Steel is generally referred to as "carbon" steel, because it is a combination of iron atoms interspersed with carbon atoms. The overall structure of steel is a crystalline lattice comprising both elements, which provides steel with a combination of strength and ductility. Adding other alloys such as chromium and aluminum gives steel more properties such as protection against rust and lighter weight and durability.
Plain, or "carbon," steel is an alloy metal of iron and carbon. In order to produce steel, iron must first be smelted from ore in a furnace. Impurities that were present in the iron ore must be extracted. The iron that results generally still contains a carbon content which is too high for workable steel. The metal must be smelted further to reduce the carbon content to between 0.2 to 1.5 percent. Depending on how the steel will be used, the metal is subjected to additional tempering.
Carbon steel strength is due to its crystalline structure. Groups of iron and carbon atoms are arranged in a lattice, with the carbon atoms preventing the iron atoms from slipping over each other, in effect making the steel rigid. The addition of an alloy such as titanium or manganese strengthens this structure by adding different atomic sizes to the lattice. This reinforces steel's rigidity by further impeding molecular movement when the metal is it is subjected to stresses.
Steel alloys are made by combining elements during the smelting process when the iron is still molten. Other metals such as chromium, aluminum or titanium are added at this stage. Alloys have properties which make them more durable than simple carbon steel. This is due to the structural properties of how iron, carbon and other elements interact. Other metals are added to give carbon steel specific enhancements, such as extra strength, high temperature tolerance, or more malleability.
Plain carbon steel has a wide variety of applications, but must be tempered at specific heat conditions to give the steel a combination of ductility and durability. Alloying steel has advantages, such as protection against corrosion when steel is mixed with chromium. Other elements such as titanium, nickel and boron further harden steel. Weldability can be increased by adding sulfur or lead, whereas carbon steel by itself is more sensitive to cracking when being welded.
"Galvanized" steel is produced by immersion in a tank of molten zinc. Zinc atoms diffuse into the top layers of the steel, forming a protective layer against corrosion. Galvanizing can be performed on various steel alloys as an additional protection against rust. Galvanized steel is a cheaper method of rust-proofing steel than alloying it with chromium.