Study On Microstructure Control And Distortion Straightening Technology For Welded Joints Of 2205 Duplex Stainless Steel

Duplex stainless steel has excellent mechanical properties and corrosion resistance,which is widely used in petrochemical industry,marine structure and shipbuilding industry.The excellent performance of duplex stainless steel is based on the reasonable double phase ratio.However,the double phase ratio of the welded joint is unbalanced,which results in the decrease of the joint performance.In practice,the use of shielded metal arc welding(SMAW)is the most popular,so it is necessary to study the structure and properties of the welded joint after manual welding.In this paper,three welding layers,the use of two kinds of electrodes(E2209-16 and 309MoL)on the 6mm thick 2205 duplex stainless steel plate butt joint test,each of the electrodes was carried out at different welding positions,different heat input welding test.The effects of different welding positions and heat input on the microstructure and mechanical properties of the joint were studied.The results showed that there is no macroscopic defects,and the weld formation is good.The weld zone ?/? phase content of the gap between the obvious,the weld zone of austenite content is the highest,the heat affected zone is the lowest.Because the content of Ni element in the electrode 309 MoL is much higher than that of the base metal andE2209-16,the austenite content of the joint is higher than that of the electrode E2209-16.The results of XRD showed that there was no harmful secondary phase in the weld metal.SEM and energy spectrum analysis showed that the joints of alloy elements occurred diffusion in thermal cycling.When cooling,austenite is preferentially precipitated from ferrite grain boundaries,the subsequent thermal cycling results in the precipitation of a large amount of austenite.There are differences in the microstructure and the austenite content between the three layers welding.The mechanical properties of the joints showed that the tensile strength of the 309 MoL electrode was lower than that of the E2209-16 electrode,and all of the joints were broken in the weld metal.Flat rigid fixed sample extension of minimum rate,this is related to the stress concentration of the joint.In the bending test,no cracks were found on the joint surface and the back bend.The impact value of heat affected zone is higher than that of weld in impact test,There are a lot of dimples in the impact fracture of weld metal,and all are ductile fractures.However,the fracture of the HAZ has a wide range of flat cleavage surface or quasi cleavage surface and a small number of dimples,therefore,the fracture mode is brittle ductile brittle fracture mechanism.The hardness value of the joint is related to the austenite content in the region,the hardness of the heat affected zone is the highest,and the surface weld is the smallest.The finite element software ANSYS was used to simulate the temperature field and stress field in the welding process.The results show that the maximum temperature of the second layer heat transfer curve is higher than the other two layers,reaching a temperature of 2800°C.The cooling time of the joint can be prolonged,which will affect the content of austenite phase.The heat affected zone of the lower part of the joint is subjected to three thermal cycles,and the maximum temperature of each thermal cycle is higher than that of the phase-transition temperature.The stress field test show that the longitudinal and transverse residual stresses are compressive stress,the compressive stress in the region away from the weld is gradually transformed into tensile stress,the orifice method is consistent with the simulation value.Mechanical straightening of severely deformed plates,the tensile test results show that the tensile strength of the plate is slightly higher.The yield stage is not obvious in the stress-strain,and the fracture position occurred in the weld metal.There are small dimples in the fracture,and toughness was decreased.