| 摘要 |
PURPOSE: A manufacturing method for API steel of high cleanliness, ultra-low sulfur content and low nitrogen content is provided to lower the nitrogen content of molten steel and also improve cleanness through RH and VDT treatments. CONSTITUTION: A manufacturing method for API steel of high cleanliness, ultra-low sulfur content and low nitrogen content comprises the steps of: performing RH-treatment of molten steel, increasing temperature through OB(oxygen blowing), and performing VTD-treatment of the treated molten steel. The RH-treatment is performed at the degree of vacuum less than 13.3mbar for over 3 minutes in order to remove gas from the molten steel. The VTD-treatment includes bubbling performed at the degree of vacuum of 267~933mbar and the gas flow rate of 0.43~0.65Nm3/hr.ton-steel. |
