Experimental Analysis on the Causes of the Breakout of Continuous Cast Steel Slab

Abstract:

The paper deals with investigation into segregation behavior of selected elements in longitudinal cut of continuous steel slab, in the breakout area. The breakout occurred after a flying change of tundish in order to begin casting of another steel grade. Altogether 11 samples were taken from the part of a solidified slab. Concentrations of selected elements (Al, Si, P, S, Cr, Mn, Ni and Mo) were measured in these samples using scanning electron microscope and energy dispersive spectroscopy. Using the original mathematical models the basic micro-segregation characteristics and the parameter of macro-heterogeneity were further determined for each analyzed element. Then a quantitative measurement of inclusions ("micro-purity") in the samples was performed using a metallographic microscope. Then method of differential thermal analysis was used for the measurements of temperatures of phase transformations. The following main results were found: - magnitude of micro-segregation of the analyzed elements in the measured sections of 1000 μm is approximately the same in all the analyzed samples, - chemical macro-heterogeneity is very high across the analyzed slab section, - very uneven mixing of melts of both steels was probably one of the main causes of formation of the breakout.

• Periodical: Materials Science Forum (Volume 782)
• Pages: 67-72
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.782.67
• Online since: April 2014
• Authors: Jana Dobrovská, Hana Francová, Bedřich Smetana, Karel Stránský, Věra Dobrovská, František Kavička
• Keywords: Breakout, Continuously Cast Slab, Intermixing, Micro-Segregation, Steel

References

[1] X. Huang, B.G. Thomas, Intermixing Model of Continuous Casting during a Grade Transition. Metall. Trans. B, 27B (1996) 617-632.

DOI: 10.1007/bf02915660

[2] K. Michalek, et al. Type of submerged entry nozzle vs. concentration profiles in the intermixed zone of round blooms with a diameter of 525 mm, Materiali in Tehnologije, 46 (2012) 581-587.

DOI: 10.2478/v10172-012-0171-8

[3] F. Kavička, et. al. Analysis of atypical breakout during a radial continuous casting of a slab in the straightening zone. I. Numerical simulation of temperature field of a slab. Hutnické listy (accepted for publication).

[4] J. Miettinen, Calculation of solidification-related thermophysical properties for steels. Metall Mater Trans B, 1997, Vol. 28, No. 2, pp.281-297.

DOI: 10.1007/s11663-997-0095-2

[5] M.N. Gungor, A statistically significant experimental technique for investigating micro-segregation in cast alloys. Metall. Trans. A, 1989, Vol. 20A, pp.2529-2533.

DOI: 10.1007/bf02666687

[6] J. Dobrovská et. al. Investigation into segregation of selected elements in the breakout area of a continuously cast steel slab. In METAL 2012: 21st International conference on metallurgy and materials, Tanger Ltd, Ostrava, 2012, pp.115-121.

[7] L. Zhang, B.G. Thomas, Inclusions In Continuous Casting of Steel. In XXIV National Steelmaking Symposium, Morelia, Mich, Mexico, 26-28, Nov. 2003, pp.138-183.