ASSESSMENT OF THE DISTRIBUTION OF NON-METALLIC INCLUSIONS IN STEEL PRODUCTS USING THE STEREOLOGICAL RECONSTRUCTION METHOD

Abstract

It is known that spinel in steels forms harmful inclusions that degrade the quality of the finished product. At the same time, to date, the mechanism of spinel formation and its stability in steel melts have not been fully elucidated, since the thermodynamic parameters of these processes have not been sufficiently studied, namely the free energies of formation and the activity of components in the range of solid solutions. It is shown that numerous scientific studies have studied the thermodynamic equilibrium in systems where spinel is formed and have proven the stability of spinel depending on the content of oxygen, aluminum and magnesium. Therefore, the purpose of our research was to determine the free energy of formation of magnesium and spinel at the temperatures of steelmaking processes, their activity coefficients and determine to which type of solid solutions the spinel solid solution can be attributed from the point of view of Raoult's law. At the first stage of our research, a thermodynamic analysis of the free energy of formation of spinel and its components was carried out using the equation of the chemical reaction isotherm, which relates the activities of reactants to the equilibrium constant of the chemical process. This allowed us to establish the main equations describing the change in Gibbs energy with temperature for each substance. Next, we conducted experimental studies using the method of establishing chemical equilibrium to determine the coefficients of spinel and its components. In the process of determining the activity of components in the spinel phase, a solid solution of spinel with a nonstoichiometric composition was in equilibrium with liquid copper in a graphite crucible at a constant gas ratio. After establishing chemical equilibrium, the activity of the components was determined using the equations that were derived during the thermodynamic analysis. We confirmed the formation of spinel in our experiments by X-ray diffraction and chemical analysis. The equilibrium content of aluminum and magnesium in copper was determined using inductively coupled plasma spectroscopy. In the course of the research, the phase boundaries of the spinel solid solution were determined using the diffusion vapor method. As a result of the work, the free energies of formation of magnesium oxide and spinel, as well as the activity of these components were determined using the chemical equilibrium method. It was found that the spinel solid solution demonstrates a negative deviation from Raoult's law.