| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain an extra-low carbon steel having high cleanliness while restraining the reaction between FeO as well as NnO in the slag after Al deoxidation and Al in a molten steel by executing decarburizing treatment and successively deoxidizing treatment to the molten steel sucked into a vacuum vessel, and adding an NgO.Al2 O3 base flux into the obtd. slag. SOLUTION: After Al deoxidation, at the time of adding the MgO.Al2 O3 base flux into the molten steel in the vacuum vessel of a vacuum degassing apparatus, the flux is floated up in the molten steel due to circulating flow and reaches the slag. During this operation, alumna inclusion produced by the Al deoxidation is floated up and absorbed into the slag in the same way. The m.p. of the slag is raised with the reaction between the flux and the slag, and as a result, the viscosity of the slag is raised and the fluidity thereof is lowered. By this method, the reaction speed between FeO as well as MnO in the slag and the residual Al in the molten steel, is lowered, and the production of the new alumna inclusion can be restrained. The MgO.Al2 O3 in the flux is desirable to be >=80 wt.%.</p> |
