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Processes
- Ferrous (Iron / Steel): Degassing / Refining
 Ladle
Refining
A number of processes are often used to refine the molten steel in a
ladle after it leaves the BOF or EAF prior to casting (see the diagram on the
right). Ladle refining processes include Argon Oxygen Decarburization (AOD), ladle
metallurgy, vacuum arc re-melting, and vacuum degassing. Processes selected are
based on the desired metallurgy and purity. In ladle metallurgy, alloys are added
to the molten steel, which is then reheated to produce the desired metallurgy.
In vacuum degassing, molten steel is subjected to a vacuum for de-oxidation, degassing
(hydrogen removal), de-carburization, and removal of other impurities from the
steel.
Ladle refining
is generally performed by electric arc re-heating. The molten metal bath is stirred
throughout the process to provide for thermal and chemical homogenization and
to accelerate metallurgical reactions. Stirring is provided by inert gas introduced
near the bottom of the ladle using porous plugs, tuyeres, or lances. Gas injected
from above using water-cooled, refractory-coated metal lances is considered safer
than porous plugs or tuyeres; but maintenance is high and heat efficiency reduced.
Because of
the high temperatures, erosion from the stirred bath, and high corrosiveness of
the metallurgical slag, high-alumina and magnesia-based (slag line) castable refractories
are preferred for ladle linings. Still, life remains short (30 to 50 heats). Ladles
are continuously repaired or re-lined. After re-lining, drying is performed. Also
ladle heating (usually natural gas or oxy-fuel burner) is used to pre-heat ladles
prior to filling with molten metal.
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