Experimental Study On Thin Hastelloy Plate Laser Welding With Filler Wire

Under the influence of energy shortage and environmental pollution,nuclear power is increasingly valued by countries due to its many advantages.China is also focused on the development of the advanced large passive water reactor CAP1400 with China's independent intellectual property rights.Compared with AP1000,CAP1400 reactor installed more power,higher security and reliability,and the material of nuclear reactor coolant pump can was Hastelloy C-276,with the thickness of 0.3~0.7 mm,the length of even longer than 4000 mm,the diameter of more than 600 mm,the higher diameter precision requirements,which made the can welding formation more difficult.Laser welding could replace argon arc welding process as the important technical of pump can welding formation with the characteristics of more concentrated energy density,smaller welding deformation and better joint performance.But laser welding without filler wire had higher clamping precision and poorer gap tolerance,which was easy to produce negative reinforcement,affecting the overall performance of pump can.In this paper,pulsed laser welding with filler wire technology(LWFW)of thin Hastelloy C-276 plate was studied,the forming mechanism of weld morphology of the laser welding with filler wire and the influence of the laser welding with filler wire process on the microstructure,tensile and electrochemical corrosion performance of the material were revealed,providing theoretical and technical guidance for the manufacture of high reliability nuclear pump can.The main research contents were as follows:(1)Building of laser welding with filler wire experimental platform.According to the 0.5 mm diameter of filler wire,the existing wire feeding equipment was improved,and a cross slider wire feeding nozzle adjusting system was designed so as to meet the fine adjustment of wire feeding nozzle in the Y/Z directions and within a certain range wire feeding angle,providing a technical basis for the laser welding with filler wire experiment.(2)Research on the weld formation.The effects of pulsed laser parameters(single pulse energy,pulse frequency,pulse duration and defocus)and the relative fill amount(wire feeding speed and welding speed)on the weld morphology were studied by single factor experiment.The optimization principle of process parameters was put forward,the relationship between the laser parameters and relative fill amount was obtained.(3)Research of the microstructure of weld joint.Based on the characteristics of Hastelloy C-276 microstructure,the characteristics of microstructure,element distribution and micro-hardness of the weld joint were observed and studied by scanning electron microscopy(SEM),electron probe micro-analyzer(EPMA),energy dispersive X-ray spectrometry analysis(EDS)and hardness tester,which were compared with the microstructure of weld joint by laser welding without filler wire.And the influence of the filler wire on the microstructure of the material was revealed.(4)Research on the tensile and electrochemical corrosion performance of weld joint.The tensile tests of base material and the weld joint were carried out.The influence of laser welding with filler wire on the material tensile properties was obtained.Based on the polarization curves,the electrochemical corrosion resistance of base metal and the weld in neutral and acidic environments were studied.The corrosion mechanisms of base metal and the weld in different environments were studied by laser scanning confocal microscope(LSCM)and energy dispersive X-ray spectrometry analysis(EDS).