Study On The Microstructure And Properties Of Q345/316L Dissimilar Metal TLP Welding Joint

The physical and chemical properties of dissimilar metal materials are many different.There are also large differences in chemical composition.Dissimilar metals are generally more difficult to weld than the same metals.The welding structure of Q345 low alloy steel and 316L stainless steel dissimilar steel is widely used in many industrial fields.The characteristics of the conventional welding process such as high temperature,uneven heating,and the need to melt the base material are likely to cause the difference in the properties of the Q345/316L base material to be amplified and affect the performance and stability of the joint.Transient liquid phase-diffusion bonding(TLP-DB)is a new connection technology that combines the advantages of brazing and solid-phase diffusion,and is very suitable for dissimilar steel welding.In this paper,TLP welding method is used,with Cu foil and amorphous BNi-2 foil as the intermediate layer.Control welding temperature,holding time and pressure as variables to weld Q345/3 16L dissimilar metals.The microstructure,element migration,phase formation,and mechanical properties of the obtained joints are tested and analyzed.The conclusion is as follows:(1)Using Cu foil or amorphous BNi-2 foil.as the intermediate layer material for TLP welding to connect Q345/316L with different steel in atmospheric environment can achieve effective metallurgical bonding.(2)Using Cu foil or amorphous BNi-2 foil as the intermediate layer material for TLP welding to connect Q345/316L with different steel in atmospheric environment can achieve effective metallurgical bonding.Temperature and time will affect the mutual conversion between elemental Cu and solid solution Cu0.81Ni0.19.With the increase of temperature,the shear strength of the joint shows a trend of increasing first and then decreasing.When the welding parameters were 1130℃,1 5min,and 4MPa,the shear strength of the welded joint was 437MPa.The microhardness of the base metal and the weld seam both decrease with the increase of welding temperature.The welding strength of the sample obtained at the welding parameter of 4MPa and 1130℃ reached a maximum value of 462MPa after 25minutes of heat preservation.The microhardness of the center of the welding seam shows a trend of decreasing first and then increasing as the holding time increases.The phase transformation of Ni-Cr-Fe,Fe-Cr,[Fe,Ni],Cr0.19Fe0.7Ni0.11 and precipitation behavior affect the hardness change.The size of the pressure determines the remaining amount of the middle layer Cu liquid after being extruded.The greater the pressure,the narrower the connection layer.The greater the pressure,the lower the mass fraction of Cu element in the connection area.The shear strength and microhardness of the welded joint increase with the pressure,and the maximum value can reach 482MPa and 180.1HV.(3)When BNi-2 is the intermediate layer and the welding temperature is the variable,the width of the connection layer increases as the temperature increases.Maximum exceeds 50μm.There is a clear connection interface on the side of the weld connection layer near Q345.The interface morphology of the weld connection layer on the side near 316L is similar to the austenite grain boundary.The connection interface becomes more curved as the temperature increases.The shear strength of the sample increases first and then decreases with increasing temperature.When the welding parameters are 10min and 1050℃,the shear strength of the sample can reach 402MPa.With the holding time as a variable,the tissue composition of the middle layer and 316L tends to be the same as the holding time increases.A structure similar to the austenite grain boundary will be precipitated in the connection layer area of the joint obtained by holding for 20 minutes.When the holding temperature is 1000 ℃,the shear strength of the sample increases with the holding time(329MPa,368MPa,374MPa).When the holding temperature is 1050 ℃,the shear strength of the sample increases first and then decreases with the increase of holding time(402MPa,416MPa,413MPa).When the holding temperature is 1100℃,the shear strength of the sample decreases with the increase of holding time(400MPa,387MPa,377MPa).(4)Using pure Cu foil as the intermediate layer and welding process parameters of 1130℃,25min,and 6MPa,weld joints with high shear strength can be obtained.Welded joints with high shear strength can be obtained with amorphous BNi-2 foil as the intermediate layer and welding process parameters of 1050℃,15min and 4MPa.