PURPOSE: To produce molten steel having low N content by efficiently executing reduction- refining of molten steel with stirred small grain Al with inert gas under the reduced atmospheric pressure after executing decarburize-refining by oxygen-blowing refining of the molten steel in the low vacuum range and finish refining under the reduced atmospheric pressure.
CONSTITUTION: At the time of producing a low carbon stainless steel by executing the decarburize-refining to a raw high Cr steel with a VOD method, at first C in the molten steel is oxidized by the oxygen-blowing in the low vacuum atmosphere to execute the decarburization, and in order to lower further C content, the oxygen-blowing is executed in the low CO partial pressure at ≤10Torr to execute the finish decarburize-refining to the aimed low carbon grade. Successively, in the condition of holding the refining atmosphere to high vacuum at ≤10Torr, the blowing quantity of inert gas of Ar, etc., from the bottom blowing tuyere is increased and the stirring energy Eg shown in the equation is made to be ≥400W/ton of molten steel to stir the molten steel. On the stirred molten steel surface, the small grain Al having ≤30mm grain diameter is added to reduce the oxide of Cr, etc., produced by oxygen-blowing. As this operation is executed in the high vacuumn atmosphere, absorbing action of nitrogen from the air is not executed and the extra low N stainless steel can be produced.
SHINKAI AKIO
YUKI TOSHITAKA
SUGANO KOJI
