Agglomeration of Non-metallic Inclusions at the Steel/Ar Interface: Model Application
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NOZZLE clogging is a well-known problem for continuous casting process. In order to understand the mechanism, a huge number of publications are summarized in References 1 through 4. Among the mechanisms, inclusion agglomeration is one of major importance. Besides nozzle clogging, inclusion agglomeration can also lead to mechanical defects if the agglomerate remains in the solid steel product.[1,2] However, agglomerated inclusions are generally easily removed during Ar bubbling.[5–7] Previous experimental studies[8–16] reported the in-situ observation of inclusion agglomeration at the steel/Ar interface by confocal laser scanning microscope (CLSM) as a means to understand more deeply inclusion agglomeration behavior during Ar bubbling. Moreover, capillary interaction between inclusions partly immersed at the steel/Ar interface is WANGZHONG MU, NESLIHAN DOGAN, and KENNETH S. COLEY are with the Department of Materials Science and Engineering, McMaster Steel Research Centre, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Contact emails: [email protected] and [email protected] Manuscript submitted January 27, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
reported to be one mechanism for agglomeration.[8–13] In order to investigate this mechanism, a theoretical model based on Kralchevsky-Paunov model[17,18] has been subsequently used by Nakajima and co-workers[10,11] and Jo¨nsson and co-workers.[12,13] These workers showed good agreement between their experimental data for attractive force of inclusion agglomeration at the steel/Ar and steel/slag interfaces. However, to date, quantitative evaluation of the agglomeration tendency of different inclusions has not been reported. In the present work, the physical properties including inclusion density, contact angle between inclusions and liquid iron/steel, surface energies of inclusions, interfacial energies between inclusions and liquid iron/steel are used to represent different inclusions. The present capillary force model[19,20] is applied quantitatively, to evaluate the attractive capillary force for the agglomeration of different inclusions at the interface between Ar and liquid iron/steel. Thereafter, the coagulation coefficient, which can be used to evaluate the inclusion agglomeration tendency in the liquid iron/steel matrix, is calculated, and quantitative comparison of different inclusions is performed. Subsequently, the inclusion collision volume (Wij) and collision rate (Nij) for inclusion collision in the liquid iron/steel matrix are calculated using the Hamaker constant and coagulation
coefficient. Finally, the effects of inclusion composition, size, and number density are investigated, and, thus, the contribution to inclusion agglomeration by each factor is considered. The present work aims to offer a better understanding of the mechanisms of inclusion agglomeration at the steel/Ar interface and the liquid steel matrix as well as inclusion elimination for clean steel manufacturing.
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METHODOLOGY
A. Capillary Force Model of
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