| As the mains of transportation of oil and gas,pipeline transportation has developed rapidly both at home and abroad because of its security and ecnomy.However,the frequent occurrence of oil and gas leakage,pipe explosion and other issues has gradually aroused widespread concern.Corrosion failure is the key factor which affects service life and reliability of pipeline system.The layered composite material can make dissimilar materials realize perfect metallurgical combination and fully display the characteristics of each material although the difference of their strength,melting point and thermal expansion coefficient.In this paper,TA1 and Q235 dissimilar metals were taken as the research object.Based on the non-uniform temperature field and microstructure matching of the melt welding,the problems of TA1 and Q235 weld strength and toughness and transition layer interface adaptation were analyzed.The test designed transition layer material matched with base material by multi component alloy elements Cu、V、Mo and Ni as metallurgical control elements.At the same time,the TA1/Q235 and TA1/Cu/Q235 layered composites were welded by two kinds of welding materials.In addition,the welding processes had been developed combined with the use of base metal and welding forming technology.The results show that the Cu-V-Mo flux-cored wires achieve weiding of dissimilar materials TA1 and Q235 as matching welding materials.The compound zone is formed at the interface titanium-weld and steel-weld and the core of the weld is copper based solid solution.But there are pores and high melting point in the weld due to the excessive high melting point elements in the alloy composition.In order to reduce the melting point and improve the ductility and toughness of welding materials,welding core has been added Ni.The metallographic examination results show that the high melting point of the weld zone is reduced and the hardness values of the weld zone are kept below 500HV0.1,which has a certain degree of decline.In order to further explore the match of designed welding material in welding process of titanium and steel,fusion test has carried out on TA1/Q235 composite plate with two kinds of flux cored wire Cu-V-Mo,Cu-V-Mo-Ni as the transition layer.The results show that the welding current of Cu-V-Mo is so large that a large number of Ti and Fe in the weld.The micro structure of the weld mainly distributed Ti-Cu and Ti-Fe compound and the thickness of compound layer is larger in the interface region.However,the required welding heat input is small and the micro structure of the weld is copper based solid solution when the Cu-V-Mo-Ni flux-cored wire is used as filler metal in welding.Besides,the thickness of the compound layer in the interface region is controlled at about 50μm and the mechanical properties are obviously improved.In order to adjust the distribution of the triangular zone of the weld metal and the base metal and reduce the intermetallic compound,the Cu layer was added at the interface of composite plate by explosive cladding.Subsequently,the three layer composite pipe was welded by Cu-V-Mo-Ni flux cored wire.According to the analysis results of line scan,EDS and XRD,the Ti and Fe mixing zone of weld and triangle region are improved effectively and the mechanical properties are improved obviously. |
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