PURPOSE: To accelerate decarburizing speed in the range of critical, carbon concn. or lower by stirring a slag having a specific m.p. while using a specific valiable related to the stirring power density at the time of decarburize-refining a high chromium steel under vacuum.
CONSTITUTION: The high chromium steel. is decarburize-refined in a vacuum refining furnace at the content of critical carbon or less. At this time, the m.p. of the slag is set to ≤1800°C on CaO-SiO2-Cr2O3 system phase diagram. Further, the slag quantity Ws kg/t is set to Ws≤0.07, =(0.0285QT/Wm) log{1+(H /148).(760/P)}, wherein : stirring power density W/t, Q: bottom blowing gas quantity Nl/min, T: molten steel temp. K, Wm: molten steel wt. ton, H: molten steel depth cm, P: vacuum degree Torr. By this method, slag fluidity is increased and oxygen supplying rate from the slag to the metal is increased, and the free surface area of the molten steel at the decarburizing reaction site is increased in the bottom blowing gas floating-up range and the decarburizing reaction in the range of critical carbon concn. or less is accelerated.
AIDA KIMIHARU
SAKURATANI TOSHIKAZU
Next Patent: METHOD FOR DECARBURIZING-REFINING CHROMIUM-CONTAINING MOLTEN STEEL