Steels that protect against external threats from incoming projectiles – bullets, blast debris, etc – are called armour protection, or ‘ballistic protection’ steels.
The constituent chemicals in such steels are iron (Fe) and Carbon (C). The ‘hardness’ required is a result of the mix of varying amounts of carbon and another alloying element like chromium, nickel, or molybdenum, a combination of which is then put through a specialised heat treatment process.
The heat treatment process can be either...