Using tungsten and carbon as raw materials, tungsten powder with an average particle size of 3-5 micron was dried mixed with carbon black of the same amount by ball mill. After fully mixing, it was pressed into graphite disc and heated to 1400-1700 C in graphite resistance furnace or induction furnace, preferably at 1550-1650 C. In the hydrogen flow, W2C is initially formed and then reacts at high temperature to form WC. Or, tungsten powder can be prepared by thermal decomposition of hexacarbonyl tungsten in 650-1000 (?) C and CO atmosphere, and then reacted with carbon monoxide at 1150 (?) C to form W2C at a temperature higher than that.
Chemical Reaction Formula:
W + C = W 2C
W + C = WC
Tungsten powder (average particle size 3-5 micron) was prepared by hydrogenation and reduction of tungsten trioxide WO3. Then the mixture of tungsten powder and carbon black in equal molar ratio (dry mixing with ball mill for about 10 h) was formed under pressure of about 1 t/cm 2. The pressure moulding material is put into a graphite plate or crucible, heated to 1400-1700 (- 35 dew point pure hydrogen) by graphite resistance furnace or induction furnace in hydrogen flow (preferably 1550-1650 dew point), and then carburized to form WC. The reaction starts around tungsten particles, because W2C is formed in the early stage of the reaction. Because of the incomplete reaction (mainly the low reaction temperature), there are still unreacted W and intermediate W2C besides WC. So it must be heated to the above high temperature. The maximum temperature should be determined according to the particle size of raw tungsten. If the average particle size is about 150 micron, the reaction will be carried out at high temperature of 1550-1650 C.
Chemical Reaction Formula:
WO3+3H2_W+3H2
2WO3+3C_2W+3CO2
W + C = W 2C
W + C = WC
According to the requirement of WC particle size of tungsten carbide, tungsten carbide with different particle sizes is used for different purposes of cemented carbide; carbide cutting tools, such as foot cutter blade V-CUT cutter, are used for superfine tungsten carbide; coarse tungsten carbide is used for rough processing alloys; medium coarse tungsten carbide is used for gravity cutting and heavy cutting alloys; Coarse tungsten carbide is used for rock hardness and high impact load; medium-sized tungsten carbide is used as raw material for wear-resistant parts with small impact load; ultra-fine and medium-sized tungsten carbide is used as raw material when stress is laid on its wear resistance, compression resistance and surface finish; medium-sized and coarse-sized tungsten carbide is used as main raw material for impact-resistant tools.
The theoretical carbon content of tungsten carbide is 6.128% (atom 50%). When the carbon content of tungsten carbide is greater than the theoretical carbon content, free carbon (WC+C) appears in tungsten carbide. When the free carbon exists in tungsten carbide, the grain of tungsten carbide around it grows up, resulting in uneven grain size of cemented carbide. Tungsten carbide generally requires high combined carbon (> 6.07%) free carbon (< 0.05%) and the total carbon depends on the generation of cemented carbide. Production process and application scope.
Under normal conditions, the total carbon of tungsten carbide used in vacuum sintering of paraffin process is mainly determined by the oxygen content in the compact before sintering, which increases by 0.75 carbon, i.e. WC total carbon = 6.13%+oxygen content%*0.75 (assuming that the sintering furnace is neutral atmosphere, in fact, the total carbon of tungsten carbide used in most vacuum furnaces for carburizing atmosphere is less than the calculated value). The total carbon content of tungsten carbide in China can be roughly divided into three kinds: the total carbon of tungsten carbide used in vacuum sintering of paraffin process is about 6.18 (+0.03%) and the total carbon content of tungsten carbide used in hydrogen sintering of paraffin process is 6.13 (+0.03%). The total carbon of tungsten carbide used in hydrogen sintering of rubber process is 5.90 (+0.03%).
The total carbon of WC used in alloys with different application range, cobalt content and grain size can be adjusted slightly. Tungsten carbide with high total carbon can be used for low cobalt alloy and tungsten carbide with low total carbon can be used for high cobalt alloy. In a word, the particle size of tungsten carbide varies with the demand of cemented carbide.
Langsun Carbide has all kinds of shapes and sizes of cemented carbide products including carbide rods, carbide plates, carbide rings, carbide bushings, carbide nozzles, carbide balls, valves and nonstandard carbide parts. We feel very pride that our tungsten carbide products are widely used in the following fields, Mechanical seals, oil and natural gas industry, New Energy, Military industry, Aerospace, Auto parts industry, Steel smelting, Coal mining, Chemical industry. More detail: www.ls-carbide.com
