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A Study on the Correlation between Ladle Glaze and Non-Metallic Inclusions in the Ladle Treatment
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis, the correlation between ladle glaze and non-metallic inclusions in the ladle treatment was studied. A number of industrial trials with full scale ladle and laboratory works were performed to investigate the inclusions in the ladle treatment.

BaO was used as tracer in the ladle slag to investigate the effect of slag on inclusion composition and the formation of non-metallic inclusions by ladle glaze. BaO was detected in the inclusions of all followed heats. This observation showed strong evidence for the generation of non-metallic inclusions by the ladle glaze. The increase of the fractions of BaO containing inclusions and their average content of BaO in the first heat with tracer suggested that the effect of slag on the composition of inclusions was a very slow process.

The detachment of ladle glaze and the chemical transformations of oxide solution in the MgO matrix were investigated. The experimental results evidently showed that the ladle glaze could be the source of inclusions continually during the ladle treatment. Samples of liquid oxide solution to simulate the liquid oxide inclusions carried over from EAF were equilibrated with molten steel under controlled atmosphere. The results along with thermodynamic calculation suggested that the SiO2 content of inclusions from EAF could be considerably reduced by dissolved aluminium in the steel. This would explain the vanishing of inclusions containing high SiO2 content after deoxidation.

Due to the lack of experimental data, the viscosities of slags in the Al2O3-CaO-MgO-SiO2 system were measured using the rotating cylinder method in the temperature range of 1720 to 1910 K. Eight different slag compositions related to the secondary steel making operations were selected. Viscosities in this system and its sub-systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH.

The activities of oxide components in the Al2O3-CaO-MgO-SiO2 systems at 1873 K were measured by equilibrating liquid slag and metal. Either silicon or copper was used as the metal phase and the oxygen partial pressure was controlled with different mixing rates of Ar and CO gas flow in equilibrium with graphite. Iso-activity lines were drawn from the measured activity values in the isothermal section of the slag systems.

Nine series of industrial trials were carried out using the same ladle in each series to examine the effect of ladle slag on the number of non-metallic inclusions in the next heat. It was found that the number of inclusions increased with SiO2 content of the ladle slag in the previous heat. No clear trends were found for the effects of viscosity and MgO activity of the previous slag on the number of inclusions. Theoretical analysis based on the experimental results suggested that the formation of 2CaO∙SiO2 followed but the dusting of the compound made the refractory more porous, which was reasonable for the number of non-metallic inclusions.

Place, publisher, year, edition, pages
Stockholm: KTH , 2011. , v, 59 p.
Keyword [en]
non-metallic inclusions, ladle treatment, ladle glaze, tracer, tool steel, viscosity, activity, modelling, Al2O3-CaO-MgO-SiO2 system
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-27640ISBN: 978-91-7415-841-0 (print)OAI: oai:DiVA.org:kth-27640DiVA: diva2:379374
Public defence
2011-01-28, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2010-12-21 Created: 2010-12-17 Last updated: 2010-12-21Bibliographically approved
List of papers
1. Study of the Formation of Non-metallic Inclusions by Ladle Glaze and the Effect of Slag on Inclusion Composition using Tracer Experiments
Open this publication in new window or tab >>Study of the Formation of Non-metallic Inclusions by Ladle Glaze and the Effect of Slag on Inclusion Composition using Tracer Experiments
2009 (English)In: Steel Resarch International, ISSN 1611-3683, Vol. 80, no 10, 753-760 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, BaO was used as tracer in the ladle slag to investigate the effect of slag on inclusion composition and the formation of non-metallic inclusions by ladle glaze. Experiments were carried out at Uddeholm Tooling AB, Hagfors, Sweden. In the first heat of each series, about 20 mass% BaO was added to the ladle slag. In the next heat(s) using the same ladle, no BaO was added. BaO was detected in the inclusions. This observation showed strong evidence for the generation of non-metallic inclusions by the ladle glaze. Even in the second and third heats, the fractions of BaO containing inclusions were still very high in all stages of the ladle treatment, indicating that ladle glaze was one of the major sources of inclusions. The sizes of the BaO containing inclusions were relatively big. The average size was 20 mu m, while the biggest was around 100 mu m. The increase of the fractions of BaO containing inclusions and their average content of BaO with the treatment stage suggested that the effect of slag on the composition of inclusions was a very slow process, due to the low solubility of Ba in the steel.

Keyword
non-metallic inclusion, ladle treatment, ladle glaze, tracer, steel, interface
Identifiers
urn:nbn:se:kth:diva-18911 (URN)10.2374/sri09sp063 (DOI)000271324500009 ()2-s2.0-73249153379 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-12-21Bibliographically approved
2. Mechanism study on the formation and chemical changes of calcium aluminate inclusions containing SiO2 in ladle treatment of tool steel
Open this publication in new window or tab >>Mechanism study on the formation and chemical changes of calcium aluminate inclusions containing SiO2 in ladle treatment of tool steel
2010 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Article in journal (Refereed) In press
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-27724 (URN)
Note
QC 20101221Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2017-12-11Bibliographically approved
3. Viscosities of the Quaternary Al2O3-CaO-MgO-SiO2 Slags
Open this publication in new window or tab >>Viscosities of the Quaternary Al2O3-CaO-MgO-SiO2 Slags
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 3, 260-268 p.Article in journal (Refereed) Published
Abstract [en]

Viscosities of some quaternary slags in the Al2O3-CaO-MgO-SiO2 system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub-systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso-viscosity contours in the Al2O3-CaO-MgO-SiO2 system relevant to ladle slags were calculated at 1823K and 1873K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.

Keyword
Viscosity, Slag, Al2O3-CaO-MgO-SiO2 system, Modelling, Ladle refining
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-27725 (URN)10.1002/srin.201000150 (DOI)000289061100014 ()2-s2.0-79952211172 (Scopus ID)
Note
QC 20101221Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2011-04-20Bibliographically approved
4. Activity measurements in Al2O3-CaO-SiO2(-5 mass% MgO) slag systems at 1873 K
Open this publication in new window or tab >>Activity measurements in Al2O3-CaO-SiO2(-5 mass% MgO) slag systems at 1873 K
(English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Other academic) Submitted
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27726 (URN)
Note

QC 20101221

Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2017-12-11Bibliographically approved
5. Effect of ladle slag of the previous heat on the number of non-metallic inclusions in ladle treatment of tool steel
Open this publication in new window or tab >>Effect of ladle slag of the previous heat on the number of non-metallic inclusions in ladle treatment of tool steel
2011 (English)In: Ironmaking and Steelmaking, ISSN 0301-9233, Vol. 38, no 8, 584-589 p.Article in journal (Other academic) Published
Abstract [en]

Nine series of industrial trials were carried out using the same ladle in each series to examine the effect of ladle slag on the number of non-metallic inclusions in the next heat. Steel and slag samples were taken after ladle vacuum treatment for chemical composition analysis. Samples of the final steel product were examined to determine the number of non-metallic inclusions. It was found that the number of inclusions increased with SiO(2) content of the ladle slag in the previous heat. No clear trends were found for the effects of viscosity and MgO activity of the previous slag on the number of inclusions. Theoretical analysis based on the experimental results suggested that the formation of 2CaO.SiO(2) followed, but the dusting of the compound made the refractory more porous, which was reasonable for the number of non-metallic inclusions.

Keyword
Ladle treatment; Ladle glaze; Slag; Non-metallic inclusions; Tool steel
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27727 (URN)10.1179/1743281211Y.0000000030 (DOI)000296765900004 ()2-s2.0-80755168948 (Scopus ID)
Note
Updated from submitted to published. QC 20120119Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2012-01-19Bibliographically approved

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