軟窒化処理材におけるショットピーニング効果に関する研究  [in Japanese] Study on Shot Peening Effect of Nitrocarburized Material  [in Japanese]

The authors investigated the refined surface characteristics and fatigue strength of Nitrocarburized (N) materials treated by Electro-polishing (EP), Double Shot Peening (DSP) and Stress Double Shot Peening (SDSP). The results obtained are summarized as follows: (1) Increased hardness with the diffusion layer between the surface and depth of 400 μm by DSP. (2) Remarkably high compressive residual stresses by DSP: Surface residual stres =-701 MPa, Maximum compressive residual stress=-733 MPa. (3) On the loading condition of stress ratio (R)=0, the fatigure limits of DSP and SDSP materials were 33% and 58% higher than that of N material, respectively. However, on the condition of R=-1, these were 28% and 39% higher than that of N material, respectively. (4) Same fatigue limit of both DSP and EP+DSP materials. (5) On the condition of R=0, the fatigue limit becomes high according to the lager compressive residual stress. However, on the condition of R=-1, the above relation is not necessarily valid to yield of the material by the compressive loading stress.