Central segregation—a common defect in continuous casting—significantly impacts the homogeneity and mechanical properties of steel products. Addressing this issue requires a holistic approach, combining modern process controls, innovative equipment design, and strict operational protocols. Below are key strategies to minimize central segregation, enhance slab quality, and ensure final product integrity.
Enhancing Molten Steel Purity
Improving the purity of molten steel is a foundational step in reducing central segregation. Effective filtration systems, such as foam ceramic filters or fiberglass filters, can substantially reduce non-metallic inclusions. These filters operate through mechanisms like direct interception, inertial collision, and diffusion deposition, lowering the total oxygen content by 30–50% and minimizing stress concentration sites that exacerbate segregation . For high-carbon steel grades (e.g., tire cord steel), precise control of composition and superheat (e.g., tundish temperature at 1483–1503°C) further limits segregative elements like sulfur and phosphorus .
Optimized Soft Reduction Techniques
Dynamic soft reduction (DSR) is critical in the final solidification stage. By applying mechanical pressure in regions where the solid fraction reaches 0.35–1.0, DSR counteracts shrinkage-induced flows of solute-rich liquid. Key parameters include:
Reduction amount: Total reduction of 10.0–15.5 mm, with single-frame reductions ≤4.0 mm .
Solid-phase rate control: Reduction is adjusted based on real-time solid fraction (e.g., 3.5 mm at fs = 0.63–0.67) to suppress carbon segregation, achieving a segregation index of 0.96–1.05 .
Roll geometry: Convex-shaped rolls improve pressure distribution across the slab width, reducing edge stress and focusing compression on the central zone .
Bulging Control Through Roll Design
Bulging between rolls exacerbates segregation by inducing internal flows. Solutions include:
Compact roll arrangements: Smaller diameters and reduced pitch distances curb unsteady bulging by up to 50% .
Rigid multi-section rollers: These prevent deformation under high thermal loads, ensuring alignment accuracy ≤1 mm .
Advanced simulations: Tools like Fourier transform-based models optimize roll geometry pre-installation, enhancing stability at high casting speeds .
Precision Control of Temperature and Casting Speed
Regulating thermal parameters minimizes the mushy zone width, a key factor in segregation:
Low superheat practices: For medium/high-carbon steels, a tundish superheat of 250–300°C narrows the solidification front .
Secondary cooling uniformity: Water ratio of 0.18–0.28 L/kg and surface temperature maintenance at 780–950°C prevent reheating cracks and ensure steady solidification .
Casting speed modulation: Speeds of 0.65–0.80 m/min for blooms align with reduction zones, avoiding premature solidification endpoints .
Supplementary Segregation-Reduction Measures
Electromagnetic stirring (EMS): Applying M-EMS (e.g., 500 A, 2.4 Hz) refines dendrites and promotes equiaxed crystals, reducing segregation channels .
Shrinkage cavity management: Mechanical reduction after full solidification (fs = 1.0) counters thermal shrinkage voids, a common post-solidification defect .
Slag removal: Rapid inclusion extraction prevents nozzle clogging and shell thinning, safeguarding against surface defects that indirectly affect internal homogeneity .
Conclusion
Central segregation control demands integrated strategies—from steel purity management and advanced reduction protocols to robust equipment design. By coupling dynamic soft reduction with precise thermal-mechanical controls, producers can achieve segregation indices ≤1.05 and significantly improve product durability, especially in high-carbon steels for critical applications like tire cords or heavy plates .
