Radiative heat transfer in transition metal oxides contained in mold fluxes

Abstract

Transition metal oxides FeO, MnO and Ti02 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 5.5-6.3xl04Wm-2 to 4.3-5.1 xl04Wm-2, 3.4-4.2x104 Wm-2 and 3.9-5.4X104 Wm -2 with 2-8% MnO, 1-3% FeO and 2-8% Ti02 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 Ti02 have great influence on viscosity and melting temperature of mold fluxes, but FeO has little influence. XRD results show that Mn2Si04, Fe2Si0 4, CaTi03 and other minor phases were precipitated after transition oxides added. Grain size of crystals enlarges from 12.5 to 100 μ m with increasing of holding temperature. At 800°C, the radiation heat flux is 1.25X104 Wm-2, and decreases to 0.84xlO 4Wm-2 at 900°C. Above 900°C, the radiation heat flux increased on the contrary. The radiation heat flux increased from to 0.84X104 Wm-2 to 1.0xl04Wm-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. © 2009 ISIJ.