Abstract
Ultra low carbon (ULC) steel grades for packaging or automotive industry are produced in ARCELOR group either by RH or Vacuum Tank Degasser (VTD) routes. Industrial Operations Research Center (IORC : ex IRSID) has developed kinetic models of decarburization, based on the physical description of the different reaction sites for each type of reactor. These models have been largely used in past years to adjust the operating conditions during decarburization. To go further, the computational fluid dynamics Fluent software, used to characterize the ladle hydrodynamics in terms of velocity and turbulence of the liquid steel flows, was coupled to the kinetic models in order to better assess the effect of metal liquid flow on the performances of decarburization. Numerical computations have been performed in such a way, from industrial configuration and running conditions. Computations show that, whatever the reactor-type, heterogeneity in carbon concentration is generated during the vacuum decarburization treatments of ULC steels. The highest differences become apparent at the beginning of the treatment and can reach up to 80 ppm in RH, then progressively decrease. Heterogeneity in concentration still exists after 15 or 20 minutes for a classical treatment time. The maximum differences between poor and rich areas in ladle vary from 5 ppm to 10 ppm, depending on stirring and fluid flow conditions. They are more pronounced in RH than in VTD and affect a larger volume of metal. But, in both cases, heterogeneity completely disappears 3 to 4 minutes after killing. These numerical results are consistent with specific measurements, carried out on an industrial installation. A finer description of the RH reactor from a chemical point of view, obtained from residence time distribution computations, largely improves the numerical results and gives some complementary explanations on the RH working.
Published Version
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