公开(公告)号：US20240271234A1

公开(公告)日：2024-08-15

申请号：US18289968

申请日：2022-05-12

Applicant: JFE STEEL CORPORATION

Inventor： Chikashi TADA ,  Hidemitsu NEGISHI

IPC: C21C7/072 ,  C21C7/00 ,  C21C7/10

CPC classification number: C21C7/072 ,  C21C7/0006 ,  C21C7/10

Abstract: A method for secondarily refining molten steel s by which a low nitrogen concentration range can be stably reached at high speed without causing operational problems, and a method of producing steel are proposed. In the method for secondarily refining molten steel, CaO-and-Al2O3-containing slag is formed by a combination of an Al addition step of adding a metal-Al-containing substance to molten steel to turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel, and then an oxygen blowing process including a denitrification process is performed by blowing oxygen-containing gas so as to pierce the slag to reach the Al-containing molten steel, in which an Al concentration [Al]i (mass %) in the molten steel immediately before the oxygen blowing process is equal to or higher than a value [Al]e calculated by Formula (A) based on a stirring power density ϵ (W/t) during formation of the slag, and an Al concentration [Al]f upon completion of the oxygen blowing process is 0.03 mass % or higher. In the method of producing steel, the obtained molten steel is cast after adjusting the composition.


[Al]e=−0.072×In(ϵ)+0.5822 . . . (A)

公开(公告)号：US20240263261A1

公开(公告)日：2024-08-08

申请号：US18565348

申请日：2022-05-12

Applicant: JFE STEEL CORPORATION

Inventor： Hidemitsu NEGISHI ,  Rei YAMADA ,  Chikashi TADA

IPC: C21C7/072 ,  C21C7/10

CPC classification number: C21C7/072 ,  C21C7/10

Abstract: A method wherein a denitrification treatment allows an extremely low nitrogen concentration range to be stably and quickly reached, so denitrification and/or desulfurization of molten steel can be efficiently performed. Wherein CaO-and-Al2O3-containing slag is formed on top of molten steel charged in a vessel and an oxygen-containing gas is blown from above, while the slag and the molten steel are brought into contact with each other to remove nitrogen in the molten steel. An Al concentration in the steel is kept at or higher than a value determined by Formula (1) according to a stirring power density, and the gas is blown so a ratio between a thickness Ls0 of the slag and a depth Ls of a depression in the slag resulting from blowing of the gas meets Ls/Ls0≥1:


Al concentration (mass %) in molten steel=−0.072×ln(stirring power density (W/t))+0.5822  (1)