S (Fe), better known as iron, and carbon (C). Iron is the main component in most types of steel. Steel is classified in three grades: – Unalloyed steel (containing up to 1% alloy elements). This type of steel is also termed mild steel, carbon steel and carbon manganese steel. – Low alloy steel (containing 1–5% alloy elements). – High alloy steel (containing more then 5% alloy elements).
Alloy elements are metals such as manganese (Mn), silicon (Si), chrome (Cr), nickel (Ni), molybdenum (Mo). Carbon is not an alloy element. Unalloyed steel Often referred to as carbon steel, mild steel or black steel. On board a ship, unalloyed steel will usually be found in the superstructure. Angle iron, flat iron and rod iron are usually in unalloyed steel. A common composition of this type of steel is as follows (%): C Mn Si 0.18 1.30 0.40 Al P S 0.057 0.02 0.03 Fe C M.