Research On The Influence Of Fluorine And Boron On Crystallization Behavior Of Continuous Casting Slag Film

Nowdays,under the background of steel overcapacity and energy conservation in the steel industry,actively looking for substitutes to fluorine in mold fluxes and developing new fluorine-free mold fluxes have become an important way to achieve green and efficient continuous casting production.As an ideal substitute for fluorine,boron has become a new research focus of fluorine-free mold fluxes technology due to its economic cost and fluxing effect,There were few studies to use borax instead of fluorite.The performance of mold fluxes were measured by preparing mold fluxes with mineral materials,the crystallization rate and phase structure of mold fluxes were identified;The melting and crystallization process of mold flux was studied by thermodynamics and molecular dynamics,and the influence mechanism of fluorine and boron content on the crystallization behavior of mold fluxes was analyzed.The performance and phase structure of slag film were studied.The results show that with the increase of fluorite（6%～21%）,the crystallization temperature increases,and the crystallization rate increases from 80%to 95%.The phases are cuspidine（Ca₄Si₂F₂O₇）and merwinite（Ca₃Mg Si₂O₈）.The crystallization ability of cuspidine at 1200℃is the strongest,the crystallization of merwinite at 1100℃,the melting temperature and viscosity decrease;with the increase of borax（4%～16%）,the crystallization temperature decrease,the crystallization rate decreases from 90%to 5%,and the phase are calcium borosilicate(Ca₁₁Si₄B₂O₂₂)and merwinite.The crystallization ability of calcium borosilicate at 1100℃is the strongest,the merwinite has the highest degree of development at 1200℃and the melting temperature,viscosity decrease.On this basis,in order to further explore the microstructure characteristics of slag,the melting and crystallization mechanism of fluorine and fluorine-free mold fluxes was studied by using Raman,Scigress and Fact Sage.The results show that with the increase of fluorite,the structural units Q⁰,Q¹,Q² increase,Q³ decreases,the DOP of the slag network decreases.With the increase of borax,the coordination number of B-O in the slag increases,[BO₃]^3-into[BO₄]^4-,and the structural unit transforms from island-like structure,ring structure to complex layered and framework-like structure,forming a complex borosilicate structure,increasing the DOP of the slag,and inhibiting the crystallization of the mold flux,the content of the precipitated main crystalline phase calcium borosilicate drops sharply.The experimental results provide a theoretical basis for the development of a new type of fluorine-free mold fluxes.Figure 44;Table 36;Reference 80.