Transport Behavior of Molten Steel in the Mold at Increased Casting Speed for Φ150 mm Round Billet

To increase the casting speed of φ150 mm round billets, a 3D mathematical model is established to investigate the effects of casting speed, mold parameters, and electromagnetic stirring (M‐EMS) on molten steel flow and heat transfer. The results indicate that higher casting speeds deepen the impingement zone and enlarge the high‐temperature region, leading to thinner shells and higher surface temperatures. When casting speed rises from 2.2 to 2.6 m min −1 , mold level fluctuation amplitude increases from 0.652 to 2.013 mm, and surface flow velocity rises from 0.0247 to 0.0293 m s −1 . Using a submerged entry nozzle (SEN) with a 25 mm diameter shifts the high‐temperature zone upward, accelerates superheat dissipation, and enhances heat transfer to the mold wall. The velocity distribution of molten steel near the solidification front correlates positively with shell growth in the M‐EMS zone. Both shell uniformity and remelting index decrease with increasing current intensity of M‐EMS. Industrial trials on 20# steel show that center porosity and segregation are controlled at grade 0.5 or below. When the superheat exceeds 25 °C, the proportion of billets with center shrinkage cavities below grade 0.5 decreases from 84.62% to 65%, while the occurrence of core defects increases significantly.