A steel alloy with a major iron component, but without the other metals required to make it a stainless steel. Most alloy steels can be successfully cut with CO2 lasers using oxygen and nitrogen.

A steel to which one or more alloying elements other than carbon and the commonly accepted amounts of manganese, silicon, sulfur, and phosphorus have been deliberately added (e.g. chromium, nickel, molybdenum) to achieve a particular physical property.