Fluid Force-Induced Detachment Criteria for Nonmetallic Inclusions Adhered to a Refractory/Molten Steel Interface
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NONMETALLIC inclusions (NMIs) in steel have a considerable impact on the final product quality with regard to properties such as dynamic loads, corrosion resistance, and optical appearance. An excessive number of microinclusions or inclusions with an unsuitable morphology can also lead to problems in the processing of steel, such as clogging, during the continuous casting process or breakage during cold drawing.[1] Since inclusions cannot be completely avoided, a greater understanding of the formation, development, and evolution of inclusions through each processing step of steel manufacturing is necessary. The present article mainly focuses on the behavior of small oxidic inclusions with a diameter below 10 lm in the fluid flow control system of a continuous caster. These micro-oxide inclusions mostly result from the deoxidation of the steel and the subsequent interaction with ladle slag and ladle lining.[1,2] Initially, very small
UXIA DIEGUEZ SALGADO, SUSANNE K. MICHELIC, and CHRISTIAN BERNHARD are with the Department of Ferrous Metallurgy, the Montanuniversitaet Leoben, Leoben, 8700, Austria. Contact email: [email protected] CHRISTIAN WEIß is with the Department of Environmental and Energy Process Engineering, the Montanuniversitaet Leoben, Leoben, 8700, Austria. Manuscript submitted November 13, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
particles collide and agglomerate in liquid steel to form larger particles. Ladle stirring is the most common method to stimulate the agglomeration and flotation of particles and finally to separate the particles into the slag. Nevertheless, a large number of microparticles stay suspended in the liquid steel and pass onto the next processing stage, the casting process.[1–3] Over the entire process, interfacial phenomena significantly influence nucleation, agglomeration, flotation, or separation of the particles.[3] NMIs may, depending on their composition, size, and morphology, become troublesome in the fluid flow control system of a caster tundish, namely, in the submerged entry nozzle (SEN). The SEN, which is presented schematically in Figure 1(a), is a pipelike refractory component placed between the tundish and the mold in a continuous caster. It prevents the steel from oxygen and nitrogen pickup and ensures a stable casting operation in the mold.[1] The adhesion of oxide particles at the SEN surface is one of the commonly recognized initial stages for the development of clogs. This results in an uneven reduction of the inner diameter of the nozzle; consequently, the caster operation may be seriously disrupted, possibly diminishing the slab surface and subsurface quality.[2] The phenomenon described previously is known as clogging,[1–6] and these deposits are found along the SEN as well as in areas of the stopper rod, as shown in Figure 1(b).
Numerous studies have been carried out in order to elucidate the clogging mechanism for deposits at the nozzle in continuous casting. Rackers and Thomas,[2] Singh,[5] and Thomas and Bai[8] summarized the clogg
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