When was steel discovered?
The production of iron by humans began probably sometime after 2000 BCE in south-west or south-central Asia, perhaps in the Caucasus region.
The first steel produced were cast iron, an alloy of iron and carbon with a carbon content higher than approx 2%. This kind of material is very hard but also brittle. The steel that we use today is the result of a continuous improvement in the making of iron alloys.
The mass-production of cheap steel only became possible after the introduction of the Bessemer process, named after its brilliant inventor, the British metallurgist Sir Henry Bessemer (1813-1898).
source
http://www.anselm.edu/homepage/dbanach/h-carnegie-steel.htm
http://42explore.com/ironsteel.htm
http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_5/advanced/t5_1_4.html