The principal consumables employed in steel production
are iron ore, coal, scrap metal and electrical energy. The
importance of each of these consumables depends upon the
technological processes adopted at each mill. In a classic
integrated mill, coal and iron ore are the main consumables. In semi-integrated mills, scrap iron is the mainstay.
An integrated mill comprises four basic operations –
reduction, refining, solidification, and rolling – to convert iron ore into semi-finished or finished (rolled) steel products.
• Reduction The objective is to convert iron ore – naturally occurring in the form of ferrous oxide – into pig iron.
In this operation, a coker converts coal into coke that is
then combined with iron ore in a blast furnace to produce
molten pig iron.
• Refining Converting pig iron into steel is called refining. The most common technology is the basic oxygen
furnace (BOF) which injects oxygen into the molten metal
to adjust the carbon content and reduce contaminants
such as sulfur, nitrogen, and oxygen. Alloying elements
needed to obtain desired chemical and mechanical
properties are also added during refining.
• Solidification The most widely employed method of
solidification is continuous casting, developed in the
1950s to replace conventional ingot casting.
• Rolling This final phase of integrated production
converts semi-finished products such as slabs, blooms,
and billets into finished products.
In addition to iron ore and coal, integrated mills use
limestone in blast furnaces and oxygen in converters.
Semi-integrated mills operate in three phases – refining,
solidification, and rolling – by using scrap iron as the basic feedstock. At these mills, liquefaction of the metallic charge is carried out in electric arc furnaces with electricity as the main energy source. Since scrap iron already contains carbon, there is no need to add carbon by using coal or coke, eliminating the need for blast...