Numerical Simulation of Solute Transport Behavior During the Grade Transition of Round Billet Continuous Casting

Grade transitions in continuous casting can significantly improve casting machine productivity and reduce production costs. Accurate prediction of the mixing zone length is essential. A two‐dimensional transient model for grade transition in continuous casting is developed by integrating fluid flow, thermosolute transfer, and solidification. The model predicts the mixing zone changes at various casting speeds. The results indicate that positive segregation of the old steel (Q355NE) occurred at the billet's center, while the maximum negative segregation appears in the billet shell region. The process involves pausing the solidification of the grade transition connectors and the billet shell before casting is resumed with the introduction of a new steel (42CrMo). The extent of the mixing zone is determined by the carbon concentration at the centerline and 1/2 R. Numerical simulations of the temperature field and solute distribution trends are closely aligned with experimental data, validating the accuracy of the solute transport model. Although excessively slow speeds may disrupt the straightening process, reducing the casting speed and decreasing the mixing zone size. This study result provides theoretical guidance for the grade transition in large section round billet continuous casting.