Steel is the most commonly used metal on Oerth, and is an alloy of Iron and carbon in various amounts, and sometimes small amounts of other metals to alter its properties.
Carbon steel is one of the most commonly used variants of steel, due to it being easy to produce en-masse, as it is just a blend of iron with large amounts of coal carbon. It is hard and good for making blades, but depending on the quality can occasionally be quite brittle in places.