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INTERNATIONAL TUNGSTEN INDUSTRY ASSOCIATION
Information on tungsten: sources, properties and uses
Intermediates
Ammonium Paratungstate (APT)
APT [(NH4)10[H2W12O42] · 4 H2O] is the main intermediate and also the main tungsten raw material traded in the market. APT is usually calcined to yellow (WO3) or blue oxide (WO3-X; a slightly substoichimetric trioxide with varying oxygen content). 
Tungsten Metal Powder (W)
Yellow or blue oxide is reduced to tungsten metal powder by hydrogen. The reduction is carried out either in pusher furnaces, in which the powder passes through the furnace in boats, or in rotary furnaces, at 700-1,000°C.
Tungsten Carbide (WC)
Most of the tungsten metal powder is converted to tungsten carbide (WC) by reaction with pure carbon powder, e.g. carbon black, at 900 - 2,200°C in pusher or batch furnaces, a process called carburization.
Tungsten carbide is, quantitatively, the most important tungsten compound. Because of its hardness, it is the main constituent in cemented carbide (hardmetal).
Cast Carbide
By melting tungsten metal and tungsten monocarbide (WC) together, a eutectic composition of WC and W2C is formed. This melt is cast and rapidly quenched to form extremely hard solid particles having a fine crystal structure. A tough, feather-like structure is preferred over the brittle, blocky structure obtained by insufficient quenching. The solids are crushed and classified to various mesh sizes.