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Formation of non-metallic inclusions and the possibility of their removal during ingot casting
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present study was carried out to investigate the formation and evolution of non-metallic inclusions during ingot casting. Emphasize have been on understanding the types of inclusions formed and developed through the casting process and on the development of already existing inclusions carried over from the ladle during casting. Industrial experiments carried on at Uddeholm Tooling together with laboratory work and Computational Fluid Dynamics (CFD) simulations.

Ingots of 5.8 tons have been sampled and the types of inclusions together with their distribution within the ingot have been characterized. Two new types of inclusions have been found. Type C1 is found originated from casting powder and in the size from a few μm to 30 μm. Type C2 is of macro inclusion type sizing up to 70 μm. The presence of C2 inclusions are few but very detrimental for the quality of the steel. Both types, C1 and C2 consist of alumina, indicating that reoxidation is the main reason for their existence.

The protecting argon shroud has been studied by the use of a 1:1 scaled 2D model. Both flow pattern and oxygen measurement have been carried out. CFD has also been used as an auxiliary tool. It has been found that the oxygen pickup through argon gas shroud depends mostly on the distance between the ladle and the collar placed on top of runner. Further increase of gas flow rate above 2.5 m3.h-1 had very little effect on the oxygen distribution since both the flushing effect and the entraining effect with respect to oxygen are enhanced by further increase of inert gas flow rate. In the case of dual gas inlet, the flow in the shroud was found much less diffused compared with either vertical or horizontal injection system. The oxygen content in this arrangement was also greatly reduced.

Studies of the runner after casting revealed a sparse non-metallic network structure around the periphery of the steel rod remained in the runner. The surface of the refractory had been severely attacked by the mechanical force from the streaming steel. The erosions of the centre stone and the end stone were on the other hand negligible. CFD calculations showed that the flow at those locations is almost stagnant. The surface of the refractory in contact with the steel was found to have an increased content of alumina. The source for the alumina could come from either exchange reaction of dissolved aluminium replaces the silica or reoxidation products origin from oxygen pick up during the transfer from the ladle to the vertical runner. Inclusions were also found entrapped in the steel refractory interface.

It was also found that a formation of a liquid slag film as early as possible during casting would increase the possibility to remove inclusions and especially inclusions generated by the casting powder.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , viii, 49 p.
Keyword [en]
Ingot casting, tool steel, inclusion, runner, refractory, erosion, casting powder, cold model, argon shroud, reoxidation, oxygen measurement, CFD, PIV
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-12458ISBN: 978-91-7415-620-1 (print)OAI: oai:DiVA.org:kth-12458DiVA: diva2:312395
Public defence
2010-04-30, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100617Available from: 2010-04-23 Created: 2010-04-23 Last updated: 2011-02-08Bibliographically approved
List of papers
1. Inclusions Generated during Ingot Casting of Tool Steel
Open this publication in new window or tab >>Inclusions Generated during Ingot Casting of Tool Steel
2010 (English)In: STEEL RESEARCH INTERNATIONAL, ISSN 1611-3683, Vol. 81, no 1, 40-47 p.Article in journal (Refereed) Published
Abstract [en]

An industrial trial study was carried out at Uddeholm Tooling AB, Sweden, to investigate the mechanisms of the formation of inclusions, especially macro inclusions during ingot casting. Strong evidence of reoxidation was observed. Two types of inclusions generated during casting were detected in the ingot. Inclusions of Type C1 originated from mould powder with reoxidation product Al2O3 as a part of it. Inclusions of this type were usually small. The number of Type C1 inclusions increased from the centre of the ingot toward the side wall of the mould. Type C2 inclusions were macro size. They could be the results of reoxidation and erosion of runner.

Keyword
NONMETALLIC INCLUSIONS, CARBON STEEL
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-12457 (URN)10.1002/srin.200900064 (DOI)000274847200007 ()2-s2.0-77949472317 (Scopus ID)
Note
QC 20110121Available from: 2010-04-23 Created: 2010-04-23 Last updated: 2011-01-21Bibliographically approved
2. Erosion of runners in ingot casting
Open this publication in new window or tab >>Erosion of runners in ingot casting
2009 (English)In: AISTech - Iron and Steel Technology Conference Proceedings, 2009, 1077-1087 p.Conference paper, Published paper (Refereed)
Abstract [en]

Substantial erosion of the runner, especially the horizontal runner was noticed during casting. CFD simulation of the flow showed that the velocities were almost zero close to the centre stone and end stone. The low velocities well explained the minor erosion of the two types of stones. The CFD calculation also indicated that the velocities in the horizontal were not evenly distributed. Velocities as high as 3 m/s could be found at the entrance of the horizontal runner and close to the entrance of the ingot. This result was in good agreement with the experimental observation that the erosion close to the entrance of the horizontal runner was much more profound. The runner surface was found to react with the dissolved aluminium forming a layer of higher alumina content. The zigzag surface of the refractory could entrap inclusions and provide good condition for agglomeration. The detachment of the agglomerated inclusions along with the pieces of refractory could be an important source of the formation of macro inclusions during casting. The higher alumina contents in the inclusions found in the steel rod in comparison with that found in the ladle suggested possible reoxidation of the steel during casting.

Keyword
Erosion; Ingot casting; Non-metallic inclusions; Runner; Tool steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-13387 (URN)2-s2.0-70349923896 (Scopus ID)
Note
QC20100617Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2010-06-17Bibliographically approved
3. Physical and mathematical modelling of argon shroud for protection of steel stream during casting
Open this publication in new window or tab >>Physical and mathematical modelling of argon shroud for protection of steel stream during casting
2010 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 23, no 6, 368-374 p.Article in journal (Refereed) Published
Keyword
argon shroud, ingot casting, reoxidation, cold model, PIV, CFD
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-13393 (URN)10.1179/136404610X12738456167302 (DOI)000281639600007 ()2-s2.0-77956455296 (Scopus ID)
Note
QC 20100617 Uppdaterad från submitted till published (20101129). Tidaigare titel: "Physical and mathematical modelling of argon shroud for the protection of steel stream during casting"Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2010-11-29Bibliographically approved
4. Oxygen penetration in the protection shroud in steel casting
Open this publication in new window or tab >>Oxygen penetration in the protection shroud in steel casting
2010 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 81, no 11, 965-973 p.Article in journal (Refereed) Published
Abstract [en]

Physical modelling of argon shroud used in ingot casting was carried out using a 2D 1:1 scaled model in order to determine the oxygen distribution around the steel stream. The oxygen concentrations were measured by an oxygen sensor. Complementary PIV measurements were also carried out for a gas inlet configuration using dual (horizontal and vertical) gas inlet. The main findings were: (1) The oxygen concentrations were considerably high in the ordinary operation conditions. The oxygen contents were the highest in the case of vertical gas injection (higher than 11% in all cases). (2) A minimized distance between the ladle and the collar on the top of the vertical runner would reduce the oxygen entrainment by convection and diffusion, in the case of horizontal gas injection and a dual gas inlet configuration. (3) A modest flow rate of argon gas should be used. Further increase of the gas flow would not improve the protection. (4) A dual gas inlet configuration would be more effective than a single inlet, especially in the case of larger distances between the ladle and the runner.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2010
Keyword
argon shroud, ingot casting, reoxidation, cold model
National Category
Materials Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-13397 (URN)10.1002/srin.201000088 (DOI)000284863500007 ()2-s2.0-84859585529 (Scopus ID)
Note

QC 20100617 Uppdaterat från submitted till published 20101223

Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2016-07-19Bibliographically approved
5. Flow pattern in ingot during mould filling and its impact on inclusion removal
Open this publication in new window or tab >>Flow pattern in ingot during mould filling and its impact on inclusion removal
2010 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 37, no 5, 347-352 p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional non-steady state computational fluid dynamic model was employed to gain a basic understanding of the flow in the ingot during casting. The surface velocity was found to be affected by the inlet angle and was found to vary with the casting level. The information of surface velocity was related to the probability of the inclusion removal. Water model experiments were also conducted to help the understanding. The model calculation revealed the same trends as the results of water model experiments. Both computational fluid dynamic data and the physical modelling showed that the inlet angle of 5 degrees currently used in the industry was a good alternative regarding inclusion removal. The present work suggests strongly that the melting shop should try to obtain a liquid or semiliquid film at as early stage as possible in ingot casting.

Keyword
Inclusions, Casting powder, Ingot casting, Cold model, CFD
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-13398 (URN)10.1179/030192310X12683045806062 (DOI)000280123300006 ()2-s2.0-77954705959 (Scopus ID)
Note
QC 20100617 Uppdaterad från accepted till published (20110208). Tidigare titel: "Flow pattern in the ingot during mould filling and its impact on inclusion removal"Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2011-02-08Bibliographically approved

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