High Cycle Fatigue Property Research Of Laser Welded Joints Of Hasteloy C-276 Thin Sheet With Filler Wire

With the development of science and technology,nuclear power has drawn more and more attention due to the shortage of energy.Based on the third generation nuclear power station AP1000,China has developed the advanced large passive water reactor CAP1400 with our own intellectual property rights.The CAP 1400 has the advantage of more power,higher security and reliability.The critical part of CAP1400 reactor is the canned reactor collant pump whose stator can and rotator can is made of Hastelloy C-276 thin sheet by welding.The cans are designed to serve in a long time,so the weld joints of cans should have high quality and reliability.In this paper,respond surface method was applied to establish the regression equation between weld parameters and weld geometry to optimize weld parameters.The weld joints stress distribution was calculated by Finite element method to evaluate fatigue strength.The high cycle fatigue strength of laser weld joint with filler wire were tested by up and down method.The fracture morphology were observed to analyze the crack origination and propagation.The main research contents were as follows:(1)Research on relation between weld parameters and weld geometry.The RSM experiment was designed to evaluate the influence of defocus length,welding speed and feeding speed on weld geometry.(2)Research on weld joint microstructure and participates.Based on the characteristics of Hastelloy C-276 laser weld joints'microstructure,the weld joints were divided into different regions.The distribution and chemical composition of participates were studied by SEM and EDS.And the influence of participates on fatigue strength was studied.(3)Research of stress distribution of weld joints.With help of finite element method software,the stress distribution of weld joints were calculated.The peak stress and local plastic deformation were evaluated.The risk of crack origination which is critical to fatigue life were compared for weld joints with different weld geometries.(4)Fatigue strength and fracture morphology observation.The 2×10~6 cycle fatigue strength of weld joints were tested by up and down method.The crack propagation behaviors were analyzed by fracture morphology observation.(5)Crack origination position and crack propagation path analysis.The cross-section of fracture surface were observed to evaluate the crack origination position and crack propagation path.Based on microstructure and participates,the mechanism of crack origination,the crack propagation in early stage,the crack stable propagation and fracture stage were discussed.