The film, which is formed by mold flux in the continuous casting mold, plays very important roles in terms of lubrication or heat transfer. However, the thickness or structure of it has not been adequately clarified. In this study, the sample of actual flux film was taken from the continuous casting mold just after the cast, keeping its position as it was during the cast. Thanks to this trial, thickness of the flux film at the meniscus in the mold could be clarified. According to the observation on the flux film section by microscope, the structure of the flux film was discussed, in terms of its crystallization. Furthermore, based on the results of the observation mentioned above, the heat transfer phenomenon through the flux film in the mold was discussed. As a result of the discussion, the following conclusions were obtained. 1) The mold flux film can be considered to be about 1 mm. Glassy layer, which has been considered to be molten flux on the top of molten steel during the cast and covered the film just after the cast, can be assumed to make up the film during the cast. 2) The liquid layer in the film is as thick as that is estimated on the basis of mold flux consumption during the cast. 3) In the case that the film at the meniscus in the mold is about 1 mm thick, total thermal resistance of radiation and conduction is equivalent to interfacial thermal resistance between the film and the mold. 4) The reported values of interfacial thermal resistance can be considered to be larger than that in the actual mold during the casting. The reason seems to be that they were measured in conditions without any pressure by the molten steel, like that in the mold. In the actual mold, the interfacial thermal resistance seems to be smaller.
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