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

With the growing energy demand,long distance transportation of oil and gas has become inevitable,but oil and gas leakage and pipeline explosion accident frequency,oil and gas pipeline corrosion resisancetance is 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 material such as stainless steel,titanium alloy in preparation of oil and gas pipelines,but the high cost makes people have to find another way.Titanium-steel bimetal composite tube is integrating the strongpoint of titanium/steel,very good to solve the problem.At present,titanium-steel composite boards both at home and abroad adopt way of lap welding,has yet to see the butt fusion welding reports,however,the particularity of structure of oil and gas pipelines makes it hard for lap welding method on it to the application.This paper was subjected to develop the intermediate materials to join the explosive bonded TA1-Q235 bimetallic sheet.The matching welding materials were designed based on the non-uniform temperature field of welding process and the microstructure in TA1-Q235 bimetallic sheet.Furthermore,the corresponding welding parameters were drawn up combined with the service environment and welding specification of the TA1-Q235 bimetallic sheet.The explosive bonded TA1-Q235 bimetallic sheet was applied as the base metal.The welding conditions were chosen in order to minimize melting volume in the interface of explosion-bonded TA1-Q235 bimetallic sheets.Argon gas with the purity of 99.999%was used as a shielding gas.In order to minimize the oxidation at top,rear and back of the joints,argon gas with total flow of 15L/min was applied.According to the welding performance of the base metal and filler materials,TIG welding method was applied to weld Ti and intermediate materials and MAG welding method was employed to weld the ER50-6 solid wires.In previous work,Cu,V solid wires were selected as the intermediate and ER50-6 solid wire was employed as the filler metal based on the non-uniform temperature field of welding process and surface welding tests.However,this kind of intermediate materials were not feasible because of the coarse microstructure and low toughness detected in the joints.The microstructure and mechanical properties were significantly improved with the developed Cu-V flux-cored wire.The microstructure in the Ti weld metal turned into fine isometric crystal and dendrite.Continuously distributed microstructures was obtained between the α phase in Ti weld metal and ferrite and pearlite in steel weld metal.However,the bend toughness was almost zero.Based on the mass technical tests,the welding parameters were optimized with the current range of 120～140A in TIG welding method and 200～230A in MAG welding method.The based metal was subjected to the deformation angle of 1.7～1.9° before welding procedure.With the developed welding parameters and the Cu-V flux-cored wire,strength and toughness of the joints were improved.