高Cr-Ni基合金INCONEL625材の壊食特性および疲労特性評価に基づく水車ランナ溶接補修材への適用に関する検討

概要

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In hydraulic turbine runners, accidents due to cyclic loading often occur. In this study, cyclic tension-compression loading tests and fatigue crack growth tests using compact tension specimens under the stress ratio R-constant and repeated two-step load sequences were carried out for welding material INCONEL625, in order to clarify fatigue properties, fracture mechanisms, fatigue crack growth and closure properties. The test results are summarized as follows : (1)The volume loss rate of INCONEL625 improves 30% than that of SUS309 by using a test apparatus an ultrasonic vibratory cavitation device. (2)The S-N curve of welding material INCONEL625 used in this study has narrow scatter and the tension-compression fatigue strength was higher than the test data of the stainless cast steel SCS5 used as hydraulic turbine runner material. (3)From SEM observation of the fracture surfaces, there were two types of fracture origin ,that indicate fatigue crack initiation by slip deformation at surface and from the casting defects. (4) Fatigue crack growth rates of the specimens which are the vertical and the parallel to welded direction under the stress ratio R-constant could be correlated with the effective stress intensity factor range ΔKeff. And ΔKeff under varying loading was the same as that under the stress ratio R-constant. Crack propagation rate under varying loading could be predicted by fatigue crack growth data under constant amplitude loading.