Research On Electron Beam Welding Simulation And Welding Process For Port Stubs Of Vacuum Vessel Sectors With Large Complex Contour

Human survival and development are closely related to energy.However,with economic development,all humanity are faced with the contradiction between the increasingly urgent energy demand and the decreasing resources.Controlled fusion energy is considered as one of the most ideal new energy.The Chinese Fusion Engineering Test Reactor,which is under construction by China,is the next-generation magnetic confinement fusion test resctor.The double-wall shell vacuum vessel is one of the core components of the magnetic confinement fusion test reactor,with functions of establish,maintain,support,provide an ultra-high vacuum environment,assist heating and diagnosis.Therefore,the vacuum vessel needs to have an extremely high reliability.The port stubs are the connecting section between the interior of the vacuum vesssel and the external ports.Its outline is complicated,and it is difficult to manufacturing by hot pressing.This study supported by the special project of the International Thermonuclear Fusion Experimental Reactor Program "Research on the key technology of vacuum vessel forming,welding and assembly",the method of combining numerical simulation and welding tests were used to study the welding deformation control theory and the key technical issues of the quality control of the thick plate electron beam welding(EBW)joint,for the vacuum vessel complex outline port stubs.Firstly,based on the welding simulation method of thermo-elastic plastic theory,the dynamic process of EB butt welding of 50mm thick ultra-low carbon austenitic stainless steel extracted from the vacuum vessel port stub was simulated,the thermal cycle curve and residual stress distribution have being studied to reveal the forming mechanism of high energy density welding for the thick plate.Secondly,the inherent strain of the welding seam and heat affected zone of the local model after single pass welding were extracted,and applied to the welding simulation software Sysweld-Weldplanner,which was based on the inherent strain theory.The influence of the welding sequence and the clamping conditions on the deformation and residual stress during the welding process of the vacuum vesssel port stubs were discussed.Finally,the optimal welding sequence and clamping conditions were obtained,and the reliability of the simulation was verified by the actual welding of port stubs.The welding procedure of ultra-low carbon austenitic stainless steel thick plate EBW was studied.The parameters such as focusing current,welding speed and beam current were optimized by continuous adjust,and the appropriate parameters were found.By comparing with the properties of welded joints with and without beam oscillation,the welding seam forming has been improved,and obtained a uniform parallel welding seam.The non-uniform characteristics of the thick plate EBWed joints were analyzed.Along the penetration direction,the difference and change rule of grain size,grain composition,element composition,microhardness and mechanical properties(tensile strength and impact strength)of welded joints were analyzed in different sections of welded joints,and the correlation between microstructures and mechanical properties were explored in depth.The study revealed the relationship between the solidification rate,solidification mode,microstructures and mechanical properties of thick plate austenitic stainless steel EB Wed joints.Finally,the process optimization plan and the tooling design optimization of EBW technology were proposed.It provided theoretical basis and technological support for the development of the port stubs of the vacuum vessel,and had engineering application value.