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Slag, Steel, Ladle and Non-metallic Inclusions Equilibria in an ASEA-SKF Ladle Furnace
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
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 [en]
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: urn:nbn:se:kth:diva-102149ISBN: 978-91-7501-489-0 (print)OAI: oai:DiVA.org:kth-102149DiVA: diva2:551100
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
List of papers
1. Slag-Steel Equilibrium Calculations by Computational Thermodynamics: Comparison with the Plant Data
Open this publication in new window or tab >>Slag-Steel Equilibrium Calculations by Computational Thermodynamics: Comparison with the Plant Data
2011 (English)In: Proceeding of the International Symposium on Liquid Metal Processing and Casting (LMPC 2011), Institut Jean Lamour -Ecole des Mines de Nancy , 2011, 127-134 p.Conference paper, Published paper (Refereed)
Abstract [en]

This study presents a comparison between the measured and calculated results of the slag-steel equilibrium in the ASEA-SKF ladle furnace. The new software LiMeS available with the Thermo-Calc software package was applied in order to calculate the slag-steel equilibrium after the argon degassing process. The input data used in the calculations were those achieved by instrumental analysis of the slag-steel samples that were taken before starting the argon degassing process. The results were compared with the measured values. The calculated Al, Mn and Si contents in the molten steel, and the amounts of Al2O3 and SiO2 in the slag, were in good agreement with the measurements. The calculated and the measured O, S and Mg contents in the molten steel, and the S, CaO and MgO contents of the slag, were not in good agreement. It was concluded that LiMeS is a useful tool for slag-steel equilibrium calculations.

Place, publisher, year, edition, pages
Institut Jean Lamour -Ecole des Mines de Nancy, 2011
Keyword
Slag steel equilibrium, Thermo-Calc, LiMeS, Computational thermodynamic
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101464 (URN)
Conference
International Symposium on Liquid Metal Processing and Casting (LMPC 2011)
Note

QC 20120917

Available from: 2012-08-30 Created: 2012-08-29 Last updated: 2012-09-17Bibliographically approved
2. Oxygen activity calculations of molten steel: comparison with measured results
Open this publication in new window or tab >>Oxygen activity calculations of molten steel: comparison with measured results
2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 2, 136-145 p.Article in journal (Refereed) Published
Abstract [en]

This study sets out to find some model/s that could calculate the closest oxygen activity of molten steel to the measured oxygen activity in an ASEA-SKF ladle furnace. Ten steel heats grade SAE 52100 were chosen, the oxygen activities of the molten steel after vacuum degassing process were measured, then by means of two different equations and one computer programs the theoretical oxygen activities were calculated and compared to the measured results. In order to calculate the activities of Al2O3 in the top slag four different models and two different constants were applied. Both Wagner and Turkdogan's equations were found to be useful. It was seen that increasing the wt% Al from 0 up to 0.05 in molten steel, increasing CaO/Al2O3 ratio in top slag, and reducing equilibrium temperature of slag-steel could contribute to reduction of oxygen activity of molten steel. The scanning electron microscope observations revealed that the main types of observed non-metallic inclusions in these samples were spinels and calcium aluminates and by increasing the CaO content of the inclusions their equivalent circle diameters grew.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlagsgesellschaft, 2013
Keyword
oxygen activity;Wagner equation;thermodynamic model;Al2O3 activity;steel;slag;Thermo-Calc;SEM;ECD
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101465 (URN)10.1002/srin.201200114 (DOI)000314469400005 ()2-s2.0-84873397448 (Scopus ID)
Note

QC 20130214

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2017-12-07Bibliographically approved
3. Comparison between measured CaO and Al2O3 normalised to CaO-Al2O3 in top slag, calcium aluminate inclusions, and results of theoretical calculations
Open this publication in new window or tab >>Comparison between measured CaO and Al2O3 normalised to CaO-Al2O3 in top slag, calcium aluminate inclusions, and results of theoretical calculations
2013 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 5, 369-375 p.Article in journal (Refereed) Published
Abstract [en]

This study sets out to compare the wt-% CaOslag and Al 2O3 slag in the binary system of CaO-Al 2O3 that were measured in the top slag before teeming, the CaOincl and Al2O3 incl in calcium aluminates that were analysed by scanning electron microscopy of the steel samples and the CaOcalc and Al2Ocalc 3 that were achieved from theoretical calculations using the total measured elements in the top slag and steel before teeming. The CaO incl and Al2O3 incl in all of the calcium aluminate inclusions of this study did not have the same ratio; in the opposite, they covered a large range. The average CaOincl and Al 2O3 incl in all samples had nearly similar compositions that were close to the border of the phase Ca12Al 14O33 in the binary phase diagram of CaO-Al 2O3. The CaOslag and Al2O 3 slag in all samples had almost similar compositions that were close to the border of the phase Ca3Al2O6 in the binary phase diagram of CaO-Al2O3. The results of theoretical calculations were close to the CaOslag and Al 2O3 slag, but they did not follow the same maximum and minimum tendencies of CaOslag and Al2O 3 slag.

Place, publisher, year, edition, pages
UK: , 2013
Keyword
CaO, Al2O3, Top slag, Calcium aluminate, Inclusions, Theoretical calculations
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101467 (URN)10.1179/1743281212Y.0000000046 (DOI)000320448900007 ()2-s2.0-84880640021 (Scopus ID)
Note

QC 20150629

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2017-12-07Bibliographically approved
4. Development of oxide inclusions during vacuum degassing process
Open this publication in new window or tab >>Development of oxide inclusions during vacuum degassing process
2013 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 4, 290-297 p.Article in journal (Refereed) Published
Abstract [en]

This article sets out to study the development of oxide inclusions during the vacuum degassing process at the ASEA-SKF ladle furnace. During the degassing process, five steel and top slag samples were taken, and their chemical compositions were analysed. All steel samples were further analysed by scanning electron microscopy. It was concluded that the vacuum degassing process was a dynamic process during which spinel and calcium aluminate inclusions were dominant. In addition, it was seen that during this process, the percentage share of calcium aluminates compared with spinels, the Ca weight per cent content of the oxides, the average equivalent circle diameter (ECD) of the oxides and the percentage share of the oxides with bigger ECD were increasing, and the oxides tended to form more round shapes.

Place, publisher, year, edition, pages
UK: Maney Publishing, 2013
Keyword
SEM analysis, ECD, Non-metallic inclusions, Spinel, Calcium aluminates
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101468 (URN)10.1179/1743281212Y.0000000049 (DOI)000318680800009 ()2-s2.0-84877156028 (Scopus ID)
Note

QC 20140613

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2017-12-07Bibliographically approved
5. Top slag optimization in an ASEA-SKF ladle furnace
Open this publication in new window or tab >>Top slag optimization in an ASEA-SKF ladle furnace
2011 (English)In: Proceeding of the Richard J. Fruehan Symposium: Physical Chemistry of Sustainable Metals, USA: AIST (Association for Iron & Steel Technology) , 2011, 311-320 p.Conference paper, Published paper (Refereed)
Abstract [en]

The aim of this study was to increase the sulphur distribution ratio between slag and steel of the synthetic top slag that was used in the ASEA-SKF treatment plant of Ovako Hofors AB. In this paper the synthetic top slag of the ASEA-SKF ladle furnace was studied by means of thermodynamic calculations using the TC-LiMeS software. It was thus concluded that if fluorite was added to the synthetic top slag (%S)/[%S] ratio would be enhanced. By considering this, four plant test charges with addition of fluorite to the top slag were performed and compared with 24 reference charges that had already been produced in the same plant. The final results showed that by adding 200 kg fluorite to a top slag of 1200 kg, it was possible to achieve a steel sulphur content of less than 10 ppm and a (%S)/[%S] ratio of 1570.

Place, publisher, year, edition, pages
USA: AIST (Association for Iron & Steel Technology), 2011
Keyword
Ladle furnace, Desulphurization, Fluorite, Steel, Slag, TC-LiMeS, Thermo-Calc
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101469 (URN)
Conference
Richard J. Fruehan Symposium: Physical Chemistry of Sustainable Metals
Note

QC 20120917

Available from: 2012-08-30 Created: 2012-08-29 Last updated: 2012-09-17Bibliographically approved
6. Effect of vacuum degassing on non-metallic inclusions in an ASEA-SKF ladle furnace
Open this publication in new window or tab >>Effect of vacuum degassing on non-metallic inclusions in an ASEA-SKF ladle furnace
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
Keyword
Calcium aluminate; Vacuum degassing; ECD; Spinel; SEM analysis; Non-metallic inclusions
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101471 (URN)10.1179/174328113X13711140547880 (DOI)000322793600010 ()2-s2.0-84883268385 (Scopus ID)
Note

QC 20130909

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2017-12-07Bibliographically approved

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Output format
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