Study On Reactivity And Rheological Properties Of High-Al Silicon Steel Mould Fluxes

Mould fluxes with the five functions of heat insulation,preventing secondary oxidation,controlling heat transfer,lubrication and absorption inclusions is a very important and critical material during continuous casting of steel.Due to the high Al and Si contents in the high-Al silicon steel,the SiO₂ in the mould fluxes is reduced by Al in the molten steel during the casting process,so that the SiO₂ content decreases and the Al₂O₃ content increases in mould fluxes,resulting in changing the composition and performance of the mould fluxes,and the content of Si in the steel will have a certain effect on the reaction.Meanwhile,the C content in the high-Al silicon steel is ultra low,so that the solidified hook is easy to occur when the molten steel is solidified in the mould,resulting in deterioration of the surface quality of the slab.In this paper,combined with the research status of high-aluminum steel mould fluxes and ultra-low carbon steel mould fluxes at home and abroad,and the key issues of high-alumina silicon steel mould fluxes were analyzed.Slag-steel reaction leads to the increase of the viscosity of mould fluxes,which will help to reduce solidified hook and improve the surface quality of the slab.However,when the amount of slag-steel reaction is too large,the viscosity and solidification temperature of mould fluxes will increase sharply,resulting in poor slab lubrication,or cracks and depressions on the surface of the slab.In this paper,high-alumina silicon steel mould fluxes of Baosteel as the research object,and the slag lubrication performance and slab surface quality coordination control as the main line of the research.First,the kinetic model was used to calculate the amount of slag-steel reaction corresponding to different Al and Si contents,and then the final composition of mould fluxes was obtained.The rheological properties of CaO-SiO₂-Al₂O₃ slag system were studied,including viscosity with constant temperature,non-Newtonian fluid characteristic,break temperature?Tbr?and liquid slag film fraction.The main research work and conclusions were listed in the following:?1?Calculation of the Amount of Slag-Steel Reaction1)The relationship between the content of the component and the reaction time was calculated by the kinetic model.As the reaction of the slag-steel reaction progressed,the reaction amount gradually increased until the reaction reached the dynamic equilibrium,and the reaction amount of the slag-steel reaction reached equilibrium as the basis of the design of experimental slag composition;2)The results show that the content of Al in molten steel has the greatest effect on the amount of slag-steel reaction,while the content of Si in molten steel has little effect on the amount of slag-steel reaction.?2?Study on the Viscosity Characteristics with Constant Temperature1)Constant temperature and speed viscosity test and analysis results : a.With the increase of Al₂O₃/SiO₂ ratio,the viscosity of mould flux also showed an increasing trend.The reason for the increase of viscosity was the change of slag structure due to the change of Al₂O₃/SiO₂ ratio;b.With the increase of CaO/SiO₂ ratio,the viscosity also showed a tendency to decrease.Structural analysis showed that CaO played a role in reducing viscosity;c.After F was instead of Na2 O in slag,rapid increase of viscosity was slowed down due to the increase of Al₂O₃/SiO₂ ratio,and the rheological properties of the slag were improved effectively.The viscosity stability was improved obviously of the slag area after the flux substitution,which reduced the deterioration of the rheological properties.2)Variable speed viscosity test and analysis results: a.The slag with higher Al₂O₃/SiO₂ ratio had obvious non-Newtonian fluid characteristic,while the slag with low Al₂O₃/SiO₂ ratio had no obvious non-Newtonian fluid characteristic;b.After F replaced Na2 O,the non-Newtonian fluid characteristic of the slag was weakened.?3?Study on Viscosity Characteristics with Variable Temperature1)The effect of CaO/SiO₂ ratio on Tbr?break temperature?was small.As the CaO/SiO₂ ratio decreases,Tbr exhibited a tendency to decrease first and then increase;2)Al₂O₃/SiO₂ ratio had a great influence on Tbr value,and the increase of Al₂O₃/SiO₂ ratio was the main reason for the deterioration of rheological properties of slag.In the composition range of Al₂O₃ = 15-23mass%,the increase of Al₂O₃/SiO₂ ratio led to the sharp increase of Tbr value;3)F to replace Na2 O can reduce the Tbr value,making the low Tbr slag area to expand,to avoid a sharp increase in Tbr,thereby improving the rheological properties of mould fluxes.?4?Evaluation of Rheological Properties of mould Fluxes Based on DHTT1)With the increase of Al₂O₃/SiO₂ ratio,the liquid slag film fraction of the mould fluxes showed a decreasing trend,and the rheological properties of mould fluxes were deteriorated;2)The CaO/SiO₂ ratio had no significant effect on the liquid slag film fraction of the mould fluxes in the slag area studied;3)After F replaced Na2 O in slag,the liquid slag film fraction increased,thereby improving the rheological properties of mould fluxes.