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Solubility of hydrogen in slags and its impact on ladle refining
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0003-0856-3417
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: urn:nbn:se:kth:diva-172462ISBN: 978-91-7595-594-0 (print)OAI: oai:DiVA.org:kth-172462DiVA: diva2:848439
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
List of papers
1. Characterization of melting of some slags in the Al2O3-CaO-MgO-SiO2 quaternary system
Open this publication in new window or tab >>Characterization of melting of some slags in the Al2O3-CaO-MgO-SiO2 quaternary system
2006 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 4, 614-616 p.Article in journal (Refereed) Published
Abstract [en]

A number of slag compositions in the Al2O 3-CaO-MgO-SiO2 quaternary system was investigated. The Al2O3, CaO, and SiO2 oxide powders were calcinated at 1073 K for 24 hours before being mixed in an agate mortar. The oxide mixtures were further pressed into small pellets and sealed in a glass bottle. A horizontal platinum furnace and platinum crucibles were used and each slag composition was investigated four times to confirm the reproductibility of the process. Efforts were made to carry out the experiments with identical quenching speed. The slags were quenched from 1793 K to examine the liquidity of the slag samples at lower temperatures. It was revealed that the quenched samples were multi-phase mixtures instead of melting at the experimental temperature under the influence of the phase diagrams.

Keyword
Calcination, Crucibles, Lime, Mixtures, Mortar, Ore pellets, Oxides, Platinum, Powders, Quenching
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6248 (URN)10.2355/isijinternational.46.614 (DOI)000238231000022 ()2-s2.0-33745042993 (Scopus ID)
Note

QC 20101109

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
2. Water vapor solubility in ladle-refining slags
Open this publication in new window or tab >>Water vapor solubility in ladle-refining slags
2006 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 3, 389-393 p.Article in journal (Refereed) Published
Abstract [en]

A thermo-gravimetric technique was used to determine the hydrogen solubilities of some Al2O3-CaO-MgO-SiO2 quaternary slags. The focus of the work was to determine the water capacities in slags having lower SiO2 concentrations, which were relevant to industrial practices. The majority of the experiments were carried out in the temperature interval 1747 to 1827 K with water pressure of 157 mbar. The reliability of the experiments was confirmed using a quenching technique. The temperature was found to have a negligible effect on the water solubilities. The composition of the slag did not seem to significantly affect the water capacity. However, as the slag composition approached CaO saturation, a considerable increase of the solubility was noticed.

Keyword
Alumina, Lime, Silica, Solubility, Thermal effects, Thermogravimetric analysis
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6249 (URN)10.1007/s11663-006-0023-x (DOI)000237948700007 ()2-s2.0-33845681523 (Scopus ID)
Note

QC 20101110

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
3. Water capacity model of Al2O3-CaO-MgO-SiO2 quaternary slag system
Open this publication in new window or tab >>Water capacity model of Al2O3-CaO-MgO-SiO2 quaternary slag system
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.

Keyword
Al2O 3-CaO-MgO-SiO2, Ladle slag, Model, Thermogravimetric method, Water capacity
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6250 (URN)000248267600004 ()2-s2.0-34547250781 (Scopus ID)
Note

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

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
4. Hydrogen pick-up after vacuum degassing
Open this publication in new window or tab >>Hydrogen pick-up after vacuum degassing
2015 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 42, no 1, 49-54 p.Article in journal (Refereed) Published
Abstract [en]

The present work aimed at determining the major source for hydrogen pick-up of the steel after vacuum degassing but before casting. Samples of slag and metal were taken at different stages during ladle treatment at SSAB. Hydrogen increase after vacuum treatment was observed. Moisture contents of the industrial slags were analysed and their water capacities 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 increase after degassing was due to the slag-metal reaction.

Keyword
Hydrogen, Steel making, Vacuum treatment, Hydroxyl capacity, Ladle, Industrial slag
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-158428 (URN)10.1179/1743281214Y.0000000199 (DOI)000346147400007 ()2-s2.0-84911164886 (Scopus ID)
Note

QC 20150109

Available from: 2015-01-09 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved
5. Nitrogen and Hydrogen Refining During Vacuum Treatment of Liquid Steel
Open this publication in new window or tab >>Nitrogen and Hydrogen Refining During Vacuum Treatment of Liquid Steel
2011 (English)In: PR-258-024, 2011, no 6Conference paper, Published paper (Refereed)
Abstract [en]

Nitrogen and hydrogen strongly affects mechanical properties of steel. This is why control of liquid steel nitrogen and hydrogen contents is of the utmost importance. In this paper, the nitrogen and hydrogen refining during vacuum treatment and the variation of nitrogen and hydrogen content in the tundish, have been investigated. The results clearly show that the nitrogen refining depends on the gas pressure inside the tank as well as steel sulfur content and vacuum treatment time, while the hydrogen refining seems to reach equilibrium within the varied process parameters. It is further shown that the nitrogen and hydrogen contents vary during casting. A model predicting this variation as function of time is also presented.

Keyword
Steel, vacuum, degassing, nitrogen, hydrogen, refining, tundish
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-172464 (URN)
Conference
Intl. Symposium on Recent Developments in Plate Steels
Note

QC 20150825

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

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