Research On The Microstructure And Properties Of 20 Steel/316L Stainless Steel Dissimilar Metal TLP Welded Joints

With the increasing application of new materials,new methods and new processes,and the increasingly stringent service conditions of industrial components,single metal materials can not fully meet the actual working conditions.As one of the most widely used bimetal materials,20 steel/316L stainless steel dissimilar metals have great welding problems.Therefore,this project uses amoqphous Ni foil and Sn/Cu/Sn as the intermediate layer material in TLP welding process.The welding temperature and duration are set as variables.By studying microstructure,phase formation and element migration,shear strength and microhardness,the variation rules of joints under different welding parameters are obtained.The conclusions are as follows:(1)Amorphous Ni foil and Sn/Cu/Sn are used as TLP soldering interlayer materials,all of which achieve good metallurgical bonding,and when the intermediate layer material is Sn/Cu/Sn,compared to single-layer Cu foil The forming of the connection interface has been significantly improved.(2)When the intermediate layer is an amorphous Ni foil and the welding temperature is a variable,it is found that there are two layers of the diffusion-dissolving layer on the side of the joint 316L at a soldering temperature of 1140 0 C,and the possible phase in the diffusion-dissolving layer Ⅰ is Fe0.64Ni0.36 solid solution,the possible phase of diffusion dissolved layer Ⅱ is Cr0.19Fe0.7Ni0.11 solid solution.The mechanical properties test shows that with the increase of welding temperature,the shear strength increases with the maximum at 1140℃.342 MPa),but with the increase of welding temperature,the microhardness at the center is decreasing;when the holding time is variable,the diffusion dissolved layer is gradually opened and continuously thickened with the increase of holding time,316L side The structure produces a multi-component combination of carbide,austenite and solid solution austenite.The main phase is[Fe,Ni],Ni2Si,Cr0.19Fe0.7Ni0.11 solid solution structure,and when the holding time is 60 min,A similar two-layer diffusion dissolution layer of 4#sample(1140℃,40 min)appeared.The mechanical properties showed that the shear strength increased first and then decreased,the peak value was 352.2 MPa(50 min),and the microhardness was The trend of rising first and then rising,the peak value is 172.5 H V(30 min).(3)When the intermediate layer is Sn/Cu/Sn and the welding temperature is a variable,it is found that at 1100℃,obvious Kirkendall pores appear,and as the temperature rises,the Kirkendall hole gradually disappears,but Solid-liquid shrinkage cracks appeared,the temperature was further increased,the crack disappeared,and the main phase at the joint was Fe4Cu3,Cu-Sn compound and solid solution.The mechanical properties showed that the shear strength continued to rise and reached 74 MPa,and the microhardness first appeared.The peak value of the appreciation(280.1 HV),then decreased;when the holding time is a variable,the Kirkendall hole has a process of occurrence,increase and disappearance.The phase and element migration are consistent with the samples at different welding temperatures,and the mechanical properties indicate shear resistance.The shear strength continued to increase to 66 MPa,and the microhardness first rose to the peak(270.0 HV)and then decreased.