Abstract
Three different mold slags have been sampled in dependence of time during slab casting of TRIP steel, and compositional changes have been analyzed. Mass transfer coefficients governing the decrease of silica and increase of alumina have been determined. Moreover change of manganese content was investigated in dependence of the initial manganese content of the mold powder which was close to zero for one of the powders investigated. The following findings have been revealed: Mass transfer coefficients are rising with increasing elapsed time or decreasing silica content, respectively. An initial increase of manganese content by oxidation from the steel followed by later reduction has been observed for the manganese free mold powder. For interpretation of these findings, further simulation according to an effective equilibrium reaction zone model was performed. It was revealed that the primary impact of the steel flow at the steel/slag interface close to the mold wall followed by a stratified flow is of major importance for the phenomena observed. Further results make it possible to predict the steady state composition and show that steady state silica content is nonzero in any case. Moreover, for the mold powders investigated here, it was concluded that manganese content does not decrease silica reduction.
Zusammenfassung
Die experimentell ermittelte Veränderung der chemischen Zusammensetzung von drei Gießschlacken beim Vergießen von TRIP Stahl diente als Grundlage zur Bestimmung der Stoffübergangskoeffizienten, die für die Beschreibung der SiO2-Verminderung und Al2O3-Erhöhung maßgeblich sind. Außerdem wurde die Veränderung des MnO-Gehaltes untersucht, wobei ein Gießpulver praktisch MnO-frei war. Es hat sich gezeigt, dass die Stoffübergangskoeffizienten mit fortschreitender Zeit bzw. sinkendem SiO2-Gehalt steigen. Bei dem MnO-freien Gießpulver konnte ein anfänglicher Anstieg des MnO-Gehaltes beobachtet werden, sowie ein darauffolgender Abfall. Zur Interpretation dieser Ergebnisse wurde ein thermochemisches Prozessmodell erstellt. Dabei zeigte sich, dass die Schichtenströmung des Stahls in der oberen Konvektionswalze entlang der Phasengrenze Stahl/Schlacke zu einer Verminderung des Al-Gehaltes führt, wodurch eine Oxidation von Mn möglich wird. Weitere Ergebnisse gestatten die Berechnung der stationären Zusammensetzung und zeigen, dass der stationäre SiO2-Gehalt nicht null sein kann. Für den hier untersuchten Gießprozess ist eine Verminderung der SiO2-Reduktion durch einen Mangangehalt des Gießpulvers nicht möglich.
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Acknowledgements
The research program of the competence center “Advanced Metallurgical and Environmental Process Development” (K1-MET) is supported within the Austrian program for competence centers COMET (Competence Center for Excellent Technologies) with funds of the Federal Ministry for Transport, Innovation and Technology, the Federal Ministry of Economy, the provinces of Upper Austria and Styria, the Styrian Business Promotion Agency, of the Tyrol and the Tyrolian Future Foundation.
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Harmuth, H., Xia, G. Change of Mold Slag Composition during Slab Casting of Steel with High Al Content. Berg Huettenmaenn Monatsh 159, 447–453 (2014). https://doi.org/10.1007/s00501-014-0304-7
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DOI: https://doi.org/10.1007/s00501-014-0304-7