Tungsten Carbide Direct Reduction and Carbonization Technology

The ultrafine cemented carbide made of ultrafine tungsten carbide powder has the characteristics of high strength and high hardness. It effectively solves the contradiction between hardness and strength of traditional cemented carbide, widely used in the production of integrated circuit board micro drill, dot matrix printer print needle, precision mould, tool, woodworking tools, medical drill etc..

Direct reduction and carbonization technology is an advanced technology for producing ultrafine tungsten carbide powder. Generally, tungsten precursor powder and a certain proportion of carbon source are heated in a non oxidizing atmosphere, and the reduction reaction and carbonization reaction are carried out at the same time to obtain tungsten carbide powder. The main processes are as follows:

1.The precursor powder was wet-milled in an alcohol solution for 12 to 30 hours and dried for 5 to 30 hours, sieved, loaded into a graphite boat, and once carbonized under a non-oxidizing atmosphere with a carbonization temperature of 1000 to 1400 ℃, the mass percentage of carbon black in the precursor powder is 13.4-14.5% and the balance is purple tungsten with the particle diameter less than 12 um, and the primary carbonization time is 1-3 hours to obtain the primary carbonized product;

2.The obtained carbonization product was ball mixed for 2 to 3 hours, the carbon content was measured, the amount of carbon was adjusted to 6.10 to 6.30%, and then ball milling for 3 to 6 hours followed by hydrogenation under a second carbonization temperature 1200 ~ 1300 ℃, the carbonization time is 1 ~ 3 hours to obtain the second carbonization product;

3.The obtained secondary carbide ball milling 4 to 6 hours, sieved to obtain ultrafine tungsten carbide powder.

To get a better particle size distribution, can be added in the chromium oxide precursor powder as crystal growth inhibitors, and ball milling. The optimum addition ratio of chromium oxide precursor powder weight 0.7% ~ 1%.

In the process, the violet tungsten after long time milling, fine granularity, direct reduction carbonization under suitable conditions, can make the carbon content of the products get better control, so the production of ultrafine tungsten carbide powder with narrow particle size distribution, dispersion and uniformity is better, more close to the total carbon content of stoichiometric amount of carbon, lower carbon free.

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