Corrosion resistance investigation of Cronidur30 high-nitrogen martensitic stainless steel by quasi-in-situ SKPFM and DFT calculation

Nitrogen alloying improves the mechanical performance of martensitic stainless steel, while tempering is required to mitigate brittleness and enhance processability. However, tempering-induced microstructural changes markedly influence the semiconducting properties of the passive film, thereby affecting corrosion resistance. This work examines the passive film of high-nitrogen martensitic stainless steel (HNMSS) tempered at different temperatures. Tempering at 200 °C yields the highest pitting potential (461.28 mV), attributed to the transformation of CrN to Cr 2 O 3 , which enhances film protection. At higher temperatures, abundant Cr-rich nitride/precipitate (M 2 N) depletes N and Cr in the matrix. The increase of precipitate/matrix interfaces and defect density in the passivation film impairs pitting corrosion resistance. First-principles calculations and quasi-in-situ scanning Kelvin probe force microscopy reveal that M 2 N precipitates exhibit a higher Volta potential and the highest work function than those of the matrix, acting as cathodes to accelerate localized matrix dissolution, which reduces nitrogen incorporation into the passive film. These findings clarify the relationship of tempering, microstructure, and corrosion in the HNMSS.