Decarburization end point determination method, decarburization end point determination device, secondary refining operation method for steel making, and method for producing molten steel

A decarburization end point determination device that determines a completion time point of vacuum decarburization treatment in a facility that performs the vacuum decarburization treatment of reducing carbon concentration of molten steel by degassing a vacuum chamber, the device comprising a processor comprising hardware, the processor being configured to:

• estimate the carbon concentration and oxygen concentration of the molten steel and carbon dioxide gas concentration of exhaust gas in the vacuum chamber during the vacuum decarburization treatment by using measurement values of the carbon concentration and the oxygen concentration of the molten steel before the vacuum decarburization treatment is started, a measurement value of internal pressure of the vacuum chamber, and a model formula of the vacuum decarburization treatment;
• correct a parameter included in the model formula in such a manner as to reduce
• a difference between an estimate value and a measurement value of the oxygen concentration of the molten steel at timing when the oxygen concentration of the molten steel is measured during the vacuum decarburization treatment and
• a difference between an estimate value and a measurement value of the carbon dioxide gas concentration of the exhaust gas at timing when the carbon dioxide gas concentration of the exhaust gas is measured during the vacuum decarburization treatment;
• estimate the carbon concentration of the molten steel by using the model formula in which the parameter is corrected;
• determine timing when an estimate value reaches a target value as the completion time point of the vacuum decarburization treatment;
• and
• perform operation end determination of a secondary refining process for steel making by terminating the vacuum decarburization treatment at the determined completion time point.