Study On Physical Properties Of CaF₂-CaO-SiO₂ ESR Slags

Electroslag remelting technology has attracted much attention from engineering and technical circles at home and abroad since it can obtain steel ingots with high purity,low sulfur content,less non-metallic inclusions,compact texture and smooth surface.The slag plays the role of heating,refining,molding,insulation and heat conduction in electroslag metallurgy.The physicochemical properties of electroslags,such as viscosity,surface tension,density and electrical conductivity,have important effects on ensuring the smooth progress of smelting and controlling the quality of product.In order to smelt low oxygen clean steel without aluminum,the viscosity,surface tension and density of CaF₂-CaO-SiO₂?-Al₂O₃-MgO?slag with temperature and composition were investigated under extreme composition conditions in this paper.Besides,an attempt was made by employing continuously varying cell constant?CVCC?method to study the electrical conductivity of 80%CaF₂-10%CaO-10%SiO₂ melt with temperature in a capillary-type conductance cell built with pyrolytic boron nitride?PBN?tube.The viscosity of CaF₂-CaO-SiO₂?-Al₂O₃?melt with different bacisities and CaF₂contents was determined by rotating cylinder method,and the water-quenched melt sample obtained in 1773 K was analyzed by Fourier transform infrared?FT-IR?spectroscopy for clarifying the relationship between the melt structure and the viscosity variation.The results show that the viscosity of the melt decreases with the increase in temperature at the experimental conditions.However,the range of activation energy of the viscous flow in each melt varies from 26.7 to 66.9 kJ/mol,the viscosity of the melt system is not obvious with temperature.The viscosity decreases with the increases of basicity from 1 to 3 and of CaF₂ content from 40%to 80%.The effect of Al₂O₃ on viscosity is related to basicity.After adding 10%Al₂O₃ into two groups of B=1 and 2melts,the viscosity of the melt with lower basicity decreases,while the viscosity of the melt with higher basicity increases.The viscosity of these melts decreases with adding MgO into the melts.The surface tension of CaF₂-CaO-SiO₂?-Al₂O₃-MgO?melt was measured by the pull-cylinder method and the the effects of basicity and CaF₂ content,as well as the addition of Al₂O₃ and MgO on the surface tension were analyzed.The results show,as the basicity increases from 0.5 to 3 in 60%CaF₂-xCaO-ySiO₂ melt,the surface tension of the melt increases first and then decreases,and reaches a maximum value of 390mN/m at B=2.For 80%CaF₂-xCaO-ySiO₂ melt,the surface tension gradually increases from 317 mN/m to 379 mN/m as the basicity increases from 1/3 to 3.For the CaF₂-xCaO-xSiO₂ melt with an basicity of 1,as the CaF₂ content increases from 30%to80%,the surface tension decreases from 399 mN/m to 325 mN/m.The addition of 10%Al₂O₃ reduces the surface tension of 60%CaF₂-x CaO-ySiO₂ melt.MgO was added into60%CaF₂-xCaO-ySiO₂ melt for instead of CaO and SiO₂ under the condition of basicity fixing and the surface tension of the melt gradually decreases with the increase of MgO content.The density of CaF₂-CaO-SiO₂?-Al₂O₃-MgO?melt was determined by Archimedes method and the effects of basicity,Al₂O₃ and MgO addition on density were analyzed.The results show that the density of 60%CaF₂-xCaO-ySiO₂ melt reaches the maximum density of 2.562 g/cm³ at B=2 and then decreases to 2.554 g/cm³ with basicity increasing from 1 to 3.The density of 80%CaF₂-xCaO-ySiO₂ melt decreases with the increases in temperature and basicity.The addition of 10%Al₂O₃ increases the density of 60%CaF₂-xCaO-xSiO₂ melt.The effect of Al₂O₃ on density is most obvious when the basicity is 2.The addition of MgO increases the density of the melt because MgO can depolymerize complex anions.The capillary-type conductance cell was constructed by PBN tube,and the electrical conductivity of 80%CaF₂-10%CaO-10%SiO₂ melt was determined by CVCC method.The results show that the electrical conductivities of 80%CaF₂-10%CaO-10%SiO₂melt at 1663,1693,1723 and 1753 K are 4.53,4.59,4.73 and 4.85 S/cm,respectively.According to Arrhenius equation,the activation energy of conductivity is about 18.9kJ?mol^-1 by fitting measured values with the least square method.The measured electrical conductivity and the conductivity activation energy reasonably match with the values reported in relevant literatures.It can be inferred that the electrical conductivity of 80%CaF₂-10%CaO-10%SiO₂ molten slag could be feasible measured by CVCC method in PBN capillary-type conductance cell.