| 摘要 |
PURPOSE:To obtain low-nitrogen steel subjected to denitrification treatment down to a desired low nitrogen level by utilizing a vacuum degassing treatment by subjecting the crude high-carbon molten steel produced in a steel making furnace to top blowing of gaseous O2 under the reduced pressure to decarburize said steel and accelerating the denitrification arising in this stage. CONSTITUTION:Two immersion pipes 3a, 3b of a cylindrical reflux type degassing device 3 are immersed into a crude molten steel 1 contg. >=0.1 (C) which is refined for a carbon steel by a steel making furnace and is charged into a ladle 2. Gaseous Ar is supplied 7 to the inside of the pipe 3a and the inside of the device 3 is evacuated 6 to a reduced pressure. The inside of the device 3 is evacuated to suck up the crude molten steel 1 in the ladle 2 from the pipe 3a by the relux gas from the pipe 3a into the device 3 and to return the molten steel from the other pipe 3b into the ladle 2, thereby circulating the molten steel. Gaseous O2 is blown to the molten steel in the direction diagonal with the molten steel bath surface from a top blowing lance 4 provided to the peripheral wall of the device 3 during this time to accelerate the decarburization and denitrification reaction. The molten steel subjected to the denitrification treatment until the required components are obtd. is continuously cast and the casting steel is in succession made into a sheet material by a rolling state. The final product is obtd. by annealing continuously the sheet material. |
