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Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Northeastern University, China.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-3548-8638
2014 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 12, 2813-2820 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, inclusions in calcium-treated steel after RH treatment, in the tundish and in bloom were studied. Only two types of inclusions were detected in all steel samples, namely liquid calcium aluminate inclusions and inclusions of two phases with spinel in the center surrounded by the liquid calcium aluminate. The attachment of the inclusions on the inner surface of SEN was investigated for two types of refractory materials. The results indicated that liquid calcium aluminate inclusions could attach on the wall of SEN, when the refractory had big grain size and big cavities on the surface. On the other hand, tiny grain size and smooth surface of the SEN showed no attachment of the inclusions. The different behaviors of the two types of SEN were well explained using the results of flow calculation in the nozzle. The mechanism of the attachment was also discussed based on the experimental results and the CFD calculation. The tiny nodules formed on the surface of the inner nozzle due to inclusion attachment could be a source of macro inclusions.

Place, publisher, year, edition, pages
2014. Vol. 54, no 12, 2813-2820 p.
Keyword [en]
calcium treatment, calcium aluminates, spinel, inclusions, clogging, submerged entry nozzle
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-159637DOI: 10.2355/isijinternational.54.2813ISI: 000347278400020Scopus ID: 2-s2.0-84920496504OAI: oai:DiVA.org:kth-159637DiVA: diva2:786478
Note

QC 20150205

Available from: 2015-02-05 Created: 2015-02-05 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Study on the Interaction between Refractory and Liquid Steel Regarding Steel Cleanliness
Open this publication in new window or tab >>Study on the Interaction between Refractory and Liquid Steel Regarding Steel Cleanliness
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis focuses on the interaction between refractory and liquid steel. The aim of this work is to understand the interaction behavior between refractory and liquid steel regarding steel cleanliness. The effect of different refractories on different inclusions in Al-killed steel was studied in a furnace. The sintering mechanism of filler sand were also investigated in laboratory. In the industrial trials, the attachments of different oxides on the walls of submerged entry nozzle (SEN) were discussed in the cases of high strength low alloy steel (HSLA) and ultra-low carbon steel (ULC).

It is found that the effect of alumina and spinel refractory on all the three types of inclusions is very little, while MgO refractory influences the inclusions depending on the activity of dissolved oxygen in liquid steel. At low oxygen level, alumina inclusions could transform into spinel inclusions with the help of MgO refractory, while the effect on spinel and calcium aluminate inclusions is not evident. On the other hand, when the activity of dissolved oxygen is high enough, the evolution of spinel inclusions from alumina inclusions could not be seen.

The reaction between chromite and silica grains leading to liquid formation is the main mechanism for the sintering of filler sand. The factors viz. steel composition, silica size and content, operation temperature and process holding time have a strong influence on the sintering of the filler sand. Smaller size and higher content of silica in sand, steel grades containing higher Mn and Al contents, higher temperature and longer holding time would result in serious sintering. The choice of the sand needs to take those factors into account.

The results show that solid alumina particles are always agglomerated on the inner wall of SEN in the case of ULC steel. The top slag with high FeO and MnO contents is considered as the main reason of this kind of attachments. The removal of slag might be a good method to avoid the attachments. In the case of HSLA steel, liquid calcium aluminate inclusions could attach on the inner wall of SEN as well. The smoothness of the inner wall of the SEN holds the key of liquid attachments. In addition, the attachment situation on the outer wall of SEN depends on the operations. The oxygen entrainment through the mold powder would result in the formation of plate-like alumina attachments. The control of reoxidation due to oxygen entrainment would help to avoid this situation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 48 p.
Keyword
refractory, inclusions, Al-killed steel, submerged entry nozzle, clogging
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-190071 (URN)978-91-7729-006-3 (ISBN)
Public defence
2016-09-15, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160816

Available from: 2016-08-16 Created: 2016-08-04 Last updated: 2016-08-16Bibliographically approved

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