Having addressed surface pinhole issues, we now turn our attention to the most stubborn internal quality defect of cast slabs: centerline segregation. This is a phenomenon that is almost unavoidable in continuous casting but must be strictly controlled. Centerline segregation manifests as an enrichment of elements like carbon, phosphorus, and sulfur in the central region of the slab thickness. During subsequent rolling, this segregation leads to banded structures and hard phases, severely damaging the steel's low-temperature toughness, hydrogen-induced cracking (HIC) resistance, and weldability. For products like line pipe steel, pressure vessel steel, and heavy plates, centerline segregation is a key indicator determining whether they can pass stringent certifications. How can you effectively control centerline segregation in continuous casting slabs and minimize its harmful effects? Wuxi WeiDa Cored Wire Co.,Ltd provides comprehensive solutions based on soft reduction technology and electromagnetic stirring optimization.
The Formation Mechanism of Centerline Segregation: The "Enrichment Effect" at the Solidification End
The solidification of a continuous casting slab progresses from the surface to the center. In the final stages of solidification, "bridging" between dendrites traps the remaining enriched solutes (carbon, phosphorus, sulfur, manganese, etc.) in the central region. This solute redistribution mechanism leads to centerline segregation. The severity of segregation depends on solidification speed, steel superheat, secondary cooling intensity, and slab cross-sectional dimensions. Traditional solutions – such as reducing superheat or increasing cooling intensity – while effective, are often constrained by the need to balance productivity and quality control.
Our Solution: Synergy of Electromagnetic Stirring and Dynamic Soft Reduction
Wuxi WeiDa, although not a manufacturer of continuous casting equipment, leverages its deep understanding of metallurgical processes to help you maximize the effectiveness of your existing equipment and provide auxiliary optimization through cored wire technology. First, optimize electromagnetic stirring (EMS) parameters. Mold electromagnetic stirring (M-EMS) and final electromagnetic stirring (F-EMS) are core methods for reducing centerline segregation. We recommend adjusting stirring intensity and frequency based on your slab cross-section and steel grade to break up columnar crystals and expand the equiaxed crystal zone, thereby reducing "bridging."
Second, implement dynamic soft reduction technology. Applying pressure at the solidification end of the slab, mechanical squeezing compensates for solidification shrinkage and "pushes" the enriched solutes back into the liquid phase, thus reducing centerline segregation. Our technical team can help you optimize key parameters like reduction amount and reduction zone for dynamic soft reduction, developing differentiated strategies for different steel grades (e.g., high-carbon steel, peritectic steel, line pipe steel).
Third, perform "micro" control via cored wire technology. Although cored wire cannot directly control the solidification process, it can mitigate the impact of segregation by optimizing the steel's "intrinsic" quality:
•Rare earth treatment: As mentioned previously, rare earths (RE) can modify MnS inclusions. Even if segregation persists in the central region, globular rare earth sulfides are far less harmful to toughness than elongated MnS.
•Microalloying for grain refinement: By feeding titanium, niobium, and vanadium cored wires, fine carbonitride particles form during solidification. These particles act as heterogeneous nucleation sites, promoting equiaxed crystal formation and indirectly reducing segregation.
•Sulfide morphology control: Thorough calcium treatment can modify MnS into globular CaS or Ca-S-O complexes, significantly reducing the severity of banded structures.
Fourth, optimize the secondary cooling regime. Inappropriate secondary cooling can exacerbate centerline segregation. We provide optimization recommendations for dynamic secondary cooling models, adjusting water spray rates in different cooling zones in real-time based on your casting speed and steel grade, ensuring uniform surface temperature drop and avoiding reheating that could worsen centerline segregation.
Systematic Control to Meet the Most Stringent Standards
For products that must meet stringent requirements like drop weight tear testing (DWTT) and hydrogen-induced cracking (HIC) testing, controlling centerline segregation is critical. Wuxi WeiDa's service is not just about providing products; it's about helping you establish a full-process control system from steel composition to solidification end. By organically combining electromagnetic stirring, soft reduction, and cored wire technology, you can significantly reduce centerline segregation ratings and produce high-quality slabs meeting the requirements of X70, X80, and even higher-grade line pipe steels.
Want to master the core technologies for centerline segregation control in continuous casting slabs? Need a guide for optimizing soft reduction process parameters? Please visit https://www.weidamaterials.com/ to engage in an in-depth discussion with our continuous casting process experts.