FLUORINE-FREE MOULD SLAGS FOR SLAB CASTING: UTILISATION OF THE HOT THERMOCOUPLE TECHNIQUE TO BUILD TTT DIAGRAMS
Klug, Jeferson Leandro; Hagemann, René; Heck, Nestor Cezar; Vilela, Antônio Cezar F.; Scheller, Piotr Roman
http://dx.doi.org/10.4322/tmm.2012.005
Tecnol. Metal. Mater. Min., vol.9, n1, p.30-36, 2012
Abstract
The elimination of fluorine from slags is necessary because F-bearing materials pollute the environment and cause machinery corrosion at steelworks. Regarding the development of F-free mould slags for slab casting, the main problem is how to control the heat transfer between steel shell and mould. In commercial products the heat transfer control is obtained through the crystallisation of cuspidine (3CaO.2SiO2.CaF2) from mould slag. Thus, the fluorine-free slag which would be used as the substitute must show similar crystallisation behaviour. This paper shows results of a cooperation work between Technische Universität Bergakademie Freiberg and Universidade Federal do Rio Grande do Sul. Ti-bearing slags were studied through the Single Hot Thermocouple Technique, building time-temperature-transformation (TTT) diagrams. The results indicate that the system CaO-SiO2-TiO2-Na2O can be used as substitute for F-bearing slags, regarding crystallisation behaviour, since the incubation times at TTT diagram can be similar to commercial products. This is possible because addition of Na2O shorten intensely the incubation times from the CaO-SiO2-TiO2 slag system
Keywords
Mould slags, Slab casting, Hot thermocouple technique, TTT diagrams
Referências
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2 HOOLI, P. Study on the layers in the film originating from the casting powder between steel shell and mould and associated phenomena in continuous casting of stainless steel. 2007. Thesis (Doctoral in Materials Science and Engineering) – Helsinky University of Technology, Helsinky, 2007.
3 ORRLING, C. et al. Observations of the melting and solidification behavior of mold slags. Iron & Steelmaker, v. 27, n. 1, p. 53-63, 2007.
4 SCHULZ, T. et al. Entwicklung umweltfreundlicher Stranggießschlacken. Stahl Und Eisen, v. 128, n. 4, p. 65-78, Apr. 2008.
5 NAKADA, H.; NAGADA, K. Crystallization of CaO–SiO2–TiO2 slag as a candidate for fluorine free mold flux. ISIJ Internationa, v. 46, n. 3, p. 441-9, Mar. 2006. http://dx.doi.org/10.2355/isijinternational.46.441
6 WEN, G. et al. Development of fluoride-free mold powders for peritectic steel slab casting. ISIJ International, v. 47, n. 8, p. 1117-25, Aug. 2007. http://dx.doi.org/10.2355/isijinternational.47.1117
7 XIN QI; WEN, G.-H.; PING TANG. Investigation on heat transfer performance of fluoride-free and titanium-bearing mold fluxes. Journal of Non-Crystalline Solids, v. 354, n. 52-4, p.5444-52, 2008.
8 LACHMANN, S.; SCHELLER, P. R. Effect of Al2O3 and CaF2 on the solidification of mould slags and the heat transfer through slag films. In: INTERNATIONAL CONFERENCE ON MOLTEN SLAGS, FLUXES AND SALTS, 8., 2009, Santiago. Proceedings... Santiago: Gecamin, 2009. p. 1101.
9 PATNAIK, P. Handbook of inorganic chemicals. New York: McGraw-Hill, 2003.
10 SCHENCK, H.; FROHBERG, M. Viskositätsmessungen an flüssigen Schlacken des Systems CaO-SiO2-TiO2 im Temperaturbereich von 1300 bis 1600°C. Archiv für das Eisenhüttenwesen, v. 33, n. 7, p. 423-5, July 1962.
11 KASHIWAYA, Y.; CICUTTI, C. E.; CRAMB, A. W. n Investigation of the crystallization of a continuous casting mold slag using the single hot thermocouple technique. ISIJ International, v. 38, n. 4, p. 357-65, Apr. 1998. http://dx.doi. org/10.2355/isijinternational.38.357
12 MIZUNO, H. et al. Analysis of the crystallization of mold flux for continuous casting of steel. ISIJ International, v. 48, n.3, p. 277-85, Mar. 2008. http://dx.doi.org/10.2355/isijinternational.48.277
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