Manufacturing method of the high cleanliness very low carbon steel

摘要

PURPOSE: To provide the production method of a high cleanness extra carbon steel used for a large immersion tube. ;CONSTITUTION: In the vacuum refining method in which one leg cylindrical immersion tube is immersed into molten metal in a ladle, the inside of immersion tune is evacuated and an inert gas is blown from the projection area of immersion tune and/or the lower inner wall of immersion tube at the lower part of ladle, while satisfying the conditions of (1) to (3) described below, an immersion tube is immersed and then vacuum, decarburization is executed, Al containing substance is added under the condition that the carbon content after decarburization is ≤30ppm, and then deoxidizing of ≥5min is executed. (1) A ratio between the inner diameter of immersion tube D and the inner diameter of ladle D₀ D/DDD₀:0.5-0.8. (2) FeO in the slag in ladle before vacuum decarburization :2-15%, (3) A ratio between CaO and Al₂O₃ in the slag in ladle CaO %/Al₂o₃%:0.8-2.5 before vacuum decarburization and after decarburization. By this method, FeO concentration is lowered while maintaining a good decarburization speed, a high cleanness extra low carbon steel is obtained in short time, further the damage to a refractory of immersion tube is suppressed.;COPYRIGHT: (C)1996,JPO