Under industrial conditions, the process can be performed in two steps, one following the other. The first step-reduction-affords the complete exclusion of hydrogen and is performed in nitrogen atmosphere. In the presence 0f hydrogen, water vapor would form which generates tungsten crystal growth and consumption of carbon (C+H2O→CO+H2). This carbon consumption is not only restricted to the carbon black or graphite used as reagent (disturbance of the carbon balance), but also to the furnace carbon tube (shortening its lifetime). The second step-carburization-needs a hydrogen atmosphere, which supports the carbon transport via methane to the tungsten particle surface.
Accordingly, the direct carburization process starts with a pelletized mixture of WO3 and graphite passing step-by-step two rotary furnaces, the first operating at 950-1250℃ under nitrogen (reduction) and the second at 1400℃ under hydrogen (carburization).
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