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Study on the Interaction between Refractory and Liquid Steel Regarding Steel Cleanliness
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling. School of Metallurgy, Northeastern University, China.
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 [en]
refractory, inclusions, Al-killed steel, submerged entry nozzle, clogging
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-190071ISBN: 978-91-7729-006-3OAI: oai:DiVA.org:kth-190071DiVA: diva2:950940
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
List of papers
1. Effect of Refractory on Nonmetallic Inclusions in Al-killed Steel
Open this publication in new window or tab >>Effect of Refractory on Nonmetallic Inclusions in Al-killed Steel
2016 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Refereed) Epub ahead of print
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-190072 (URN)10.1007/s11663-016-0746-2 (DOI)
Note

QC 20160809

Available from: 2016-08-04 Created: 2016-08-04 Last updated: 2016-08-16Bibliographically approved
2. Mechanism Study of the Blocking of Ladle Well Due to Sintering of Filler Sand
Open this publication in new window or tab >>Mechanism Study of the Blocking of Ladle Well Due to Sintering of Filler Sand
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArticle in journal (Refereed) Published
Abstract [en]

The present work is aimed at a mechanism study of blocking of ladle well by filler sand. Laboratory experiments are carried out using two different chromite-based filler sands. The interaction between the liquid steel and the sand is also studied by using steels containing different contents of Mn and Al. The reaction between the silica phase and the chromite phase is found to be the main mechanism for the sintering of sand. The reaction results in a liquid oxide phase, which becomes the binding phase between the solid oxide grains. The amount of silica phase and its grain size are found to have great impact on the formation of the liquid oxide phase. Faster formation of the liquid oxide phase leads to more serious sintering of the sand. It is found that liquid steel can hardly infiltrate into sand. On the other hand, the presence of steel considerably increases the amount of liquid phase and enhances the sintering of the sand.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015
Keyword
Filler sand, Ladle free opening, Liquid steel, Sintering, Chromite, Chromite deposits, Fillers, Ladles, Liquids, Manganese, Sand, Silica, Binding phase, Chromite phase, Laboratory experiments, Liquid oxides, Liquid Phase, Liquid steels, Mechanism studies, Solid oxide
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-176191 (URN)10.1002/srin.201500118 (DOI)2-s2.0-84933544611 (ScopusID)
Note

QC 20151125

Available from: 2015-11-25 Created: 2015-11-02 Last updated: 2016-08-16Bibliographically approved
3. Effects of Temperature and Holding Time on the Sintering of Ladle Filler Sand with Liquid Steel
Open this publication in new window or tab >>Effects of Temperature and Holding Time on the Sintering of Ladle Filler Sand with Liquid Steel
2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 7, 921-929 p.Article in journal (Refereed) Published
Abstract [en]

In the present work the effects of temperature and holding time on the sintering of ladle filler sand are studied. Laboratory experiments are carried out using pellets made of chromite based filler sand and two steel grades containing different contents of Mn and Al. It is found that the liquid steel plays a major role in the sintering behavior. The results also show that the amount of liquid phase in the sintered sand pellets increases with the increase of temperature and holding time. The Al2O3 content increases substantially in the chromite phase (spinel), especially in the region close to the liquid phase, when the temperature is high enough or when the holding time is long enough. Higher content of dissolved Al would accelerate the formation of the alumina-rich chromite.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-190073 (URN)10.1002/srin.201500277 (DOI)
Note

QC 20160809

Available from: 2016-08-04 Created: 2016-08-04 Last updated: 2016-08-16Bibliographically approved
4. Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel
Open this publication in new window or tab >>Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel
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.

Keyword
calcium treatment, calcium aluminates, spinel, inclusions, clogging, submerged entry nozzle
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-159637 (URN)10.2355/isijinternational.54.2813 (DOI)000347278400020 ()2-s2.0-84920496504 (ScopusID)
Note

QC 20150205

Available from: 2015-02-05 Created: 2015-02-05 Last updated: 2016-08-16Bibliographically approved
5. Attachment of Alumina on the Wall of Submerged Entry Nozzle During Continuous Casting of Al-Killed Steel
Open this publication in new window or tab >>Attachment of Alumina on the Wall of Submerged Entry Nozzle During Continuous Casting of Al-Killed Steel
2016 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 3, 2015-2025 p.Article in journal (Refereed) Published
Abstract [en]

The mechanisms of the formation of different attachments on the walls of submerged entry nozzle (SEN) were studied for the processes of Al-killed steel (Ca-treated, HSLA) and ultra-low carbon Al-killed steel (ULC). To understand the mechanism, the types of inclusions in the steel taken in tundish and in bloom (or slab) were identified. In the case of ULC, the reoxidation product, micro-alumina particles were found to be the source of attachment on the inner wall of the SEN. To avoid reoxidation of the steel by the top slag, removal of the slag could be considered in order to improve the situation. No attached layer was found on the outer surface of the SEN after casting of the ULC steel. In the case of HSLA steel, an attached layer composed of plate-like alumina crystals was found in some trials. The entrainment of oxygen through the mold powder due to improper operation would be the reason for the formation of this type of attachment. The formation of the plate-like crystals was discussed with the help of CFD calculation.

Place, publisher, year, edition, pages
Springer, 2016
Keyword
Alumina, Aluminum, Carbon, Continuous casting, Nozzles, Slags, Al-killed steel, Alumina particles, Mold powders, Outer surface, Plate-like crystals, Re-oxidation, Submerged entry nozzles, Ultra low carbon, Low carbon steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-186945 (URN)10.1007/s11663-016-0624-y (DOI)000375451200050 ()2-s2.0-84959077209 (ScopusID)
Note

QC 20160518

Available from: 2016-05-18 Created: 2016-05-16 Last updated: 2016-08-16Bibliographically approved

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