Thermodynamic analysis of the interaction between chromium and oxygen in the liquid iron

The study of the possibility of the interaction between chromium and oxygen during the production of chromium-containing steels is one of the practically important tasks for the steelmaking. In the present work, thermodynamic modeling of phase equilibria in the temperature range 1600-1800 °C for the Fe-Cr-O system was carried out. Thermodynamic analysis was performed using the method for constructing of the surface solubility of components in a metal, which is a diagram linking changes in the compositions of the liquid metal with changes in the compositions of the resulting interaction products. For the simulation, we used the data on the equilibrium constants of the reactions occurring in the melt, as well as the values of the first-order interaction parameters (according to Wagner) of the components in the liquid iron. In the course of the work, it was found that, in the temperature range 1600-1800 °C, the following products can be formed as interaction products: liquid oxide nonmetallic inclusions of variable composition (FeO, CrO, Cr2O3); solid particles of the ferrochromite FeCr2O4; pure solid chromium oxide Cr2O3; solid particles of the compound Cr3O4. The boundaries of the thermodynamic stability of these oxide phases formed in the melt of the Fe-Cr-O system were also determined. According to the calculation results, the deoxidizing ability of chromium in an oxygen-containing iron-based melt was evaluated. It is determined that the maximum deoxidizing ability of chromium at 1600 °C falls on the equilibrium region of the liquid metal with the solid chromium oxide Cr2O3, while the minimum oxygen concentration is 0.0204 wt. % for 5.31 wt. % chromium. The results obtained in the course of this calculation were compared with the available literature data.