Crucible Steel

Iron can be produced on the Moon in a number of ways. Pure iron is not a particularly strong metal. It can be softer than aluminum. It will suffice for low stress parts but for things like regolith mining machines we will want strong steel. On Earth, steel is made by burning excess carbon out of cast iron with oxygen. On the Moon, we will want to add carbon to iron to convert it to steel. It is possible to take iron rods or bars and pack them in carbon powder, or take plates of iron and sandwich carbon powder between them, and bring the iron to red heat in a furnace for several days while the carbon dissolves into the iron. This old and outdated method for making steel might find new life on the Moon. Life support systems will probably come first when it comes to lunar carbon supplies, but since steel commonly contains only 0.2% to 1.5% carbon the demand for carbon by steel makers might not be intolerable. Carbon is used to harden steel on Earth because it is cheap on Earth. Various other alloying elements which can harden steel are expensive. What the cost to benefit ration for various alloying elements on the moon will be is yet to be determined.