Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al_2O_3-Based Inclusions from Liquid Steel

摘要

Dissolution of Al_2O_3-based inclusions are paramount during production of special steel and slag engineering is key to enhance this phenomenon. This work evaluates the influence of thermodynamic driving force (ΔC) and effective viscosity (η_e) on steel cleanliness of three distinct steel grades and slag composition (Steel/Slag A, Steel/Slag B and Steel/Slag C). Initial and final steel and slag samples were withdrawal on an electric steelmaking facility. The first samples after addition of aluminum as deoxidizer and the second after vacuum degassing stage. X-ray fluorescence and optical spectrometry obtained initial and final samples chemical composition. An ASPEX Explorer acquired inclusions data and FactSage v.7.2 performed thermodynamic calculations. Analysis of steel Al and O content highlighted an inefficient dissolution of Al_2O_3-based inclusions for Steel/Slag A, deteriorating steel cleanliness. Furthermore, this phenomenon is supported by average inclusions composition on initial and final samples plotted in pseudo-ternary diagram. Steel/Slag B and C provided improved results regarding the dissolution of Al_2O_3-based inclusions with a final inclusion density below 0.50 mm~(-2). These two slags composition achieved values of ΔC above 25 and η_e close to 0.10 Pa·s. In addition, their combined effect (ΔC/η_e) presented values above 250 and had the highest linear fit among these analyses. These properties are influenced by slags chemical composition and can be improved controlling parameters as binary basicity and CaO/Al_2O_3 ratio. Slags B and C were selected to define an optimal range for these parameters, with binary basicity between 3.00-3.50 and CaO/Al_2O_3 ratio in a range from 2.50-3.50.