Thermodynamic analysis of liquid steel refining by complex alloy containing La - Ce -Al

Alloys containing rare-earth metals (REM) are increasingly used in production of steels and alloys. After modification and microalloying of steel with REM, structure of primary metal is refined, its mechanical characteristics are upgraded, concentration of oxygen dissolved in liquid iron is decreased significantly, and originated nonmetallic inclusions do not exceed several microns in size and are of predominantly globular shape. Due to relatively high cost of REM, it is proposed to calculate their consumption at each stage of technological process to determine optimal amount required for deoxidation or modification. In this work, thermodynamic modeling of phase equilibria in liquid metal of Fe - La - Ce -Al - O system has been performed. The authors provide a base of thermodynamic data of the system under study: temperature dependences of the equilibrium constants of reactions between the components, values of the first-order interaction parameters (according to Wagner) for elements in liquid iron, values of energy parameters of the theory of subregular (for oxide melt) and regular (for solid solution) ionic solutions. Based on coordinates of calculated isothermal (1600 °С) isostructural (0.01 wt. % aluminum) cross section of solubility surface of components in metal (SSCM) of the Fe - La - Ce -Al - O system, lanthanum and cerium flow diagrams were constructed for various initial oxygen concentrations (metal is pre-deoxidized with aluminum). It has been shown that costs of expensive REM used in microalloying and metal modification strongly depend on composition of the initial metal.

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