Thermodynamic Analysis of Liquid Steel Refining by Complex La–Ce–Al-Based Alloy

Alloys containing additions of rare-earth metals (REMs) are increasingly used in the production of steels and alloys. After modification and microalloying of steel with REMs, the structure of a primary metal becomes finer, its mechanical characteristics are improved, and the oxygen concentration dissolved in liquid iron decreases significantly. The size of the forming nonmetallic inclusions does not exceed several microns in size, and they have a predominantly globular shape. Due to relatively high cost of REMs, it is proposed to calculate their consumption at each technological process stage to determine optimal amount required for deoxidation or modification. In this work, thermodynamic modeling of phase equilibrium in liquid metal of the Fe–La–Ce–Al–O system has been performed. We present a thermodynamic database of this system: temperature dependences of equilibrium constants found in reactions between components, the first-order parameters of interaction (according to Wagner) for elements in liquid iron, the energy parameter values of the theory of subregular solutions (for oxide melt) and regular ionic solutions (for solid solution). Based on coordinates of the calculated isothermal (1600°C) isostructural (0.01 wt % Al) section found on the solubility surface of metal components (SSSM) of the Fe–La–Ce–Al–O system, we have plotted the consumption diagrams of La and Ce for various initial oxygen concentrations (metal is pre-deoxidized with aluminum). The consumption of expensive REMs used in microalloying and metal modification has been shown to strongly depend on the initial metal composition.