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Most relevant mechanisms of inclusion growth in an induction-stirred ladle
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.
2002 (English)In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 31, no 3, 210-220 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study has been to theoretically evaluate which inclusion growth mechanisms are important in an inductively stirred ladle. This has been done using data from a computational fluid dynamics model of a real ladle. The data was utilized as the input to the different collision equations. It was concluded that diffusion of oxygen and deoxidant to the inclusion surface, diffusion coalescence and Brownian motion collisions contribute very little to growth of inclusions during the stirring period in the ladle. This was in accordance with earlier findings in the literature. This study also showed that laminar shear collisions could be excluded from a growth model. The major growth mechanism is turbulent collisions. It was also shown that a 700-A stirring current leads to more growth due to turbulent collisions than a 500-A stirring current. The importance of a correct value of the collision efficiency coefficient for turbulent collisions was pointed out. If a large difference in inclusion size exists then collisions due to difference in buoyancy (Stokes collisions) also need to be considered in a growth model. Finally, it is concluded that the variation in fluid flow and turbulent properties in different parts of the ladle should be incorporated into a growth model, since it can affect average turbulent collision volumes by 25-30%.

Place, publisher, year, edition, pages
2002. Vol. 31, no 3, 210-220 p.
Keyword [en]
CFD, Inclusion growth, Induction stirring, Ladle
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-7511DOI: 10.1034/j.1600-0692.2002.310308.xISI: 000176797200008OAI: oai:DiVA.org:kth-7511DiVA: diva2:12559
Note
QC 20100923Available from: 2004-11-15 Created: 2004-11-15 Last updated: 2017-12-14Bibliographically 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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