method of refining Al killed steel havig superior cleanness for cold steel sheet

摘要

PURPOSE: A method for refining aluminum deoxidized super clean steel for cold rolled steel plate is provided to greatly improve cleanliness of steel by decreasing a content of lower oxides in a slag after completing increase of a temperature in the Ladle Furnace (LF) refining method. CONSTITUTION: A method for refining aluminum deoxidized super clean steel for cold rolled steel plate comprises the processes of finishing increase of temperature by having 0.035 to 0.045 wt.% of aluminum out of a molten steel in the Ladle Furnace refining process; injecting Al-CaOCO3 based slag formation of 0.5 to 0.75 kg/ton-steel per ton of a molten steel into the molten steel right after terminating the temperature increase; and bubbling the molten steel so that inclusions in the molten steel are separated and phased by the slag. The bubbling is carried out in a way that bottom bubbling is done in a flow rate of 0.7 to 0.9 m3/min for 3 to 5 minutes. An occurrence ratio of defects on a steel plate surface after cold rolling can be remarkably reduced, and an actual yield of a product can be improved by improving cleanliness of a molten steel.