Effect Of Brazing Layer Thickness On Microstructure And Mechanical Properties Of 42CrMo/Q345 Dissimilar Steel Welded Joints

The single application of 42CrMo and Q345 is not limited to its own performance characteristics.In order to meet the material's development towards multifunctionality,the welding of 42CrMo/Q345 heterogeneous steel structural components has received extensive attention,while brazing has a small impact on the base metal Low-cost welding methods have been widely used.Therefore,the influence of different brazing layer thicknesses on the microstructure and mechanical properties of dissimilar steel 42CrMo/Q345 welded joints was explored in this paper.Oxygen-free copper TU1 was selected as the brazing filler metal for furnace brazing.The brazed joints of 0.25 mm,0.35 mm,0.50 mm,0.75 mm,1.10 mm,and 1.50 mm,and their microstructure and mechanical properties are studied,and the conclusions are as follows:(1)The base metal on both sides was tightly combined with the solder,and the interface is clear.No defects such as pores,cracks,and inclusions were found.Due to the interdiffusion of the solid base metal and the liquid solder,a significant infiltration of Cu into the base metal between the base metal can be seen in the joint,and as the thickness of the weld decreases,the diffusion distance of Cu also increases.slowing shrieking.(2)The tensile test results showed that the specimens with a thickness of 0.75 mm,1.10 mm,and 1.50 mm were fractured at the weld,and their tensile strengths were 482.61 MPa,475.38 MPa,and 462.95 MPa,respectively.Increasing the tensile strength of welded joints is decreasing,and the tensile strength of welded joints with a thickness of 0.75 mm can reach 2.76 times that of Cu.The specimens with brazing thicknesses of 0.15 mm,0.25 mm,0.35 mm,and 0.50 mm were all fractured in the Q345 base metal,so the tensile strength of the four groups of welded joints exceeded the Q345 base metal tensile strength.Tensile fracture shows that a large number of dimples were distributed on the fracture surface,and the fracture mode is ductile fracture.(3)The impact results showed that as the thickness of the weld increases,the impact energy of the specimen decreases first and then increases.The fracture morphology of the impact specimen showed that a large number of dimples of different sizes were distributed at the fracture.(4)The bending test results showed that the joints with weld thicknesses of 1.10 mm and 1.50 mm were completely broken,and the remaining joints did not crack.As the thickness of the brazing intermediate layer increased,the bending strength increased and then decreased.(5)The hardness of the weld was basically unchanged,ranging from 80 HV to 95 HV.There is a slight increase at the boundary between the weld and the base metal,and there is no significant change with the thickness of the weld.(6)Fatigue tests showed that at 220 MPa stress amplitude,fatigue fractures of the specimens with weld thicknesses of 0.50 mm,0.75 mm,1.10 mm,and 1.50 mm occurred at the weld,and the rest did not fracture,and with brazing the thickness of the layer increases,the number of cycles of the joint gradually decreases.It can be seen that the fatigue strength of welded joints has some relationship with tensile strength,but there are also differences.The fatigue S-N curve of the joint with a clearance of 0.35 mm is drawn,and the fatigue limit is about 235 MPa.