The present analysis of the experimental data by Yamamoto et al. permitted to determine the rate controlling mechanisms for the decarburization and evaporative manganese loss concurrently taking place during the oxygen refining process of ferromanganese melt.When oxygen is supplied by a top lance blowing mode, the decarburization reaction takes place by three different mechanisms in sequence. The chemical reaction at the melt-gas interface controls the rate of decarburization during the first period, the rate of oxygen supply through the boundary layer in gas during the second period, and the mass transfer rate of carbon in melt during the third period when the carbon content is less than 2 mass%.Manganese is lost primarily by evaporative reaction, but its dynamics are affected by the prevailing excess oxygen after accounting for CO formation. The excess oxygen and manganese vapor establish counter-current flux and form MnO mist at some distance away from the metal-gas interface. This creates two diffusion boundary layers, one for the flux of manganese vapor adjacent to the melt-gas interface and the other for the flux of excess oxygen in the gas phase. When the vapor pressure of manganese at the metal-gas interface is low, the rate of manganese vapor loss is controlled by the flux of excess oxygen. Otherwise, it is determined by the flux of manganese vapor.

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The lattice site ratio model proposed by Chipman describes the activity of the interstitial solutes in the alloy systems in terms of the ratio of filled to unfilled sites as a concentration parameter. Chipman and co-workers successfully applied the model to describe the solution behavior of C and S in the various alloy systems. The meaning of the lattice for the liquid system is not same as that for the solid system, as it does not retain the rigidity of a solid crystalline structure and a long-range order in the atomic arrangement. Still, the liquid system maintains a short-range order with a similar structure to that of the close-packed solid system, and the application of the lattice site ratio model to the liquid system is justified. The present study assessed the thermodynamic properties of the liquid Fe-Mn-C system with the use of the lattice site ratio model. It was found that the solution properties of the ternary Fe-Mn-C system can be represented as linear combinations of those of the constituent binary systems if they are defined in the lattice site ratio model. This is not the case when the solution properties are given in the mole fraction coordinate. The lattice site ratio model reproduced closely the experimentally determined solubility of C and the activities of C and Mn in the Fe-Mn-C system.

A review of studies by Safarian et al. and Kim show that the smelting reaction at equilibrium for ferromanganese and silicomanganese alloys is defined by the coupled reaction in the carbon-saturated condition $$ 2\underline{\text{Mn}} + \, \left( {{\text{SiO}}_{ 2} } \right) \, = { 2 }\left( {\text{MnO}} \right) \, + \underline{\text{Si}} $$ 2 Mn ̲ + SiO 2 = 2 MnO + Si ̲ . The behavior of slag at equilibrium is described by MnO and SiO2 as dependent variables and by non-reacting species, CaO, MgO, and Al2O3, as independent variables. Its characteristic behaviors are assessed in the pseudobinary system of MnO and SiO2 fixed by non-reacting components with analyses of ferromanganese and silicomanganese slag from one-month smelting operations. The behavior of fluid slag is defined by their melting temperature provided by phase equilibria of slag system. Liquidus of manganese slag systems by Kang et al., Zhao et al., and Roghani et al. is reconstructed in coordinates of MnO and SiO2 at fixed contents of CaO, MgO, and Al2O3. Conditions for fluid smelting slag are examined by referencing characteristic behaviors of smelting slag to liquidus of manganese slag systems to assess the effect of MgO and Al2O3. MgO facilitates fluid silicomanganese slag but would make ferromanganese slag viscous. Al2O3 makes silicomanganese slag fluid at Al2O3 content with 0.41 by weight ratio to SiO2. At higher contents of Al2O3, silicomanganese slag would be viscous with low MnO contents in slag. Al2O3 facilitates the development of fluid ferromanganese slag.