(STSI-69)Steel quality and transient flow in tundish casting: features and countermeasuresthrough validated modelling

摘要

In steelmaking, the most critical steps forproduct quality and process regularity are related totransient operations. This especially holds for thetundish, playing the role of steel buffer in the castingmachine. Typical drawbacks can occur especially atladle change and drainage at sequence end. At ladlechange, tundish steel from ‘old’ and ‘new’ ladles has‘intermixed’ composition that can be unacceptableleading rejection and consequent yield affection. Alsosteel cleanliness is affected at ladle change, whenhigh flow rates from the ladle during refilling induceflow ‘short-circuit conditions’ and higher probability ofnon-metallic particles dispersed ‘inclusions’ to bedragged towards the strands. Moreover, at endcasting, vortices formation can induce slagentrapment or inclusion dragging into the strands.With Computational Fluid Dynamics validated tools,the mentioned aspects related to industrial tundishesin current operating conditions were investigated.Focus has been given on long product castingtundishes, where multi-strand V-shaped layoutsmake the process more prone to the unevennessaspects indicated. As a matter of fact, the differentsteel path to reach different strands cause often toohigh temperature differences and different ‘strandcleanliness levels’, with ‘internal’ strands, generally‘hotter’ and less clean, and the ‘peripheral’ ones,slightly ‘colder’ but with less inclusion content.Multiphase models together with advanced meshingtechniques and validated boundary conditions areused to represent tundish refilling and emptyingsteps. Thermal and fluid flow relevant features,together with typical non-metallic inclusions path inthe metal, were achieved suggestingcountermeasures to enhance steel quality.