Applied Basic Research On MgO（-Mg₂SiO₄）-SiC-C Refractory For Lf Ladle Slag Line

MgO-C refractory as a common refractory for LF ladle slag line has problems such as increased carbon content in molten steel and increased greenhouse effect due to high graphite content.The reduction of carbon content in MgO-C refractory has become an inevitable requirement of the steel and metallurgical industry for the refractory industry.However,the reduction of carbon content in MgO-C refractory makes it difficult to exert the advantages of graphite such as low expansion coefficient and non-wetting with slag,which has a negative impact on the thermal shock stability and slag corrosion/penetration resistance of MgO-C refractory.In this dissertation,the MgO-Mg₂SiO₄-SiC-C refractory was designed and prepared based on the comprehensive analysis of matrix and aggregates,and the applied basic research on refractory was carried out.MgO-SiC-C refractory was prepared by in-situ synthesis of SiC whiskers in the matrix.The effects of different carbon sources,ratio of composition,and particle grading systems in the raw materials on the in-situ synthesis of SiC and the properties of MgO-SiC-C refractory were studied.The carbon content of MgO-SiC-C refractory was less than 3%,and SiC whiskers formed a ceramic combined carbon structure with graphite,which compensated for the problem of the inability to form a complete carbon network due to insufficient carbon content.SiC reduced the thermal expansion coefficient and improved the thermal conductivity of the system,to improve the thermal shock resistance of MgO-SiC-C refractory.Compared with low-carbon MgO-C refractory,the residual compressive strength ratio after the thermal shock tests was increased by 16.15%.MgO-Mg₂SiO₄multiphase refractory aggregates with the micro-nano pore structure were prepared by the addition of silica sol.The formation and evolution of the dual-scale pore structure were affected by the surface action,superplasticity,and particle size of the nano sol.The micro-nano pore MgO-Mg₂SiO₄aggregates and the matrix formed an interlocking structure in MgO-Mg₂SiO₄-SiC-C refractory,which improved the thermal shock resistance compared to MgO-SiC-C refractory.The residual compressive strength ratio increased by 3.54%after thermal shock tests.The slag resistance of MgO-SiC-C refractory and MgO-Mg₂SiO₄-SiC-C refractory was studied by corrosion experiments.Since SiC in MgO-SiC-C refractory could promote the polymerization of molten slag and increase the viscosity of the liquid phase,the slag resistance of MgO-SiC-C refractory was improved compared to low-carbon MgO-C refractory,and the corrosion index was reduced by 47.8%.Due to the composition and structure of MgO-Mg₂SiO₄aggregates,the viscosity of slag contacted with MgO-Mg₂SiO₄aggregates was 39.4%higher than that of fused magnesia.Compared with MgO-SiC-C refractory,the slag resistance of MgO-Mg₂SiO₄-SiC-C refractory improved and the penetration index was decreased by 43.2%.The interfacial bonding mechanism of MgO-SiC-C refractory and MgO-Mg₂SiO₄-SiC-C refractory was studied by the molecular dynamics method.The crystal plane phase relationships observed in HRTEM images were consistent with the results of the molecular dynamics simulation.SiC formed direct bonding interfaces with MgO and graphite respectively.Mg₂SiO₄formed direct bonding interfaces with MgO,SiC,and graphite respectively.MgO and graphite did not form direct bonding interface.Compared with the single-chain bonding formed by SiC in MgO-SiC-C refractory,the network bonding formed by SiC and Mg₂SiO₄in MgO-Mg₂SiO₄-SiC-C refractory used as bridges,which indirectly combined periclase with graphite to effectively enhance the refractory.