Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al₂O₃-Based Inclusions from Liquid Steel

Abstract

Dissolution of Al 2 O 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 2 O 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 2 O 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 2 O 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 2 O 3 ratio in a range from 2.50-3.50.

Formation and Evolution Mechanism of the Inclusions of Al2O3·SiO2·CaO and Al2O3·SiO2·CaO·MgO in Seamless Steel Tube Steel

“…[25] The erosion of the furnace lining results in some MgO entering into the molten slag, and the increase in the contents of Al 2 O 3 and SiO 2 also decreases the MgO content in the slag, so the MgO content in the molten slag changes little. These results are basically consistent with those of Yang et al [25] The changes in average contents of the oxides and the corresponding R values in the Al 8) and (9).…”

“…In recent years, some investigations on the formation of the inclusions in steel were carried out with thermodynamic analysis. [5][6][7][8][9][10][11] For example, Wang et al [7] investigated the effect of oxide component content on the low melting point zone in the Al 2 O 3 •SiO 2 •CaO•MgO system using FactSage software. It was found that the low melting point zone becomes wide with the increase in CaO content within the range of 0-30 mass% and the decrease in SiO 2 content within the range of 5-25 mass%.…”

Thermodynamic evaluation of viscosity behavior for CaO–SiO2–Al2O3–MgO slag systems examined at the temperatures range from 1500 to 1700 °C

“…Each chemical composition of the liquid phase resulting is then used as input data for the calculation of the viscosity in the Viscosity module. Phase diagram module for computation of phase equilibria in the quaternary phase diagram of CaO–SiO 2 –Al 2 O 3 –(0–15%) MgO slag were also used 14 , 17 , 24 , 25 , 27 , 28 , 50 .…”

“…From the Viscosity module (Melts database) is calculated the liquid slag viscosity (hl) 14 , 17 , 24 , 25 , 27 , 28 , 50 . This software uses the modified Quasichemical model (MQM), to describe the thermodynamic behavior of the liquid slag, which used quadruplet data detained from MQM, to calculate the viscosity of liquid 42 , 46 – 48 .…”

Laboratory Evaluation of Tundish Covering Powders and Rice Hull Ash on Cleanliness for a SAE 1055 Modified Steel

“…Elemental compositions of the tundish covering powders and of the rice hull ash, in wt.% (as-received industrial samples).height. The experiments were carried out in a resistive furnace 'HT-2100-Spezial'; details on this apparatus can be found in10 . The furnace works with a constant flux of argon (82 liters per hour) to avoid reoxidation by air.…”