Iron Pig iron is cast iron high (over 4%) in carbon, liable to break or crack under shock. Wrought iron comes from burning off some of the carbon in pig iron and working it (hammering, drilling, forging) to make it tougher against shock, more resistant to corrosion. It combines strength with malleability. Steel has even less carbon than wrought iron and is more flexible and stronger, and takes more stress. Layered steel, invented in Nurenberg, extra-strong blades are produced by folding cementation steel edge over itself, re-hammering and refolding and re-hammering it repeatedly as in making Samurai swords. Crucible steel was invented by Benjamin Huntsman in 1740 and especially serves the making of springs.