Research On Weld Performance Optimization Of AISI 430 Ferritic Stainless Steel Via Deep Penetration TIG Welding And Pivotal Techniques

Deep penetration TIG welding is a recently developed keyhole welding process,which adopts large welding current and unrestrained arc.This process enables single pass welding,without filler metal addition or joint preparation.The equipment cost and production cost are low and it is convenient for site welding.Deep penetration TIG process has great potential in the welding of medium thickness plate.Due to the large amount of heat input of deep penetration TIG welding,when applied to some materials,the microstructure and performance of the joints are unsatisfactory.That limits the application of deep penetration TIG welding.8 mm thick AISI 430 ferritic stainless steel was successfully welded via deep penetration TIG process.The phase composition of the joints was analyzed.The mechanical properties and corrosion resistance of the joints were tested.Due to the weld pool volume of deep penetrating TIG welding is large,the flow behavior is complex.In order to further understand the stability of the molten pool and the formation of defects,titanium tracer and 3D reconstruction method were combined to study the flow behavior of deep penetration TIG weld pool in 3D scale.Three joint performance improved methods were investigated.High-frequency welding current was adopted to decrease the heat input.AISI 304 austenitic stainless steel interlayer was added to increase the austenitic phase in the molten pool.The postwelding heat treatment process was introduced to improve the tensile properties of the joints.The fusion zone was composed of columnar ferrite grains.Retained austenite distributed along the grain boundaries.Granular martensite was observed inside the ferrite grains.The joint reached same tensile strength as joints produced via SMAW,GMAW and GTAW process.The corrosion resistance properties of the joint degraded.Ideal deep penetrating TIG weld pool was composed of three regions,which were Marangoni convection,a transition layer,and a convection driven by Lorentz force,respectively.Compared with the constant-current welding process,high-frequency pulse current significantly reduced the heat input,the weld decreased,the retained austenite content increased and the width of the thermal influence zone reduced.The tensile properties and impact performance of the joints were obviously improved,and the corrosion resistance of joints had no obvious change.Due to the addition of austenite interlayer,a large amount of primary austenite phase generated.Tensile properties and impact properties of the joint improved,and the corrosion resistance had significant improve.After post welding heat treatment process,the carbide precipitation and martensite rediffused.The tensile properties of the joint were better than that of the base metal.However,the corrosion resistance of the joint had a certain decline.