Effectiveness of Ultrasonic Shot Peening on Stainless Cast Steel SCS6 Containing a Fatigue Crack

In order to investigate the effectiveness of ultrasonic shot peening treatment (USP) as repairing method for SCS6 material with surficial fatigue crack for hydraulic turbine runner, plane bending fatigue tests were carried out for USP treated SCS6 containing a surface fatigue crack with 1 mm in length and the fatigue crack propagation after USP was observed by a plastic replica method. As a result, the fatigue crack propagation life of SCS6 containing a surface fatigue crack was dramatically improved by USP treatment. Furthermore, the initial effective stress intensity factor ranges were calculated in the USP treated and untreated SCS6 containing a surface fatigue crack, respectively. According to the calculation, it was clear that the surficial fatigue crack could be harmless under the condition that the calculated initial effective stress intensity factor range considering the stress opening a fatigue crack, which was acquired by the unloading elastic compliance method, was less than the threshold of effective stress intensity factor range. Therefore, USP treatment is effective for repairing method of SCS6 containing surficial fatigue crack for hydraulic turbine runner.