Pig, Cast, Wrought Iron, Steel
Iron is an ore mined from the ground. After iron is melted, you get pig iron.
In the refining process, if you have 2-4.5% of carbon in the iron, then you have cast iron. Cast iron is great for things like skillets and fire protectors, but not good for buildings. Won't bend. Want to get rid of more carbon.
If you burn off carbon and get .2-2% of carbon, you get wrought iron. You can make more things with this. It's stronger and more flexible.
To get steel, you have to get .1% of carbon in iron.