Steel Reoxidation by Gunning Mass and Tundish Slag
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TUNDISH, as the final vessel in contact with molten steel during the steel production, provides the last opportunity to optimize the steel cleanliness and is therefore of significant importance for steel quality control. However, it could also introduce exogenous inclusions through refractory erosion, slag entrapment, and steel reoxidation,[1–3] contaminating molten steel and degrading steel cleanliness. In general, the steel reoxidation in the tundish results from several reasons[3,4]: (1) air infiltration, which can be prevented by using tundish cover powder, e.g., rice hull ash or tundish slag; (2) slag– steel interaction, i.e., the reducible compounds react with molten steel due to the low oxygen activity in molten steel; and (3) gunning mass (GM)–steel interaction, i.e., the reducible compounds in GM provide oxygen to reoxidize molten steel. Since the steel cleanliness can be hardly improved after the tundish refining, it is essential to control the steel cleanliness beforehand and prevent the steel reoxidation in the tundish.
PENGCHENG YAN, formerly a PhD student with the Department of Materials Engineering, KU Leuven, 3001 Louvain, Belgium, is now Research Associate with the Department of Materials Science and Engineering (MSE), Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA 15213. Contact e-mail: [email protected] SANDER ARNOUT, Managing Director, is with the InsPyro NV, 3001 Louvain, Belgium. MARIE-ALINE VAN ENDE, Postdoc Fellow, is with the Department of Mining and Materials Engineering, McGill University, Montreal, Canada. ENNO ZINNGREBE, Principal Researcher, is with the Tata Steel Europe RD&T, 10000, Ijmuiden, Netherlands. TOM JONES, Project Manager, BART BLANPAIN, Professor, and MUXING GUO, Senior Scientist, are with the Department of Materials Engineering, KU Leuven. Manuscript submitted September 13, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
Steel reoxidation by refractory material and slag during the refining process have been widely investigated. Several groups[1,2,5,6] have confirmed that FeO and MnO impurities in refractory materials contribute to steel reoxidation and result in steel contamination by introducing exogenous inclusions. SiO2 in refractory materials can also lead to severe steel reoxidation.[1,5] Higher contents of reducible compounds in refractory materials considerably increase the total oxygen content in molten steel and lead to steel degradation.[5,6] On the other hand, MgO in the refractory is found to be reduced by carbon at high temperature,[6–8] and the resulting Mg vapor reacts with non-metallic inclusions present in the steel, forming MgOÆAl2O3 inclusions, which are even more harmful to steel quality than the original Al2O3 inclusions. The effects of gunning mass on steel cleanliness have been studied by Mantovani et al.[2] and also in our previous research[1]. It was found that compared to MgO and MgO + 2MgOÆSiO2 GM, the use of Al2O3 GM resulted in an improved steel cleanliness due to its low reducible oxides content.[1,2] The oxidation capacity of gun
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