Continuous Casting of Steel
Continuous Casting of Steel Continuous Casting of Steel
ME8109 ME8109 –– Casting and Solidification MaterialsCasting and Solidification Materials
Mechanical & Industrial Engineering DepartmentMechanical & Industrial Engineering Department
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MajidMajid HaghighiHaghighi
Ryerson University Ryerson University -- W2012W2012
500421732500421732
Continuous Casting of Steel
Outline
• Introduction & Objective
• Continuous Casting Methods
• Steel Casting Process
• Fluid Flow & Solidification
• Porosity Sources
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• Porosity Sources
• Heat Transfer and Casting Speed
• Primary & Secondary Cooling Zoon
• Conclusion
Continuous Casting of Steel
Introduction & Objective
� Slabs, Billets, Blooms depending on dimensions of the strand
� Higher capital cost and lower operating cost , less deformation
� The most efficient process and energy
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Slab
Billet Bloom
Continuous Casting of Steel
Continuous Casting Methods
* Vertical Casting
• Mold axis and fluid flow are in vertical position
• Casting non-ferrous alloys such as Aluminum
• Produce ingots as a row material for Extrusion, Forging or Rolling
• Stop periodically to remove the cast ingot
• Speed is slow to avoid internal cracks and metallurgical length shorter
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* Horizontal Casting
• Mold axis and fluid flow are in horizontal position
• Casting Steel or Copper alloys
• Withdrawal the strand through the hot rolling after spray chamber
• Produce ingots as a row material for Extrusion, Forging or Rolling
• Hot condition to pre-shap the final strand
• Cut the strand into different size by gas torches
Continuous Casting of Steel
Continuous Casting Methods
* Strip Casting
• Casting Steel or other metals
• Solidify thin layer of steel by passing the molten steel
through large rotating rollers
* Curved Casting
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• Mold axis and fluid flow are in curved (V &H ) position
• Casting steel alloys
• Semi-finished products such as Slabs, Billets and Blooms
• Molten steel pours into the mold through a ladle and tundish
• Speed is Fast and continuously, metallurgical length longer
* Other Continuous Casting
• Electro-Slag Re-melting (ESR) or Vacuum Arc Re-melting (VAR)
to cast supper-alloys (aerospace application)
Continuous Casting of Steel
The steel heated above liquidustemperature in the furnace
(Superheating degree)
Enters molten steel into the mold through Submerge entry nozzle
(SEN)
Steel Casting Process
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Cooling continuous by quenching with water spray
along the whole of the strand
Entering liquid steel into the mold can cause unbalances
and clogging and possibly break out
Melting Point of steel : 1370 C
http://www.youtube.com/watch?v=d-72gc6I-_ESteel : Iron + Carbon (0.2% - 2.1%)
Continuous Casting of Steel
Fluid Flow & Solidification
Initial Solidification
•The time-dependent shape of the meniscus
•Liquid flux flow into the shell-mould gap
•Local superheat contained in the flowing steel
•Conduction of heat through the mould
•Liquid mold flux and re-solidified flux rim
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Continuous Casting of Steel
Superheat Molten Steel and Level Fluctuation
• Hottest, area midway between SEN and narrow face
• Coldest area, at the meniscus cause freezing meniscus and lead to:
• To avoid Freezing Meniscus, reach the metal flow to the surface quickly
• To avoid breakout, no gap between shell and mold
Fluid Flow & Solidification
Superheat = Steel Temperature Entering – Steel Melting Point
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Mold Powder
• Act as a lubricant between strand and mold
• Improve heat transfer from strand to mold
• Protect liquid steel against reoxidation
• Absorb inclusions that rise to the metal surface
• Provide thermal and chemical insulation of the top surface
• To avoid breakout, no gap between shell and mold
• Level Fluctuation can reduce by flow pattern
• Increase casting speed impact on transient turbulent fluctiuation
• Surface velocity keep under the critical value
Temperature and super heat distribution in the mould
1)Turbulence, 2) Level Fluctuation, 3) Vortexing, 4) Emusification
Continuous Casting of Steel
Clogging at SEN
• Dislodged Clogs or change the flux composition and
leading to defect on molten steel
• Change the nozzle flow pattern (Asymmetrical) leading
to slag entrainment and surface defect
• Clogging interferes with mold level control
Fluid Flow & Solidification
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* Using control device (stopper rod or slide gate) to
compensate for the clog and ensure a smooth flow pattern
Caster Curvature
• Vertical Caster (at least the top 2.5 m section)
• Less Particle defects
Continuous Casting of Steel
• Reduce nozzle clogging
• Influence and control the flow pattern in the mold
Without Gas With Gas
Argon Gas Injection
Fluid Flow & Solidification
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• Influence and control the flow pattern in the mold
• Generating serious top surface fluctuation
• Capturing inclusions
• Capture solid oxide particles and lead to surface slivers
Electromagnetic Forces
AC electromagnetic fields of high or low frequencies:
•Oscillation marks
•Lateral cracks
•Entrapment of inclusions and bubbles
Continuous Casting of Steel
Porosity Sources
Air Entrainment
• Failure to eliminate all air in the mold cavity
Oxides
• Re-oxidation inclusion (porosity remains when inclusion material removed by blasting)
• High level of oxygen reduce surface tension that must become to form a bubble
Shrinkage
• Shrinkage occurs when liquid metal becomes denser solid
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• Shrinkage occurs when liquid metal becomes denser solid
• Drop the pressure in the liquid metal below atmospheric
Heat Treatment and Casting Speed
•Lower casting speed, higher metallurgical length
•Higher casting speed, higher temperature in SCZ
•Higher casting speed, consequently temperature
distribution on the Walls
•Cast Speed depends on Product type & size
*Regular : 0.5 – 4 m/min
*High speed: 1.5-2.8 m/min
Continuous Casting of Steel
Heat Treatment and Casting Speed
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Continuous Casting of Steel
Heat Treatment and Casting Speed
Mould Lubrication
• Helping to avoid breakout in high speed casting
• Occurs by influence of slag into the strand
Vm = mould speed
V = casting speed
fl = η (Vm – Vc ) / dl
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Vc = casting speed
η = viscosity of liquid slag film
dl = thickness of slag film.
ηs = coefficient of solid friction
H = ferrostatic pressure of molten steel
fs = ηs H
Continuous Casting of Steel
* Passing the molten steel through the water-cooled tank
� Temperature of solid
� Casting speed
� Solidification time
� Cooling rate
Primary & Secondary Cooling Zoon
Good quality
&
Thickness of the crust
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* Key factors affecting on quality of strand in SCZ area
� Cooling water spray rate
� Metallurgical Length consideration
� Superheat of liquid steel
Continuous Casting of Steel
Conclusion
Quality of final product depend on:
� Liquid level in the mold
� Powder feeding rate
� Casting speed
� Gas injection
� Slide gate opening
� Nozzle position
� Cooling water rate
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Benefit of continuous casting of steel:
� Considerable energy saving
� Less scraped produced
� Improved labour productivity
� Improved quality of steel
� Reduced pollution
� Reduced capital costs, time saving, casting process
� Increased use of purchase scraps when output is maximized
� A highly productive process that can be fully automated
� Cooling water rate
Continuous Casting of Steel
[1] Brian G. Thomas, “Continuous Casting of Steel”, Chapter 15 in Modeling for Casting and Solidification Processing, O. Yu, editor, Marcel Dekker, New York, NY,
2001, pp. 499-540.
[2] S. Mazumdar, “Solidification control in continuous casting of steel”, Sadhana,Vol. 26, Parts1 & 2, February–April 2001, pp. 179–198. © Printed in India
[3] T. Merder et al. “Modeling of flow behavior in a six strand continuous casting tundish”,
METABK 46 (4) 245-249 (2007)
[4] B.G. Thomas, “Continuous Casting”, Yearbook of Science and Technology, McGraw-Hill, 2004.
[5] S. Mizoguchi, T. Ohashi,“Continuous casting of steel”, Ann. Rev. Mater. Sci. 1981, 11:151-69
[6] S. R. Bragança, “Reduction of the hydrogen content in the continuous casting of steel” Laboratório de Cerâmicos da Universidade Federal do Rio Grande do Sul –
LACER/UFRGS
[7] N. Zapuskalov, “Comparison of Continuous Strip Casting with Conventional Technology” ISIJ International, Vol. 43 (2003), No. 8, pp. 1115–1127.
[8] H. Bay, B. G. Thomas, “Effects of Clogging, Argon Injection and Continuous Casting conditions on Flow and Air Aspiration in Submerged Entry Nozzles’
Metallurgical and materials transactions B Volume 32B, August 2001—722.
[9] “Politehnica” University of Timisoara/Department of Automation and Applied Informatics, Timisoara, Romania [email protected], [email protected].
[10] Zhenping Ji, School of Information Science and Engineering Shenyang Ligong University Shenyang, China
References
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[10] Zhenping Ji, School of Information Science and Engineering Shenyang Ligong University Shenyang, China
[11] H. Shin, G. Lee, W. Choi, S. Kang, J. Park, S. Kim, B. G. Thomas ‗Effect of Mold “Oscillation on Powder Consumption and Hook Formation in Ultra Low
Carbon Steel Slabs” AIS Tech 2004, Nashville, TN, Sep. 15-17, 2004.
[12] Lifeng Zhang, Brian G. Thomas, “Inclusion in Continuous Casting of Steel”, XXIV National Steelmaking Symposium, Morelia, Mich, Mexico, 26-28, Nov.2003,
pp. 138-183.
[12] Mohammad Sadat, Ali Honarvar Gheysari, Saeid Sadat, “The effects of casting speed on steel continuous casting process”, Heat Mass TransferSpringer-Verlag,
Published online: 3 June 2011
[13] R&D center for Iron and Steel, Steel Authority of India Ltd (SAIL), Ranchi, India “Solidification control in continuous casting of steel”, Vol. 26, Parts 1 & 2,
February–April 2001, pp. 179–198.
[14] R. Monroe, “Porosity in Castings”, Steel Founders’ Society of America, Crystal Lake, Illinois, Copyright 2005 American Foundry Society, Page 1 of 28
[15] B.G. Thomas, “Continuous Casting: Modeling, the Encyclopedia of Advanced Materials” Pergamon Elsevier Science Ltd., Oxford, UK, Vol.
2, 2001, 8p, (Revision 3, Oct. 12, 1999)
[15] Ken-ichi Miyazawa, “Continuous Casting of Steel in Japan”, Science and Technology of Advanced Materials, 2001, 59-65
[16] Wenhon Liu, Zhi Xie, Zhenping Ji and Biao Wang, “Research and Application of Dynamic Control System for Secondary Cooling of Billet Continuous Casting”,
School of Information Science and Engineering Northeastern University Shenyang, Liaoning Province, China, 2007 IEEE
[17] Steeluniversity.org, “Continuous Casting Simulation”, version 1.60 User Guide
Continuous Casting of Steel
Thank You
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