水車ランナ材SCS6Xの疲労強度特性評価

抄録

Hydraulic power generation facility has a turbine runner for converting the kinetic energy to the rotation work, and the stainless cast steel SCS6 has been used as the material of the turbine runner. However, a fatigue damage in hydraulic turbine runners has become a problem in recent years. In order to response to this problem, it is thought to alternate a material of SCS6 for stainless cast steel SCS6X, but there are few researches about the fatigue strength characteristics of SCS6X. Therefore, in order to clarify fatigue properties and fracture mechanism of stainless cast steel SCS6X, a plane bending fatigue test and a tension-compression fatigue test were performed for this material and the fracture surface and the fatigue crack growth behavior were observed in detail. The test results are summarized as follows : (1)The S-N curve of SCS6X used in this study has wide scatter and the fatigue strength of the tension-compression was lower than that of the plane bending fatigue test. (2)According to the results of SEM observation for the fracture surfaces, crack initiation sites were found to be the casting defect, which consist dendritic phase and pore.(3)It is possible to evaluate the fatigue life of SCS6X by using the casting defect size (area)^1/2 and the initial stress intensity factor calculated by defect size.