312 ショットピーニング処理ADI材の長寿命域高サイクル疲労特性(OS1-2 高強度材の超高サイクル疲労(2))(OS1 高強度材・表面改質材の疲労と破壊)  [in Japanese] 312 High Cycle Fatigue Property of Shot peening Treated ADI in Long Life Fatigue  [in Japanese]

Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) with shot-peening (SP) treatment, and influences of the SP treatment on fatigue property and fracture morphology were investigated. As results, the improvement of fatigue strength of shot-peened ADI specimens was identified before the region of the 10^7cycles. Therefore, the S-N diagram of shot peened ADI and fatigue strength of non shot-peened ADI cross at near 10^8cycles. It is expected that the SP treatment results not only the high level work hardening and the high level compressive residual stress on the surface layer of the specimens, but also the decrease in casting defeats in near surface. Generally they lead a considerable improvement of fatigue strength. So the hardness distribution in the surface layer of the SP treated specimens was measured. Furthermore, the fatigue fracture mechanism was discussed in detail from fracture morphology that obtained by observation of crack initiation site with a scanning electron microscopy.