低合金鋼SCM435窒化材の疲労強度とfish-eyeを伴う内部破壊過程

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This paper describes the fatigue strength and subsurface crack initiation behaviour in gasnitrided low alloy steel, SCM 435. Cantilever type rotating bending fatigue tests have been conducted at room temperature in laboratory air using smooth specimens with different nitrided depths, and the effect of nitrided depth on fatigue strength was evaluated and the fracture process with fish-eye was studied on the basis of detailed fractographic examination. The fatigue strength increased with increasing nitrided depth and could be evaluated by the equation of σ_w/σ_n=D/(D-2d_n), where σ_w is the fatigue limit of nitrided materials, σ_n is the maximum applied stress in the core at the fatigue limit, D is the specimen diameter, and d_n is the nitrided depth. Subsurface crack mitiation was observed in all nitrided specimens regardless of nitrided depth and stress amplitude and a fish-eye was always seen with an inclusion at the crack initiation site. Based on some detailed analyses of fish-eye, it was indicated that the fatigue process of nitrided specimens was dominated by the crack growth from inclusion to the formation of fish-eye.
一般社団法人日本機械学会の論文
2001-01-25