BFI VDEh-Betriebsforschungsinstitut GmbH

Initial situation:

• Ladle stirring is of great interest to the steel plants, as it has major impact in the cleanness and quality of the steel. At the same time, stirring intensity and time is influencing the temperature decrease of the liquid steel, and therefore an important parameter regarding energy efficiency of steel production.
• Stirring is often carried out on the basis of static pre-set parameters, without regard to the changing metallurgical specifications between one heat and the next, and only monitored manually by operators.
• This greatly limits the stability and repeatability of the stirring process as well as the possibility to adapt the process to the varying demands of individual steel heats.
• Unnecessary long stirring is also less energy efficient.

Project targets:

The main objective of this research project was to develop, establish and verify heat-individual dynamic ladle stirring policies in secondary steelmaking. In dynamic ladle stirring, the stirring processes are tailored to the individual needs of each treated steel melt. The main target was to improve the energy efficiency of the ladle stirring processes while maintaining or enhancing the cleanness of the final steel product.

The partial objectives of the project targets were:

• Enhanced knowledge about slag-metal reactions and separation of non-metallic inclusions
• Stirring advisory systems recommending suitable heat-individual stirring parameters
• Improvement and comparison of imaging/vibration-based monitoring systems for control of ladle stirring processes
• Improved process control of ladle stirring at different process steps:
• CAS-OB (Compositional Adjustment by Sealed Argon Bubbling, with Oxygen Blowing)
• VD (Vacuum Degassing)
• FT (Final Treatment (rinsing, soft bubbling))

Innovative approaches:

• Develop dynamic stirring policies in secondary steelmaking at different treatment stations (VD, CAS-OB, FT).
• Monitor actual stirring by imaging systems, compare it to ideal treatment according to stirring policies and advise correct stirring accordingly.
• Tailoring the stirring process to the individual need of each treated steel melt, based on metallurgical fundamentals.
• Improve energy efficiency of the ladle stirring processes while maintaining the cleanness of the final product.

Benefits for the industry:

The project has combined measurement techniques, software engineering, plant trials and thorough analysis of samples and process data to reach its aims. Practical and theoretical knowledge has been gained and shared between the project partners.

Overall, the benefits for industry are reduced process time, reduced Ar consumption, reduced temperature loss, and stable process conditions by detailed monitoring of stirring processes.

During this research project, the following optimisations of stirring processes were possible to im-prove energy efficiency and maintain or even improve steel cleanness:

• Reduction of vacuum degassing time by 20 % for tool steel with low Si content and by 33,3 % for tool steel with high Si content
• Reduction of stirring gas flow rate by 50 % and of stirring time by up to 40 % for bearing steel grade 100Cr6 with high cleanness demands.