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Effect of vacuum degassing on non-metallic inclusions in an ASEA-SKF ladle furnace
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
(Materials Research and Development, Ovako Hofors AB,)
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
2013 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 6, 470-477 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this research was to study non-metallic inclusions during vacuum degassing in an ASEA-SKF ladle furnace. Five steel and top slag samples were taken before, during and after vacuum degassing for chemical analysis and scanning electron microscopy. It was concluded that the average CaO/Al2O3 ratios in the top slags became close to the phase C3A. The average CaO/Al2O3 ratios in the inclusions of this study were close to the phase CA6, but at the end of degassing, the average CaO/Al2O3 ratios in the calcium aluminates by subtracting the Al amounts of the inclusions that were assumed to form spinel phases with the available Mg amounts in the inclusions were situated between the phases C12A7 and C3A. By decreasing the S and Al contents of molten steel and at [S]3.[Al]2 less than around 10−7 , the ratio of calcium aluminates to spinels increased continously. It was finally concluded that by increasing the Ca amount in inclusions, their equivalent circle diameters grew, and their aspect ratios went toward unity, and when the amount of Ca measured in the inclusions was more than 25 wt-%, inclusions with bigger equivalent circle diameters appeared.

Place, publisher, year, edition, pages
UK: Maney Publishing, 2013. Vol. 40, no 6, 470-477 p.
Keyword [en]
Calcium aluminate; Vacuum degassing; ECD; Spinel; SEM analysis; Non-metallic inclusions
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-101471DOI: 10.1179/174328113X13711140547880ISI: 000322793600010Scopus ID: 2-s2.0-84883268385OAI: oai:DiVA.org:kth-101471DiVA: diva2:547873
Note

QC 20130909

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Slag, Steel, Ladle and Non-metallic Inclusions Equilibria in an ASEA-SKF Ladle Furnace
Open this publication in new window or tab >>Slag, Steel, Ladle and Non-metallic Inclusions Equilibria in an ASEA-SKF Ladle Furnace
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study explores the possibility of prediction and modification of some of the physicochemical properties of non-metallic inclusions by considering top slag-steel-ladle equilibria in an ASEA-SKF ladle furnace. To test the reliability of an available computational thermodynamic computer program, the first sub project was done. It was concluded that LiMeS, an interface for Thermo-Calc, is a useful tool for slag-steel equilibrium calculations. The second sub project was set out to find some model/s that could calculate the most accurate oxygen activity of molten steel compared to the measured one. This study concluded that both Wagner’s and Turkdogan's equations are useful. It was further seen that increasing the Al contents in the molten steel, increasing the CaO/Al2O3 ratio in the top slag, and reducing the temperature, resulted in reduction of the oxygen activity of the molten steel. In the third sub project a comparison was made between measured CaO and Al2O3 (normalised to CaO-Al2O3) in top slag, calcium aluminate inclusions, and the results of theoretical calculations. The average contents of CaO and Al2O3 in all inclusions were close to the composition of the phase Ca12Al14O33 and the contents of CaO and Al2O3 in the slags were close to the composition of the phase Ca3Al2O6 in the binary phase diagram of CaO-Al2O3. The forth sub project set out to study the effect of vacuum degassing time on non-metallic inclusions. It was concluded that during the vacuum degassing process the share of calcium aluminates compared to spinels, Ca content of the oxides, and the average equivalent circle diameters of the oxides were increasing, and oxides tended to form spherical shapes. Finally, based on the preceding four sub projects, the fifth sub project aimed to optimize the steel treatment in an ASEA-SKF ladle furnace. The final results showed that by adding 200 kg fluorite to the top slag of 1200 kg, it was possible to achieve a sulphur content of less than 10 ppm in the steel and a sulphur ratio between slag and steel of 1570, and at the same time reduce the oxygen activity of the molten steel and the degassing time.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 62 p.
Keyword
Clean steel, Top slag, Non-Metallic Inclusions, Oxides, Vacuum Degassing, Deoxidation, Desulphurization, Equilibrium, Computational Thermodynamics, Scanning electron microscopy
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-102149 (URN)978-91-7501-489-0 (ISBN)
Public defence
2012-10-05, sal B2,, Brinellvägen 23, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20120917

Available from: 2012-09-17 Created: 2012-09-10 Last updated: 2012-09-18Bibliographically approved

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