Study On Brazing Of Cemented Carbide To Steel Using Cu-Based Microcrystalline Brazing Alloy Foils

In this paper, high-frequency induction brazing of YG6 to 0Crl8Ni9Nb and vacuum brazing of YG6 to 25Cr3MoA were conducted by using Cu-based microcrystalline brazing alloy foils. The microstructure of joint, phase constitution of brazing seam and distributions of main elements within the joint were investigated, and the shearing strength of joints was tested. A interdiffusion model of atoms between liquid brazing alloy and parent metals was established and atoms mutual diffusion was analysed theoretically. Moreover, the characteristics of brazing technique and joint properties were compared between tow kinds of brazing techniques.The results indicate that the diffusion brazing of cemented carbide to steel could be realized using Cu-based microcrystalline brazing alloys instead of expensive Ag-based brazing alloys. The brazing alloys perform an excellent wettability and spreadability in brazing process, thus the brazing seams spreaded soundly and the joints have a high welded ratio. There is no porosity and inclusion in 0Crl8Ni9Nb/Cu-7%Sn/YG6 joints and the seam microstructure was homogeneous without brittle intermediate phase in it. There is also no porosity and inclusion in 0Crl8Ni9Nb/Cu-13.5%Sn/YG6 joint, but the phase constitution gets complex , which consists of a few of Cu₃Sn phase, Cu₉NiSn₃ phase and Ni₁₇Sn₃ phase except main phase a-Cu solid solution due to the higher Sn content in Cu-13.5%Sn brazing alloy. The 25Cr3MoA/CuSnNi/YG6 joint has a good appearance with smooth transition around the brazing seam. The microstructure of joint consists mainly of a-Cu phase, a few of Cu₃Sn phase, Cu₉NiSn₃ phase and (Fe) phase. The diffusion depth of Cu atoms from brazing seam to base metal reaches to 2.5μm in vacuum brazing joint. The shearing strength of the joint obtained by vacuum brazing using Cu-based microcrystalline brazing alloy is high up to 169MPa. Thus, it was obviously that vacuum brazing is likely to obtain joints with sound seam microstructure and well alloying extent between brazing alloy and base metals compared with high-frequency induction brazing method.