PURPOSE: To easily add and control the aimed nitrogen content in high accuracy by setting pressure of nitrogen gas atmospheric zone corresponding to increasing quantity to the aimed nitrogen and passing-through quantity of molten steel stream based on the pre-obtd. relation between the above both.
CONSTITUTION: The nitrogen gas atmospheric zone A is constituted with a sealing pipe 6 and a sealing cover 7 through a sliding gate 5, and at the upper position in this inner part, a pipe 8 for blowing the nitrogen gas is set and communicated with a pressure tank through an outer piping 9. The pipe 8 is made to the round pipe, e.g. along inner periphery of the sealing cover 7, and at lower part of the periphery thereof, plural holes or slit-state gas injecting hole are arranged to uniformly inject the gas to the whole zone A. Further, the relation between the gas pressure supplied and sealed in the zone A, and the molten steel flow rate and nitrogen increased quantity in the molten steel, is beforehand obtd. with experiments, etc., and based on this relation, while controlling the nitrogen adding rate to the optimum, the prescribed nitrogen- containing steel is produced.
SANADA TAKEJI
OKADA KAZUO
