| The welding between cemented carbide and steel is mainly used for cutting tools,mining tools and wear-resistant parts such as wiredrawing dies.The joints obtained can make the strength and toughness complement each other,up to 1+1>2 the function.The study of microstructure and properties of cemented carbide and DC53 brazing joint will provide experimental basis and theoretical basis for the connection of drawing die and other workpieces.In this paper,vacuum brazing of YG8 and DC53 steel was carried out with different types of solders.By controlling the technological parameters,the connection of YG8/DC53 steel was realized.The microstructure,element distribution and fracture characteristics of the joint were studied by metallographic microscope(OM),scanning electron microscope(SEM)and energy dispersive analyzer(EDS).The mechanical properties of the joint were tested by microhardness tester and universal testing machine to explore the evolution law of the joint microstructure during brazing.Vacuum brazing of YG8 and DC53 steel was performed with S201 solder.The solder had good wetting property on both sides of the base metal,compact interface,no cracks,pores and other defects in the joint.The brazing joint was formed with?-Cu solid solution matrix,Fe-Co solid solution and Cu5Sn phase,and ?-Cu solid solution dissolved into C element to form interstitium solid solution.The microhardness is 220HV,and the Fe-Co base replacement solid solution is formed near YG8 side at the brazing temperature of 1130?,and the microhardness is 122.5HV.When pure copper solder is used,thermal stress and solder diffusion along the grain boundary of the base metal lead to poor interfacial plasticity and cracks along the interface.The high hardness brittle ? phases of nickel-tungsten and iron-tungsten are formed on the YG8 side by BNi2 solder,which leads to radial cracks in the joint.Composite solders(Cu58ZnMn/Ag45CuZn,Cu58ZnMn/Cu/Ag45CuZn)were used for vacuum brazing of YG8 and DC53 steel.The base metal on both sides of the solder was well wetting,the interface was compact,and the joint had no cracks and other defects.Large ?-Cu and Ag solid solutions are alternately distributed in the brazing joint matrix,and the distribution becomes more dispersed as the temperature increases to 940?.Using Cu58ZnMn/Cu/Ag45CuZn filler metal,?-Cu solid solution,Ag-based solid solution and Ag-Cu eutectic microstructure are formed in the brazing joint area.With the increase of brazing temperature from 900? to 1000?,the more dissolved in the interlayer,the more dispersed the distribution of ?-Cu solid solution,and the higher the microhardness is.The brazing temperature is 1000?,the maximum microhardness is 272.6HV.When Cu58ZnMn/BNi2/Ag45CuZn is used,the Si and B in the intermediate layer of BNi2 are too late to diffuse to the base metal on both sides,forming brittle eutectic and leading to crack propagation.The microhardness of the nickel base solid solution in the brazing crack is up to 323.4HV.When the S201 solder is used and the brazing temperature is 1130?,the shear strength of the YG8/DC53 brazing joint is 133MPa.Crack and deformation occur at the joint YG8/brazing joint,leading to the shear fracture of the joint.The fracture is mainly brittle fracture,and a small amount of shear dimps are generated.The shear strength of YG8/DC53 brazed joints is 157MPa with the brazing temperature of 900?and Cu58ZnMn/Cu/Ag45CuZn solder.The shear fracture initiation occurs at the DC53/Ag-based solid solution interface,and extends along the pure Cu intermediate layer to the ?-Cu solid solution,leading to the shear fracture of the joint.The fracture is dominated by tearing brittle fracture and shear dimples are produced locally.The microstructure and mechanical properties of vacuum brazing joints of YG8 and DC53 steel were compared under different process parameters.The results show that the joint shear strength is 157MPa with Cu58Zn/Cu/Ag45Cu composite filler metal,brazing temperature 900?,holding time 20min. |
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