Thermodynamic Model Of Mold Flux And Kinetic Model Of Reaction Process In Continuous Casting Of High Aluminum Steel

The traditional protective slag system of the mold for high-aluminum steel continuous casting contains a high concentration of SiO₂.High aluminum steel will chemically react with SiO₂ in the protective slag due to its high aluminum content,resulting in a sharp decrease in SiO₂ content and a sharp increase in Al₂O₃ content,destroying the original composition of the protective slag,resulting in drastic changes in the viscosity,melting point,crystallization properties and other physical and chemical properties of the protective slag,and the continuous casting process will be affected accordingly.The study of the thermodynamics of the reaction in high-aluminum steel continuous casting（especially the activity of the components in the protective slag）and the kinetic characteristics of the reaction in the system has important guiding significance for the design and continuous casting production of the protective slag component of the high-aluminum steel continuous casting crystallizer.In this study,the activity and activity coefficient of SiO₂ and Mn O were determined by equilibrium experiments of CaO-SiO₂-Al₂O₃-Mg O-Mn O-Ca F₂ slag system at low SiO₂ concentration,copper as solvent and C as reducing agent.An improved molecular ion coexistence model considering the influence of Si-O complex anions on the activity of components in the slag was established,and the activity of SiO₂ under the CaO-SiO₂-Al₂O₃-Mg O-Mn O-Ca F₂ slag system was calculated.In addition,based on the above model,the activity of SiO₂,Al₂O₃ and Mn O in the CaO-SiO₂-Al₂O₃-Mg O-Mn O slag system is also simulated and calculated.The activity of Mn O and Fe O under CaO-SiO₂-Fe O-Mg O-Mn O slag system was simulated and calculated.The calculation results are verified with the measured values.Finally,based on the double slag film model of slag metal reaction,a dynamic model of composition change in the continuous casting process of high-aluminum steel is established,and verified by the measured values on site.In addition,the influence of the process parameters of continuous casting and the composition of the steel slag itself on the composition change of the continuous casting process was studied by the established dynamic model.Research shows that:（1）At 1450°C,at low concentration of SiO₂,CaO-SiO₂-Al₂O₃-Mg O-Mn O-Ca F₂slag system,x _SiO2 is 0.051～0.269,alkalinity（CaO%/SiO₂%）is 0.99～7.50,the activity and activity coefficient of SiO₂ increase with the increase of x _SiO2,but decrease with the increase of alkalinity;When x _SiO2 is 0.051～0.269 and x _Al2O3 is 0.115～0.233,the activity and activity coefficient of SiO₂ decrease with the increase of x _Al2O3.When x _SiO2is 0.051～0.269 and x _{Ca F2} is 0.162～0.218,the activity and activity coefficient of SiO₂decrease with the increase of x _SiO2.When x _SiO2 is 0.051～0.269 and x _CaO/x _Al2O3 is1.65～2.99,the activity and activity coefficient of SiO₂ increase with the increase of x CaO/x Al2O3.（2）At 1450°C,at a low concentration of SiO₂,CaO-SiO₂-Al₂O₃-Mg O-Mn O-Ca F（?）2 slag system,x _{Mn O} at 0.0021～0.0054,alkalinity at 0.99～7.50,the activity and activity coefficient of Mn O decreased with the increase of x _{Mn O},and increased with the increase of alkalinity;When x _{Mn O} is 0.0021～0.0054 and x _SiO2 is 0.051～0.269,the activity of Mn O decreases with the increase of x _SiO2.（3）At 1450°C,the relative error between the calculated value of SiO₂activity and the experimental value calculated by the CaO-SiO₂-Al₂O₃-Mg O-Mn O-Ca F₂ slag system at low concentration SiO₂ was within 25%considering the effect of Si-O complex anion on the influence of Si-O complex anion on the activity of the components in the slag on the basis of the molecular ion coexistence model.（4）At 1450°C,CaO-SiO₂-Al₂O₃-Mg O-Mn O slag system,SiO₂ concentration22.7～55.3（wt%）,alkalinity in the range of 0.73～1.75,the activity of SiO₂ was calculated in the original molecular ion coexistence model,and the model value could not be well matched with the experimental value;Considering the improved model after considering the influence of Si-O complex anions,the activity model calculation value of SiO₂ is in good agreement with the experimental value.In the range of Al₂O₃concentration of 11.5～35.6（wt%）and the binary alkalinity is 0.58～1.41,the calculated value of Al₂O₃ model is in good agreement with the actual value,and the model agreement considering Si-O complex anion is slightly higher than that of the model without Si-O complex anion.In the activity calculation of Mn O,it is found that the model value is in good agreement with the actual value,but the agreement of the complex anion model without considering Si-O is slightly higher than that of the model considering Si-O complex anion.（5）At 1450°C,the activity of Mn O and Fe O was calculated by the model of CaO-Mg O-Mn O-Fe O-SiO₂ slag system,and the molecular ion coexistence model considering or not considering the influence of Si-O complex anion hardly affected the calculation results of Mn O and Fe O activity under the slag system.（6）For the on-site continuous casting production process of 20Mn23Al V high aluminum steel,the calculated value of the change of the concentration of each component in the continuous casting process is highly consistent with the experimental value by using the established kinetic model.On this basis,the simulation calculation results show that with the increase of tensile speed,the rate of change of protective slag composition in the direction of change of each component increases slightly,the decrease of SiO₂ and the increase of Al₂O₃ increase during the continuous casting process.With the decrease of the slag weight of the liquid slag layer,the rate of change of the protective slag composition in the direction of change of each component increased,and the decrease of SiO₂ and the increase of Al₂O₃ remained unchanged.With the decrease of slag consumption,the change rate of protective slag composition in the continuous casting process increases,the decrease of SiO₂ increases,and the increase of Al₂O₃ increases.With the increase of Al content in steel,the rate of change of protective slag composition in the direction of change of each component in the continuous casting process increases,the decrease of SiO₂ increases,and the increase of Al₂O₃ increases.With the increase of the concentration of SiO₂ in the slag or the decrease of the concentration of Al₂O₃,the rate of change of the composition of the protective slag in the direction of change of each component during the continuous casting process increases,the decrease of SiO₂ increases,and the increase of Al₂O₃ increases.