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Mechanism Study of inclusion removal around open-eye in ladle treatment
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-3548-8638
2007 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 34, no 3, 253-261 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, the inclusion removal mechanism by rising bubbles around the open eye in a gas stirred ladle was investigated using a cold model. Water and silicone oils were employed to simulate liquid metal and slag respectively, Both fine silicone oil droplets and charcoal particles were used to simulate inclusions. Around the open eye, the oil layer exhibited a sphere bed structure when a critical gas flowrate was reached. The sphere bed was composed of many oil droplets, each of which was coated with a thin water film. The injected inclusions mostly followed the stream of water flow and were brought up to the open eye by the gas-water plume. A fraction of the inclusions were captured by the sphere bed when passing through the openings between the oil droplets, while the rest of the inclusions came back to the water bath and joined the stream of the flow again. The sphere bed was found to function as a filter to the tiny particles or oil droplets. On the basis of this mechanism, a preliminary comparison of the contribution of inclusion removal by metal-gas plume in the open eye region with the contribution of buoyancy was made.

Place, publisher, year, edition, pages
2007. Vol. 34, no 3, 253-261 p.
Keyword [en]
Cold model; Gas injection; Inclusion removal; Ladle refining; Metal-gas plume; Buoyancy; Charcoal; Inclusions; Liquid metals; Silicones; Slags; Water
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-6822DOI: 10.1179/174328107X168101ISI: 000246963400011Scopus ID: 2-s2.0-35348993737OAI: oai:DiVA.org:kth-6822DiVA: diva2:11640
Note
QC 20100803. Uppdaterad från In press till Published 20100803.Available from: 2007-02-28 Created: 2007-02-28 Last updated: 2012-03-22Bibliographically approved
In thesis
1. Some aspects of non-metallic inclusions during vacuum degassing in ladle treatment: with emphasize on liquid CaO-Al2O3 inclusions
Open this publication in new window or tab >>Some aspects of non-metallic inclusions during vacuum degassing in ladle treatment: with emphasize on liquid CaO-Al2O3 inclusions
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The present thesis was to study non-metallic inclusions during vacuum degassing in ladle treatment. Emphasize was mostly given to liquid CaO-Al2O3 inclusions. A series of industrial experiments were carried out at Uddeholm Tooling AB, Hagfors, Sweden. To gain an insight into the industrial findings, laboratory investigations were also performed.

Large number of steel samples were collected and examined. Liquid calcium aluminate inclusions with low SiO2 and high SiO2 were often found with spinel inclusions before vacuum degassing. Laboratory experiments showed that spinel would react with the dissolved Ca in the liquid steel forming calcium aluminate inclusions. This laboratory results agreed with the industrial observation that spinel phase was quite often found in the center of the calcium aluminate phase.

After vacuum degassing, most of the inclusions were calcium aluminate liquid inclusions. When dissolved Al level was low, 2 types of liquid calcium aluminate inclusions with considerably different SiO2 contents were found to coexist even at the end of the process. In view of the lack of the thermodynamic data for SiO2 activities in the low silica region, thermodynamic measurements were conducted in the CaO-Al2O3-SiO2-MgO system. The experimental results could reasonably explain the coexistence of the two types of the liquid oxide inclusions.

While the total number of inclusions decreased during vacuum degassing, the number of bigger inclusions (>11.3 μm) increased generally in used ladles. This finding was in accordance with the previous studies, wherein, ladle glaze was found to be responsible for the supply of bigger inclusions.

The behaviors of several types of inclusions in liquid steel were examined using a laser scanning confocal microscope (LSCM). While alumina inclusions tended to impact on each other, agglomerate and grow very quickly, none of the other types of inclusions, such as spinel and calcium aluminate was observed to agglomerate. The results of LSCM study agreed well with the industrial observation. Examination on a huge number of inclusions did not show any indication of impact and physical growth of the inclusions, except the alumina inclusions.

The removal of inclusions around open-eye in a gas-stirred ladle was experimentally studied by a cold model with oil and water. Most of the simulated inclusions were brought up to the oil phase by gas-water plume. Inclusion removal into oil layer took place when the inclusions passed through the sphere-bed of the oil layer around the open-eye. A calculation showed that the contribution of metal-gas plume in inclusion removal was much larger than that of buoyancy mechanism.

The results of the industrial experiments revealed that the inclusions distribution strongly depended on stirring condition. When a ladle was stirred by both gas and induction, inclusion removal near slag layer was significant.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vii, 40 p.
Series
ISRN KTH/MSE, 2007:04
Keyword
non-metallic inclusions, ladle refining, vacuum degassing, ladle glaze, spinel, SiO2 activity, agglomeration, cold model, open-eye, inclusion removal
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-4288 (URN)978-91-7178-571-8 (ISBN)
Public defence
2007-03-07, Sal D3, KTH, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100803Available from: 2007-02-28 Created: 2007-02-28 Last updated: 2010-08-03Bibliographically approved

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