The investigation was made for evaluating influences of SiO2 formed from SiC on corrosion resistance of a　castable for blast furnace main trough metal line. In Al2O3－Spinel－SiC－C system castable refractory, SiO2 content is increased by two different means, i.e. simply adding fumed silica to the castable, and oxidizing SiC in the castable by CO（g）. The deterioration in corrosion resistance is clearly recognized on the specimen added fumed silica. On the other hand, in the sample containing SiO2 from SiC, the deterioration is less than the silica-added specimens. Microscopic observations on SiC oxidized material reveals the traces of liquid phase formation, which is explainable as the result of reaction among SiO（g）evaporated form SiC, Mg（g）evaporates from spinel, and Al2O3 in its castable matrix. Since formed liquid phase has enough solubility of SiO2, SiO（g）dissolves into the liquid pool under the equilibrium conditions. That is, SiO2 oxidized from SiC is condensed and localized in the material. While, in fumed silica added material, homogenously dispersed silica components are observed. It can be concluded that the influence of SiO2 on the corrosion resistance is attributed to the SiO2 component configuration, localized or even dispersed.

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