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Growth of Small Alumina Clusters during Ladle Deoxidation
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.
2009 (English)In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 28, no 6, 347-368 p.Article in journal (Refereed) Published
Abstract [en]

For the first time, the size distribution of small clusters was determined in a systematic manner from samples taken during deoxidation with aluminium in an induction-stirred ladle. Chemical and microscopic analyses of samples were performed. The results indicated rapid cluster growth throughout the experiment and at the end of the experiment a majority of the small inclusions were found to be bound in clusters. The cluster growth was concluded to be by collision. Growth-model calculations were carried out to verify the experimental findings. In order to perform these calculations, a method first needed to be developed for conversion of the experimental data determined per unit area to data given per unit volume. Next, the cluster collision diameter was modelled using a theory for fractal aggregates. The results from the growth-model calculations, simulating deoxidation with aluminium, were found to agree well with the experimental results.

Place, publisher, year, edition, pages
2009. Vol. 28, no 6, 347-368 p.
Keyword [en]
Deoxidation, Alumina clusters, Growth, Collisions, Inclusions, Ladle
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-32679DOI: 10.1515/HTMP.2009.28.6.347ISI: 000279749700002Scopus ID: 2-s2.0-77954720742OAI: oai:DiVA.org:kth-32679DiVA: diva2:411488
Note

QC 20110418. Previous title: Growth of small alumina clusters during deoxidation in a ladle

Previous title:

Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Growth and removal of inclusions during ladle refining
Open this publication in new window or tab >>Growth and removal of inclusions during ladle refining
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.

Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.

In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.

The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

Place, publisher, year, edition, pages
Stockholm: Materialvetenskap, 2004
Keyword
Meteorology, inclusions, steel, ladle, cluster growth, modelling, Meteorologi
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-45 (URN)91-7283-886-8 (ISBN)
Public defence
2004-11-15, B3, KTH, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-11-15 Created: 2004-11-15 Last updated: 2014-03-20

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