Analysis of solidification shrinkage of hypoperitectic steel in the mold during ultra-high-speed continuous casting

In ultra-high-speed billet continuous casting, achieving a mold geometry that accommodates the shrinkage behavior of the solidifying shell is essential, as variations in shrinkage rate challenge the applicability of conventional taper designs. This study systematically investigates the thermo-mechanical stress–strain response of a hypoperitectic steel shell under casting speeds ranging from 3.0 to 6.5 m/min and superheats of 10-30 K, based on a fully coupled thermo-mechanical model. The results indicate a pronounced reduction in both stress and shrinkage at ultra-high casting speeds. When the casting speed increases to 6.5 m/min, the maximum corner stress and equivalent strain decrease by 63.01% and 18.58%, respectively, compared with those at 3.0 m/min, while corner shrinkage is reduced by 41.84%. In contrast, variations in superheat exert a negligible influence on the stress–strain evolution, confirming that casting speed is the dominant governing parameter. These findings demonstrate that mold taper design must be speed-dependent, as shell contraction diminishes with increasing casting speed. Spatial analysis further reveals that the most severe contraction occurs in the vicinity of the meniscus, whereas the upper-middle region of the mold exhibits an outward expansion followed by inward contraction. The quantified solidification shrinkage characteristics obtained in this study provide a robust theoretical basis for optimizing mold taper design under ultra-high-speed conditions. Overall, these results elucidate the thermo-mechanical behavior of the shell and establish a scientific foundation for speed-dependent mold taper optimization, offering important guidance for industrial ultra-high-speed billet casting applications.