Evaluation of Fatigue Properties and Study on the Fatigue Crack Propagation Behaviour in Welding Material SUS309 for Hydraulic Turbine Runner
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概要
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In hydraulic turbine runner, accidents due to fatigue often occur. In this study, cyclic tension-compression tests and fatigue crack growth tests using compact tension specimens under the stress ratio R-constant were carried out for welding material SUS309, in order to clarify fatigue properties, fracture mechanisms, fatigue crack growth and closure properties. The test results are summarized as follows : (1)The S-N curve of welding material SUS309 used in this study has narrow scatter and the tension-compression fatigue strength was lower than the test data of the stainless cast steel SCS6 used as hydraulic turbine runner material. (2)From SEM observation of the fracture surfaces, crack initiation sites were found to be surface slip, and the casting defect in the bond region. (3) Fatigue crack growth rates of the specimens which is the vertical and the parallel to welded direction could be correlated with the stress intensity factor range ΔK in the Paris's law. (4)It is considered that threshold stress intensity factor range ΔKth is influenced by plastic zone and grain size, and the ΔKth of parallel direction specimen is lower than that of vertical direction specimen.