G0310601 超音波ショットピーニング処理による発電用水車ランナ材SCS6の疲労強度改善(材料力学部門一般セッション:表面処理・改質)

Abstract

In this study, the effect of ultrasonic shot peening (USP) treatment on the fatigue strength of stainless cast steel SCS6 for hydraulic turbine runner was investigated carrying out plane bending fatigue tests for USP treated material and untreated material. According to the fatigue test results, it was clear that the fatigue strength of SCS6 was improved by USP treatment, especially, the fatigue limit was 60 % improved. The reasons of the fatigue strength enhancement are thought to be the effects of high hardness and compressive residual stress generated by USP treatment. In addition, the effectiveness of USP treatment on the fatigue strength of SCS6 having the fatigue crack was also examined, The specimen was made by performing USP treatment after creating the fatigue crack of about 1 mm by using the plane bending fatigue test machine. The results of the fatigue tests indicated that USP treatment delayed the fatigue crack propagation compared with the case of USP untreated, The main reason of above results was that the fatigue crack propagation resistance was increased by the compressive residual stress generated by USP treatment, in other words, the stress intensity factor K was decreased by that factor. According to these results, it can be said that USP treatment is very effective method to improve the fatigue strength of SCS6.