Steel production:
When iron is
smelted from its ore, it contains more carbon than is desirable. To become
steel, it must be reprocessed to reduce the carbon to the correct amount, at
which point other elements can be added. In the past, steel facilities would
cast the raw steel product into ingots which would be stored until use in
further refinement processes that resulted in the finished product. In modern
facilities, the initial product is close to the final composition and is continuously cast into
long slabs, cut and shaped into bars and extrusions and heat treated to produce
a final product. Today only a small fraction is cast into ingots.
Approximately 96% of steel is continuously cast, while only 4% is produced as
ingots.[14]
The ingots
are then heated in a soaking pit and hot rolled into
slabs, billets, or blooms. Slabs are hot or cold
rolled into sheet metal or plates. Billets are hot or cold
rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural
steel, such as I-beams and rails.
In modern steel mills these processes often occur in one assembly
line, with ore coming in and finished steel products coming out.[15] Sometimes
after a steel's final rolling it is heat treated for strength, however this is
relatively rare.[16]