Abstract
This study aimed to examine the effect of ultrasonic shot peening (USP) process on the fatigue strength of stainless cast steel JIS SCS6 for hydraulic turbine runner. Fatigue test was carried out in laboratory air room temperature using the specimens which was treated USP (USP specimen) and was not (Virgin specimen). It was found that the modified layer formed by USP process had high hardness and compressive residual stress. The fatigue strength of USP specimen rose about 60% in comparison with Virgin specimen. The fatigue crack in each type specimen was observed in detail by using plastic replica technique. The fatigue crack initiation life of USP specimen was more extension than that of Virgin specimen. The fatigue crack propagation rate of USP specimen was lower than that of Virgin specimen. The modified layer formed by USP process affects the fatigue crack initiation life and the propagation rate. The two reasons are the factor of the improvement of the fatigue strength by USP process.
