Secondary cooling dynamic control and internal quality optimization of SWRH82B continuous casting billet based on precise control of solidification structure

: Solidification structures and center segregation often exhibit considerable instability during the continuous casting of high-carbon steel billets. To address these issues, this study proposes a novel secondary-cooling strategy based on a solidification index. Industrial trials combined with heat-transfer simulations were conducted to establish correlations among temperature gradient, solidification rate, and secondary dendrite arm spacing (SDAS). A solidification index incorporating these parameters was then developed as the dynamic control target for individual cooling zones. The results indicate that the conventional static water-distribution mode led to pronounced fluctuations in the solidification structure of the billets. Under static cooling conditions, the center segregation index exhibited considerable scatter, with its standard deviation reaching a maximum value of 0.127 at a casting speed of 1.30 m/min. After applying the solidification-index-based water distribution control strategy, the local solidification state of the billets was markedly stabilized under different casting speeds. The mean center segregation indices at casting speeds of 1.30, 1.40, 1.50, and 1.60 m/min were 1.10, 1.10, 1.10, and 1.11, respectively, and the maximum standard deviation was reduced to 0.042. Thus, the developed secondary-cooling control strategy based on the solidification index can effectively suppress solidification disturbances induced by casting-speed fluctuations, thereby improving the consistency of internal billet quality.