Superfine Tungsten Powder to Boost Super Coarse Grained Cemented Carbide

The main method of producing super coarse grained cemented carbide is the use of super coarse tungsten carbide powder and cobalt powder as raw materials. It is pressed and sintered to become a product after batching, ball milling, drying and granulation. However, the ultra coarse tungsten carbide powder will break in the process of ball milling, and the grain size will decrease greatly. During the sintering process, the WC grain can not grow into an ultra coarse grained WC grain.

Some scholars have provided a preparation method of super coarse crystalline cemented carbide. In the process of sintering, there are WC grain with different grain size. The energy of the system is not balanced. The coarse WC grain will grow up to be super coarse WC grain through dissolution precipitation mechanism, the fine WC grain will gradually decrease and eventually become super coarse WC-Co cemented carbide. In this scheme, a suitable amount of fine tungsten carbide powder is added to the raw material. Through suitable ball milling and sintering process, the super coarse grain hard alloy with grain size of 6.0-14.0μm can be prepared successfully, which includes the following steps:

(1) The steps of preparation of fine tungsten carbide powder: Select the fine tungsten carbide powder with an average size of 0.4μm, with the purity of WC more than 98wt%, wet grinding in a rolling ball mill with anhydrous alcohol as the medium, the ratio of the ball to the cemented carbide grinding ball and the fine tungsten carbide powder is 6: 1, the liquid and solid ratio of the anhydrous alcohol and the fine tungsten carbide powder is 280mL/kg. After the ball milling, the ball mill is 72 hours after the ball mill. After vacuum drying, the average particle size of fine tungsten carbide powder after ball milling is 0.2μm.

(2) The step of mixture preparation: Using super coarse tungsten carbide powder of 20.7μm as the main raw material, adding tungsten fine carbide powder, cobalt powder, cobalt powder to make up 10wt% of the total raw material, 10wt% of fine tungsten carbide powder, the rest of super coarse tungsten carbide powder, and paraffin form agent, paraffin and tungsten carbide powder 2.0wt% of the total weight of tungsten carbide powder and fine tungsten carbide powder, then wet grinding in a rolling ball mill with anhydrous alcohol as medium, the ratio of the ball material of hard alloy grinding ball to solid material is 2.5: 1, the liquid and solid ratio of water alcohol and solid material is 280mL/kg, the mixture are prepared by vacuum drying after the ball milling for 18 hours. It contains ultra coarse tungsten carbide powder and fine tungsten carbide powder with an average particle size of 7.5μm and 0.2μm respectively.

(3) The mixture is passed through a mesh of 80 mesh and rolling for 2 minutes in the granulator, so that the mixture has a certain fluidity. The mixture is pressed into compacted blank, and the pressing pressure is 150MPa.

(4) The pressed blank is sintered into a super coarse WC-Co cemented carbide, when sintering, the pressed blank is sintered under the vacuum condition, the sintering temperature is controlled at 1450 °C, the heat preservation time is controlled for 1 hours, the pressure in the sintering furnace is kept at 1000Pa. The final average grain size of the prepared crystal is 10 μm, the particle size distribution is uniform.

This method has the characteristics of simple process, low production cost and uniform particle size distribution of WC in alloy products. It is an effective preparation method for the effective super coarse WC-Co cemented carbide.

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