:Effect of microstructure on the deformation and fracture mode of the monolithic castable refractories was investigated to understand their mechanical behavior from both experimental and analytical points of view. Mesoscale FEM, finite element method, was applied for the analytical work. X－ray CT images of the castable refractories were processed to obtain the ２－dimensional mesoscale FEM model which consists of aggregates, matrix, interfacial transition zone and pores. Using the model, the analysis was carried out on stressing with both compression and bending in consideration of fracture due to the stress exerting in both matrix and interfacial transition zone. In the analysis of compression, macroscopic softening behavior has been observed in the material containing aggregates with accordance to the experimental result. It was clarified by the analysis that the macroscopic softening was originated by micro-cracking occurred numerously in the mesoscale structure. Furthermore, from both analyses in compression and bending, it was resulted that strength of the material containing aggregates was considerably lower than that without them. These analytical results agreed well to those from experimental work.

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The Al4SiC4-C samples heated in carbon powder were studied, in order to clarify a high temperature reaction mechanism of Al4SiC4 added to carbon containing refractories. Al4SiC4 reacted with CO gas to form mainly α-Al2O3 and SiC above 1000℃. This reaction proceeded at lower temperature as the grain size of Al4SiC4 decreased. Al4C3 did not form at any grain size and heating temperature. A reaction layer of around 15μm thickness was formed at the surface of Al4SiC4 grains at 1500℃ for ５ hours. This indicated that the reaction occurred from the surface toward the inside of Al4SiC4 grain. The thickness of the reaction layer was constant at any Al4SiC4 grain size. As a result, the reaction was accelerated as the Al4SiC4 grain size decreased, because the small grain had a large surface area. The reaction layer was composed of SiC and carbon. It was estimated that aluminum vaporized from Al4SiC4 and dispersed to the surrounding texture, and then Al2O3 and carbon were condensed in the pore, and densification of the texture occurred.

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