Research On Effects Of Transition Metal Oxides On Thermal Conductivity Of Mold Fluxes

Mold powders are the key auxiliary materials in continuous casting due to their functions of lubricating strand and providing uniform heat transfer across the infiltrated slag layer between strand and mold, which are very important for favoring continuous casting and the slab surface quality. The researches on effects of transition metal oxides on physical properties and thermal conductivity of mold fluxes are not only helpful for both optimizing the composition of mold fluxes and also coordinating the contradiction between lubrication and heat transfer of mold fluxes in mould to improve the quality and production of the slabs. In addition, these researches are important for heat transfer calculation and practical application in continuous casting of titanium and chromium stainless steel.In this paper, the effects of transition metal oxides including TiO₂, MnO and Cr₂O₃ on physical properties and thermal conductivity of mold fluxes, the basicity of which are 0.9, 1.1 and 1.3 respectively, were studied by rotary viscometer, melting point apparatus, mineralographic microscope, XRD, DSC and the conduction heat transfer testing device which was established by hot wire method.Results of characterizing the physical properties showed that:(1)The melting temperature of the mold fluxes can be decreased when TiO₂ (contents 0⁴wt%) or MnO (contents 0⁸wt%) was added. The more TiO₂ or MnO content, the more melting temperature decreased. The melting temperature of the mold fluxes can be increased when Cr₂O₃ (contents 0⁴wt%) was added.(2)The viscosity of the mold fluxes with basicity of 0.9 or 1.1 can be deceased when TiO₂ (contents 0⁸wt%) or MnO (contents 0⁸wt%) was added in, while the viscosity of the mold fluxes with basicity of 1.3 can not be deceased when TiO₂ or MnO was added in. The viscosity of the mold fluxes decreased first and then increased with content of Cr₂O₃ was added.Thermal conductivity results showed that:(1)The lattice conductivities of the liquid slags were very low(about 0.25～0.77 W/(m·K)), while that of the solid slags were 1.53～2.19 W/(m·K) at temperature of the slags are 1000℃. Around 800℃the lattice conductivities reached maximum because of the debye temperature.(2)The lattice conductivities of the mold fluxes can be increased with increasing the basicity of the mold fluxes below 1100℃when therewas no transition metal oxide added. However, the lattice conductivities of the mold fluxes can be decreased with increasing the basicity of the mold fluxes above 1200℃.(3)The thermal conduction properties of the mold fluxes can be weakened obviously when 0⁸wt% TiO₂ was added. The lattice conductivities decreased about 5% whenever increasing 2wt% TiO₂.(4)The lattice conductivities of the mold fluxes can be greatly reduced about 10% when 2wt% MnO was added. Then the lattice conductivities increased slowly when the MnO contents in mold fluxes was 2⁸wt%. The lattice conductivities decreased about 2% whenever increasing 2wt% MnO.(5) The lattice conductivities of the mold fluxes decreased with increasing Cr₂O₃ in the range of 0²wt%, while the lattice conductivities of the mold fluxes increased with increasing Cr₂O₃ in the range of 2⁴wt%. Nevertheless, the lattice conductivities of the mold fluxes can be decreased when Cr₂O₃ was added.