Effect of Segmented-Roll Electromagnetic Stirring on Solidification Behavior and Central Macrosegregation in Continuously Cast Ultra-Thick Slabs
摘要
To address the challenges of severe central macrosegregation and non-uniform end-of-solidification (EOS) morphology in the continuous casting of 450 mm ultra-thick slabs, a three-dimensional coupled electromagnetic–flow–heat transfer–solute-transport model was established to systematically investigate the effects of segmented-roll electromagnetic stirring configurations and stirring-current intensity on solidification and solute transport. The model was validated using measured magnetic flux density, shell thickness, surface temperature, and carbon segregation data, showing strong predictive reliability. Results indicate that the downward-penetrating jet generated by electromagnetic stirring significantly alters the solidification front and solute distribution. Higher penetration velocities carry latent heat and intensify non-uniform solidification under asymmetric modes. In Case 3, the centrally focused jet slows mid-width solidification, counteracts secondary-cooling-induced undercooling, and greatly improves transverse solidification uniformity. Different stirring modes significantly affect the EOS morphology and macrosegregation characteristics. The left–right EOS offsets reach 0.98 and 1.11 m for Cases 1 and 2, with maximum positive segregation indices of 1.39 and 1.42, respectively. Case 3 achieves uniform solidification with the index reduced to 1.27, whereas Case 4 exhibits the lowest solidification uniformity, with an EOS offset of 5.5 m and an index of 1.53. The stirring-current intensity serves as a critical control parameter. Under Case 3, reducing the current from 350 to 250 A confines the EOS offset within 0.1 m and decreases the central segregation index to 1.233. When the current exceeds 400 A, the index slightly decreases, but the intensified lateral concentration gradient deteriorates the internal-quality uniformity. Overall, under the industrial continuous-casting conditions and parameters considered in this study (slab cross-section: 450 × 2500 mm; casting speed: 0.45 m min−1), adopting Case 3 (dual-converging inflow) with a stirring current of 250 A enables highly uniform control of both solidification and solute distribution, providing quantitative and practical guidance for high-quality continuous casting of ultra-thick slabs.