Study On Preparation Process Of Super-coarse Composition And Cemented Carbides

Cemented carbide for mining and construction are increasingly demanded day by day. These parts are usually work at high temperature near 1000℃, high-impact loads under extremely harsh conditions, strong abrasive wear, etc. Due to good fracture toughness, thermal conductivity and thermal fatigue resistance, ultra coarse WC-Co cemented carbide with WC average size 6-10μm gradually get attention. However, the study was only carried out in recent years in domestic and there was small amounts of literature was reported. So this paper attempts to explore the preparation method of super coarse grain WC-Co cemented carbide with high performance which the grain size is more than 6μm.Firstly, the WC-Co mixture was prepared by liquid phase reduction method and the influence of different process parameters on the overall effect of the powder was analyzed, and the optimum process was obtained. Then super coarse grain WC-Co cemented carbide was fabricated by vacuum. The effect of pressing pressure, carbon content,sintering process on the comprehensive performance and the microstructure of the alloys was studied and super coarse grain WC-Co cemented carbide of high performance was obtained through continuous optimization process. The following conclusions were obtained:(1) The dispersion of WC-Co composite powders was good by the liquid phase reduction method. The uniformity of the distribution of the hard phase and binder phase was effectively improved for a lot of ultrafine cobalt binder phase coated on the surface of WC particles.The optimum parameters were determined: the raw powder was processed by ultrasonic for 40 min firstly, then the mechanical stirring(1200r/min) and ultrasonic vibration were used simultaneously; the reaction temperature was 70℃; the amount of reducing agent was n(N2H4/Co2+)=3, n(Na H2PO2/Co2+=0.6), the concentration of cobalt salt was 0.1mol/L; the acceleration of the reducing agent was 5ml/min; the p H was controlled in the range of 11.5~12.(2) Via changing the composite powder compaction pressure, carboncontent, and sintering process, the parameter values were gradually determined. In this experiment, when the compacting pressure was 2T,the carbon content was 6.09%, the sintering temperature was 1480℃and the sintering time was 60 min, the resulting coarse-grained WC-Co cemented carbide achieved uniform microstructure and great performance.The average grain size of WC was 9.6μm, impact toughness and bending strength was 4.39J·cm-2 and 2687 MPa each other. And the hardness was85.3HRA.