Research On Technology And Mechanism Of Joining Cemented Carbide To Carbon Steel

In order to meet the urgent requirement of high-quality compound roller in iron and steel industry, vacuum brazing of cemented carbide to carbon steel was carried out using Ni-based brazing alloy with and without Cu intermediate layer. The influence of brazing temperature over microstructure and mechanical property of the vacuum brazed joints was analyzed, and the mechanism of the formation of interfacial microstructure was investigated. The MARC software was applied to study the postweld residual stress field of the compound rollers, which were brazed with and without Cu intermediate layer.The interfacial reactions of the WC-Co/Steel joints brazed using Ni-based brazing alloy were discussed experimentally and theoretically. The results showed that microstructure of the joint was Steel/Fe-Ni(s.s)/γ-Ni(s.s)/ W-Co-Ni rich /WC-Co when brazing temperature was 1040℃. In addition, the width of the interfacial reaction layers changed obviously with the variation of the brazing temperature, and the reaction layers, especially W-Co-Ni rich, exerted a great influence over the mechanical property of the brazed joints. The maximum shear stress was 340MPa, which was achieved when the brazing temperature was 1040℃, and fractures occurred at WC-Co cemented carbide.In order to reduce the postweld residual stress of the compound roller, a novel technology of brazing using Ni-based brazing alloy with Cu intermediate layer was put forward. The results showed that the shear stress of the brazed joints increased with the increment of the brazing temperature when the thickness of Cu was 250um. When brazing temperature was 1070℃, microstructure of the joint was Steel/Fe-Ni(s.s)/Cu/Ni-Co(s.s)/WC-Co, and the shear stress reached 272MPa. Fractures occurred along the Cu/WC-Co interface. When the thickness of Cu was 100um, the shear stress decreased to 211MPa.The residual stress distribution of compound rollers brazed at the two different conditions was investigated by numerical simulation. The results showed that the cooling speed had a great influence over the postweld residual stress. Taking all the factors into consideration, the optimum value of cooling speed was 30℃/min. Under such cooling speed, the maximum residual stress of roller brazed using Ni-based brazing alloy was 434MPa. However, it decreased dramatically to 69MPa when the optimum Cu intermediate layer of 250um was applied. The results proved that the novel brazing technology with Cu intermediate layer could reduce postweld residual stress successfully.