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Solid inclusion transfer at a steel-slag interface with focus on tundish conditions
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2005 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, 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.

Place, publisher, year, edition, pages
2005. Vol. 45, no 11, 1597-1606 p.
Keyword [en]
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: urn:nbn:se:kth:diva-7800DOI: 10.2355/isijinternational.45.1597ISI: 000233421700011Scopus ID: 2-s2.0-31144438556OAI: oai:DiVA.org:kth-7800DiVA: diva2:12930
Note
QC 20100823Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2017-12-14Bibliographically approved
In thesis
1. A Mathematical and Experimental Study of Inclusion Behaviour at a Steel-Slag Interface
Open this publication in new window or tab >>A Mathematical and Experimental Study of Inclusion Behaviour at a Steel-Slag Interface
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis work is to increase the knowledge of inclusion behavior at the steel-slag interface by mathematical modeling and in-situ Confocal Scanning Laser Microscope experiments. Mathematical models based on the equation of motion predicting liquid and solid inclusion behavior was first investigated. Four main forces, the buoyancy force, the added mass force, the rebound force and the drag force, act on the inclusion as it crosses the interface. There are three types of behavior an inclusion at the steel-slag interface can adopt. These are a) pass, which means that the inclusion is separated to the slag, b) remain, where the inclusion stays at the interface without being fully transferred to the slag or c) oscillate, and the inclusion rises and descends at the interface until the motion is dampened out by the interfacial forces. The studies showed the importance of accurate experimental physical property data. Application of the models to industrial conditions illustrated that useful plots could be made showing the industry how to optimize their interfacial properties in the ladle and tundish to obtain maximum inclusion separation.

In-situ Confocal Scanning Laser Microscope (CSLM) experiments were carried out in order to study agglomeration of liquid and semi liquid inclusions at the steel-gas and steel-slag interfaces and in the slag. Liquid-liquid inclusion agglomeration at steel-gas and steel-slag interfaces was seen to not occur without using force. However, when already transferred to the slag the inclusions agglomerated freely due to a higher free energy force. Comparison of experimental and theoretical agglomeration force showed good agreement between experiments and theory.

The main conclusion of this work is that inclusion separation is a complex field of study and there exist no model that takes everything into account. Here the tendency for inclusion transfer and how to manipulate the physical properties for inclusion separation together with agglomeration experiments have been studied. For the future maybe coupling of models for computational fluid dynamics, agglomeration, inclusion separation, dissolution and slag entrainment in addition with experimental physical property data can provide a better overview and understanding.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vii, 58 p.
Series
KTH/MSE, 2007:60
Keyword
mathematical modeling, inclusion separation, tundish, ladle, slag, steel-slag interface, CSLM experiments, agglomeration, physical properties
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-4574 (URN)978-91-7178-781-1 (ISBN)
Public defence
2007-12-19, Sal B2, KTH, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100823Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2010-08-23Bibliographically approved
2. A study of solid and liquid inclusion separation at the steel-slag interface
Open this publication in new window or tab >>A study of solid and liquid inclusion separation at the steel-slag interface
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
Materials science, mathematical modeling, inclusion separation, tundish, ladle, slag, steel-slag interface, physical properties, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-307 (URN)91-7178-069-6 (ISBN)
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

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