In traditional metallurgical furnace use graphite electrode, the
electric arc furnace refining operations refer to removing the
phosphorus, sulfur, aluminium, silicon, manganese and carbon from steel.
In recent times, dissolved gases, especially hydrogen and nitrogen,
have been recognized as a concern. Traditionally, refining operations
were carried out following meltdown i.e. once a flat bath was achieved.
The availability of oxygen determines this refining reaction. At the end
of melting, oxygen is sprayed to reduce the carbon content in the bath
to the level required for tapping. Most compounds to be removed during
the refining process have a higher affinity for oxygen than carbon.
Therefore, oxygen will preferentially react with these elements to form
oxides, which will float out of the steel and enter the slag.

In
modern electric arc furnace operations, especially those that operate
with molten steel and residual slag "hot heel", such as metallurgical
furnace use graphite electrode for metal smelting, most of the heat may
blow oxygen into the molten pool. As a result, some smelting and
refining operations are carried out simultaneously.

Phosphorus
and sulfur are usually present in the furnace charge at a concentration
higher than that normally allowed in steel, and therefore must be
removed. Unfortunately the conditions favorable for removing phosphorus
are the opposite of those promoting the removal of sulfur. Therefore,
once these materials are pushed into the slag stage, they may be reduced
to steel. Phosphorus retention in the slag is a function of the molten
pool temperature, slag basicity and FeO content in the slag. At higher
temperatures or lower FeO content, phosphorus will be returned from the
slag to the molten pool. Phosphorus removal is usually performed as
early as possible during heating. Hot heel exercises are very good for
phosphorus removal, because oxygen can be sprayed into the molten pool
when the oxygen temperature is very low. In the early stages of heating,
the slag will contain the high FeO content brought about by the
previous heating, thus helping to remove phosphorus. Blast furnace slag
alkalinity (that is, high lime content) is also conducive to phosphorus
removal, but care must be taken not to let the slag be saturated with
lime. This will lead to an increase in slag viscosity, which will make
the slag less effective. Sometimes fluorspar is added to help fluidize
the slag. Stirring the bath with inert gas is also beneficial because it
can renew the slag/metal interface, thereby improving the reaction
kinetics.

Generally, if a particular steel grade requires
low phosphorus content, scrap should be selected to make it low in
melting. The partition of phosphorus in the slag to phosphorus in the
bath ranges from 5 to 15. Phosphorus in EAF is reduced by 20% to 50%.

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