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Formation of non-metallic inclusions and the
possibility of their removal during ingot
casting
Lars Ragnarsson
Doctoral Thesis
Materials Processing
Department of Material Science and Engineering
School of Industrial Engineering and Management
Royal Institute of Technology (KTH)
SE-10044 Stockholm, Sweden
Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan framlägges till
offentlig granskning för avläggande av Teknologie Doktorsexamen, fredag den 30 april,
2010, kl 10:00 i sal F3, Lindstedtsvägen 26, Kungliga Teknkiska högskolan, Stockholm
ISRN KTH/MSE--10/12--SE+MICROMODMETU/AVH
ISBN 978-91-7415-620-1
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Lars Ragnarsson, Formation of non-metallic inclusions and the
possibility of their removal during ingot casting
Division of Micro-Modeling
Department of Materials Science and Engineering
School of Industrial Engineering and Management
Royal Institute of Technology (KTH)
SE-100 44 Stockholm, Sweden
ISRN KTH/MSE--10/12--SE+MICROMODMETU/AVH ISSN-1104-7127
ISBN 978-91-7415-620-1
© Lars Ragnarsson, March 2010
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“What we can´t imagine within ourselves, will likely never take place outside our mind.”
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ABSTRACT
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 m
3
.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.
Key words; Ingot casting, tool steel, inclusion, runner, refractory, erosion, casting powder,
cold model, argon shroud, reoxidation, oxygen measurement, CFD, PIV.
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ACKNOWLEDGEMENT
I would like to express my gratitude to Professor Du Sichen. It has been a very interesting
journey through tough decisions and challenges. The guidance to see beyond the horizon of
experimental results and conclusions will always be on my mind and in my heart.
Thanks to the people at Uddeholm Tooling AB, who have given me a good insight in both
research and production of world class quality tool steel.
I am grateful for the support from Alf Sandberg and his truly passion for finding new ways
to improve the steel making process. Without your support and dedication we wouldn´t go
far.
Thanks to all my foreign friends who are working everyday in close contact with customers
relaying on the quality of the steel.
I also want to thank Dr. Mårten Görnerup at Metsol AB for fruitful discussion about the
industrial perspectives of steel making.
Jernkontoret and its staff, especially Lars-Henrik Österholm for the strive to build bridges
between Swedish steel companies and form platforms for scientific discussion and joint
projects together with researchers from institutes and the academic world.
Financial support for this work provided by Uddeholm Tooling AB and Jernkontoret (for the
last months) is gratefully acknowledged.
I also want to thank Professor Yonglin Ma and Wei Song at Inner Mongolia University of
Technology and of course all the teachers and students who made my stay and work joyful
and interesting.
Thanks are also due to Professor Pär Jönsson and all the colleagues at the department of
Materials Science and Engineering for many interesting discussions and social activities.
Thanks to all my friends who put up with my, from time to time, pressed schedule and your
encouragement to take breaks and enjoy the life.
And of course I want to a specially thank my beloved family who are always helpful and
there for me when it is needed.
Stockholm, 23 March 2010
Lars Ragnarsson
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SUPPLEMENTS
This thesis is based on following papers:
Supplement 1: “Inclusion generated during ingot casting of tool steel”
Lars Ragnarsson and Du Sichen
Steel Research International, Volume 81, 2010, No. 1. pp. 40-47.
Supplement 2: “Erosion of runners in ingot casting”
Lars Ragnarsson and Du Sichen
AISTech 2009 Proceedings - Volume I, March, 2009, Saint Loius,
USA, pp. 1077-1087.
Supplement 3: “Physical and mathematical modelling of argon shroud for the
protection of steel stream during casting”
Lars Ragnarsson, Wei Song, Yonglin Ma and Du Sichen
Sent to International Journal of Cast Metals Research for publication.
Supplement 4: “Oxygen penetration in the protection shroud in steel casting”
Lars Ragnarsson, Wei Song, Yonglin Ma and Du Sichen
Sent to Steel Research International for publication.
Supplement 5: “Flow pattern in the ingot during mould filling and its impact on
inclusion removal”
Lars Ragnarsson, Mattias Ek, Anders Eliasson and Du Sichen
Ironmaking and Steelmaking, accepted for publication, 2010-01-19.
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TABLE OF CONTENTS
Content
1. INTRODUCTION ................................................................................................................ 1
2. EXPERIMENTAL ............................................................................................................... 3
2.1. Industrial Process ........................................................................................................... 3
2.2. Industrial Sampling and Analysis .................................................................................. 4
2.2.1. Ingot ........................................................................................................................ 4
2.2.2. Runner ..................................................................................................................... 5
2.3. Modeling of Argon Shroud ............................................................................................ 6
2.3.1. Argon flow in shroud using PIV technique – Physical model ................................ 7
2.3.2. Oxygen measurement within argon shroud – Physical model ................................ 8
2.4. Cold model for Inclusion Removal by Slag film in Ingot ............................................. 8
3. CFD MODELING .............................................................................................................. 10
3.1. Modeling of Mould Filling ......................................................................
