Direct Reduction & Carburization Processing For Ultrafine WC-based Hardmetal Powder & Materials

WC-based hardmetals have been widely used for cutting tools, dies, mining tools and wear resistant machine parts as they have superior mechanical properties, such as wear resistance, rigidity, toughness, strength, etc. With the development of ultrafine/ nanophase hard metal, it has been found increasing usage in areas such as miniature drills for highly integrated printed circuit boards (PCBs), pins for dot-printers, pinhead, cutting tools for hard materials, exact moulds, etc. The properties of WC-based hardmetals can be increased observably by the decrease of particle sizes. The key techniques are powder synthesis and materials sintering.The direct reduction & carburization process is an advanced industrialized technology for produce ultrafine hardmetal powder. It has a series of advantages including low reaction temperature, a rather simplified course, low cost with better properties. All these advantages imply a widely application prospect of this technology.In this study, the oxide precursor powder is produced by spray - drying. The oxide precursor powder is turned to composite oxide powder by buring. The mixed powder is produced by ball-milling the oxide powder and carbon black. Through direct reduction & carburization processing, the mixed powder is converted to ultrafine WC-Co composite powder. Ultrafine WC powder can be synthesized by the same processing. In the latter course, the oxide powder is produce by burning the Ammonium metatungstate ((NH)₆(H₂W₁₂O₄₀·4H₂O, AMT). Hardmetals is produced from the WC-based powders synthesized by direct reduction & carburization processing.XRD, SEM, TEM, BET, C-S analysis system, saturated magnetization and coercivity force analysis system, and materials test system, etc. are used to characterize the WC-based powders and hardmetals.Results show that: the oxide precursor powder produced by spray - drying is constituted of sphericity particles. When the Co source is Co(NO₃)₂, the powder isconstituted of hollow sphericity which the particle size is 5²0 fxm; When the Co source is COCO3, the powder is constituted of solid sphericity which the particle size is 10⁵0 fim; the oxide powder is constituted of CoWO4 and WO3; after ball-milling, the difference caused by the different Co source can be eliminated. WC-Co composite powder without n phase can be synthesized by direct reduction & carburization processing at 900 °C for 2 h under flowing nitrogen gas. But free carbon of the powder is high. It cannot meet the requirement of raw materials for hardmetal. The production is sensetive to the carbon content.WC-Co composite powder which can meet the requirement of production can be produced by direct reduction & carburization processing at 900X/2h+1000*C/2h in vacuum furnace. Results show that carbonizing twice can decrease the reaction temperature. The mechanism of synthesis WC-Co composite powder by direct reduction & carburization process is: C0WO4 + WO3 + C-+ W2C + rj + WC ->r\ + WC->WC + Co.WC powder can be produced by direct reduction & carburization process at lSOCC/2h+lSOOXh in vacuum furnace. The reaction mechanism is WO3+ C -w->w2c->wc ; The hardmetal is produced from ultrafine WC-Co composite powder with 92.0 HRA and 1820 MPa TRS. The hardmetal is produced from ultrafine WC powder with 91.3 HRA and 3350 MPa TRS.