Thermodynamic Fundamentals for Alumina-content Control of Oxide Inclusions in Mn-Si Deoxidation of Molten Steel

抄録

In the deoxidation producing the MnO-SiO₂-Al₂O₃ inclusions, the significant ununiformity in the temperature dependence of equilibrium constant among the deoxidation reactions may cause the inclusions to change in their composition in cooling processes till solidification of steel melt. The present work concerns the compositional variation of the inclusions formed in the Mn-Si deoxidation of steel, focused on alumina content in the cooling process from 1848 to 1773 K.
In order to take the mass balances of the components involved in a reaction system, a reaction region was introduced which consisted of liquid steel bath and a certain amount of the oxides belonging to added flux and refractory of refining vessels. The compositional variation of the inclusions was estimated on the basis of the deoxidation equilibria and the mass balances. The thermodynamic analysis has revealed that the composition of inclusions has such a temperature dependence as to be considerably influenced by the initial total contents of reactants involved in the deoxidation system. It is suggested that high total contents of aluminum and oxygen in the initial state reduce the temperature dependence and thereby will facilitate the composition control in the cooling process till solidification.
In Mn-Si deoxidation, there may be two approaches to control alumina content of inclusions; one is to leave the target composition once attained at an appropriate temperature till solidification intact, and the other is to form inclusions stable on temperature falling through regulating the initial total contents of aluminum and oxygen to adequately high levels.