Steel is a metal alloy consisting mostly (95%) of iron. Its carbon content varies between 0.01% and 2.06%. The higher this value, the harder – but more brittle – the steel. Steel can be treated with heat (annealing, tempering, etc.), alloyed (with other metals or non-metallic substances), or shaped (forging, drawing, rolling).
The production of specially hardened iron dates back to the 1st century bce. Iron Age smelting techniques in domed kilns 1.5-2 m tall produced sponge iron (direct-reduce…