Research On Welding Material And Process For Fusion Weld Butt Joints Of Titanium-steel Bimetal Layer-composite Plate

With the growing of energy demand,long distance transportation of oil and gas has become inevitable,but the frequently occurrence of oil and gas leakage and pipeline explosion accident,makes the corrosion resistance of oil and gas pipeline more attracted the attention of people.Corrosion cracking is the main cause of oil and gas pipelines accidents,In order to improve the pipeline corrosion resistance,people have tried to use pure stainless steel and titanium alloy in preparation of oil and gas pipelines,but the high cost makes people have to fund another way.Titanium-steel bimetal composite plate is integrating the corrosion resistance of titanium and high strength and toughness of steel and good to solve the problem.But the large difference of physical and chemical characteristics for titanium and steel,making it too difficult to fusion weld joint.At present,lap welding method used on titanium-steel bimetal composite plate weld both at home and abroad,and has yet to see the butt fusion welding reports,however,the particularity structure of oil and gas pipelines makes lap welding is hard for composite plate weld.Based on the TAl-X80 composite panels as the research target,TAl-Q235 composite board as the test base metal,from the particularity and suitability of melting welding non-uniform temperature field and the layers of weld metal solidification of titanium-steel composite panels,analyze the differences of titanium-steel weld strength and toughness,transition layer interface adapter and other issues,has respectively designed composite titanium-pipeline steel plate welding materials in each layer according to the strong thinning properties of weld seam in welding process and the formation mechanism.At the same time,combining with the working condition of the base metal and pipe welding technology characteristics,has formulated the corresponding welding process.By overlaying welding and the macro and micro weld analysis found that,Ti-Al-V alloy as the welding materials for titanium layer,Ti-Ni,Ni-Cr alloy as the welding material for transition layer and using YC-GX80 for steel welding material can be well for titanium and steel metallurgical connection,but the weld microstructure was relatively bulky.Through docking tests and analysis of weld microstructure and properties found that,using Ti-Al-V(or pure titanium)for titanium welding materials,Ti-Ni to nearly titanium layer welding material,Ni-Cr to nearly steel layer welding material and YC-GX80 for steel layer welding materials can be well for the connection of titanium-steel composite plate by fusion weld.The weld microstrmcture from oversize isometric of titanium layer into a tiny isometric or dendrites gradually and interwoven connection with ferrite and pearlite organization of steel layer,and the joint tensile and yield strength has reached the expected goals,but its toughness insufficient slightly.In addition,the welding process optimization experiments revealed that,titanium layer,nearly titanium layer and nearly steel layer can both choose the TIG welding,and its welding current is 85A,110A and 120A respectively,steel layer can choose gas shielded welding,and its welding current is 170A.Besides,prior-welding deformation Angle can choose 1.7°-1.9°,this process specification can get a better welding j oint of titanium-steel bimetal composite plate.