METHOD FOR CONTROLLING FORM OF INCLUSION IN ALUMINUM KILLED STEEL FOR COLD ROLLED SHEET

摘要

PURPOSE:To obtain an aluminum killed steel for a cold rolled sheet which can avert advantageously various cracks in the stage of severe plastic working by adding a flux composed specifically of MgO, CaO and/CaF2 at a specific ratio to a molten steel subjected to a component adjustment in the stage of tapping, stirring forcibly the steel and controlling the form of the inclusion therein. CONSTITUTION:A low carbon aluminum killed steel contg. generally, by weight %, 0.01-0.08% C, 0.08% Si, 0.15-0.35% Mn, and 0.020-0.15% Sol.Al is melted in a steel making furnace. The molten steel is subjected to a required component adjustment according to a conventional method in the stage of tapping the same from the steel making furnace, for example, a converter. A flux consisting of 10-30% MgO basing on the molten steel and the balance CaO and/ or CaF2 is added to such molten steel at a ratio of 1-4kg/molten steel ton and the molten steel is forcibly stirred by the inert gas blown thereto. As a result, the Al2O3 cluster and CaO-Al2O3 inclusion of high m.p. formed in the molten steel are component-adjusted to the CaO-Al2O3-MgO inclusion of low m.p. with the target components of CaO/Al2O3 0.6-1.2, MgO=8-15%, whereby the component adjustment of the molten steel is accomplished.