Promoted rotary bending fatigue performance of a martensitic stainless steel by surface gradient-nanostructuring

Surface modification is an effective approach for enhancing the fatigue performance of metallic materials. In this study, a gradient microstructured surface layer with nanolaminates is fabricated on a 13Cr–4Ni low carbon martensitic stainless steel using surface mechanical rolling treatment (SMRT). The average grain size is refined to ∼66 nm in the topmost surface layer and gradually increases with depth. The microhardness reaches ∼5.5 GPa in the topmost surface layer, significantly higher that of as-received samples (∼3.8 GPa). And rotary bending fatigue tests reveal a ∼50 % increase in the fatigue limit compared to as-received samples. Fatigue mechanism analysis indicates that the improved fatigue performance is primarily attributed to the suppression of surface crack initiation and propagation by the gradient nanostructure.