Effect of Ni addition on microstructure and mechanical properties of high nitrogen martensitic stainless bearing steel

High-nitrogen martensitic stainless steel (HNMSS) is increasingly recognized for its excellent strength-ductility balance and superior pitting resistance, largely attributed to the solid solution strengthening effect of nitrogen. Despite significant advancements in enhancing its mechanical properties, the precise relationship between alloying elements, particularly nickel (Ni), and microstructural evolution remains insufficiently understood. The role of Ni in HNMSS was investigated by examining the effects of two different Ni contents on microstructure and deformation mechanisms. A combination of mechanical testing and microstructural characterization was employed to assess the materials’ mechanical properties and phase transformations. The key findings reveal that the steel with higher Ni content exhibits improved mechanical performance, primarily due to an increased volume fraction of retained austenite, which activates both transformation-induced plasticity and twinning-induced plasticity effects. The microstructure after deformation forms a similar multilayer core-shell structure, with twinning martensite enveloping the softer austenite, which effectively avoids the risk of cracking caused by direct collision of martensitic variants.