| Mold powder entrapment with high casting speed is a technical problem in the continuous casting of steel. The fluid steel flow and steel/slag interface behavior become more complex and the control on them are also more difficult, especially blowing argon gas from the SEN (Submerged Entry Nozzle). Therefore, it is highly emphasized to reveal steel/slag interfacial behavior and the influences of operating parameters on it. On account of the present research on the steel/slag interface and powder entrapment phenomena in the mold rarely involving high casting speed and blowing argon gas simultaneously, as well as the conditions of maintaining a double-recirculation flow pattern (DRFP) in the mold is still inexplicit, the fluid steel flow pattern and interfacial behavior of fluid steel and molten slag in a slab continuous casting mold with both high casting speed and blowing argon gas were investigated by mathematical and physical simulations in this paper. The main contents and results obtained are as follows:(1) The physical model for the mold has been established according to similarity principle. Water/oil interfacial movement and entrainment phenomena with and without blowing gas have been observed and the critical air flowrate (to maintain DRFP) have been achieved under the different casting conditions in mold model. The results of physical model are greatly essential to validate and perfect the numerical model.(2) The mathematical model to simulate the interfacial behavior between fluid steel and molten slag layer in a slab continuous casting mold with blowing argon gas has been developed by the conservation equations for mass continuity and momentum, turbulence model, Lagrange multi-phase model, VOF (Volume of Fluid) method, and CSF (Continuum Surface Force) model considering the steel/slag interfacial tension. Steel/slag interfacial transient behavior with high casting speed and blowing argon gas and the quantitative relationship between operating parameters and interfacial behavior have been described and revealed basing on the prediction results validated by the water model. In addition, the countermeasures to restrain the interface fluctuation and avoid the emulsification phenomena of the molten slag have been presented. The results show that: ①Steel/slag interface fluctuates strongly and the interface velocity increases significantly along with raising the casting speed, moreover, the maximum interface velocity is found about 1/3 of the mold width to the narrow face. Within the range of casting speed from 1.2 m/min to 2.2 m/min, the maximum wave height and the largest interface velocity increase by 8.5 mm and 0.087 m/s, respectively. Mold width has a little impact on the maximum wave height and interface velocity; nevertheless, increasing the penetration depth and downward port degree of SEN can effectively restrain interfacial oscillations and decrease the whole interface velocity. The maximum wave height and interface velocity decrease by 5.2 mm and 0.052 m/s, respectively, with the submergence depth added from 120 mm to 220 mm. Furthermore, the downward port degree increasing every 5°, the above two values approximately reduce by 3.7 mm and 0.05m/s, respectively. Molten slag viscosity has hardly influence on interfacial profile of steel and slag, however, the maximum steel/slag interface velocity decreases with increasing molten slag viscosity, and it reduces by 0.059 m/s with molten slag viscosity increasing from 0.02 kg/(m·s) to 0.50 kg/(m·s).②Blowing argon gas can reduce the steel/slag interface velocity of the region with the bubbles floating up, it also lead to wave height increasing remarkably at the same time. For a giving fluid steel mass flowrate of 3.20 ton/min (corresponding to the casting speed of 1.8 m/min), the upper circulation region is significantly suppressed with argon gas flowrate of 4.5 L/min, while the flow pattern of fluid steel changes to single recirculation, and the steel/slag interface fluctuates evidently with argon gas flowrate increasing to 9.0 L/min. The maximum wave height increases by 7.7 mm, nevertheless, the maxim interface velocity decreases by 0.111 m/s from the mold without argon gas to the flowrate of 9.0 L/min. In the process of the fluid steel mass flowrate increasing from 2.13 ton/min (corresponding to the casting speed of 1.2 m/min) to 3.91 ton/min (corresponding to the casting speed of 2.2 m/min) with the argon gas flowrate of 4.5 L/min, the upper recirculation appears again, and steel/slag interface entrainment are weakened, moreover, the maximum wave height is lowered by 2.4 mm. Fluid steel flow pattern and interfacial behavior of steel and slag strongly depend on the fluid steel mass flowrate (casting speed×mold width) and the argon gas flowrate, so it is very important that the argon gas flowrate matches the fluid steel mass flowrate for ensuring the DRFP and the even steel/slag interface.③Increasing the submergence depth of SEN is useful to reduce interfacial oscillations in the mold. The maximum wave height and fluctuation range of steel/slag interface both reduce by 3.5 mm when the submergence depth increasing from 120 mm to 220mm, moreover, bubble size also has a remarkable influence on the interfacial behavior of fluid steel and molten slag.(3) The condition for the formation of the DRFP in a slab continuous casting mold with blowing argon gas has been quantitively described using the Lagrange multi-phase flow model, and the operating parameters for maintaining the DRFP have been presented. The flow pattern of fluid steel changes from double recirculation to single recirculation with the fluid steel mass flowrate of 2.84 ton/min (corresponding to the casting speed of 1.6 m/min) and argon gas flowrate of 6.0 L/min in this study condition. The critical argon gas flowrate increases with the increasing fluid steel mass flowrate, and the range of argon gas flowrate for keeping the DRFP will be enlarged by decreasing the mold width and increasing the submergence depth of SEN as the fluid steel mass flowrate is more than 2.5 ton/min, nevertheless, the port downward angle of SEN has little effect on it. However, the operation parameters have no significant influence on it as the fluid steel mass flowrate is below 2.5 ton/min.
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