| 摘要 |
<p>PROBLEM TO BE SOLVED: To lower the ultimate carbon content in a molten chromium-containing steel to an extremely low carbon range. SOLUTION: Blowing oxygen flow rate is measured with an oxygen flow meter 16 and exhaust oxygen flow rate exhausted from a vacuum vessel is detected with an exhaust oxygen flow rate detector 32 and the height of a lance is measured with a lance height detector 41. Retained oxygen quantity storaged in the molten steel and slag is obtd. with an arithmetic means 23 based on the detected values of the oxygen flow meter 16 and the exhaust oxygen flow rate detector 37, and converted to Cr2 O3 quantity, and a target blowing oxygen flow rate and a target lance height corresponding to the converted Cr2 O3 quantify are obtd., respectively based on preset corresponding relation. An oxygen flow rate adjusting valve 17 and a lance lifting device 22 are controlled with a control means 24 so that the measured values of the oxygen flow rate and the lance height coincide with the target values, respectively. Since the converted Cr2 O3 quantity is a clear index value in the correlation with the decarburizing efficiency with control based on that, the carbon content attainment in the molten chromium-containing steel can be lowered.</p> |
