The VOD (Vacuum Oxygen Decarburisation) process is used for production of high chromium steels with lowest carbon contents. For on-line observation a dynamic process model was developed, which comprises the calculation of decarburisation, chromium loss and steel temperature.

The observation of decarburisation is based on measured values of exhaust gas flow rate and analysis. Regarding the low final carbon content, the accuracy of this carbon balance is, due to the errors of the input data, with an error standard deviation of about 0.02 % not sufficient. Therefore for the final phase of decarburisation a model-based correction calculation was developed, which improved the accuracy of the carbon content observation by a factor of 3.

In order to minimise the chromium loss during decarburisation, a dynamic control concept for the final phase of decarburisation was developed. The lance oxygen input is reduced continuously according to the decreasing demand for decarburisation, which can be observed from the decarburisation rate. 

Structure of the process model with required input data