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Water capacity model of Al2O3-CaO-MgO-SiO2 quaternary slag system
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0003-0856-3417
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0002-3548-8638
2007 (English)In: Steel research, ISSN 0177-4832, Vol. 78, no 6, 460-464 p.Article in journal (Refereed) Published
Abstract [en]

The focus of the present work was to develop a water capacity model for the quaternary slag system Al2O3-CaO-MgO-SiO2. In the model, a silicate melt was considered to consist of two ion groupings, viz. cation grouping and oxygen ion. The water capacity of a melt is supposed to depend on the interactions between the cations in the presence of oxygen ions. These interactions were determined on the basis of the experimentally measured water solubility data. Only binary interactions were employed in the model. For the system CaO-SiO2, disagreement in the literature data was found. Since the interaction between Ca2+ and Si4+ would play an important role, experiments were carried out to determine the water capacities of some CaO-SiO2 slags. For this purpose a thermogravimetric method was employed. Iso-lines of water capacities at constant MgO contents were predicted by the model and compared with the experimental data from literature. The model calculations agreed well with the experimental results.

Place, publisher, year, edition, pages
2007. Vol. 78, no 6, 460-464 p.
Keyword [en]
Al2O 3-CaO-MgO-SiO2, Ladle slag, Model, Thermogravimetric method, Water capacity
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6250ISI: 000248267600004Scopus ID: 2-s2.0-34547250781OAI: oai:DiVA.org:kth-6250DiVA: diva2:10910
Note

QC 20101110. Uppdaterad från In press till Published (20101110).

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2015-08-25Bibliographically approved
In thesis
1. Solubility of hydrogen in slags and its impact on ladle refining
Open this publication in new window or tab >>Solubility of hydrogen in slags and its impact on ladle refining
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of the present work was to clarify the mechanisms of hydrogen removal during vacuum degassing. The main reason for this was because the primary source of hydrogen pick-up in steel-making is the moisture in the furnace atmosphere and the raw material charged into the ladle furnace. Previous studies showed that the presence of hydroxyl ions in the ladle slag results in hydrogen transfer from the slag back into the steel bath. The main focus of this thesis was therefore to gain deeper knowledge of the ladle slag and its properties. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al2O3 CaO MgO SiO2 system was completely melted. These results were in disagreement with the existing phase diagrams.

Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect on the water solubilities. The experimental results showed that the water capacity values varied between 1x103 and 2x103 in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3x103. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al2O3 CaO MgO SiO2. The model was constructed by considering the affects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed well with the experimental results as well as with the literature data.

An attempt was made to develop a preliminary process model for dehydrogenation by using the results from CFD calculation. For this purpose industrial sampling was made during vacuum treatment. The hydrogen concentrations decreases fast in the initial stages of the degassing, but is slowed down in the final stage. The model calculations fit the initial stage of the dehydrogenation process well. In the final stage of the process the predicted values are somewhat lower than the plant data. The results from the model prediction showed that a dynamic process model could be satisfactorily constructed using the results from CFD calculation.

The present work aimed at determining how big impact hydroxyl ions in the slag have on the final hydrogen concentration in the liquid steel. It was found that the effect is of less importance regarding the final concentration of the metal after the degassing treatment.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 37 s. p.
Series
TRITA-ARK. Akademisk avhandling, ISSN 1402-7461
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4143 (URN)91-7178-453-5 (ISBN)
Presentation
2006-10-20, B2, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20101110

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2015-08-25Bibliographically approved
2. Solubility of hydrogen in slags and its impact on ladle refining
Open this publication in new window or tab >>Solubility of hydrogen in slags and its impact on ladle refining
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis a study of the mechanisms of hydrogen control pickup during ladle treatment was undertaken. Previous studies showed that the presence of hydroxyl ions in the ladle slag resulteds in hydrogen transfer from the slag back into the steel bath. The main focus of the present work was therefore to gain deeper knowledge of the ladle slag, its properties and impact on hydrogen concentration in the liquid steel. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al2O3-CaO-MgO-SiO2 system werewas completely melted, while the rest had solid shape present . These results were in disagreement with the existing phase diagram.

 

Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect in the water solubilities. The experimental results showed that the water capacity values varied between 1·103 and 2·103 in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3·103. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al2O3-CaO-MgO-SiO2. The model was constructed by considering the effects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed reasonably well with the experimental results as well as with the literature data.

 

The water capacity model was used in the last part of the present thesis in order to determine the major source for hydrogen pick-up of the steel after vacuum degassing but before casting. For this purpose, samples of slag and metal were taken at different stages ofduring ladle treatment at SSAB. Hydrogen increase after vacuum treatment was observed. Moisture contents of the industrial slag were analysed and the water capacities of the slags were calculated. It could be seen that the hydrogen increase was correlated to the amount of moisture in the slag and the water capacity. The study showed that the slag containing most water was also the heat having the largest hydrogen increase. The slag with most water had the highest water capacity. It could be concluded that the major source for hydrogen coming back into the steel was due to the slag-metal reaction.

A tentative process model to predict the final contents of hydrogen and nitrogen after tundish process was attempted. More work is needed to improve the model.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. viii, 44 p.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-172462 (URN)978-91-7595-594-0 (ISBN)
Public defence
2015-09-04, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150825

Available from: 2015-08-25 Created: 2015-08-25 Last updated: 2015-08-25Bibliographically approved

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