Study On Influence Of B₂O₃ On Microstructure And Viscosity Of Fluorine-Free Mold Fluxes

In the process of continuous casting production,the mold flux plays a very important role in the continuous casting production and improving the surface quality of the casting slab,it has become an important part of modern steel continuous casting technology.But a series of serious problems such as environmental pollution are caused by the fluorine which existed in the mold flux and can reduce the viscosity and melting temperature of the mold flux,control heat transfer and promote the crystallization of slag film.Therefore,the non-fluorination of the mold flux will become a trend.However,it will result in deterioration of the viscosity-temperature characteristics of the continuous casting mold flux for high carbon steel,and easy to cause bonding and bonding steel leakage,difficult to coordinate between heat transfer and lubrication for crack sensitivity medium carbon steel continuous casting flux and other series of problems after the mold flux has been non-fluorination.In order to effectively carry out the research on the fluorine-free mold flux of continuous casting mold,based on the comprehensive analysis of the development status and BMH potential function of the fluorine-free mold flux.The molecular dynamics simulation of CaO-SiO₂ system,CaO-B₂O₃ system,CaO-SiO₂-B₂O₃ system slag was carried out by Materials Explorer software to obtain information such as the radial distribution function,coordination number,and space coordinates between the particles.The structural parameters such as the average bond length between atoms,the average coordination number,the distribution of oxygen and the distribution of Qⁿ were obtained to analyze the influence mechanism of component B₂O₃ on the slag structure.At the same time,the slag of each system was tested by infrared spectroscopy,and the relevant structural information was obtained,and the simulation results were verified.Then,through the experimental test of the rotating viscosity furnace,the effect of alkalinity and typical component B₂O₃ on the viscosity of the fluorine-free mold flux was studied,and the auxiliary analysis was carried out by infrared spectroscopy and Raman spectroscopy.The simulation results show that:In the CaO-SiO₂ system and CaO-B₂O₃system,the[SiO₄]^4-tetrahedron is very stable,the B-O structure converts between trihedron,tetrahedron and pentahedron;In the CaO-SiO₂-B₂O₃ system,As the B₂O₃content increases,O_nb is converted to O_b,which complicates the network structure.In addition,the influence of B₂O₃ content is greater than the alkalinity on the coordination number of O-O,indicating that B₂O₃ is outstanding in changing the slag structure;In general,in each slag system,as the alkalinity increases,the ratio of O_nb and O_f increases,the proportion of O_b decreases,Q⁰,Q¹,Q² generally increase,while Q³ and Q⁴ decrease substantially,and the polymerization of melt The degree of reduction and the melt structure become simple.The viscosity test results show that:Within the range of fluorine-free mold flux components in this article,when w?B₂O₃?=4%,6%,8%,the viscosity of fluorine-free mold flux increases with the increase of alkalinity at 1300^oC,the viscosity-temperature curve exhibits an alkaline slag characteristic,and as the alkalinity increases,the transition temperature increases;When w?B₂O₃?=10%,12%,with the increase of alkalinity,the viscosity of fluorine-free mold flux will decrease first and then increase at 1300^oC,and the viscosity-temperature curve will exhibit acidic slag characteristics,and as the alkalinity increases,the viscosity increases as the temperature decreases.When R=1.15,with the increase of w?B₂O₃?,the viscosity of fluorine-free mold flux increases first and then increases at 1300^oC;When R=1.25 and 1.35,the viscosity of fluorine-free mold flux decreases monotonously with the increase of w?B₂O₃?at 1300^oC;Under different alkalinity conditions,w?B₂O₃?is in the range of 4⁸%,and the viscosity-temperature curve of fluorine-free mold flux exhibits alkaline slag characteristics,and with the increase of w?B₂O₃?,the transition temperature decreases;When w?B₂O₃?=10¹2%,the slag exhibits acidic slag characteristics,and the slag viscosity increases with the decrease of temperature depending on the alkalinity.In the fluorine-free mold flux,when w?B₂O₃?=6¹2%,the viscosity meets the requirements of continuous casting of peritectic steel or high carbon steel under different alkalinity conditions at 1300^oC;The viscosity-temperature curve characteristic of w?B₂O₃?=4⁸%and R=1.15¹.25 is beneficial to control heat transfer and is suitable for continuous casting production requirements of peritectic steel;The viscosity-temperature curve characteristic of w?B₂O₃?=10¹2%and R=1.15¹.35 is beneficial to improve lubrication and is suitable for high carbon steel continuous casting production requirements.The results of spectroscopy experiments show that:In the CaO-SiO₂-B₂O₃ slag,with the increase of B₂O₃ content and alkalinity,B₂O₃ is involved in the construction of the network structure,which makes the network structure of the melt more complicated,which is consistent with the simulation results.In the fluorine-free mold flux,as the alkalinity increases,w?B₂O₃?=8%,the peak intensity of the infrared spectrum and the Raman spectrum increases,indicating that the Si-O and B-O network structure becomes complicated;w?B₂O₃?=12%,the peak of the wave spectrum of the infrared spectrum of 800-1200 cm^-1 is first weakened and then enhanced,which is consistent with the increase of the high temperature viscosity with a small decrease,but the Raman spectrum peak shows an increasing trend,and the viscosity test results have certain deviation;With the increase of B₂O₃ content from 8wt%to 12wt%and alkalinity of 1.15,the peaks of infrared and Raman spectra are enhanced,indicating that the structure of slag becomes complex.When the alkalinity is 1.25 and 1.35,infrared and Raman spectra are used.The peak intensity is weakened,indicating that the slag structure is simple,which is consistent with the viscosity test results.