Creep-Fatigue Life Evaluation of HR6W (23Cr-45Ni-6W) Base Metal and Welded Joint

Creep-fatigue life evaluation method for HR6W base metal and welded joint was examined based on the results of uniaxial fatigue and creep-fatigue tests using smooth specimens at 700 and 750℃. Regarding the base metal, creep-fatigue life evaluation by linear damage rule was carried out using the creep-fatigue test results with strain holding time up to 10 hours. In the case of time fraction rule, failure criterion with intersection at (Df , Dc) = (0.1 , 0.1) gave conservative prediction even in the case of long holding time of 10 hours. In the case of ductility exhaustion model, on the other hand, life reduction with increase of strain holding time was expressed well including the dependence on strain range. With respect to the welded joint, fatigue life was shorter than that of base metal although cracks were observed at base metal near fusion line under all test conditions. From both the FEM analysis results and DIC (digital image correlation) strain measurement during the test, this was found to be caused by strain concentration due to the longitudinal variation of stress-strain behavior in the welded joint. Fatigue life of welded joint could be predicted well by using the base metal fatigue curve and the strain concentration factor obtained from FEM analysis.