THERMODYNAMIC MODELING OF PHASE EQUILIBRIA AT STEEL ALLOYED WITH MANGANESE AND CHROME

Abstract

In order to analyze the phase equilibria that are realized in the Fe–Mn–Cr–C–O system at the liquid metal existence temperatures, an extensive material on the thermodynamics of the interaction reactions of components dissolved in liquid iron has been generalized and systematized, and a database of mutually consistent data has been created. For the first time, the thermodynamic modeling of liquidus line coordinates has been performed and state diagrams for MnO–Cr2O3 and FeO–MnO–Cr2O3 systems have been plotted. The temperature for MnCr2O4 incongruent melting ( = 1812°С) and the enthalpy and entropy for formation of this compound from the components of the oxide melt of the MnO–Cr2O3 system were calculated ( = 190.77 kJ/mol and ( = 75.62 J/(mol•K), respectively). It is shown that for the FeO–MnO–Cr2O3 system phase diagram, there are extensive areas of equilibrium for the oxide melt with solid oxides solutions FeO, MnO and solid solutions of chromites FeCr2O4, MnCr2O4 with variable composition. The energy parameters of the theory of subregular ionic solutions were determined and used for calculation of the activities of oxide melt components (FeO, Cr2O3, MnO). The data obtained made it possible to refine the boundaries of the liquid metal composition in areas, which is in equilibrium with specific oxide phases. It is shown that at steelmaking temperature (1600°C) and contents of manganese and chromium in liquid iron about 1 wt. %, the formation of spinels’ solid solution inclusions is possible. Increasing the temperature to 1800°C (for example, when metal is blown with oxy-gen) can shift the equilibrium towards the formation of liquid oxide inclusions. The obtained results can be used in modeling of steel alloying with manganese and chromium. The effect of carbon on the nature of the phase equilibria that are realized in the system is taken into account. It is shown that already at a carbon content in the liquid metal at the level of 0.1–0.2 wt. %, there is a wide range of metal compositions that are in equilibrium with the gas phase {CO, CO2}. The obtained results can be used in modeling of the processes of steel alloying with manganese and chromium