Preferably, the carbon reducing agent is employed in excess of that stoichiometrically required and is usually controlled within a stoichiometric ratio of from about 1.05 to about 1.20 times that theoretically required. Amounts of carbon above about 20% in excess of that stoichiometrically required are undesirable due to the retention of excessive carbon in the resultant ferrotungsten alloy pellets, rendering them less desirable as an alloying addition agent in some instances. It is also contemplated that small percentages of the carbonaceous reducing agent, such as carbon, can be incorporated when the iron bearing material comprises metallic iron powders for the purpose of reducing any oxides present on the iron particle surfaces. Generally employing the carbonaceous reducing agent in amount up to about 1% of the iron-bearing material employed is effective for this purpose and provides for ferrotungsten alloys of relatively high purity.

The mineral concentrate, the carbonaceous reducing agent and any supplemental iron-bearing constituent are blended mechanically in appropriate proportions to form a substantially homogeneous or uniform blend. It is important that the particulated mixture is first agglomerated into briquettes or pellets of a size which facilitates their handling and also assures the formation of a porous bed to permit an escape of the volatile constituents and gaseous reaction products of the oxidized reducing agent from the agglomerates during the vacuum smelting operation. The particular configuration and size of the pellets are not critical, and to some extent, will be dictated by the particular type of agglomerating process and equipment employed. Generally, pellets of a spherical configuration, such as derived from a disc-type pelletizing apparatus, having diameters ranging from about 1/8 inch up to about 1/2 inch, are satisfactory.

 

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Rare earth usually contains one or two kinds of Y, La, Ce, Pr, Gd, Nd, etc. And the main form of adding is rare earth metal, oxide or mixed rare earth. There are some improvements of rare earth: One is due to rare earth lively properties and easily combined with Oxygen nitrogen carbon and sulfur, tungsten carbide impurities will come into being rare earth compounds and distribute in the grain boundary, which prevent liquid Co phase from dissolving and moving grain boundary. Therefore, the region growth of WC grain has been suppressed and refines the particle.

The other one is due to the spherical compound and impurity elements combine to form a rare earth element, it played on the binder phase dispersion strengthening effect, which remove impurities further and purified grain boundaries. In addition, rare earth element can also reduce the sintering temperature of tungsten carbide nozzle, to reconcile the contradiction between grain growth and sintering density and remarkably improve the toughness and bending strength of tungsten carbide.

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When a metallic iron powder is employed as the iron-bearing constituent, the average particle size is not critical and may range from about 175 microns to about 74 microns, and preferably is controlled at an average particle size of about 125 microns to about 100 microns. When iron oxide is employed as the iron-bearing material, the iron oxide may suitably be introduced in the form of a fine-sized powder, preferably of an average particle size ranging from about 44 microns to about 10 microns. The iron oxide powder preferably comprises ferric oxide (Fe2 O3), which may be conveniently derived from sources such as millscale, a by-product of hot rolling steel, or the like. When all or a portion of the iron-bearing constituent is introduced in the form of an iron oxide compound, an appropriate amount of carbonaceous reducing material or reducing agent is incorporated in the mixture to effect a substantially complete reduction of the iron oxide to the corresponding metallic state.

In addition to the mineral concentrate and any iron-bearing material, if employed, the particulated mixture contains a fine-sized particulated carbonaceous reducing agent, of which carbon powder itself of an average particle size ranging from about 44 microns to about 10 microns constitutes the preferred material. The quantity of carbon or other carbonaceous reducing agent is employed in an amount at least equal to that stoichiometrically required to effect a substantially complete reduction of the tungsten oxide and any iron oxide present to the metallic state in accordance with the following typical reaction equations: WO3 + 3C ➝ W + 3CO 2Fe2 O3 + 6C ➝ 4Fe + 6CO

 

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Some scientists have developed a new type of inhibitor, which adds the insoluble metal carbides into Co-rich matrix to form a solid solution as inhibitors. It decrease the added inhibitors Co-rich carbide substrate drops below the melting point of 1200 ℃, and formed the stable metal / non-metal atoms in the liquid phase Co group, which is W, V, Cr / C radicals.

This radical prevent W atom and C atom from moving between the grains in liquid phase, which decreases the speed of WC grain growth further and improves the compactness and the lifespan of tungsten carbide buttons. Aside from the grain growth inhibitor above, rare earth element also serves as a common inhibitor used to inhibit tungsten carbide grain growth and improve properties of tungsten carbide nozzle during sintering.















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