| 摘要 |
<p>PROBLEM TO BE SOLVED: To easily remove nitrogen contained in molten steel and to stably produce an extra-low nitrogen steel by adding a slag-making agent into the molten steel in a reduced pressure apparatus, raising the temp. and blowing flux for denitrification into the molten steel under the atmosphere after making the molten slag. SOLUTION: The molten steel containing 0.4% C and 30% Cr is melted with an oxygen top-blown converter, etc., and after tapping the molten steel into a ladle 1, the ladle is set into the reduced pressure vessel 2. Mixed material of Al, CaO and calcined dolomite is charged into the ladle 1, and after reducing the pressure in the reduced pressure vessel 2, Ar gas is blown from a tuyere 6 to the bottom part of the ladle 1, and also, oxygen is blown into the molten steel from a top-blown lance 3 to burn the charged Al and the temp. is raised to produce the molten slag. Successively, the pressure in the reduced pressure vessel 2 is returned back to the atmosphere, and an injection lance 4 is dipped into the depth of about 1m from the molten steel surface and the flux for denitrification composed of CaO, Al2 O3 , CaCO3 and 2-20% Al is injected into the molten steel to execute the denitrifying treatment. Successively, the low carbon and low nitrogen steel is produced by denitrifying from the slag, decarburizing with the oxygen blowing into the molten steel and reducing with Al.</p> |
