Study On 2205 Duplex Stainless Steel With Twin-CMT Welding And Numerical Simulation

The ferrite/austenitic（α/γ）ratio imbalance of duplex stainless steel welded joints severely limits the use of duplex stainless steel.Cold Metal Transfer（CMT）,developed in recent years,is a new type of welding technology,which has many welding advantages and has high research value.In this paper,the twin-CMT welding technology is applied to the welding of 16 mm thick2205 duplex stainless steel with ER2209 solid welding wire to study the droplet transfer behavior,current-voltage waveform control characteristics and weld formation characteristics of the welding process.Then the multi-pass welding process in different twin-wire matching mode was developed.The temperature field and stress field of 2205 welding process were studied by numerical simulation.The high-speed camera and welding electric signal synchronous acquisition system is used to analyze the real-time current and voltage waveform characteristics of the welding process of“pre-pulse-after-filament CMT”and“front filament CMT-post-filament CMT”droplet transfer process.The pulsed droplets undergo a coarse-drop-jet transition process with the pulse front wire current increases,and the CMT droplet transfer mode is basically unchanged;the droplet flow frequency of the pulsed wire is significantly higher than the CMT transition frequency;and the four-factor three-level weld Forming orthogonal test found that different twin-CMT matching methods obtained good weld forming parameters.Keeping front/rear wire current 270/155 A,and controlling welding speed to change heat input.The front wire mode is changed between pulse and CMT,the rear wire is CMT.Then two modes in 16mm thick V-groove multi-pass welding test results are observed.the microstructures of different regions of 2205 duplex stainless steel（DSS）welded joints were observed by OM,SEM and XRD.The mechanical properties（stretching,low temperature impact,microhardness）were tested.The impedance,polarization curve,and micro-area electrochemical（SVET）of different regions of the joint measure the local current density is obtained.The test results as following:（1）There is a large deviation in the comparison of the welded joints.The microstructure of the heat-affected zone and the weld zone is quite different,and the unevenness of the structure occurs in the top,middle and bottom parts of the weld zone.（2）The characterization results of mechanical properties show that the welded joints with tensile strengths_b≥600 MPa,d≥20%and low-temperature impact energyA_k≥60 J obtained under both processes,which meets the engineering welding requirements.（3）The low temperature impact toughness of the pulsed wire is better than that of the front wire CMT process,but the corrosion resistance is weak.The pulse front wire increases the heat input so that there are moreγ₂ in the weld and heat affected zone,which enhances toughness and weakens corrosion resistance.According to the characteristics of the double-wire CMT heat source,the finite element model of 2205 duplex stainless steel was established based on the thermo-elastic-plastic theory.The numerical simulation results were basically consistent with the thermal cycle test results,which verified the rationality of the finite element model.The numerical simulation results of anti-deformation show that the anti-deformation is beneficial to reduce the external constraint,reduce the lateral residual stress about 210 MPa,and obtain a reasonable deformation control effect when the anti-deformation angle is 1³°.