How To Prepare Coarse-grained Tungsten Carbide Powder

Coarse-crystalline tungsten carbide (WC) can improve the impact toughness of cemented carbide, so coarse-grained and ultra-coarse-tungsten carbide hard alloys are widely used in petroleum drills, stamping dies, mining tools and other fields.

The grain size of the coarse-grained cemented carbide depends on the grain size of the WC powder. At present, the methods for preparing coarse-grained WC powder mainly include: high-temperature reduction, high-temperature carbonization, addition of alkaline earth metal or alkali metal element high-temperature carbonization method, ultra-fine tungsten powder high-temperature carbonization method, coarse-fine tungsten powder mixed carbonization method, aluminothermic method, etc.  

The difficulty encountered in the above process for producing tungsten carbide is the difference in density between tungsten and carbon. The carbonization process is accompanied by grain explosion. The obtained coarse-grained WC powder is a plurality of single-crystal tungsten carbide aggregates, several tens of micrometers.  The coarse-grained tungsten carbide powder is prepared to have a grain size of only a few micrometers, which eventually leads to incomplete carbonization, which seriously affects the quality of the finished cemented carbide.

In order to solve the volume expansion of the solid reaction, the diffusion of carbon in the solid phase is slow, so that the particles are cracked. Some researchers have mixed tungsten carbide powder with cobalt powder and graphite powder, high temperature treatment; acid leaching to remove cobalt after crushing; flotation to remove free carbon; drying to obtain coarse crystal tungsten carbide, the operation process includes:

(1) The tungsten carbide powder is mixed with the cobalt powder and the graphite powder in a ratio of a ball mill, the ball-to-batch ratio is 5:1, and the ball milling time is 1 to 3 hours;

(2) The mixture obtained in the step (1) is placed in the corundum dish. In the vacuum degree ≤ 50Pa or under the protection of inert gas 1450 ~ 1550 °C high temperature treatment, the oxygen partial pressure is less than 50Pa;

(3) The high temperature treated material is pulverized to a particle size ≤ 1mm;

(4) With 1:1  Hydrochloric acid leaching, 1kg of pulverized material consumes 0.8L of the hydrochloric acid;

(5)  After drying, grinding, sieving, particle size less than 74μm;

(6)  Second leaching with 1:1 hydrochloric acid, 0.5kg of 1kg permeate  Hydrochloric acid;

(7) Using kerosene as a collector, No. 2 oil as a foaming agent to remove free carbon; (8) Coarse-grained tungsten carbide is obtained after drying.

The method is simple in process, and the conventional tungsten carbide powder is used as a raw material, and the coarse-grained tungsten carbide powder is obtained by reprocessing, and the impurity content thereof is small, and the obtained tungsten carbide crystal grains are coarse and well-developed, and the hard alloy can be applied.

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