What is stainless steel?
Stainless steel is the generic name for a number of different steels used primarily because of their corrosion resistance. All stainless steels share a minimum percentage of 10.5% chromium. Chromium is always the deciding factor, although other elements, particularly nickel and molybdenum, are added to improve corrosion resistance. The success of the material is based on the fact that it has one unique advantage. The chromium in the stainless steel has a great affinity for oxygen, and will form a film of chromium oxide on the surface of the steel at a molecular level. The film itself is extremely thin, about 130 Angstroms and one Angstrom is one millionth of a centimetre. This layer is described as passive (does not react or influence other materials), tenacious (clings to the layer of steel and is not transferred elsewhere) and self-renewing (if damaged, more chromium from the steel will be exposed to the air and form more chromium oxide). This means that over a period of years a stainless steel knife can literally be worn away by daily use and will still remain stainless.
In many cases stainless steel is the most cost efficient solution. Although producing a component or fabrication in stainless steel will often be more expensive that using ordinary steel due to the higher cost of stainless steel and expertise required during processing it is the better life cycle costs of stainless steel that make it such an attractive material. Through the use of a stainless steel a significantly longer service life and less maintenance costs for equipment can be achieved. Furthermore, stainless steel is fully recyclable and has a high scrap value on de-commissioning.
Families of stainless steels and other corrosion resistant alloys
There are several families of stainless steel: Ferritic, Martensitic, Austenitic and Duplex. These names are derived from the crystal structure of the steels, which determines their metallurgical behaviour. Other corrosion resistant alloys are nickel based alloys and titanium and its alloys.