Model for Inclusion Precipitation Kinetics During Solidification of Steel Applications in MnS and TiN Inclusions
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ONMETALLIC inclusions in steel are detrimental to properties of steel products, such as strength, toughness, fatigue strength, and surface quality.[1] Solid inclusions can also gradually deposit on the wall of a submerged entry nozzle and eventually cause its clogging. Therefore, one of the most important tasks for steelmakers is to control the inclusion formation during steelmaking and continuous casting. Exogenous inclusions mainly originate from wearing of refractory and the entrapment of slag.[1] Most endogenous inclusions are generated by the deoxidation of steel during secondary metallurgy.[1–3] Owing to the supersaturation of segregated elements in the interdendritic liquid, some new oxide and sulfide inclusions precipitate from steel during continuous casting; these could be called QIFENG SHU, VILLE-VALTTERI VISURI, TUOMAS ALATARVAS, and TIMO FABRITIUS are with the Process Metallurgy Research Unit, University of Oulu, 90014 Oulu, Finland. Contact email: qifeng.shu@oulu.fi Manuscript submitted March 21, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
‘‘secondary endogenous inclusions.’’ The secondary inclusions are typically small, but sometimes they can be harmful to the properties of steel. Therefore, it is also important to control the composition, size, and spatial distribution of inclusions during solidification to achieve a better quality of steel. Many experimental investigations have been performed on the inclusion formation during solidification.[4–9] Sui et al.[6] investigated the growth of sulfides in free-cutting stainless steel and found that sulfide inclusions are coarsened during the slow cooling and heat treatment process due to Ostwald ripening. Suzuki et al.[8] investigated the inclusion particles in continuously cast stainless steel slab and laboratory-scale ingot casting steel. They found that an Ostwald ripening model provided the best correlation with experimental data. There have been many attempts to model the formation of inclusion by combining microsegregation with thermodynamics.[10–14] Various segregation models[15–19] have been employed to calculate the element enrichments in residual liquid due to the rejection from dendrites during solidification. The formation of inclusions due to the supersaturation of solutes was further
calculated in an equilibrium manner. To this end, commercial thermodynamic tools, e.g., FactSage and ChemApp, have frequently been applied.[11–13] A thermodynamic model for inclusion formation during solidification provides only the information of equilibrated inclusion composition. The inclusion size distribution can be calculated only by a kinetic model considering the nucleation, growth, and coarsening phenomena. Only a few models[20–24] dealing with kinetics of inclusion formation have been proposed in the literature. Rocabois et al.[20] developed a model coupling nucleation, mixed-controlled growth, and microsegregation to calculate the precipitation kinetics of TiN during solidification. Their microsegregation calculation is oversimplified and size distributi
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