| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for continuously controlling a vacuum degree, in which molten steel is stably subjected to decarburization while restraining spattering of molten metal and dust and restraining oxidized loss of Cr. SOLUTION: In the method for controlling the vacuum degree of a treating vessel 2 in reduced-pressure decarburization refining of a Cr-containing molten steel 4, when CO volume-concentration in exhaust gas with the oxygen-blowing decarburization is reached to 20%, this timing is as the decarburization-starting time, and the vacuum degree at the decarburization-starting time, is set in the range of 100-300 torr and the vacuum degree is adjusted so that the maximum value of a reduced pressure changing pressure for optionally 1 min during the oxygen-blowing decarburization becomes≤30 torr/min. Further, after decarburization-starting time, until the C mass-concentration [%C] in the molten steel 4 reaches to the C mass-concentration [%C<SB>0</SB>] at the decarburization-balancing time, the reducing pressure in the treating vessel 2 is gradually progressed in the range of 0-0.8 torr/min the average reducing pressure speed. COPYRIGHT: (C)2011,JPO&INPIT |
