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A study of solid and liquid inclusion separation at the steel-slag interface
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis work aimed to provide a better knowledge of inclusion behavior at the steel-slag interface. All results are based on mathematical modeling of liquid and solid inclusion separation to the slag. The model descriptions of the inclusion transfer are based on the equation of motion at the system. It is assumed that the inclusion transfer is governed by four forces acting on the inclusion as it has reached the steel-slag interface. These are the buoyancy force, the added mass force, the drag force and the rebound force. The models assume two cases of inclusion separation depending on the inclusion Reynolds number. In the case where Reynolds number is larger or equal to unity, Re≥1, a steel film is formed between the inclusion and the slag. This steel film must first be drained before the inclusion can separate to the slag. If Reynolds number, Re<1, then no steel film is formed and the inclusion will be in direct contact with the slag. The mathematical models also propose three types of inclusion behavior as the inclusion crosses the steel-slag interface. The inclusion can either, pass and separate to the slag, oscillate at the interface with the possibility of reentering the steel bath with the steel flow or it can remain at the interface not completely separated to the slag. A parameter study for 20 μm inclusions showed that the most important parameters controlling the inclusion behavior at the steel-slag interface are the slag viscosity and the interfacial tensions between the phases. For 100μm inclusions also the inclusion density affects the inclusion behavior. The models were applied to ladle and tundish conditions. Since the slags in the chosen industrial conditions have not been studied experimentally before, estimations of the important physical property parameters were made. Future measurements will therefore be needed in order to make predictions of inclusion transfer behavior at the steel-slag interface which are more relevant for the industry. The main conclusion is that useful plots can be made in order to illustrate the tendency for the inclusion transfer and how to manipulate the physical property parameters in order to increase the inclusion separation in ladles and tundishes.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , viii, 18 p.
Keyword [en]
Materials science, mathematical modeling, inclusion separation, tundish, ladle, slag, steel-slag interface, physical properties
Keyword [sv]
Materialvetenskap
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-307ISBN: 91-7178-069-6 (print)OAI: oai:DiVA.org:kth-307DiVA: diva2:8822
Presentation
2005-05-25, B2, Brinellvägen 23, Stockholm, 14:00
Supervisors
Note
QC 20101221Available from: 2005-07-15 Created: 2005-07-15 Last updated: 2012-03-21Bibliographically approved
List of papers
1. Solid inclusion transfer at a steel-slag interface with focus on tundish conditions
Open this publication in new window or tab >>Solid inclusion transfer at a steel-slag interface with focus on tundish conditions
2005 (English)In: ISIJ International, ISSN 0915-1559, Vol. 45, no 11, 1597-1606 p.Article in journal (Refereed) Published
Abstract [en]

The separation of non-metallic inclusions from the steel to the slag phase in the ladle during secondary steel making operations and in the tundish and mold during casting is very crucial to the production of clean steel. In this work a theoretical study of the separation of solid inclusions, alumina and others, at the steelslag interface applied to the actual conditions in the tundish has been carried out. The theoretical model is based on the equation of motion with the following forces acting on an inclusion as it tries to cross the interface between the metal and the slag; buoyant, added mass, rebound and drag force. A sensitivity analysis study was carried out in order to clarify which of the parameters in the model that had the largest influence on the inclusion displacement. The results showed that the interfacial tensions (sigma(MI), sigma(IS), sigma(MS)) and the slag viscosity (us) have the largest influence on the predicted displacement. It was also concluded that the overall wettability should be positive and that the slag viscosity should be as low as possible to obtain the most favorable conditions for inclusion transfer at the steel-slag interface.

Keyword
Inclusions; Modeling; Physical properties and tundish; Slag; Steel; Transfer; Buoyancy; Drag; Ladle metallurgy; Slags; Steel; Surface tension; Interfaces (materials)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7800 (URN)10.2355/isijinternational.45.1597 (DOI)000233421700011 ()2-s2.0-31144438556 (Scopus ID)
Note
QC 20100823Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2012-03-21Bibliographically approved
2. A mathematical model to study liquid inclusion behavior at the steel-slag interface
Open this publication in new window or tab >>A mathematical model to study liquid inclusion behavior at the steel-slag interface
2005 (English)In: ISIJ International, ISSN 0915-1559, Vol. 45, no 12, 1838-1847 p.Article in journal (Refereed) Published
Abstract [en]

The separation of non-metallic inclusions at the interface between the steel and the slag in the ladle, tundish and mold is an essential part of the production of clean steel. It is therefore, of great importance to have a deep understanding of the phenomena controlling the transfer of inclusions from the steel to the slag layer. In this work a mathematical model, derived from the equation of particle motion, have been used to study the transfer of liquid inclusions to slags. The effects of the drag, added mass, buoyancy and rebound force on the inclusion transfer are considered. The model relies, to a great extent, on the availability of accurate information of the magnitude of a number of physical properties of the involved phases. Among those properties, the interfacial tension between the phases and the slag viscosity were found to be the most critical. Due to the fact that the availability of experimentally obtained high-temperature physical property data, relevant to the industrial conditions, is scarce in the literature several different model descriptions have been used in this work to estimate these properties. The mathematical model has been used to investigate the separation of liquid non-metallic inclusions, of different size and composition, to a number of different industrial ladle slag compositions.

Keyword
Mathematical model; Non-metallic incluions; Physicl properties; Steel making; Buoyancy; Interfaces (materials); Liquids; Slags; Steelmaking; Model descriptions; Non-metallic incluions; Physicl properties; Non-metallic incluions; Physicl properties Engineering main heading:
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-7801 (URN)10.2355/isijinternational.45.1838 (DOI)000234202600009 ()2-s2.0-33244489368 (Scopus ID)
Note
QC 20100823Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2012-03-21Bibliographically approved

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