Steel

[Hoofhurr]

Steel has less than 2% carbon. Probably 1%. I doubt they sprinkle additional carbon on the iron but a quick search shows that coke and limestone are often used in the making of steel. I'm not sure what coke is (can't remember) but limestone is primarily CaC03 (calcium carbonate) which is a pervasive source of carbon on earth. It's the main molecule in chitin, shells of shellfish, coral, etc. a very strong substance in it's own right. The aforementioned is not really blacksmithing but modern steel manufacturing.