| The good plasticity,toughness and corrosion resistance of 2205 duplex stainless steel are the key elements for its application in many fields such as transportation and chemical industry.However,when the traditional fusion welding method is used,the microstructure transformation of the weld and the imbalance of the two-phase ratio of austenite and ferrite will seriously reduce the performance of the joint.The welding of 2205 duplex stainless steel by narrow gap laser arc hybrid welding can greatly reduce the amount of weld filling and reduce the welding heat input,which is beneficial to the improvement of the solidification structure and performance of the weld.In the process of narrow gap welding of thick plates,defects such as pores and lack of fusion are prone to occur,which affect the performance of the joint.In this paper,for 2205 duplex stainless steel with a thickness of 12mm,the method of alternating magnetic field assisted laser arc hybrid welding is used for welding.Based on the effect of alternating magnetic field on arc morphology and molten pool metal flow,the effect of alternating magnetic field on laser arc hybrid welding on the microstructure transformation of welded joints was studied.The use of a transverse alternating magnetic field of B=20mT,f=50Hz can control the shape of the arc plasma and the flow state of the molten pool while ensuring the good coupling between the arc and the keyhole,thereby solving the defects such as unfused and undercut during the welding process,which improve the welding quality and efficiency.Compared with the non-magnetic field welded j oints,the penetration width and weld area were increased by 11.7%and 20.8%,respectively;the microstructure and grains of the welded joints were more refined.At the same time,the application of the alternating magnetic field changes the energy fluctuation of the molten pool metal,which is conducive to the precipitation of a large amount of intragranular austenite in a non-diffusion type transformation,thereby improving the two-phase comparison of the welded joint.Statistics show that the proportion of austenite in the capping bead,filling bead,overlapping area and HAZ increased by 6.7%,5.5%,13.6%and 4.4%respectively after applying a 30mT alternating magnetic field.The application of an alternating magnetic field of 20mT is beneficial to improve the uniform distribution of alloying elements in the two phases,promote the diffusion and dissolution of Ni and N elements to the γ phase,promote the transformation of α→γ phase and reduce the precipitation of Cr2N.The electron backscattered diffraction results of weld metal and heat affect zone show that the application of 30mT alternating magnetic field makes the two phases of weld metal more balanced,and the texture dispersion is weakened.The Σ3 twin boundaries of the austenite phase in weld metal transform to high angle grain boundaries,the ferrite phase undergoes dynamic recrystallization,and the austenite phase has Cube texture,Copper texture and Goss texture;the two-phase low angle grain boundaries in HAZ increased significantly,and the austenite {112}<113>texture was enhanced;the average grain size of α-phase and γ-phase in WM is obviously reduced due to electromagnetic stirring,but the austenite grains in HAZ tend to coarsen.The experimental results of macro-electrochemistry,micro-electrochemistry and slow strain rate test show that the corrosion resistance of welded joints is improved after applying alternating magnetic field.Potentiometric scanning test shows that when the magnetic field frequency is 30-50Hz and the intensity is 20-30mT,the Ecorr of the sample moves positively,the Icorr decreases,and the pitting potential increases.Through the scanning vibrating electrode technique and localized electrochemical impedance spectroscopy scanning tests,it was found that the sample applied with a 30mT magnetic field was more refined due to the increase of γ-phase,and the surface passivation film was denser,the resistance value was higher,and there was no obvious pitting feature.The SSRT test results show that the stress corrosion susceptibility coefficients Iσ、Iδ and Iφ of the welded sample with 30mT alternating magnetic field in the simulated seawater are all less than 25%,which indicates that its susceptibility to stress corrosion is weak,but it showed obvious stress corrosion cracking sensitivity in S2O32-/Cl-environment.However,compared with the stress corrosion performance of the non-magnetic field samples in the two media,under the action of a magnetic field,the refinement of α phase and the increase of γ phase can effectively inhibit the crack propagation,so that the stress corrosion sensitivity coefficientsIσ、Iδ and Iφ tend to decrease. |
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