Integrative Process Of Vacuum Brazing And Heat-treating For YG6C Cemented Carbide And 5CrMnMo Steel

In this thesis, vacuum brazing and heat-treatment between Cemented Carbide YG6C and Steel 5CrMnMo with CuMnCo filler metal had been studied. Through the wettability test, three-point bending test, SEM and EDS, the effects of brazing temperature, brazing clearance, thickness of Ni interlayer and heat-treatment on microstructure and properties of the joint were discussed. Consequently, the optimum parameters of brazing process was carried out.The wettability test shows that the CuMnCo filler metal has excellent wettability on the YG6C and 5CrMnMo. The contact angle gets smaller and smaller with the rising of brazing temperature. It shows that the wettability of the filler metal spreading to the parent metals has improved well, particularly the wettability of the filler metal to the steel is better than to the cemented carbide.The microstructure and mechanical properties of the brazed joint can be prominently influenced by brazing temperature. In the research of brazing temperature range, brazing seam is composition of brazing seam center area and bilateral interface reaction areas. The Cu-Mn based solid solution in the middle area of the brazing seam has good plasticity. And both sides reaction areas are Fe-Co based solid solution, which has high hardness, but poor plasticity. If brazing at a lower temperature, the wettability and fluidity of the filler metal are poor, and diffusion ability of the element is weak, thus less of the reaction product generated in the reaction areas, it's cannot achieve enough metallurgical combination, so the properties of the joint are poor. But if the temperature is too high, the diffusion and reaction ability get stronger between the filler metal and parent metals. And there is a lot of Fe-Co based solid solution generated in two reaction areas. Much of the reaction product reduces the plasticity of brazing seam, and the residual stress not be able to obtain to release effectively. So the properties of the joint are poor, too. The best brazing temperature is 1080℃, in which the bending strength reaches about 418 MPa.When the brazing clearance is too narrow, the elements are much easier to cross the brazing seam by the long-range diffusion, a great number of reacting products generated which can decrease the plasticity of the brazing seam and the residual stress releasing capacity. Therefore the properties of the joint are poor. But if the brazing clearance is too wide, Fe,Co elements are difficult to cross the brazing seam by the long-range diffusion and the metallurgical bonding of the joint is much weaker. So the properties of the joint are bad, too. The best brazing clearance is 0.2 mm when brazing at the best temperature 1080℃. The experiment of adding Ni interlayer indicates, whatever the interlayers thickness is thinner or thicker, the performance of the joints is worse than that does not adding interlayers, it is mainly because Ni interlayer hindered the long-range diffusion of element such as Fe, Co, and it can't form good metallurgical combination, so the performance of the joint is poor.After quenching, the bending strength of the joint has improved, the main reason is the austenite transforms into the martensite, volume expansion of the steel can offset part of the residual stress. While after tempering, it improves the steel overall performance, the performance of the joint obtains further enhance. The test shows that the integrative process of vacuum brazing and heat-treating for YG6C cemented carbide and 5CrMnMo steel is reasonable and feasible. Because it not only improves the performance of the joint, but also saves the energy.