Continuous Casting of Steel-Majid Haghighirravindr/Continuous Casting of Steel-Majid Haghighi... ·...

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

1 Ryerson UniversityCasting and Solidification Materials

MajidMajid HaghighiHaghighi

Ryerson University Ryerson University -- W2012W2012

500421732500421732


Outline

• Introduction & Objective

• Continuous Casting Methods

• Steel Casting Process

• Fluid Flow & Solidification

• Porosity Sources


• Porosity Sources

• Heat Transfer and Casting Speed

• Primary & Secondary Cooling Zoon

• Conclusion


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


Slab

Billet Bloom


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


* 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 Methods

* Strip Casting

• Casting Steel or other metals

• Solidify thin layer of steel by passing the molten steel

through large rotating rollers

* Curved Casting


• 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)


The steel heated above liquidustemperature in the furnace

(Superheating degree)

Enters molten steel into the mold through Submerge entry nozzle

(SEN)

Steel Casting Process


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%)


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



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


Superheat = Steel Temperature Entering – Steel Melting Point


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


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



* 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


• Reduce nozzle clogging

• Influence and control the flow pattern in the mold

Without Gas With Gas

Argon Gas Injection



• 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


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


• 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



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


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


* 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


* Key factors affecting on quality of strand in SCZ area

� Cooling water spray rate

� Metallurgical Length consideration

� Superheat of liquid 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


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


[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


[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


Thank You


Continuous Casting of Steel-Majid Haghighirravindr/Continuous Casting of Steel-Majid Haghighi... ·...

Documents

Transcript of Continuous Casting of Steel-Majid Haghighirravindr/Continuous Casting of Steel-Majid Haghighi... ·...