Computational Thermodynamics of Oxide Inclusion Formation During Secondary Metallurgy in Nigerian Electric Arc Furnace Steelmaking

This study applies computational thermodynamics to model the formation, composition evolution, and removal behaviour of oxide inclusions during the ladle metallurgy and continuous casting stages of electric arc furnace steelmaking at Nigerian steel plants. Non-metallic inclusions are critical determinants of final steel cleanliness and downstream product performance, particularly for wire rod and structural bar applications, and their control through secondary metallurgy optimisation requires a thermodynamic foundation that accounts for the complex multi-oxide phase equilibria in the Fe-Al-Ca-Si-O-S system. A multi-step thermodynamic calculation procedure is implemented in FactSage using the coupled FSTEL, FToxid, and FactPS databases, simulating inclusion composition changes during ladle furnace heating, calcium treatment, and argon stirring under varying steel and slag chemistry conditions. The thermodynamic model incorporates a modified inclusion flotation removal kinetics model based on Stokes' law and modified for tortuous path diffusion in turbulent steel. The model is parameterised and validated against industrial inclusion data obtained from total oxygen content measurements, automated SEM-EDS (ASPEX) inclusion analysis on tundish and strand samples collected from a cooperating Nigerian steel plant. The validated model is used to develop optimised calcium treatment and argon stirring protocols for inclusion morphology control. The study makes an original contribution to inclusion engineering for Nigerian EAF steelmaking. Keywords: oxide inclusions, computational thermodynamics, secondary metallurgy, EAF steelmaking, FactSage.