The Effect Of Welding And Heat Treatment On The Corrosion Behavior Of2205Duplex Stainless Steel Welded Joints

Duplex stainless steel is composed of the ferrite and austenite phase, and in general, theless content should reach30%. When the ratio of the two-phase is about50%, duplexstainless steel will have excellent mechanical properties and corrosion resistance properties.Duplex stainless steel has excellent toughness and weldability that the austenitic stainlesssteel has and the high intensity and resistance to chloride stress corrosion that the ferriticstainless steel has, which make it be used especially in the fields of petrochemical industry,Marine transportation and food engineering, and so on.2205duplex stainless steel is usedwidely, accounting for80%of the total. The key to the application of duplex stainless steelis welding. During the welding process, due to the reaction of thermal cycles, which causesthe occurring of complex phase change, so it is difficult to control the two-phase ratio of thejoint; in addition, the inevitable stress and deformation will destroy the properties of thewelding joint which is caused in the welding process. Therefore, the research inmicrostructure and properties of the welded joint and the welded joint with heat treatmenthad some guiding significance for practical production.In this paper, TIG welding was used in the welding of the2205duplex stainless steel.Then the change in microstructure and comprehensive performance of the welded joint wasinvestigated, which processed through the various welding processes and heat treatmenttemperature. Microstructure of the welded joint with heat treatment was researched by OM,SEM, EDS. Mechanical properties and corrosion resistance of the welded joint with heattreatment were analyzed by micro-hardness measurement, tensile test, electrochemical test,and stress corrosion test.The microstructure of welded joint showed that: it was made up of austenitic andferritic phase. Due to the changes in heat input and the protective gas, the content of thetwo-phase in welding joint changed significantly. The content of austenite phase in thewelded joint with the nitrogen protective gas increased, while the content of ferrite phasedecreased. Obvious changes had been observed in the joint microstructure after solutiontreatment of1050℃, for example, the two-phase distributed evenly, the size of grainbecame thinner, the austenitic content increased significantly and the ratio of two-phasetended to1:1.The experiment of micro-hardness indicated that the hardness of welded joints could meet the standard, the hardness increased a little after heat treatment under600℃; however,it decreased after solution treatment under1050℃, and the difference of hardness betweenheat-affected area and matrix reduced, the difference between weld area and matrix had thesame trend. The maximum tensile strength of welded joints could reach819Mpa under Arand110A current while minimum elongation rate was obtained and joints tended to actbrittle fracture. Tensile strength decreased with120A current and protection with Ar and2%N2while elongation rate increased with dimple morphology of fracture, which indicatedwelded joints had the best plasticity under these conditions. Mechanical properties ofmaterials could be affected significantly by the addition of N2, and the increased austenitecould improve elongation rate of joints and reduce tensile strength.The results of electrochemical test, electrochemical impedance spectroscopy, andcirculation polarization showed that: the welding joint with120A current and protectionwith Ar and2%N2erosion resistance was the best, after600℃heat treatment, the Eb-EPofthe specimens increased, so the ability of pitting reparation was poor. After solutiontreatment under1050℃, the joint have excellent corrosion resistance, which was closed tothe base metal.Through the slow strain rate test and the analysis of fracture morphology, the weldedjoints with120A current and protection with Ar and2%N2had the best stress corrosionresistance; After600℃heat treatments, stress corrosion resistance is poor; the1050℃solution treatment made the stress corrosion resistance of welded joints become better.