Radiative Heat Transfer in Transition Metal Oxides contained in Mold Fluxes

Abstract

Transition metal oxides FeO, MnO and TiO₂ contained in mold fluxes were prepared and measured by a FTIR spectrometer. Characteristics of absorption/extinction coefficient were obtained through infrared spectrum analysis. Relation between radiative heat transfer and the transition oxides was calculated by a heat exchange model. The result indicates that the transition oxides have the great negative effect on radiative heat transfer during the wavelength of 1–6 μm. Radiation heat flux, q₁₂ decreases from 5.5–6.3×10⁴ W m⁻² to 4.3–5.1×10⁴ W m⁻², 3.4–4.2×10⁴ W m⁻² and 3.9–5.4×10⁴ W m⁻² with 2–8% MnO, 1–3% FeO and 2–8% TiO₂ added, respectively. Due to the great refraction and scattering at surface and grain boundaries, the negative effect in crystalline samples was much larger than that happened in the glassy ones. MnO and TiO₂ have great influence on viscosity and melting temperature of mold fluxes, but FeO has little influence. XRD results show that Mn₂SiO₄, Fe₂SiO₄, CaTiO₃ and other minor phases were precipitated after transition oxides added. Grain size of crystals enlarges from 12.5 to 100 μm with increasing of holding temperature. At 800°C, the radiation heat flux is 1.25×10⁴ W m⁻², and decreases to 0.84×10⁴ W m⁻² at 900°C. Above 900°C, the radiation heat flux increased on the contrary. The radiation heat flux increased from to 0.84×10⁴ W m⁻² to 1.0×10⁴ W m⁻². Industrial trial shows that the transition oxides contained in mold fluxes are good at coordination of heat transfer controlling and strand lubricating, and the occurrence of longitudinal cracks is greatly decreased. Further studies in the transition metal oxides contained in mold fluxes will be valuable for improving strand surface quality of crack sensitive peritectic steels.