Thermodynamic modeling of phase equilibria with the subsequent construction of the phase diagram of the SrO–Al2O3 system has been carried out. To calculate the activities of the oxide melt in the course of this work, we used the approximation of the theory of subregular ionic solutions, with the most optimal values of the energy parameters Q1112 = –104 349: Q1122 = –217 689; Q1222 = –104 436 J/mole. The results obtained for the liquidus line in this work are in good agreement with the literature experimental data. In the course of the calculation, the values of the equilibrium constants for the formation of strontium aluminates from the components of the oxide melt were estimated.
At the moment, to improve quality of metal (especially low-alloyed), out-of-furnace steel processing technologies are used with complex alloys utilization, which include alkaline earth metals (ALM) in addition to silicon. Study of strontium additives effect on deoxidation and liquid steel modification processes is one of the promising areas of research in field of metallurgical technologies. Thermodynamic modeling of phase equilibria in Fe – Sr – Si –C– O system melt was carried out using method of constructing surface of components solubility in metal. Solubility surface determines stability limits of non-metallic phases formed during deoxidation, depending on composition of liquid metal of the studied system. The calculation was carried out using equilibrium constants of reactions occurring in the melt during deoxidation, as well as the first order interaction parameters (according to Wagner) of elements in liquid iron. Activity of the oxide melt components was determined using theory of subregular ionic solutions. Activity of the gas phase was calculated taking into account partial pressures. Simulations were performed for two temperatures (1550 and 1600 °C) for fixed carbon concentrations (0 (no carbon in liquid iron) and 0.1 % (low-carbon metal melt)). It has been shown that, in comparison with silicon, strontium is stronger deoxidizing agent in liquid metal. According to the simulation results, liquid oxide non-metallic inclusions of variable composition or strontium ortho- and metasilicates Sr2SiO4 and SrSiO3 (with an increase in strontium concentration) should be the main oxide phases in deoxidation products. Decrease in the temperature of liquid metal leads to changes in phase formation (formation of SrSiO3 silicate becomes possible).
Phase diagram of the ternary oxide system FeO - SrO -Al2O3 was constructed for the first time. In this system, the following compounds can be formed: hercynite FeAl2O4 and five strontium aluminates - Sr4Al2O7 , Sr3Al2O6 , SrAl2O4 , SrAl4O7 , SrAl12O19 . According to the calculations performed, solid solutions of oxides are not formed in the system, as it is confirmed by the literature data. In the course of modeling, the optimal energy parameters of the theory of subregular ionic solutions were selected for the components of the oxide melt (FeO, SrO, Al2O3 ). Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum was carried out using the technique for constructing the surface of solubility of strontium and aluminum in metal for steelmaking temperatures (1550 and 1600 °C) and carbon concentrations of 0.1 and 0.4 %. The equilibrium constants of the reactions of formation of strontium aluminates Sr3Al2O6 and SrAl2O4 from the components of the metal melt were calculated for the temperature range of 1550 - 1650 °C. It was found that the rest of strontium aluminates can be formed in liquid metal only at temperatures above 1750 °C. The base of thermodynamic data for the studied systems is given: temperature dependences of equilibrium constants for reactions occurring between components; values of interaction parameters of the first order (according to Wagner) for elements in liquid iron; values of energy parameters of the theory of subregular ionic solutions (for oxide melt). It follows from the calculations that the formation of strontium monoaluminate SrAl2O4 and corundum Al2O3 is most probable as the interaction products in Fe -Al - Sr - O and Fe -Al - Sr - C - O systems.
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