Improvement of ladle stirring to minimise slag emulsification and reoxidation during alloying and rinsing (STIMPROVE) : final report

The objective of this research project was to improve steel metallurgy and quality by optimisation of the ladle stirring process. Throughout the project, the interactions between solid, liquid and gaseous phases involved in ladle stirring were examined. • Melting of alloying materials was investigated using mathematical models and camera-based monitoring. It was found that typical alloying materials are molten and homogeneously distributed after 360 s, even with soft stirring. • Emulsification of liquid slag into the steel around the open eye was investigated using theoretical considerations, physical modelling and camera-based monitoring of the open eye. The coarse contour of the open eye was found to be two times larger than expected. A threshold value of 15-25 STP m3/h stirring gas flow rate was suggested to minimise emulsification. • Reoxidation was investigated using camera-based monitoring of the open eye and sampling during industrial trials. It became clear that the camera-based technique is suitable to monitor stirring efficiency, whereas no clear correlation between the stirring gas flow rate and the size of the open eye could be observed. • Rinsing and the removal of inclusions were investigated using camera-based monitoring, theoretical considerations and sampling during industrial trials. Control of rinsing without the open eye was found to be difficult. Good removal of inclusions relies on low stirring gas flow rates and long stirring times. Optimised stirring procedures with stirring intensity reduced by 25-50 % were applied in a steelworks. Such stirring did not deteriorate the quality of the steel, while consumption of stirring gas was reduced. Further investigations, e.g. of the yield of alloying additions, produced promising prospects. As part of this project, the transfer of optimised stirring procedures into the steelworks was only just started. The implementation and adaptation of optimised stirring procedures in the steelworks and careful verification of the benefits should be the focus of further investigations.