Study Of Microstructure And Properties Of 42CrMo/45 Steel Welding Joint With Different Brazingjoint Clearance

In this paper,low-strength pure copper solder is used to braze high-strength 45 steel and 42CrMo steel.The joints are in the form of large-area butt joints.Under the same conditions as other welding processes,the thickness values are obtained by designing different gaps for the solder joint.Six groups of brazed joints are 0.05 mm,0.10 mm,0.30 mm,0.50 mm,0.80 mm,and 1.10 mm,and the micro structure and mechanical properties of the welded joints are analyzed.The influence of performance can be concluded as follows:(1)The brazing joint in the brazed joint is tightly combined with the base material,and the joint formation effect is good.When the liquid solder contacts the solid base material,the liquid Cu first diffuses to the surface of the solid base material,and a local area on the surface of the base material produces a "free structure" that gradually disengages from the base of the base material and migrates to the center of the joint.The Fe in the base material The elements are continuously dissolved and segregated into the solder to form a black iron-rich phase.The uniform distribution of Fe elements in the solder joints achieves the dual effects of solid solution strengthening and precipitation strengthening;(2)Tensile experiments show that as the thickness of the joint increases,the tensile strength of the joint increases first and then decreases.When the joint thickness is 0.30 mm,the joint has the highest tensile strength,reaching 607.06 MPa.The tensile fracture locations of the specimens are all in the center of the joint,and the fracture type is a ductile-brittle mixed fracture.Impact tests show that as the thickness of the joint increases,the impact toughness of the joint increases.The impact fracture location of the specimen is in the center of the brazing joint,and the fracture type is a tough and brittle mixed fracture.The bending test results show that as the thickness of the brazing joint increases,the bending strength increases first and then decreases.When the thickness of the brazing joint is 0.50 mm,the bending strength is the highest,reaching 825 MPa.The hardness test results show that the hardness value of the brazing joint region is basically stable at about 80 HV,and the hardness of the 42CrMo steel base material is stable at 200-250 HV.The hardness value of the base metal is stable at 150-230 HV,and the hardness value of the bonding interface between the solder and the base material is between the two;(3)The fatigue test results show that when the stress amplitude is 275 MPa,the fatigue strength of the joint as a whole increases first and then decreases as the thickness of the joint increases.Under the stress amplitude of 255 MPa,the survival rate of the fatigue specimen of the joint with a thickness of 0.30 mm reaches 50%;under the stress amplitude of 245 MPa or less,the fatigue specimen has not passed through 1×107 cycles.Fracture occurs,so its fatigue limit is 250 MPa;...