| 摘要 |
PURPOSE:To reduce the nitrogen content in molten steel, by blowing Ar gas on the molten steel surface in a vacuum chamber at the time of vacuum- degassing-treating the molten steel and reducing the partial pressure of nitrogen in the molten steel surface. CONSTITUTION:The end parts of one pair of submerged tube 5 composing of an uptake tube and a downtake tube for circulating flow type degassing apparatus is dipped into the molten steel 2 in a ladle 1. Ar gas 4 is injected from a nozzle 6 fitted to the side part of uptake tube and floated up in the molten steel as bubbling state and the molten steel 2 is flowed into the vacuum chamber 3 passing through uptake tube from the ladle 1 and circulated by descending into the ladle 1 through the downtake tube. In this case, the Ar gas 4 from a vertical lance 7 arranged in the vacuum chamber 3 or from a lance 7 arranged at the side part of vacuum chamber 3 is injected on the molten steel surface and the partial pressure of N2 in the vacuum vessel 3 is remarkably reduced, to diffuse N2 gas in the molten steel 2 into the vacuum chamber 3 and the low nitrogen steel having <20ppm N2 content is produced by the vacuum degassing method.
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