What are garage door springs made of?

Most springs are made of Oil-tempered steel, and there are some made of galvanized steel. The best ones are oil tempered because the are hot drawn wire and there for don't lose their tension like the cold drawn galvanized wire. Oil tempered springs do require oil of some kind to keep rust off. Use 3 and 1 oil or motor oil works well, just do not use a penetrating oil like wd-40.