METHOD FOR CONTROLLING MOLTEN STEEL TEMPERATURE IN VACUUM LADLE REFINING FOR HIGH CHROMIUM STEEL

摘要

PURPOSE:To freely adjust molten steel temp. by decreasing O2 gas for blowing to the limited flow rate from O2 quantity in waste gas and holding the gas pressure for blowing with inert gas at the time of refining with oxygen top blowing while stirring the molten high Cr steel in a ladle in vacuum vessel. CONSTITUTION:The ladle 4 charging the molten high Cr steel 2 is set in the vacuum vessel 6 and by blowing the inert gas of Ar, etc., from blowing hole 14 at the bottom part, the molten metal 2 is stirred and also by blowing O2 gas on the surface of the molten steel 2 from a top blowing lance 16, C in the molten steel 2 is oxidized and decarbonized. As the ladle 4 is set in the vacuum vessel 6, CO partial pressure in the atmosphere is low, and C in the molten steel is oxidized with priority without oxidizing Cr in the molten steel. In this case, the waste gas is taken from a dust 10 and the remained O2 is analyzed by a continuously analyzer 20 and the O2 limited flow rate from the lance 16 at the time when the remained O2 quantity starts to rapidly increase, is found. The gas pressure from the lance 16 by mixing inert gas of Ar, etc., is held to normal-state and lowering of penetration of the mixed gas into the molten steel is prevented, and lowering of decarbonizing reaction after that caused by the lowering of the molten steel temp. is prevented.