Phase formation in the WC–Fe$_2$O$_3$–NiO–Co$_3$O$_4$ carbide-oxide system with and without free carbon during the heating in vacuum and in an argon atmosphere is studied. Superfine soot and sucrose are used as free carbon. As established, at the absence of free carbon in the carbide-oxide system the active interaction between carbon from tungsten carbide and oxygen from metal oxides takes place that shows up in the formation of a complex oxide (MeWO$_4$), intermetallic compound (Me$_7$W$_6$) and pure tungsten. The addition of free carbon allows keeping tungsten carbide partly or completely and reducing metals from their oxide. If there is a lack of free carbon, some part of the carbon contained in tungsten carbide begins to interact with oxygen and complex carbides of the type Me$_6$C, Me$_{12}$C are formed in the system. With the required amount of carbon, tungsten carbide is preserved and a matrix metal is formed in the form of a solid solution with f.c.c. or b.c.c. structure. The crystal structure of the solid solution is determined by the proportion of metal oxides in the initial mixture. During heating process in vacuum, more carbon is spent to remove the same amount of oxygen in comparison with heating in an argon atmosphere.