Crystallization behaviors of mold fluxes containing Li2O using single hot thermocouple technique

Abstract

Minor addition of Li2O (<2 mass%) can significantly alter the melting temperature and viscosity of a mold flux. However, the crystallization tendency of mold fluxes containing Li2O more than 2 mass% hasn't been understood. In this paper, single hot thermocouple technique, X-ray diffraction, and Back Scattered Electron (BSE) were employed to investigate the crystallization behavior concerned with CCT and TTT diagrams of mold fluxes containing high content of Li2O. The critical cooling rate and crystallization rate of samples were increased with the addition of Li 2O, whether there is Na2O or not. But the incubation time was reduced obviously with Li2O more than 6 mass% in mold fluxes. The critical cooling rate and incubation time of NL15 sample (Na 2O=8mass%, Li2O=1.5mass%) were close to those of L 7 sample (Na2O=0mass%, Li2O=7 mass%). Moreover, there is no difference in the crystal phase of the two samples, and the crystal phases precipitated at high temperature and low temperature were respectively Ca2(SiO4) and Ca4Si2O 7F2. Li-cuspidine was promoted to precipitate when the basicity of the sample was increased. The small, dense grains of cuspidine were observed in NL15 sample, and the thickness of slag film was 0.4 mm more than that of L7 sample. The heat flux of NL15 sample measured was 10% less than that of L7 sample, as expected. Therefore, high content of Li2O can be substituted by the combination of Na2O and minor of Li2O, as is the composition in the commercial mold fluxes. © 2009 ISIJ.