Stainless steel is a special type of steel that is much more resilient towards corrosion, rust and staining than ordinary steel. Stainless steel is also known as inox and contains at least 10.5 percent chromium. When the exact alloy type and grade is undefined, stainless steel is often referred to as corrosion resistant steel. Different alloy types and grades will have different properties, and it is therefore important to select the ideal alloy type and grade when you intend to use stainless steel for sensitive tasks, such as construction work. Stainless steel is a popular building material in anything from small storage facilities to huge skyscrapers. One example of a famous building utilizing stainless steel is the New York City Chrysler Building. The Chrysler Building was built in 1930 and consists mainly of brick – its is the highest brick building in the world – but its characteristic seven-story pinnacle is decorated with lustrous stainless steel cladding. The ornamentation is based on the hubcaps that could then be found on Chrysler made cars. The Chrysler building is considered one of the most outstanding examples of Art Deco architecture in New York City.
Chromium is hard metal with a steel-gray color. It is lustrous and has a high melting point (1907 ° C, 3465 ° F). In the periodic table, you will find chromium as number 24. It is abbreviated Cr and considered a transition metal. If you want to create stainless steel that has a high oxidation resistance when kept in normal air, you should usually aim for a chromium content of 12 weight percent or more. The chromium will provide the steel with a protecting layer, by binding with the surrounding oxygen and forming chromium (III) oxide. In such a molecule, there will be three oxygen atoms bound to two chromium atoms and this layer will be very difficult to penetrate for the remaining oxygen in the air. A layer of chromium (III) oxide will also by hard for water to penetrate, thus protecting the underlying steel even in moist environments. If the chromium oxide layer is dented or scratched, it will rapidly reform and continue to protect the steel.
Chromium is not the only material that can be deliberately added to stainless steel. Nickel and manganese are two examples of frequently included metallic compounds that will alter the properties of the stainless steel and make it more suitable for certain tasks. Nickel is a silvery white metal belonging to the iron group. It is hard, but still ductile and malleable. Nickel can be added to austenite iron in order to stabilize its molecular structure. Austenite iron containing nickel will become less brittle at low temperatures, and also loose its magnetic properties. Just like nickel, manganese will serve to stabilize its molecular structure in austenite iron, but significant amounts must be added. Since manganese is less expensive than nickel, it still offers a way of making stainless steel more affordable.
The fact that steel is labeled “stainless” or “corrosion resistant” does not mean that it will never corrode. Even the greatest stainless steel alloy will corrode under certain conditions and this must be taken into account when stainless steel is used in cars, airplanes, buildings etcetera. Three problem causing forms of corrosion are pitting corrosion, roughing corrosion and weld decay. These three corrosion types are less noticeable than common rust, and are therefore often allowed to develop during long periods of time.
