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Pores, inclusions and electromagnetic stirring: Topics from the continuous casting of steel
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.ORCID iD: 0000-0001-6477-5487
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with two topics of relevance to the continuous casting of steel,in view of their importance as regards the quality of the final solidified structure.The first concerns the precipitation of gas pores and inclusions in the interden-dritic region of the solidifying metal. Motivated by experimental results thatindicate the formation of pore-inclusion clusters in the final cast structure, a the-oretical model is developed to describe how thus might occur; the model makesuse of the basic principles of fluid mechanics and heat transfer, with asymptoticmethods then being used in order to obtain solutions. In particular, it is foundthat soluto-thermocapillary drift in a direction perpendicular to the direction ofcasting, as a consequence of the dependence of surface tension at the pore-metalinterface on temperature and sulphur concentration, could explain cluster forma-tion. The second is a theoretical study concerning longitudinal electromagneticstirring (EMS), which is often used in the continuous casting of blooms in order toimprove product quality. Via an analysis of the three-dimensional (3D) Maxwellequations for the components of the magnetic flux density, a flaw is found inthe way that the components of the stirring Lorentz force have previously beencalculated; this is corrected and the new results are confirmed by comparison ofsolutions obtained from asymptotic analysis and time-dependent 3D computa-tions using finite-element methods. The analysis identifies the importance of theproduct of the bloom width and the wave vector of the applied field as a keydimensionless parameter.

Abstract [sv]

Avhandlingen fokuserar på två frågeställningar som är relevanta för stränggjut-ning av stål med avseende på deras betydelse för kvaliteten på den stelnadestrukturen. Den första frågeställningen fokuserar på bildningen av porer och in-neslutningar i interdendritiska områden i den stelnade metallen. Experimentellaresultat påvisade en bildning av klusters bestående av porer och inneslutning-ar, vilket motiverade en utveckling av en teoretisk modell som beskriver dettafenomen. Modellen bygger på grundläggande principer för fluidmekanik och vär-meöverföring i kombination med asymptotiska metoder för att erhålla en lösningtill problemet. Resultaten visar att soluto-termokapillära driftkrafter, som ver-kar i en riktning vinkelrät mot stelningsriktningen, kan förklara uppkomsten avklusterbildningen. Specifikt så beror dessa krafter av ytspänningen vid metall-porgränsskiktet, som i sin tur påverkas av temperaturen och svavelkoncentrationen imetallen. Den andra frågeställningen är en teoretisk studie fokuserad på longitu-dinell elektromagnetisk omrörning (EMS), vilken ofta används vid stränggjutningav blooms i syfte att öka kvaliteten av det gjutna ämnet. Genom att analysera detredimensionella Maxwellekvationerna för komponenterna tillhörande magnetiskaflödestätheten, så hittades en felaktighet med avseende på hur komponenterna förLorentzkrafter tidigare beräknats. Dessa felaktigheter har korrigerats och de nyapredikteringarna med modellen har verifierats både med asymptotiska lösningaroch tredimensionella beräkningar med användande av finita elementmetoder. Re-sultaten visar på betydelsen att ta hänsyn till bredden på blooms och det användafältet som dimensionslösa parametrar vid denna typ av simuleringar

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. , p. 194
Series
TRITA-ITM-AVL ; 2020:12
National Category
Metallurgy and Metallic Materials Mathematical Analysis
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-271222ISBN: 978-91-7873-468-9 (print)OAI: oai:DiVA.org:kth-271222DiVA, id: diva2:1416097
Public defence
2020-04-15, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2020-03-23 Created: 2020-03-20 Last updated: 2020-03-23Bibliographically approved
List of papers
1. On the Relationship Between Inclusions and Pores, Part I: Precipitation
Open this publication in new window or tab >>On the Relationship Between Inclusions and Pores, Part I: Precipitation
2012 (English)In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, Vol. 65, no 6, p. 791-794Article in journal (Refereed) Published
Abstract [en]

Formation mechanism and clustering of TiN-Al2O3 inclusions precipitated during solidification of austenitic stainless steel is analyzed in this paper. Steel sample are taken from a continuously cast bloom. Clustering of inclusions was examined with a hypothesis that inclusions gather inside the pores. Precipitation of the inclusions occurs through segregation in the residual melt in the interdendritic area. Size and mean distance of the inclusion particles are calculated with mass balance. Impact fracture test in cryogenic temperature reveals clusters of inclusions inside pores on the fracture surface. Size and distribution of the inclusions are examined using light optical microscopy and scanning electron microscopy. Inclusion's composition is investigated with energy dispersive X-ray spectroscopy analysis. Differential thermal analysis and differential scanning calorimetry Tests determined the transformation temperatures. Results of the experiments are in good agreement with theoretical analysis.

Keywords
Solidification, Inclusions, Steel, Nucleation, Cluster
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-107066 (URN)10.1007/s12666-012-0224-8 (DOI)000310461100049 ()2-s2.0-84897098067 (Scopus ID)
Note

QC 20150630

Available from: 2012-12-07 Created: 2012-12-06 Last updated: 2020-03-20Bibliographically approved
2. Pores and clustering of inclusions in the continuous casting of steel: Precipitation
Open this publication in new window or tab >>Pores and clustering of inclusions in the continuous casting of steel: Precipitation
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-174087 (URN)
Note

QS 2015

Available from: 2015-09-30 Created: 2015-09-30 Last updated: 2020-03-20Bibliographically approved
3. On the relationship between inclusions and pores, Part II: Dendritic structure, pressure drop in the liquid and pore precipitation
Open this publication in new window or tab >>On the relationship between inclusions and pores, Part II: Dendritic structure, pressure drop in the liquid and pore precipitation
2014 (English)In: 6th International Conference on Solidification and Gravity, 2014, Vol. 790-791, p. 302-307Conference paper, Published paper (Refereed)
Abstract [en]

There is a relationship between pores and inclusions. Inclusions and pores are both formed during solidification inside the interdendritic melt. As hypothesis goes, porosity moves to absorb inclusions and form clusters. Focus of this paper is how solidified dendritic structure affects pore precipitation in austenitic stainless steel. Steel sample is a continuously cast bloom. Temperature profile and width of the mushy zone of the strand is modeled according to a constant temperature at the strands surface. Thermal analysis has been performed with differential thermal analysis (DTA) and differential scanning calorimeter (DSC). Primary dendrite arm spacing (PDAS) is measured with light optical microscopy (LOM) and scanning electron microscopy (SEM). PDAS is represented as the weight average of the distance between parallel sets of primary dendrite stems. Pressure field is calculated based on Darcy's law. Pore formation is described through segregation of the gas components and pressure field in the liquid.

Series
6th International Conference on Solidification and Gravity, ISSN 0255-5476
Keywords
Porosity, Pressure, Segregation, Solidification, Surface, Austenitic stainless steel, Continuous casting, Differential scanning calorimetry, Differential thermal analysis, Liquids, Scanning electron microscopy, Segregation (metallography), Surfaces, Constant temperature, Dendritic structures, Differential scanning calorimeters, Differential thermal analyses (DTA), Light optical microscopies, Primary dendrite, Primary dendrite arm spacings, Temperature profiles, Surface segregation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-167554 (URN)10.4028/www.scientific.net/MSF.790-791.302 (DOI)2-s2.0-84901408673 (Scopus ID)9783038350934 (ISBN)
Conference
2 September 2013 through 5 September 2013, Miskolc, Lillafured
Note

QC 20150608

Available from: 2015-06-08 Created: 2015-05-22 Last updated: 2020-03-20Bibliographically approved
4. Relationship between motion of bubbles and agglomeration of inclusions into clusters during solidification of continuously cast steel
Open this publication in new window or tab >>Relationship between motion of bubbles and agglomeration of inclusions into clusters during solidification of continuously cast steel
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The possibility of cluster formation during solidication of steel is explored to explain structures that are seen on the fracture surface of the steel. A hypothesis is built that postulates porosities provide favourable locations for inclusions to agglomerate and form clusters.  A thermodynamic model is constructed to describe precipitation of porosity and inclusions. Formation of inclusions follow a nucleation and growth mechanism. Porosities on the other hand are the product of pressure balance in the liquid.  Motion of pores and inclusions is analysed based on the drag force and  surface  stresses. Gradient of surface tension is also identied as a driving force which acts on the pore surface and would cause motion. It is shown that relative motion of pores and inclusions coupled with  the inclusion tendency to get attached on pore surface makes or a viable mechanism explaining agglomeration of inclusion particles to clusters

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. 38
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-174077 (URN)978-91-7595-685-5 (ISBN)
Presentation
2015-10-09, Sal M131 Sefström, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150930

Available from: 2015-09-30 Created: 2015-09-29 Last updated: 2020-03-20Bibliographically approved
5. Analysis of a model for longitudinalelectromagnetic stirring in the continuous casting
Open this publication in new window or tab >>Analysis of a model for longitudinalelectromagnetic stirring in the continuous casting
(English)In: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800Article in journal (Refereed) Submitted
National Category
Metallurgy and Metallic Materials Mathematical Analysis
Identifiers
urn:nbn:se:kth:diva-271221 (URN)
Available from: 2020-03-20 Created: 2020-03-20 Last updated: 2020-03-20
6. On longitudinal electromagnetic stirringin the continuous casting of steel blooms
Open this publication in new window or tab >>On longitudinal electromagnetic stirringin the continuous casting of steel blooms
2020 (English)In: Journal of Engineering Mathematics, ISSN 0022-0833, E-ISSN 1573-2703Article in journal (Refereed) Published
National Category
Metallurgy and Metallic Materials Mathematical Analysis
Identifiers
urn:nbn:se:kth:diva-271220 (URN)10.1007/s10665-019-10035-5 (DOI)
Available from: 2020-03-20 Created: 2020-03-20 Last updated: 2020-03-20

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