Effects Of Typical Fluxes CaF₂ And B₂O₃ On Physicochemical Properties Of CaO-Al₂O₃ Mold Flux

CaO-Al₂O₃-based mold flux can effectively solve the slag-metal reaction problem between high aluminum steel and trasitional CaO-Si O₂-based mold flux.However,compared with CaO-Si O₂basedmold flux,as the high melting temperature,great viscosity,and complex crystal morphologies and crystalline phases of CaO-Al₂O₃ based mold flux will affect the controlling of heat transfer and lubrication between mold flux and steel during casting.The typical fluxes Ca F₂ and B₂O₃can added into mold flux to adjust the viscosity,crystallization ability and melting temperature.Therefore,the influences of Ca F₂ and B₂O₃ on the physical and chemical properties of CaO-Al₂O₃-based mold flux is studied in this work.The present results would provide the theoretical basis for development of an optimized high aluminum steelmold flux based on CaO-Al₂O₃ system.Firstly,the effects of Ca F₂ and B₂O₃ on the structure of CaO-Al₂O₃-based mold flux were studied by molecular dynamics simulation.Then,the effects of Ca F₂ and B₂O₃on the crystallization products and crystal morphology of CaO-Al₂O₃-based mold flux were investigated by emperiments.Additionally,since B₂O₃ is prone to react with[Al]during the high aluminum steel casting,the effect of B₂O₃ on slag-metal reaction between CaO-Al₂O₃-based mold flux and high aluminum steel were also investigated.Finally,a new type of CaO-Al₂O₃-B₂O₃-Ca F₂-based mold flux was designed and synthesized in order to exploring the physical and chemical properties.The main results are concluded as follows:The fluorine ion is more likely to form Ca-F linkage,and more calcium ions are coordinated with fluorine ions as an increased Ca F₂.There were no obvious changes in polymerization of CaO-Al₂O₃-Ca F₂ systems and a slight decrease of the viscosities with an increased Ca F₂,with an increased Ca F₂.B³⁺mainly forms[BO₃]and[BO₄].With the increase of B₂O₃,the bridge oxygen increases while the atomic cluster Qⁿ in the high polymerization state decreases overall.The reduction of CaO-Al₂O₃-B₂O₃-based mold flux melt network polymerization can cause the reduction of viscosity.CaF₂ has no obviouseffect on the main crystal phase,but with the increase of Ca F₂to 6%,a new phase of Ca F₂ is precipitated.The size of Ca₁₂Al₁₄O₃₃ and Ca F₂ gradually were increased as the increase of Ca F₂ and Ca F₂can promote the crystallization of Ca₁₂Al₁₄O₃₃and Ca F₂.With the content of B₂O₃ gradually increasing,the crystalswere changed from Ca₁₂Al₁₄O₃₃ to Ca₃B₂O₆ and Ca_xAl_yO_n.The Ca/Al ratio of calcium aluminate gradually decreases by the addition of B₂O₃,and B₂O₃can refine the crystal size and reduce the crystallization.Meanwhile,the high content of B₂O₃can promote the formation of Ca₃B₂O₆crystals.The addition of 5%B₂O₃,the slag-metal reaction hardly occurred.With the increased of[Al]in steel,the content of B₂O₃in CaO-Al₂O₃-based mold flux and the reaction time,the reaction rate was increased rapidly.The melting temperature of CaO-Al₂O₃-B₂O₃-CaF₂-based mold flux was 1212?,and the viscosity was 0.22 Pa s at 1300°C,which were within the range of traditional CaO-Si O₂-based mold flux.The crystallization process was extremely rapid from CSLM esperiments.The morphology of the primary crystal,Ca₁₂Al₁₄O₃₃and Ca₃B₂O₆,are large sheet with cloudy dendrites and small faceted shape.