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Euler-Euler Large Eddy Simulation (EELES) scheme has been developed to simulate the two-phase flow of argon gas and molten steel in slab continuous casting mold. The Euler-Euler approach is used to describe the equations of motion of the two-phase flow. The drag force, lift force and virtual mass force are incorporated in this model. Both turbulence of argon gas and molten steel are simulated using large eddy simulation (LES). Simulation results agree acceptably well with the water model experimental measurements of instantaneous flow structures. The flow pattern in the lower recirculation zone is expected to be asymmetrical between the left and right sides of the mold. The flow pattern is changeover; the direction of flow deviation is different from time to time. The time intervals for changeover appeared to vary randomly. The long-term asymmetry in the lower roll is due to the turbulent nature instead of the variation of other operating parameters. The turbulent flow in the mold includes multiple vortices. Those vortexes make the flow field to be more complex. Two typical transient flow structures, consisting of clockwise or counterclockwise rotational direction vortices, are found in the upper roll.

A population balance model based on the multiple-size-group (MUSIG) approach has been developed to investigate the polydispersed bubbly flow inside the slab continuous-casting mold and bubble behavior including volume fraction, breakup, coalescence, and size distribution. The Eulerian-Eulerian approach is used to describe the equations of motion of the two-phase flow. All the non-drag forces (lift force, virtual mass force, wall lubrication force, and turbulent dispersion force) and drag force are incorporated in this model. Sato and Sekiguchi model is used to account for the bubble-induced turbulence. Luo and Svendsen model and Prince and Blanch model are used to describe the bubbles breakup and coalescence behavior, respectively. A 1/4th water model of the slab continuous-casting mold was applied to investigate the distribution and size of bubbles by injecting air through a circumferential inlet chamber which was made of the specially-coated samples of mullite porous brick, which is used for the actual upper nozzle. Against experimental data, numerical results showed good agreement for the gas volume fraction and local bubble Sauter mean diameter. The bubble Sauter mean diameter in the upper recirculation zone decreases with increasing water flow rate and increases with increasing gas flow rate. The distribution of bubble Sauter mean diameter along the width direction of the upper mold increases first, and then gradually decreases from the SEN to the narrow wall. Close agreements between the predictions and measurements demonstrate the capability of the MUSIG model in modeling bubbly flow inside the continuous-casting mold.

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The influence of magnesium on the phase transformation and mechanical properties has been investigated by means of dilatometric and microstructural analysis in low carbon microalloyed steel. The thermal simulation experiments were performed on a Gleeble-3800 system equipped with a high-speed deformation dilatometer. The results reveal that, by adding with Mg, the pearlite transformation is delayed, and the pearlite has a scattered distribution even at low cooling rates from 0.1 to 0.5 K/s. It also shows that Mg tends to promote the bainite transformation as a result of the formation of acicular ferrite and granular bainite. Acicular ferrite is attributed to the change of dominant oxide inclusions from inert Al 2 O 3 , to xMgO Á Al 2 O 3 , which serves as an effective nucleant for acicular ferrite. Moreover, bainitic structure obtained by the addition of Mg into the molten steel exhibits the remarkable improvement of toughness and tensile properties.