When the majority of people think of steel they will in fact be thinking of Carbon Steel, an alloy comprised simply of Iron and Carbon. Carbon steel is essentially steel at its most basic. It is easy for us to create, it has been in use longer than any other type of steel, and its properties make it suitable for a wide range of purposes.
Despite its prominence in the material's name, carbon steel actually only contains roughly 2% of carbon, the rest being iron. This 2% makes a good deal of difference to the properties of iron, increasing its yield strength, raising its melting point and making it less brittle, but despite these improvements carbon steel still retains one of iron's greatest weaknesses: it rusts.
Rust is a result of a reaction which takes place between the iron content in steel and the oxygen in the air, which is catalysed by water; and when it takes hold it will eat away at the metal until eventually it flakes, chips and peels away to nothing. Steel and iron can be treated with protective coats and lacquers to prevent rusting, but these require a degree of upkeep and will not prevent rusting from occurring if the reaction has already begun.
There are however many different types of steel, each containing small portions of other elements such as nickel, magnesium, molybdenum, silicon, copper, vanadium, etc. and depending on the other element that is included into the steel's mix, the kind of steel produced changes, as will its properties; for example if Chromium is added then the type of steel produced will be Stainless Steel.
The additional properties of stainless steel, originally known as Rustless Steel, are rather self-evident; it does not rust. This is because, when exposed to oxygen, the chromium forms a protective layer that sits on top of the material which, whilst incredibly thin, is enough to keep water and oxygen away from the iron contained within the steel.
If this protective layer of chromium is ever scratched, then a new layer will form very quickly, ensuring that its protection is all but absolute. This passivation layer does more than just prevent rust, it also adds acid and corrosion resistance to the list of stainless steel's properties; making it an invaluable material.
Stainless steels properties also include a glistening aesthetic which is pleasing to the eye, making it a popular material in the development of sculptures, monuments and other artistic endeavours; in addition to its more practical applications, such as infrastructural fixtures, architecture, transport, surgical tools, aerospace technology, storage tanks and many, many more.