Development Of Active Flux For A-TIG Welding Of 430 Ferritic Stainless And Study On Microstructure And Properties Of Joints

Ferritic stainless steel is widely used in automobiles,sea transportation and home appliances fileds due to its advantages of low linear expansion,high thermal conductivity,and excellent corrosion resistance.However,when TIG welding is used to weld thick-plate ferritic stainless steel which required opening grooves and multi-pass welding,it is easy to cause excessive accumulation heat input resulting in excessive growth of ferrite grains in the heat-affected zone of ferritic stainless steel joint,which reduces the strength and toughness of ferritic stainless steel joint,and it limits the application of thick plate ferritic stainless steel.Using A-TIG welding can effectively reduce welding times and high temperature residence time when welding thick austenitic stainless steel,and improve the microstructure and mechanical properties of austenitic stainless steel joints.So this subject takes the thick plate（6 mm）430 ferritic stainless steel as the research object,and selects A-TIG welding as the weld method,research on the effects of welding current,welding speed,active flux kinds and proportion on the macroscopic morphology,microstructure,mechanical properties and corrosion resistance of 430 ferritic stainless steel joints.The following research results were obtained:1.Compared with no active flux,the addition of a single active flux can increase the depth of penetration and Depth/Width of 430 ferritic stainless steel A-TIG joints to varying degrees,and reduce the fusion width.The effect of the active flux on increasing the depth of penetration is Si O₂>Mn O>Cr₂O₃>Ca O>Ni O>Mg O>Cu O>Ti O₂>Without active flux.Among them,the depth of penetration without active flux TIG welding joint is 2.40mm,the width is 10.95mm,and the Depth/Width is 0.219;the best effect is obtained by Si O₂ active flux,the depth of penetration A-TIG joint is 4.95mm,and the depth/width ration is 0.475 and the depth of penetration and the Depth/Width ratio of A-TIG joint are 2.06 times and 2.17 times of TIG joint,respectively.2.Obtained the best proportion of active flux is 75%Si O₂+25%Cr₂O₃,can directly weld penetrate 6mm thick 430 ferritic stainless steel.The microstructure in the welding seam center of TIG and A-TIG joints of 430 ferritic stainless steel is ferrite+martensite duplex microstructure,and the heat-effect zone is divided into coarse-grained zone and fine-grained zone.More lath martensite with high hardness and toughness was formed in the weld seam center of A-TIG;A-TIG butt joints can obtain a finer heat-affected zone structure than TIG butt joints,so the hardness of the weld bead center and heat-affected zone of A-TIG joints is higher than that of the corresponding regions of TIG joints.3.The fracture morphology showed that the tensile samples of TIG and A-TIG joints of 430 ferritic stainless steel both fractured in the heat-affected zone,The ferrite grains of the A-TIG joint fracture were obviously finer than those of the TIG fracture.Meanwhile,the addition of the active flux increases the tensile strength of the A-TIG butt joint by 5.69%compared with the TIG butt joint,and the fracture mode of butt joint changed from brittle cleavage fracture to quasi-cleavage fracture,indicating that the addition of active flux improved the toughness of 430 ferritic stainless steel A-TIG joint.Furthermore,the addition of active flux can improve the seawater corrosion resistance and the pitting resistance of Fe Cl₃ of 430 ferritic stainless steel A-TIG joint.