A low-expansion type MgO-C material was newly developed as nozzle materials for continuous casting. The alumina-buildup characteristics and concentration changes of the molten steel were evaluated by an erosion/ corrosion test with comparing the MgO-C with Al2O3-C or Al2O3-SiO2-C materials under the same vol% of C. The average alumina-buildup rate became lower in the order of MgO-C, Al2O3-C, Al2O3-SiO2-C. Therefore, the rate of alumina-buildup decreased for the MgO-C. The concentration changes of C in the molten steel were studied before and after the test, C in molten steel with MgO-C material was lower than that of Al2O3-SiO2-C, by approximately 40%. The alumina-buildup rate in the MgO-C was lower than those of Al2O3-C or Al2O3-SiO2-C materials and less inclusions from refractories were dissolved into the molten steel. It was attributed to be low permeability of a smooth and highly dense continuous layer with high MgO content formed on the hot face.

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: MgO reduction by C, which spontaneously occurs at high temperature in low oxygen atmosphere, is one of the important wear factors of MgO-C bricks. In this paper, we will report the influence of porosity on MgO reduction. As a result of the experimental heating of porosity-varied specimens, it was verified that mass loss increased with an increase in porosity and the reaction progressed from the surface toward the inside. According to the microstructure of the post-heated specimen, the reaction front, which is the boundary between reacted eripheral and unreacted inside, was clearly recognized. Thus, it is assumable that MgO reduction occurs only at the peripheral. Based on the experimental results, we constructed a “reaction front model” that describes the influence of the porosity of each brick on the migration speed of the reaction front. The results calculated by the model well-agreed with the previously published data and experimental results.

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