Fluid-Flow and Stress Analysis of Steel Continuous Casting

Brian Thomas, University of Illinois at Urbana-Champaign

Usage Details

Brian Thomas, Seid Koric, Ahmed Taha, Lance Hibbeler, Rui Liu, Kai Jin, Seong-Mook Cho, Hyunjin Yang, Matthew Zappulla, Thierry Coupez, Xiaolu Yan

Continuous casting is an important commercial process to solidify molten metal into semi-finished billets, blooms, or slabs for subsequent rolling. It produces over 95 percent of steel in the world today, so small improvements have huge impact. Many defects in final steel products originate in this process. Hot molten steel flows through the ladle, tundish, upper tundish nozzle, slide gate, submerged entry nozzle (SEN) and into the mold. The metal starts cooling against the water-cooled copper mold to form a solidified shell. The shell acts as a container for the molten steel after it is withdrawn from the bottom of the mold. Defects arise due to problems with the flow pattern, such as excessive surface-level fluctuations from excessive velocity and turbulence, or meniscus freezing from insufficient surface flow. Argon gas is often injected into the nozzle to prevent clogging and to help carry away inclusions, in order to improve the steel quality, and also to control the flow. The molten steel flow is also controlled by the nozzle geometry and by Electromagnetic Braking. A static magnetic field is generated by applying a direct current to coils, and since molten steel is a conductor, a current field is generated in the fluid, which causes a Lorentz force that affects flow in the mold cavity. Usually this system will slow and diffuse the jet exiting the SEN, which decreases meniscus velocity and fluctuations in the meniscus profile. The solidifying shell is very brittle, and if subjected to excessive mechanical or thermal distortion, can form internal cracks, called hot tears. These cracks can lead to oxidized slivers, macrosegregation, and other defects in the final product, or to expensive and dangerous breakouts, where the solidifying shell tears open to spill molten metal over the casting machine and plant floor. This project aims to improve understanding of this complex process using comprehensive computational models, and to apply those models to find operating conditions to improve the process. Specifically, this project consists of 1) two-way coupled multiphase fluid flow (steel and Ar gas) simulation in the SEN and mold region under the influence of electromagnetic fields and 2) stress analysis of the solidifying steel, including a microscale model that resolves the shape of the evolving dendritic solidification front.

http://ccc.illinois.edu/projects.html