Effect Of Nickel And Vanadium Intermediate Layer On Microstructure And Properties Of MAG+ Laser Welded Joint Of Titanium-Steel Composite Plate

Titanium-steel composites are widely used in chemical,aerospace,marine and other industries because they have good corrosion resistance of titanium and good weldability of steel.However,due to the difference in physical and chemical properties between titanium and steel,The intermetallic compounds that cause brittleness during welding make the process used in engineering very limited.It is necessary to solve the problem of welding to put it into use in engineering.The purpose of this thesis is to deal with the welding of titanium steel composite plates for explosive welding,especially in the welding of titanium steel composite plates for petroleum pipelines.Due to the difference in physical and chemical properties of iron and titanium,direct welding can lead to brittle fracture of joints.The laser+MAG single-sided welding process of the transition layer,in which the transition layer adopts nickel and vanadium powder with good solubility to iron and titanium,and the method of laser cladding is used to add nickel and vanadium to the welded joint,and the test and the result are obtained.After the test and the comparative analysis of the results,the appropriate process parameters are determined to obtain a macroscopically qualified welded joint.Then we can evaluate the weld joints through a series of experiments to compare the micro-hardness,tensile properties,impact properties,shear properties and bending properties of the welded joints,and analyze the micro-morphology of various fractures,and through the metallographic test,XRD,SEM,EBSD and other test methods to observe and analyze the microscopic features,phase composition and microscopic characteristics of phase composition,grain size and residual strain of welded joints.The joint performance of welded joints with nickel and vanadium as transition layers is stronger than that of joints without transition layer.The tensile strength of the welded joint without transition layer is only 249MPa,which is far lower than the 396MPa for the transition layer of nickel and the 398MPa for the transition layer of vanadium.The fracture analysis is that the steel side is ductile fracture,while the titanium layer with vanadium as the transition layer acts as the mixed fracture,and the rest are brittle fracture.The tensile and impact of the joint with vanadium as the transition layer is stronger than that of the joint with nickel as the transition layer.XRD analysis shows that brittle FeTi and Fe₂Ti intermetallic brittle compounds are formed at the interface of iron-titanium without transition layer.The transition layer forms a NiTi intermetallic compounds at the nickel-titanium interface,and vanadium-titanium transition layer has no intermetallic compounds.The EBSD results also show that there is a NiTi phase distribution in the nickel-titanium interface.The addition of the transition layer leads to an increase in the heat input,which leads to the growth of the grain of the titanium layer.There is a large residual strain in the titanium layer.The residual strain in the transition layer of nickel and vanadium is small.