(NSF) GOALI: Flow Dynamics and Inclusion Transport in Continuous Casting of Steel (2001-2004)

B.G. Thomas, S.P. Vanka, L. Zhang, Q. Yuan, and B. Zhao.

R. O'Malley, Nucor Steel Decatur, AL
J. Schade, AK Steel
P. Dauby and M. Assar, LTV Steel
M. Jenkins, Monash University, Clayton, NSW, Australia
J. Cui and L. Zhu, Bao Steel, Beijing, China (contributed very important data on inclusion measurements used in model validation)
K. Cai, University of Science and Technology, Beijing
W. Pluschkell, Technical University of Clausthal, (Robert-Koch-Str.42, D-38679, Clausthal-Zellerfeld), Germany

National Science Foundation GOALI DMI 01-15486, Continuous Casting Consortium

National Science Foundation Support:

DMI 01-15486
9/1/2001 to 8/31/2004
NSF Program Director: Delcie R. Durham (703) 292-7060
NSF Grants Official: Maria Valerio (703) 292-8212

Industry Support and Partnerships:

Continuous Casting Consortium

Steel-related companies are members of the Consortium and contribute funding, measured plant data obtained at the steel plant, and advice, to the Consortium, which is helpful to the success of the project. Companies most relevant to this project include LTV Steel and AK Steel.

LTV Steel (Cleveland, OH)

LTV Steel was an organizationl partner for this project. Experiments were conducted by UIUC students and LTV Steel staff together using the water modeling facilities and extensive PIV measurement apparatus at the Technical Research Center in Cleveland, OH. LTV Steel also contributed as a member of the Continuous Casting Consortium. Specific research collaborators: Pierre Dauby, M. Assar, and G. Lawson

The following companies provided Financial Support (CCC membership), In-kind Support, Facilities (water models and plant measurements), and Research direction:

LTV Steel (Cleveland, OH)
AK Steel Company (Middletown, OH)
Allegheny Ludlum (Brackenridge, PA)
Columbus Stainless Steel (Middleburg, SA)
Stolberg, (Niagara Falls, NY)
Hatch Associates, (Buffalo, NY)
Accumold, (Huron Park, Ontario)

Project Summary

Computational models of transient, multiphase fluid flow are being developed, validated, and applied to improve understanding of transient flow, inclusion transport and defect formation in the mold region during the continuous casting of steel slabs. Process parameters, such as nozzle geometry and gas injection rate, which are easy to change and yet profoundly influence both flow and product quality, are being optimized. Models to compute the transport and entrapment of inclusion particles are being tested through water model experiments, steel plant trials, and metallographic measurements at several steel companies who are cosponsoring this research.

Summary of Activities Click here for full Activities PDF (486 KB)

Activities for this diverse multi-faceted research project proceeded along several related parallel tracks, which are divided here into seven different subprojects:

Each subproject required a student to develop a computational model, to obtain experimental measurements, usually gained through working with researchers at the steel plants, and to apply the validated model to learn something of practical interest. The results of each subproject were presented by each student to steel industry representatives at the annual meetings of the Continuous Casting Consortium at the University of Illinois from Spring 2002 to Spring, 2005. In addition, the results formed the basis for over 50 (total) technical publications or presentations, including reports, conference presentations, journal papers, book chapters, graduate theses, and short courses to industry.

First, models of three-dimensional, transient fluid flow using Large Eddy Simulation (LES), which were previously validated and used to predict flow in the process, were used here to predict the accompanying transport of inclusion particles. The models were first validated with a rigorous mesh refinement study. They were then further validated by comparison with measurements of the top surface profile, and with inclusion entrapment fractions, measured in both water models and actual casters. Criteria were then developed to predict the entrapment of inclusions into the solidifying steel shell, based on a balance of forces in the boundary layer arising from 10 different phenomena. The criteria were then incorporated into the LES model and applied to predict inclusion entrapment and removal in a typical continuous casting operation. The distribution of inclusions in the final solidified slab was computed, both during average (steady) casting conditions, and after a sudden burst of inclusions. A simulation was also conducted to track the entrainment of inclusions entering the steel from the top surface slag layers.

Second, the computational models were applied to investigate the effect of nozzle geometry on flow and inclusion removal. This effort was assisted by parametric studies with a multiphase water model and plant measurements.

Third, because inclusion removal in the mold was found to be quite small, modeling was extended upstream to investigate inclusion removal during ladle refining. Specifically, equations were developed using a new size grouping model to efficiently predict inclusion size distribution evolution starting from nucleation, and including the effects of diffusion, Ostwald ripening, Brownian motion, and turbulent collisions on the size distribution evolution.

Fourth, the entrapment of inclusions by collisions with bubbles was computed in a fundamental study, involving many thousands of computations on the scale of an individual bubble moving through the molten steel. This model was implemented into the commercial program, FLUENT, and applied to simulate inclusion removal in both a steel refining ladle and in the continuous casting mold.

Fifth, behavior of the top surface mold flux layers, which is important to inclusion removal, was computed, including the effects of natural convection. After validation with literature experiments, criteria were developed for the critical cross-flow velocity that controls the transition from multiple cell flow structures to a single recirculation region in a typical idealized continuous casting operation.

Sixth, accurate simulation of superheat transport in the molten pool of the continuous caster due to jet impingement was undertaken using Large Eddy Simulation. The model was validated through comparison with temperature measurements in the liquid steel in the mold, and applied

Seventh, a model was developed of the behavior of the interface between the solidifying steel shell and the mold, including heat transfer, mass and momentum transfer of the mold flux layers, and friction with the oscillating mold wall. The model was validated with comparison to a range of plant measurements and was then applied to predict several phenomena of practical interest, such as when fracture of the flux layer and corresponding surface defects are likely.

Summary of Findings Click here for full Findings PDF (1.55 MB)

Advanced computational models have been developed to predict quantitatively, the removal of inclusions in the mold region during the continuous casting steel and related phenomena and processes. This multi-faceted research project includes the development and validation of models to predict transient fluid flow in the nozzle and mold, the transport of inclusion particles, the entrainment of particles from the top surface, the entrapment of inclusions by bubbles, the removal of particles to the top surface of the mold or their capture into the solidifying shell, and the optimization of fluid flow parameters to according to these findings. Each aspect of the models has been tested with plant measurements and applied to better understand and optimize the process to improve steel quality. Some of the significant findings from the seven subprojects include:

• Transient flow models require a fine mesh (400,000 nodes) to achieve accuracy within 17%.


• Model simulations of fluid flow can match measurements in both water models and steel casters, including liquid level variations of the top surface, calculated with a simplified model.


• At least 2500 particles are required to obtain statistics accurate within ±3% for inclusion transport in the mold. The initial removal rates are chaotic, and depend on time variations in the flow.


• Although the safe removal of inclusion particles to the top surface increases with increasing particle size, the removal fractions are still small: only ~12% of 100 μm particles or 70% of 400μm particles are removed. Only 8% of small particles (10μm and 40μm) are removed. Varying nozzle geometry, such as using a shallower port angle, can only improve removal slightly.


• The removal of slag particles entrained from the top surface depends greatly on the particle size. Most (>92%) of the 250μm - 400μm droplets simply return to the slag layer. However, more than half of the 100μm particles are eventually captured, leading to sliver defects.


• A short (9s) burst of inclusions entering the caster takes about 4 minutes to remove for the casting conditions assumed here. The captured particles concentrate mainly within a 2-m long section of slab. Using this information from together with sensors to detect when inclusion bursts occur would allow the contaminated steel to be isolated.


• Flow transport tends to concentrate entrapped inclusions within 10-20mm beneath the strand surface, especially at the corner and towards the narrow faces. Thus, it is appropriate to focus inspection and slab conditioning efforts on improving the surface.


• Particle entrapment on refractory walls is a significant inclusion removal mechanism in addition to being associated with nozzle clogging, sudden release, and other quality problems.


• An efficient size-grouping model has been developed to simulate collisions in order to better model inclusion size distribution evolution starting from nucleation to final product size. Nucleation occurs ~108 times faster than mixing in the ladle


• Mixing computations have established an accurate methodology for inclusion particle motion in ladle refining, and have revealed guidelines for efficient ladle operation.


• Argon bubbles can remove significant quantities of inclusions, especially if they are small and are not captured into the final product. In the CC mold, if bubbles are ~ 5mm in diameter, ~10% of the inclusions are predicted to be removed by bubble flotation, corresponding to around 3ppm decrease in total oxygen. Combined with ~ 8% inclusion removal by flow transport, the total roughly agrees with the measured inclusion removal rate in the mold of ~22%.


• Mold flow parameters should be optimized to minimize level fluctuations and to avoid the entrainment of slag from the top surface. Specific gas flow rates and nozzle geometries to accomplish this are suggested for a particular set of casting conditions.


• Inclusions should be removed upstream of the mold, as much as possible, in order to minimize inclusion-based defects in the final product.


• Correlations have been developed to predict surface heat removal through the top surface flux layer as a function of its thickness, properties, and the tangential molten steel velocity beneath it. Natural convection cells are unlikely for typical real fluxes, because the temperature dependency of the viscosity damps out the local recirculation. Natural convection is significant only at the corners of the layer. These results will be useful in further models of the crucial meniscus region, which governs inclusion entrapment at the meniscus and other surface quality problems.


• Methodologies to accurately predict superheat transport during flowing molten metal with jet impingement have been developed, validated with plant measurements and applied to real casters. This benchmark computation will be important for further model validation and parametric studies to lessen problems with excessive shell thinning at the impingement point, and excessive meniscus solidification (and the corresponding inclusion entrapment and other defects).


• Models of behavior of the interfacial gap have been developed. These models will be important for relating mold sensor measurements (such as friction) with surface defects (such as lubrication problems), and choosing mold flux and operating conditions in order to optimize mold operation to improve surface quality. Further details can be found in the 47 technical publications that resulted from this work.

NSF Publications

Thomas, B.G. and S.P. Vanka, “Study of Transient Flow Structures in the Continuous Casting of Steel,” Proceedings of the NSF Design, Service, Manufacturing and Industrial Innovation Research Conference, San Juan, Puerto Rico, National Science Foundation, Washington, D.C., 22 pp., Jan. 7-10, 2002. Click here for a PDF version (1.04 MB)

Thomas, B.G., Q. Yuan, L. Zhang, and S.P. Vanka; “Flow Dynamics and Inclusion Transport in Continuous Casting of Steel,” 2003 NSF Design, Service, and Manufacturing Grantees and Research Conference Proceedings, R. G. Reddy, ed., Birmingham, AL, Jan. 6-9, 2003, University of Alabama, Tuscaloosa, AL, 2328-2362, 2003. Click here for a PDF version (675 KB)

Thomas, B.G., Q. Yuan, L. Zhang, B. Zhao, and S.P. Vanka; “Flow Dynamics and Inclusion Transport in Continuous Casting of Steel,” 2004 NSF Design, Service, and Manufacture and Industrial Innovation Grantees and Research Conf. Proceedings, ed., T/BGT/1-41, Southern Methodist University, Dallas, TX, USA, Jan. 5- 8, 2004. Click here for a PDF version (891 KB)

Thomas, B.G., “Modeling of the Continuous Casting of Steel--Past, Present and Future,” Mettallurgical and Materials Transactions B, 33B, 795-812, 2002. Click here for a PDF version (2.91 MB)

Zhang, L. and B.G. Thomas, “State of the Art in Evaluation and Control of Steel Cleanliness,” ISIJ International, 43:3, 271-291, 2003. Click here for a PDF version (1.87 MB)

Meng, Y. and B.G. Thomas, “Heat-Transfer and Solidification Model of Continuous Slab Casting: CON1D,” Metallurgical & Materials Transactions B, 34B:5, 685-705, 2003. Click here for a PDF version (1.27 MB)

Meng, Y. and B.G. Thomas, “Modeling Transient Slag-Layer Phenomena in the Shell/Mold Gap in Continuous Casting of Steel,” MetallurgiYuan, Q., B.G. Thomas, and S.P. Vanka, “Study of Transient Flow and Particle Transport during Continuous Casting of Steel Slabs, Part 1. Fluid Flow,” Metallurgical and Materials Transactions B, 35B:4, 685-702, 2004.cal & Materials Transactions B, 34B:5, 707-725, 2003. Click here for a PDF version (1.13 MB)

Yuan, Q., B.G. Thomas, and S.P. Vanka, “Study of Transient Flow and Particle Transport during Continuous Casting of Steel Slabs, Part 1. Fluid Flow,” Metallurgical and Materials Transactions B, 35B:4, 685-702, 2004. Click here for a PDF version (3.26 MB)

Yuan, Q., S. Sivaramakrishnan, S.P. Vanka, and B.G. Thomas, “Computational and Experimental Study
of Turbulent Flow in a 0.4-Scale Water Model of a Continuous Steel Caster,” Metallurgical and Materials
Transactions B, 35B:5, 967-982, 2004. Click here for a PDF version (2.23 MB)

Yuan, Q., B.G. Thomas, and S.P. Vanka, “Study of Transient Flow and Particle Transport during Continuous Casting of Steel Slabs, Part 2. Particle Transport,” Metallurgical and Materials Transactions B, 35B:4, 703-714, 2004. Click here for a PDF version (1.97 MB)

Yuan, Q., B. Zhao, S.P. Vanka, and B.G. Thomas; “Study of Computational Issues in Simulation of Transient Flow in Continuous Casting,” Steel Research International, Special Issue: Simulation of Fluid Flow in Metallurgy, 76:1, 33-43, Jan., 2005. Click here for a PDF version (6.70 MB)

Zhao, B., S.P. Vanka, and B.G. Thomas, “Numerical Study of Flow and Heat Transfer in a Molten Flux
Layer,” Int. J. Heat and Fluid Flow, 26:1, 105-118, 2005. Click here for a PDF version (985 KB)

Zhao, B., B.G. Thomas, S.P. Vanka, and R.J. O’Malley, “Transient Fluid Flow and Superheat Transport in Continuous Casting of Steel Slabs,” Metallurgical and Materials Transactions B – Process Metallurgy and Materials Processing Science, 36B:12, 801-823, December 2005. Click here for a PDF version (2.07 MB)

Zhao, B., B.G. Thomas, S.P. Vanka, and R.J. O’Malley, ”Transient Flow and Temperature Transport in
Continuous Casting of Steel Slabs,” ASME Journal Heat Transfer, Vol. 127, 807, 2005. Click here for a PDF version (336 KB)

Zhang, L., J. Zhi, F. Mei, L. Zhu, X. Jiang, J. Shen, J. Cui, K. Cai, and B.G. Thomas, “Basic Oxygen Furnace Based Steelmaking Processes and Cleanliness Control at Baosteel,” Ironmaking & Steelmaking, 33:2, 129-139, 2006. Click here for a PDF version (490 KB)

Zhang, L., J. Aoki, and B.G. Thomas, “Inclusion Removal by Bubble Flotation in a Continuous Casting Mold,” Metallurgical and Materials Transactions B, 37B:3, 361-379, June 2006. Click here for a PDF version (1.04 MB)

Zhang, L., and B.G. Thomas, “State of the Art in the Control of Inclusions during Steel Ingot Casting,” Metallurgical and Materials Transactions B, 37:5, 733-761, Oct. 2006. Click here for a PDF version (1.22 MB)

Zhang, L., S. Yang, X. Wang, K. Cai, J. Li, X. Wan, and B.G. Thomas, “Investigation of Fluid Flow and Steel Cleanliness in the Continuous Casting Strand”, Metallurgical and Materials Transactions B, 38B:1, Feb., 2007, pp. 63-83. Click here for a PDF version (892 KB)

Thomas, B.G., M. Jenkins, and R.B. Mahapatra "Investigation of Strand Surface Defects Using Mold Instrumentation and Modelling," Ironmaking & Steelmaking, 31, 485-494, 2004. Click here for a PDF version (682 KB)

Zhang, L., W. Pluschkell, and B.G. Thomas, “Nucleation and Growth of Alumina Inclusions During Steel Deoxidation,” Proceedings of the 85th Steelmaking Conference, Iron and Steel Society-AIME, Warrendale, PA, 463-476, 2002. Click here for a PDF version (205 KB)

Zhang, L., B.G. Thomas, X. Wang, and K. Cai, “Evaluation and Control of Steel Cleanliness - A Review,” Proceedings of the 85th Steelmaking Conference, Iron and Steel Society-AIME, Warrendale, PA, 431-452, 2002. Click here for a PDF version (280 KB)

Zhang, L. and B.G. Thomas, “Alumina Inclusion Behavior During Steel Deoxidation,” 7th European Electric Steelmaking Conference Proceedings, Vol. 2, May 26-29, 2002, Venice, Italy, Associazione Italiana di Metallurgia, Milano, Italy, 2.77-2.86, 2002. Click here for a PDF version (238 KB)

Thomas, B.G., "Annual Report to Continuous Casting Consortium," University of Illinois at Urbana-Champaign, Oct. 15, 2002.

Meng, Y. and B.G. Thomas, “Interfacial Friction-Related Phenomena in Continuous Casting with Mold Slags,” ISSTech 2003 Steelmaking Conference Proceedings, Indianapolis, IN, Apr. 27-30, 2003, ISS-AIME, Warrendale, PA, 589-606, April 2003. Click here for a PDF version (532 KB)

Yuan, Q., B.G. Thomas, and S.P. Vanka, “Turbulent Flow and Particle Motion in Continuous Slab-Casting Molds,” ISSTech 2003 Process Technology Proceedings, Indianapolis, IN, Apr. 27-30, 2003, ISS-AIME, Warrendale, PA, 913-927, April 2003. [Robert W. Hunt Silver Medal, 2004, Association for Iron and Steel Technology] Click here for a PDF version (2.21 MB)

Zhang, L., B.G. Thomas, K. Cai, J. Cui, and L. Zhu, “Inclusion Investigation during Clean Steel Production at Baosteel,” ISSTech 2003 Steelmaking Conference Proceedings, Indianapolis, IN, Apr. 27-30, 2003, ISS-AIME, Warrendale, PA, 141-156, April 2003. Click here for a PDF version (1.24 MB)

Yuan, Q., S.P. Vanka and B.G. Thomas, “Large Eddy Simulations of Transient Flow during Continuous Slab Casting of Steel,” 3rd International Symposium on Turbulence and Shear Flow Phenomena, Sendai, Japan, 25-27 June, 2003, Conference Proceedings, 2,.681-686, June 2003. Click here for a PDF version (768 KB)

Zhang, L. and B.G. Thomas, “Fluid Flow and Inclusion Motion in the Continuous Casting Strand,” Proceedings XXIV Nat. Steelmaking Symp., Morelia, Mich, Mexico, Nov. 26-28, 138-183, 2003. Click here for a PDF version (4.44 MB)

Zhang, L. and B.G. Thomas, “Inclusions in Continuous Casting of Steel,” Proceedings XXIV Nat. Steelmaking Symp., Morelia, Mich, Mexico, Nov. 26-28, 184-198, 2003. Click here for a PDF version (2.38 MB)

Zhang, L. and B.G. Thomas, “Inclusion Nucleation, Growth, and Mixing during Steel Deoxidation,” Continuous Casting Report, 1-19, March 2002; revised Sept. 2003. Click here for a PDF version (337 KB)

Thomas, B.G. “Modeling of Continuous Casting,” Chapter 5 in Making, Shaping and Treating of Steel, 11th Edition, Vol. 5, Casting Volume, A. Cramb, ed., AISE Steel Foundation, Pittsburgh, PA, 5.1-5.24, 2003. Click here for a PDF version (3.62 MB)

Thomas, B.G. “Fluid Flow in the Mold,” Chapter 14 in Making, Shaping and Treating of Steel, 11th Edition, Vol. 5, Casting Volume, A. Cramb, ed., AISE Steel Foundation, Pittsburgh, PA, Oct., 14.1-14.41, 2003. Click here for a PDF version (2.87 MB)

Thomas, B.G., “Recent Advances in Computational Modeling of Continuous Casting of Steel,” Scanmet II Conference, 1, 243-252, MEFOS, Luleå, Sweden, June 6-9, 2004. Click here for a PDF version (4.70 MB)

Yuan, Q., B. Zhao, S.P. Vanka, and B.G. Thomas, “Study of Computational Issues in Simulation of Transient Flow in Continuous Casting,” Materials Science & Technology 2004 (MS&T2004), New Orleans, LA, Vol. II, 333-343, Sept. 26-29, 2004. Click here for a PDF version (1.77 MB)

Yuan, Q., "Transient Study of Turbulent Flow and Particle Transport During Continuous Casting of Steel Slabs," PhD Thesis, University of Illinois at Urbana-Champaign, IL, 2004.

Zhang, L., S. Yang, X. Wang, K. Cai, J. Li, X. Wan, and B.G. Thomas, “Physical, Numerical and Industrial Investigation of Fluid Flow and Steel Cleanliness in the Continuous Casting Mold at Panzhihua Steel,” AISTech 2004, Nashville, TN, Assoc. Iron Steel Technology, Warrendale, PA, 879-894, Sept. 15-17, 2004. Click here for a PDF version (857 KB)

Zhang, L., J. Aoki, and B.G. Thomas, “Inclusion Removal by Bubble Flotation in Continuous Casting
Mold,” Materials Science & Technology 2004 (MS&T2004), New Orleans, LA, Vol. II, 161-177, Sept. 26-29,
2004. Click here for a PDF version (4.35 MB)

Thomas, B.G., “Computational Modeling of Flow, Heat Transfer, and Deformation in the Continuous Casting of Steel,” First Baosteel Annual Academic Conference, 1, 13-19, Shanghai, China, May 27-28, 2004. Click here for a PDF version (6.20 MB)

Yuan Q., and B.G. Thomas, “Transport and Entrapment of Particles in Continuous Casting of Steel,” Proceedings of the 3rd International Congress on Science & Technology of Steelmaking, Charlotte, NC, 745-762, Association for Iron & Steel Technology, Warrendale, PA, May 9-11, 2005. Click here for a PDF version (1.66 MB)

Zhao, B., "Numerical Study of Heat Transfer in Continuous Casting of Steel," MS Thesis, University of Illinois at Urbana-Champaign, 2003.

Zhang, L., and B.G. Thomas, “Application of Computational Fluid Dynamics to Steel Refining and Casting Processes,” Proceedings of the Fourth International Conference on CFD in Oil, Gas, Metall. & Process Industries, SINTEF/NTNUTrondheim, Norway, No. 30, June 6-8, 2005. Click here for a PDF version (1.30 MB)

Thomas, B.G., “Modeling of Continuous-Casting Defects Related to Mold Fluid Flow,” 3rd Internat. Congress on Science & Technology of Steelmaking, Charlotte, NC, May 9-11, 2005, Association for Iron & Steel Technology, Warrendale, PA, 847-861, 2005. [keynote paper] Click here for a PDF version (4.69 MB)

Thomas, B.G., "Mathematical Modeling of Continuous Casting of Steel," Annual Report to Continuous Casting Consortium, University of Illinois at Urbana-Champaign, June 1, 2005.

Thomas, B.G., Q. Yuan, L. Zhang, B. Zhao, and S.P. Vanka; “Flow Dynamics and Inclusion Transport in Continuous Casting of Steel,” 2005 NSF Design, Manufacture and Industrial Innovation Grantees Conf. Proceedings, J. Shaw, ed., Jan. 3-6, 2005, Scottsdale, AZ, USA, Arizona State, Tempe, AZ; MPM #DMI0115486, T/BGT/1-24, 2005. Click here for a PDF version (761 KB)

Aoki, J., L. Zhang, and B.G. Thomas, “Modeling of Inclusion Removal in Ladle Refining,” Proceedings of the 3rd International Congress on Science & Technology of Steelmaking, Charlotte, NC, 319-332, Association for Iron & Steel Technology, Warrendale, PA, May 9-11, 2005. Click here for a PDF version (1.97 MB)

Zhang, L., B. Rietow, B.G. Thomas, K. Eakin, and D.Q. Baird, “Investigation of Steel Cleanliness during Ingot Teeming,” Final Report to Ingot Metallurgy Forum, Fall Meeting, Canton, OH, Nov. 2, 2005.

Thomas, B.G., “On-line Detection of Quality Problems in Continuous Casting of Steel,” in Modeling, Control and Optimization in Ferrous and Nonferrous Industry, Materials Science & Technology 2003, F. Kongoli, B.G. Thomas, and K. Sawamiphakdi, eds., Chicago, IL, Nov. 10-12, 2003, TMS, Warrendale, PA, 29-45, 2003. Click here for a PDF version (1.59 MB)