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An apparatus of the teeming in protective atmosphere that can simulates the practical operation was made in trial, then the teeming in air and in protective atmosphere was carried out. In both methods, the rate of oxidation of molten steel in air, which had effect on the occurrence tendency of the sand marks, the amount of oxide inclusions and the recovery of aluminum acting as the deoxidizer and the austenite grain refining etc., were compared each other and studied.Results were summarized as follows; 1. The occurrence tendency of the sand marks was more remarkable in the teeming in air than in that in protective atmosphere. In the case of the teeming in air, the occurrence tendency of the sand marks depended on the kind of steel; that is, more remarkable with low-carbon chromium-molybdenum steel No.21 than with medium-carbon steel SAE 1030 and 1040. In the teeming in protective atmosphere, however, no difference on it was recognized between the kind of steel.2. The amount of oxide inclusions and the oxygen content was found more in the former teeming than in the latter one, and also was found more at the top and bottom parts of the ingot than at the middle part of it on both cases.3. A strong tendency of the occurrence of the sand marks was found with forged or rolled steel having much oxide inclusions and much oxygen in comparison with that having less oxide inclusions and oxygen.4. The recovery of aluminum was higher in the teeming in protective atmosphere than in that in air. Judging from results obtained, it was really recognized that the rate of oxidation of molten steel in air had a remarkable effect on the occurrence tendency of the sand marks, the amount of oxide inclusions and the recovery of aluminum.This undesired oxidation of molten steel could be prevented by use of argon or nitrogen gas in the teeming in a protective atmosphere. Argon gas, however, was rather expensive so that nitrogen had better be used in practical operation from the economical point of view.

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