Phase equilibrium occurring during low-carbon iron-based melt deoxidation with silicostrontium

Abstract

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).