成变化，以及取决于阳极电势的选择性金属溶解。在1000 mV / _{Ag / AgCl}处发生钝化击穿，铁在铁素体上的溶解度比奥氏体相高。随着电势的增加，钝化膜变得更厚但密度更低，而下面的合金表面层变得更致密，表明镍和钼富集。Cr的快速溶解发生在≥1300mV / _{Ag / AgCl处}。