Potential Role of Grain Boundary Misorientation in the Non-monotonic Corrosion Behavior of Cr16Mn8NiMoN Metastable Austenitic Stainless Steel under Gradient Tensile Deformation

In this paper, the microstructure evolution of Cr16Mn8NiMoN metastable austenitic stainless steel under gradient tensile deformation with strain ranging from 10%–40% was systematically investigated, and its influences on microstructural transformation and corrosion resistance were further analyzed. The results indicate that the tensile specimen with 20% deformation is in the critical state of microstructural transformation. Dislocation proliferation, strain-induced martensite formation and grain refinement collectively reduce the corrosion resistance of the metastable austenitic stainless steel. Compared with the corrosion resistance degradation at 30% strain, the decline in corrosion resistance at 20% strain is mainly attributed to the increased surface energy difference, higher fraction of strain-induced martensite, and a larger number of low-angle grain boundaries. With the increase of strain, the variation of pitting nucleation sites is closely correlated with the rise in dislocation density and the growth of strain-induced martensite. Based on the above correlation, grain boundary misorientation is identified as a potential key microstructural parameter, which may play an important role in multi-factor coupling. This study provides an important theoretical basis for the precise optimization of the strength and corrosion resistance synergistic performance of metastable austenitic stainless steel via deformation processes.