| Duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel,so it is widely used in petrochemical industry,navigation ship and other fields,and welding is an essential material processing method in its application process.In recent years,GTAW+SMAW,combined the advantages of GTAW and SMAW,has been widely used in pressure vessels and pipelines of some kinds of steel,but the research and application in the field of duplex stainless steel are relatively few.At the same time,the welded joint is the weak area of corrosion,fracture and other failure behavior,which is easy to cause potential failure in engineering application.Based on the selection of appropriate welding process,reasonable heat treatment process is a more feasible technical measure to improve the comprehensive performance of the joint.Therefore,the research on the welding performance and post weld heat treatment of 2205 duplex stainless steel GTAW+SMAW is of great significance to the application and development of this kind of welding method in the field of duplex stainless steel.In this paper,GTAW+SMAW welding method was used to weld 10 mm thick 2205 duplex stainless steel,and the welding performance of 2205 duplex stainless steel GTAW+SMAW was explored.Secondly,according to the isothermal transformation curve of 2205 duplex stainless steel,the reasonable solution treatment and lowtemperature annealing process were established for the welded joint,and the effects of the two heat treatment processes on the microstructure,mechanical properties and corrosion resistance of GTAW+SMAW welded joint were studied.The main conclusions are as follows.(1)The microstructure of weld zone and heat affected zone of 2205 duplex stainless steel GTAW+SMAW welded joint is composed of ferrite and austenite,and there is no secondary phase precipitation in the joint.Due to the effect of secondary welding thermal cycle,austenite distribution is relatively uniform in the underlayer and filler layer,while the dual phase structure in the cover layer is coarse and uneven,and the austenite content in each welding layer of the weld is between 55% and 65%;the heat affected zone of joint,the austenite content in the heat affected zone of the cover layer is low,and that in other areas is 34%-38%.The hardness of weld zone and heat affected zone is higher than that of base metal,and the hardness of heat affected zone is the highest,followed by weld zone.At the same time,the hardness of the filling layer is close to that of the backing layer,and is greater than that of the covering layer.In addition,the tensile strength of the joint is high,up to 720 MPa.The impact energy of weld zone and heat affected zone is 73.5 J and 102.3 J respectively,and there is no crack after bending test.The corrosion resistance of the joint is also good,and the pitting corrosion rate is only 3.01 mdd.(2)The solution treatment of 2205 duplex stainless steel GTAW +SMAW welded joint was carried out at 950? ? 1150?.When the solution temperature was 950? and1000?,the precipitation of ? phase was serious,resulting in the decrease of mechanical properties and corrosion resistance of the joint.When the solution temperature is between 1050? and 1150?,the microstructure uniformity of weld and heat affected zone is obviously improved,and there is no secondary phase precipitation.At the same time,the joint can maintain good mechanical properties and corrosion resistance.With the increase of solution temperature,the austenite content in weld and heat affected zone increases first and then decreases.When the solution temperature is1050?,the austenite content of each welding layer is close to 60%,and the austenite content of heat affected zone is also increased to 45%.In addition,the hardness difference of each area of the joint decreases,and the overall hardness is between 270 HV ? 280 HV.The impact energy of weld and heat affected zone is increased by 10.9J and 12.2 J than that of non solution treatment,and the toughness of joint is improved obviously.Based on the comparison of microstructure,mechanical properties and corrosion resistance at different solution temperatures,the best solution treatment process of 2205 duplex stainless steel GTAW+SMAW welding joint is: solution temperature 1050?,holding time 1 h,and rapid water cooling.(3)GTAW+SMAW welded joint of 2205 duplex stainless steel was annealed at280? ? 480?.The results show that with the increase of annealing temperature,the tensile strength of the joint increases slightly,but the toughness decreases significantly.Especially after annealing at 400?,the impact fracture presents brittle fracture characteristics.At the same time,with the increase of annealing temperature,the corrosion resistance of the joint decreases obviously.Comprehensive analysis shows that the annealing or service temperature of 2205 duplex stainless steel GTAW+SMAW welding joint should not exceed 340?,and the holding time should be less than 6h. |
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