THE STAINLESS STEEL
Stainless steels are alloys consisting of iron and carbon which not only have mechanical properties but also distinctive characteristics: they resist corrosion, therefore they passivate. Passivation is the formation of an invisible oxide film which protects the surface of the metal from chemical agents. The basic composition of austenitic stainless steel is 18% Cr and 8% Ni, in A2, material n. 1.4301/03 (AISI 304). The formation of more resistant molybdenum carbides compared to chromium ones is given by a small percentage, 2-3%, of molybdenum which also guarantees a higher corrosion resistance of the chlorides (like sea water). This type of steel is in A4, material n. 1.4401/04 (AISI 316). Due to the substantial percentage of high value components, austenitic stainless steels are the most common and expensive steels. They are also used in several sectors: carpentry, pharmaceutical, food, textile, nautical, building and paper industry. They are very appreciated in the chemical industry thanks to their resistance to most chemicals.