Evaluation of creep-fatigue crack propagation for 316FR stainless steel welded joints
Takahashi Hiroyuki; Uno Tetsuro; Tanaka Kouichi
Abstract:Low carbon-medium nitrogen 316 stainless steel (316FR) with improved creep strength was developed for structural material for the demonstration fast breeder reactor (FBR). Fatigue, creep-fatigue and creep crack propagation tests have been conducted using CT specimens of 316FR welded joints at 650 degree C in order to investigate the applicability of crack propagation evaluation methods to welded joints. The results obtained are as follows. The fatigue J-integral range of welded joints could be estimated using material data of the base metal by the simplified J-integral estimation methods, the reference stress method and the GE/EPRI method, when the crack opening ratio were considered. Heating time (testing time) made a difference in creep-fatigue and creep crack propagation rates estimated by the creep J-integral range. It was considered that the degradation of microstructure (from delta ferrite into sigma-phase) by high temperature aging, which reduced ductility, affected the crack propagation behavior. Key Words:Crack propagation, Creep-fatigue, 316FR stainless steel, Welded joints, J-integral