The iron that emerges from the blast furnace contains 4 - 4.5 wt%
carbon and other impurities which makes the metal too brittle for most
engineering applications.
The Basic Oxygen Steelmaking (BOS) process takes this
liquid iron plus recycled scrap steel, and reduces the carbon
content to between 0 and 1.5% by blowing oxygen through the metal in
a "converter".
Alternatively, the Electric Arc Furnace (EAF) is used to
remelt scrap iron and steel.
Secondary steelmaking processes are then applied to make fine
adjustments to the steel composition.