Plain steels are alloys of iron and carbon in which the carbon content does not exceed about 2.1%. The carbon is present as cementite, usually as a component of pearlite. Low-carbon steels contain from 0.09% carbon to 0.2% and are soft – the same composition range as bloomery iron. Medium carbon steels contain 0.2-0.4% carbon and high carbon steels more than 0.4%. Modern alloy steels do not necessarily contain carbon in more than trace amounts, but are alloys of iron and some other elements.