Integrative Process Of Vacuum Brazing And Heat-treating For YG6C Cemented Carbide And 42CrMo Steel

Under the research background of road milling bit, this paper has studied vacuum brazing of YG6C cemented carbide and 42CrMo steel in some technological parameters. The effects of brazing temperature, joint clearance and thickness of interlayer Ni on properties of brazing joint is studied, and the optimal technological parameters are determined by three point bending experiment. The microstructure and the diffusion of elements in base metals and filler metal of the welding point is analyzed by SEM and EDS. Finally, vacuum quenching is carried out to study the effects on the properties and microstructures of the brazing joint and 42CrMo steel.The filler metal CuMnCo has good wettability on YG6C cemented carbide and 42CrMo steel when the brazing temperature is higher than 1080℃. The wettability is getting better and better with the rising of temperature.The brazing joint is constituted of the middle area and the two reaction areas. In the middle area of the brazing seam generates the Cu-Mn based solid solution which has good plastic to release the residual stress of the joint. The Fe-Co based solid solution generated in two reaction areas can effectively strengthen the metallurgical bonding of the base metals and the filler metal. The Fe-Co based solid solution has high hardness, but the plasticity is poor.If the brazing temperature is too low, the brazing joint can't form enough Fe-Co based solid solution, so the joint cannot achieve enough metallurgical combination, and the properties of the joint is poor. when the brazing temperature is too high, there are lots of Fe-Co based solid solution generated in two reaction areas. Too much of the reaction product reduce the plastic of brazing seam, and make the ability of release residual stress poor, So the properties of the joint is poor. When the joint clearance is 0.20mm, the optimum brazing temperature is 1095℃. The Fe-Co based solid solution generated in two reaction areas can effectively strengthen the metallurgical bonding of the base metals and the filler metal. In the middle area of the brazing seam generates the Cu-Mn based solid solution which has good plastic to release the residual stress of the joint.When the joint clearance is too narrow, too much of reaction product Fe-Co based solid solution generate and the joint clearance can't release the residual stress effectively. The brazing joint crack at seam near the cemented carbide. When the joint clearance is too wide, the long-range diffusion of substrates elements such as Fe,Co is difficult to cross the joint clearance to form enough Fe-Co based solid solution and the metallurgical bonding of the joint is much weaker. It will break at the brazing joint. The best joint clearance is 0.2mm through experiment.As the Ni interlayer added in the brazed joint, the long-range diffusion of substrates elements is hindered and the metallurgical bonding of the joint is too weak. So it can't increase the mechanical properties of joint.After vacuum quenching, joint strength is enhanced. 42CrMo steel can get the martensite by quenching. The hardness of 42CrMo steel is improved. The 42CrMo steel volume expansion produced in martensitic transformation can offset part of the residual stress during cooling process. The Integrative Process of Vacuum Brazing and Heat Treatment for YG6C cemented carbide and 42CrMo steel is reasonable and feasible.