In order to provide a prediction tool for sulfide/oxide/oxysulfide inclusion evolution in Mn-Al steel with a Ca addition/CaO-based flux, a comprehensive thermodynamic database for the inclusion system composed of CaO-MnO-Al2O3-CaS-MnS-Al2S3 was developed in the present study. Activity of MnS in a CaSMnS sulfide solid solution was experimentally determined by employing a chemical equilibrium technique at 1 400°C and 1 500°C. The measured activity exhibits a positive deviation from an ideal behavior, which is in consistent with the known two-phase separation of the sulfide solid solution at lower temperature (Tcr = 1 200°C). Based on the activity and the phase diagram data available in literature, a thermodynamic modeling of the CaS-MnS system was carried out. The following excess Gibbs free energy of the CaSMnS sulfide solid solution was obtained:Furthermore, using available thermodynamic modeling results for other constituent sub-systems, a larger thermodynamic database of the CaO-MnO-Al2O3-CaS-MnS-Al2S3 system was developed. A Modified Quasichemical Model in the quadruplet approximation was used to model the Gibbs free energy of the oxysulfide liquid solution. Comparisons between the model calculation and available experimental data show good agreement. The developed thermodynamic model and the database were used to predict unexplored phase diagrams with various nMn/(nCa + nMn) ratio, and sulfide capacity of the CaO-MnO-Al2O3 oxide liquid phase. The database can be used along with software for Gibbs free energy minimization in order to calculate any phase diagram section or thermodynamic property.
Understanding the essence of the flow oscillations within a submerged-entry nozzle (SEN) is essential to control flow patterns in the continuous casting mold and consequently increase the superficial quality of steel products. A numerical study of the mesoscopic fluid-particle flow in a bifurcated pool-type SEN under steady operating conditions is conducted using the lattice Boltzmann method (LBM) coupled with the large eddy simulation (LES) model. The accuracy of the model has been verified by comparing vortex structures and simulated velocities with published experimental values. The LBM modeling is also verified by comparing the “stair-step” jet patterns observed in the experiment. The geometrical parameters and operational conditions of physical experiments are reproduced in the simulations. By comparing the time-averaged velocities of Reynolds-averaged Navier–Stokes equations (RANS) with LBM models, transient mesoscopic fluid-particles and related vortex structures can be better reproduced within the SEN. The visualization of internal flow within the SEN is illustrated through the mass-less Discrete Phase Model (DPM) model. The trajectories show that the LBM–LES–DPM coupled model is good at predicting the transient vortical flow within the SEN. A large vortex is found inside the exit port and continuously changes in shape and size therein. The monitoring points and lines within the SEN are selected to illustrate the velocity variations and effective viscosity, which can reflect the oscillating characteristics even under stable operating conditions without changes at the exit from the SEN. Furthermore, the formation, development, diffusion, and dissipation of the vortex structures from the exit port of the SEN are also investigated using the Q criteria. The comparison of the power spectrum with high-frequency components along the exit port indicates that the flow oscillations must originate from within the SEN and are intensified in the exit port. The mesoscopic LBM model can replicate the fluid-particle flow and vortex structure transmission as well as their turbulence effects inside the SEN in detail.
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