Research On Microstructure And Properties Of WC Steel-bonded Cemented Carbide By Microwave Sintering

Steel-bonded cemented carbide is a new material between cemented carbide andsteel, inherited respective advantages of cemented carbide and steel, with highhardness, strength and wear-resistance as well as the steel manufacturability, heattreatment and weldability, filling in the gaps between the two materials, and widelyapplied to cutter, mould and wear parts, etc. In this paper, WC steel-bonded cementedcarbides were prepared by microwave sintering, and the effects of microwavesintering process, heat treatment process, WC content, Y₂O₃on microstructure andproperties of steel-bonded cemented carbide were systematacially studied. Themechanism of microwave sintering and rare earth modification were also discussed.The results show that the density, microhardness and the bending strength ofsteel-bonded cemented carbide increase first and then decrease with increasing thetemperature under the conditions of heating rate （15³5℃/min） and holding time（20min）, reaching the maximum values at the sintering temperature1280℃, whichis97.29%,544HV and847.37MPa, respectively. During sintering process, the phasetransformation reactions between WC and Fe are observed and the new Fe2W2Creinforcement phase is formed, which is evenly dispersed over the steel matrix and hasthe strengthening effect on the material. The microstructure of WC steel-bondedcemented carbide after sintering is composed of pearlite and hard phase, translating tomartensitic, austenite and hard phase organization during heat treatment process of thequenching （900℃） and tempering （200℃）. Meanwhile, the mechanical propertiesof the WC steel-bonded cemented carbide can be improved further after heat treatment,such as the microhardness and bending strength increasing to1024HV and1267.60MPa, respectively, higher about90%and50%compared with that of the sinteredstate samples. The wear resistance of heat treated WC steel-bonded cemented carbideis considerably improved compared with the sintered state samples, with the wearextent decreasing by about70%.Steel-bonded cemented carbide with different WC contents sintered bymicrowave sintering generate Fe7W6, Fe₂W₂C and Fe₆W₆C new phases. With the increase of the WC contents, the relative density, microhardness and bending strengthof steel-bonded cemented carbide all increase, and the fracture mode of steel-bondedcemented carbide transforms from ductile fracture to brittle fracture. The wear rate ofthe steel-bonded cemented carbide is decreased with the increase of the WC contents.The mechanical properties of steel-bonded cemented carbide with different WCcontent after heat treatment are improved obviously compared with before heattreatment.During the microwave sintering process, the addition of Y₂O₃（0.5%） can purifythe interface of Fe₂W₂C and Fe, improve the wettability, promote the densificationlevel of the sintered materials and enhance the interface bonding strength of thereinforcement phase and the matrix. At the same time, the uniformity of thereinforcement phase is improved by the addition of Y₂O₃. All of the density,microhardness and bending strength of steel-bonded cemented carbide increase firstand then decrease with increasing the Y₂O₃contents, reaching a maximum value at0.5%Y₂O₃. Moreover, the addition of nano-Y₂O₃has better effct than that ofmicron-Y₂O₃.