PROCESS AND APPARATUS FOR VACUUM DEGASSING MOLTEN STEEL

摘要

Molten steel is efficiently vacuum treated in a vacuum treatment vessel provided with a tap blow lance capable of injecting an oxygen gas and a fuel gas at desired flow rates, respectively, onto molten steel on the top of the vacuum treatment vessel in a freely vertically movable manner, by setting the lower end of the top blow lance to a level of not more than 2 m from the surface of molten steel bath and injecting only an oxygen gas onto the molten steel, and thereafter setting the lower end of the top blow lance to a level of 1.0 m or more from the surface of molten steel bath and injecting both of oxygen gas and a fuel gas from the top blow lance onto the molten steel. The process of the invention enables one to prevent a decrease in the temperature of molten steel during the vacuum treatment and also to prevent a deposition of molten steel on the inside wall of the vacuum treatment vessel without using a large scale heater of electrical resistance type.