Thermodynamic Analysis of the Processes in the High-Temperature Multicomponent Fe–Y–Si–O–C System

Special complex alloys of rare earth metals are recommended to perform deoxidation, microalloying, and modification in the production of low-carbon and high-quality steels. To reveal the mechanism of action of each alloy component, it is necessary to differentiate the action of each individual element. Yttrium is commonly referred to as rare earth metals, but its deoxidizing and modifying abilities have not been sufficiently studied. The use of yttrium is known to an increase the density, plasticity, scale resistance, and high-temperature corrosion resistance of steel and to substantially affect the shape, size, and distribution of nonmetallic inclusions. In this work, the interaction of yttrium, silicon, and carbon with oxygen dissolved in liquid iron is considered. The nonmetallic inclusions formed in this case can be determined on the FeO–Y2O3–SiO2 phase diagram. This diagram is not available in the literature; therefore, we modeled it using the available binary phase diagrams FeO–Y2O3, FeO–SiO2, and Y2O3–SiO2. Combined deoxidation with yttrium and silicon is possible only at yttrium concentrations of less than 0.0001% in liquid iron (oxide melt or yttrium silicates form as nonmetallic inclusions). If the yttrium concentration is higher than this value, yttrium is the only deoxidizer. In the presence of carbon, liquid nonmetallic inclusions can form in a very narrow liquid metal composition region, and the main nonmetallic oxide inclusion is yttrium oxide. At an yttrium concentrations below 0.0001% and a silicon concentration up to 1%, only carbon is a deoxidizer. Taking into account the Fe–Y–M–O–C (M = Ca, Mg, Al, Cr) systems studied earlier, we created a thermodynamic database was created for designing the compositions of complex yttrium-containing master alloys.