Study On Microstructure And Stress Deformation Control Of Electron Beam Welded Joints Of High Carbon And High Chromium Stainless Steel

High-carbon high-chromium stainless steel is a martensitic stainless steel containing various alloying elements such as Cr,Mo,and Ni.The carbon content is about 1%.It has high hardness,excellent wear resistance and corrosion resistance.It is widely used in many industrial fields such as machinery,construction,ships,etc.However,the welding stress and deformation,which are caused by the welding of high carbon and high chromium stainless steel,will have an impact on the mechanical structure.This thesis aims to study the angular deformation through the simulation of finite element method and the apply of the multi-beam process.Besides,the microstructure and mechanical properties of high carbon and high chromium stainless steel welded joints are also studied by means of pre-weld and post-weld heat treatment.The finite element simulation is carried out by ABAQUS software,which analyzes electron beam welding of high carbon and high chromium stainless steel.The "nail-shaped" weld shape of the electron beam welding pool is simulated through the composite heat source model composed of Gaussian surface heat source and cone heat source.According to the analysis and calculation of the temperature field and stress field distribution of the penetration structure and the non-penetration structure,which show that the residual stress of the nonpenetration structure is larger and the transverse residual stress and the longitudinal residual stress are more concentrated.The actual welding angle deformation of the penetration structure and the non-penetration structure was measured and analyzed,and it was concluded that the angular deformation of the electron beam welded joint under the penetration structure was 0.6°,and the angular deformation of the electron beam welded joint under the nonpenetration structure was less than 0.8°.The structural angular deformation is smaller than that of the non-penetration structural angular deformation.Using the multi-beam welding process,the welding angle deformation is 1.4° without auxiliary heat source;the welding angle deformation of adding auxiliary heat source before welding is 1.1°;the auxiliary heat source welding deformation angle after welding is 0.6°,and the multi-beam welding process is obtained.The corner deformation caused by welding can be effectively reduced.Depending on the effect of pre-welding heat treatment on the microstructure and properties of high-carbon and high-chromium stainless steel electron beam welded joints,it shows that the microstructure of high-carbon and high-chromium stainless steel in the annealed state is the dispersed carbide,which are particles on the ferrite matrix.After the quenched and tempered processing,the dispersed carbide is composed of tempered martensite and retained austenite.And the solid solution of carbide particles occurs,the number of particles decreases and the size increases.The microstructure of the weld area of the welded joint is composed of martensite and retained austenite,and carbon and alloying elements exist in it in the form of supersaturated solid solution.After the welding heat-affected zone undergoes the welding heat cycle,part of the carbide particles dissolves and dissolves into the matrix structure,causing the solid solution strengthening of the structure.The undissolved carbide particles are distributed on the matrix and the size is further grown.High carbon and high chromium stainless steel can effectively improve the hardness of the base metal and the welding heat affected zone after pre welding heat treatment.The hardness of the base metal is increased to 386 HV,an increase of 60%,and the hardness of the heat affected zone is increased from 588 hv to 780 HV,an increase of 35%.At the same time,the tensile strength of the welded joint is also increased by 20%,but the plastic deformation ability of the joint is reduced.Based on the post-weld tempering heat treatment of high carbon and high chromium stainless steel electron beam welded joints in the quenched and tempered state,it shows that the post-weld tempering heat treatment can promote the precipitation of supersaturated solid solution carbide particles in the matrix structure.The average size of carbide particles decreases from 0.8-1.2 ?m in the quenched and tempered state to 0.6-1.0 ?m in the tempered state after welding.Postweld tempering heat treatment also improved the mechanical properties of the welded joint,increased the nano hardness in the fusion zone and heat affected zone of the welded joint,increased the tensile strength of the joint by 33%,increased the elongation after fracture from 2% in the quenched and tempered state to 3.5%,increased the bending strength by 13%,increased the deflection by 20%,and effectively improved the strength and plasticity of the welded joint.The wear resistance of the post-weld tempering heat treatment joint is improved.The friction and wear amount are decreased from 6.7 mg to 3.9mg.Therefore,the fatigue limit of the post-weld tempered high carbon and high chromium stainless steel electron beam welded joint is up to 420 MPa.