Abstract: The movement and removal of inclusions inside the mold are mainly influenced by the flow pattern of the molten steel, and the flow pattern also directly determines phenomena such as the heat transfer and solidification during the continuous casting process. In the current study, systematically industrial trials on the macroscopic flow pattern, meniscus speed, and surface level inside a 1 300 mm×230 mm section mold were performed using nail board measurements. The effect of key continuous casting process parameters such as the casting speed, argon flow rate, and immersion depth of the submerged entry nozzle (SEN) on the flow pattern was proposed. Results indicate that the argon flow rate under low casting speeds (≤1.0 m/min) was the primary factor determining the flow pattern inside the mold. Under high casting speeds (≥1.3 m/min), the flow pattern remained as a double roll flow even with the argon flow rate increased to 6-10 L/min. The meniscus speed decreased as the SEN immersion depth increased, but the SEN immersion depth had little effect on the flow pattern. The level fluctuation increased with the increase of the casting speed and argon flow rate. After the argon flow rate increased from 6 L/min to 8 L/min, the proportions of level fluctuations greater than 3 mm at casting speeds of 1.2 m/min and 1.6 m/min increased from 0 to 6.7% and 15.0%, respectively. The critical transition relationship between the different gas volume fraction β_Ar and the steel throughput Q_steel was obtained. The relationship between the critical argon volume fraction and the steel throughput was β_Ar=-4.2+7.8Q_steel when the double roll flow changed to complex flow, and the relationship between the critical argon volume fraction and the steel throughput was β_Ar=-5.6+9.8Q_steel when the complex flow changed to single roll flow.

Key words: flow pattern, meniscus speed, level fluctuation, nail board measurement, slab continuous casting