An iron-base alloy, malleable in some temperature range as initially cast, containing manganese, usually carbon, and often other alloying elements. In carbon steel and low-alloy steel, the maximum carbon is about 2.0%; in high-alloy steel, about 2.5%. The dividing line between low-alloy and high-alloy is generally regarded as being at about 5% metallic alloying elements. Steel is to be differentiated from two general classes of “irons”: the cast irons, on the high-carbon side, and the relatively pure irons such as ingot iron, carbonyl iron , and electrolytic iron, on the low-carbon side. In some steels containing extremely low carbon, the manganese content is the principal differentiating factor, steel usually containing at least 0.25%; ingot iron contains considerably less.