Constitutional Segregation of Al 2 O 3 in Mold Slag and Its Impact on Steel Cleanliness During Continuous Casting
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MOLD powder is an auxiliary material used in continuous casting of liquid steel and is a blend of synthetic fluxes, minerals, slag components, and carbon. It is primarily used for controlling the lubrication and heat transfer along with a set of secondary objectives such as absorb nonmetallic inclusions and prevent re-oxidation of steel.[1] Mold slag is generated after melting of the powder added over the liquid steel, which infiltrates into the gap between mold and steel strand due to the friction aided by mold during negative strip cycle. The use of a suitable mold powder prevents casting defects and improves steel cleanliness and shop productivity.[2–4] Al2O3 particles are the notable indigenous inclusions in Al-killed steel, which are generated due to deoxidation practice and slag/metal reactions during continuous casting. Despite inclusion absorption with slag at ladle and tundish,[5,6] significant Al2O3 pickup with respect to slag characteristics at continuous casting mold has been reported.[7–11] Numerous studies on the effect of Al2O3 on slag viscosity, crystallization, microstructure, and heat transfer in continuous casting (CC) were also reported.[12,13] Inadequate removal of
P. PALAI, formerly Graduate Scholar with Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India, is now Technical Manager with Steel Making Technology, Tata Steel Ltd., Jamshedpur 831001, India. Contact e-mail: [email protected] P.P. SAHOO, Principal Researcher, is with the Steel Making and Casting, Tata Steel R&D. ARGHYA DEY, Researcher, is with the Teesside Technology Centre, Tata Steel RD&T, Middlesbrough TS6 6US, U.K. T.K. ROY, Head, is with the Steel Making Technology. V.V. MAHASHABDE, Chief of Technology, is with the Flat Products Division, Tata Steel Ltd. Manuscript submitted January 15, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
Al2O3 through slags at ladle, tundish, and mold leading to its entrapment with the solidifying steel and results in poor slab quality. Steel cleanliness improvement through Al2O3 pickup by slag at the continuous casting mold is viable option due to continuous slag infiltration and inclusion removal. It is the common practice at Tata Steel that slags of different composition and microstructures are selected for casting different steel grades to achieve required casting objectives. In general, controls of casting speed, mold level fluctuation, and instantaneous speed change are the common practices to avoid gross entrapment of top slag and improve steel cleanliness.[5] Yu et al.[8] and A.B Fox et al.[9] have studied extensively the Al2O3 dissolution in mold slag, and there are reports on mathematical models for prediction of Al2O3 pickup by slag.[8–11] Apart from this, there is a need of phenomenological study on Al2O3 pickup by slag at continuous casting mold. Nonetheless, as per the knowledge of the authors, there are no reports of microsegregation and Al2O3 inclusion partitioning in constituent phases in different slag
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