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Erosion of runners in ingot casting
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
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.

Place, publisher, year, edition, pages
2009. 1077-1087 p.
Keyword [en]
Erosion; Ingot casting; Non-metallic inclusions; Runner; Tool steel
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-13387Scopus ID: 2-s2.0-70349923896OAI: oai:DiVA.org:kth-13387DiVA: diva2:325029
Note
QC20100617Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2010-06-17Bibliographically approved
In thesis
1. Formation of non-metallic inclusions and the possibility of their removal during ingot casting
Open this publication in new window or tab >>Formation of non-metallic inclusions and the possibility of their removal during ingot casting
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
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:nbn:se:kth:diva-12458 (URN)978-91-7415-620-1 (ISBN)
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

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