Research Of The Activating Fluxes For A-TIG Welding Of Austenitic Stainless Steeland The Microstructure And Properties Of As-welded Joints

Austenitic stainless steel is widely used in construction,food,machinery and other related fields due to its low specific strength,excellent plasticity,corrosion resistance and non-magnetic properties.In industrial applications,it is necessary to connect stainless steel in order to obtain more complicated components.TIG welding is one of the most common welding methods.The traditional TIG method is prone to overheating and large deformation during the implementation process,which seriously affects the connection quality.Compared with the former,activating flux tungsten inert gas welding?A-TIG?energy concentration,welding deformation is small,and can partially solve the problem of deformation and overheating.Therefore,in this study,A-TIG was used to join the austenitic stainless steel.The relevant fixtures were designed to further reduce weld distortion.The effects of different activating fluxes on the joint structure were studied and the optimal process recipe was determined.Finally,a comparative analysis was carried out to summarize the effects of the addition of activating fluxes on the structure and properties.There are many activating fluxes commonly used in A-TIG welding.In this study,eight kinds of oxides,such as SiO₂,Cr₂O₃,MgO,Fe₂O₃,TiO₂,MnO₂,Y₂O₃,and La₂O₃,were selected for the A-TIG welding test of single component activating fluxes.By comparing the macroscopic morphology,penetration and microstructure of the joint,the three activating fluxes with the best effect were selected:SiO₂,TiO₂ and Cr₂O₃.Based on this,orthogonal experiments of different composite activating fluxes formulations were carried out.Compared to the one-component activating fluxes,the composite formulation activating fluxes can obtain a weld with a larger penetration.By analyzing the morphology of the joint,50%SiO₂+50%Cr₂O₃ was selected as the best activating fluxe formulation.The effects of the addition of activating fluxes on the macroscopic morphology,microstructure and mechanical properties of the joints were investigated.The microstructures of 304 stainless steel and 321 stainless steel are austenite matrix+?ferrite.The ferrite of the welded joint fusion zone is worm-like,and the ferrite in the weld zone is bone-like.The addition of the activating fluxes slightly reduces the grain size of the welded joint and slightly increases the content of Si and Cr in the weld.The tensile properties of the joints are slightly improved.The curved specimens were free from cracks.The microhardness shows the same distribution pattern:the lowest at the weld,the gradual increase near the fusion line,and the decrease to the base metal area.The effects of activating fluxes on the corrosion resistance of welded joints were investigated by conducting electrochemical corrosion tests and intergranular corrosion tests.Studies have shown that the addition of activating fluxes reduces the self-corrosion current and improves the corrosion resistance.However,the welded joints obtained by the two welding methods have very small self-corrosion currents and excellent corrosion resistance.The addition of the active agent has little effect on the intergranular corrosion performance,and both joints have good resistance to intergranular corrosion.