Phase equilibrium in aluminum and calcium treatment economically alloyed manganese steel in units lined with magnesite-based refractories

Abstract

The ever-increasing requirements for the quality of products from pipe steel grades force metallurgists to pay increased attention to technologies for producing high-purity metal from non-metallic inclusions. A technological scheme is used for refining of metal alloyed with manganese with deoxidation of melt with aluminum and modification with calcium-containing alloys. Smelting and melt treatment are performed in units lined with magnesium-containing refractory materials. Although magnesium is not used as a refining element in steelmaking, non-metallic inclusions containing compounds related to magnesium spinels of variable composition are regularly found in rolled products. Magnesium spinels are among the most harmful types of non-metallic inclusions that have a significant negative impact on the performance properties of metal products. In this regard, it is of interest to study phase equilibria in the Fe–Mg–Al–Ca–Mn–O–C system. This paper presents the results of a thermodynamic analysis of this system at the temperature of out-of-furnace steel treatment. The state diagram of the ternary oxide system CaO–MnO–Al2O3 has been calculated and plotted. The isothermal isocompositional cross sections of a surface of solubility of components in metal (SSCM) of the Fe–Mg–Ca–Mn–Al–O–C system calculated for the ratio of components characteristic of grades 09G2S and steel 20 are presented in this work. The analysis of the constructed SSCM shows that the formation of endogenous refractory magnesium-containing non-metallic inclusions in real conditions is unlikely, and their presence in steel may indicate their exogenous nature. Measures to optimize the casting process on the CCM (optimum content of calcium and aluminum) are proposed. Calculations make it possible to correct the conditions under which CaO•2Al2O3 will be the predominant type of compounds formed, the most favorable type of compounds that is easily removed from the melt and has a minimal effect on its properties