It primarily refers to steel with a carbon content of less than 2.11% and without the addition of special alloying elements; it is sometimes also known as ordinary carbon steel or simply carbon steel. It is defined as an iron-carbon alloy with a carbon content below 2.11%. In addition to carbon, carbon steel typically contains small amounts of silicon, manganese, sulfur, and phosphorus.
Carbon steels can be classified into carbon structural steels, carbon tool steels, and free-cutting structural steels.