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Jean-Francois Domgin and Pascal Gardin, IRSID, ARCELOR, Maizieres
les Metz, France
A vacuum degasser, showing the two snorkels at the bottom
The manufacture of steel products is a complex process. Demands for improved
product quality have led research centers dedicated to the steel industry
to try to better understand all phases of the manufacturing process. Improved
measurement techniques and numerical simulation are two of the many areas
where the efforts have been directed. At ARCELOR, Europe’s largest
steel producer and one of the leading steel producers in the world, FLUENT
has been used for numerical simulations of various steel production processes,
many of which involve multiphase flow. The work has been carried out at
IRSID, the company’s central research organization.
Fluid velocity for a water scale model of a ladle – FLUENT results
compared to experimental data
Purging in a ladle
Steel ladles are used for the transport of molten steel to product forming
stations, temporary holding prior to the forming operation, chemical
addition, and purging. Chemical addition is done to give the steel the
required properties, and purging, usually with jets of argon gas, is
done to homogenize the mixture, both thermally and chemically. It is
also used to promote the upward motion of inclusions, undesired particulate
matter that develops when certain substances are added. A slag, or layer
of impurities, forms on top of the molten metal, and by transporting
the inclusions to the slag layer, they can be removed with the slag prior
to product forming. Both the discrete phase model (DPM) and the Eulerian
multiphase model have been used to simulate the purging process, and results
are in good agreement with PIV measurements on water scale models.
Decarburization in a vacuum degasser
Vacuum degassing is another process that is used to purify molten steel.
The steel is drawn up from the ladle through a snorkel into a vessel held
at high temperature and low pressure, an environment that helps remove
unwanted carbon and dilute gas from the melt. The upward flow is driven
by the injection of argon or oxygen gas. The steel is returned to the
ladle through another snorkel after the degassing and decarburization
have occurred. FLUENT has been used at ARCELOR to simulate the flow field
induced by the gas injections, and to study the tracks of carbon and gas
particles in the degasser.
Behavior of inclusions injected into a continuous casting mold
Cleanliness in continuous casting
The continuous casting process has been studied carefully because it
is critical to the final product quality. Casting is most successful if
there is a gradual yet steady growth of the solidified shell, with few
or no inclusions trapped in the material. An understanding of the flow
patterns in the casting mold is therefore very important, since it is
an indicator of the inclusion behavior and can be used to evaluate the
effects of argon injection mechanisms and electromagnetic actuators. The
effect of argon injection can be simulated using either the DPM or Eulerian
multiphase model. Inclusions, on the other hand, are best modeled using
the DPM, since it more conveniently allows for a range of particle sizes
and densities. Electromagnetic fields have been incorporated into the
FLUENT simulations using a module developed at the EPM-MADYLAM Laboratory
in Grenoble. The module includes a Lorentz force term in the momentum
equations for the melt and particles that has been found to contribute
not only to the flow patterns and particle trajectories, but to the deformation
of the free surface as well.
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