Stainless steel surface coatings has also influenced its use in commercial kitchens and food processing plants. Stainless steels do not suffer uniform corrosion, like carbon steel, when exposed to wet environments. Unprotected carbon steel rusts readily when exposed to the combination of air and moisture. The resulting iron oxide surface layer (the rust) is porous and fragile. Since iron oxide occupies a larger volume than the original steel this layer expands and tends to flake and fall away exposing the underlying steel to further attack. In comparison, stainless steels contain sufficient chromium to undergo passivation, spontaneously forming a microscopically thin inert surface
Duplex stainless steel Duplex stainless steel Duplex stainless steels is the most recent family of stainless steels. They are called duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite (face-centered cubic lattice) and ferrite (body centered cubic lattice) in roughly equal proportions. They are used for their good mechanical properties in the as-cast (and therefore as-welded condition) and/or their excellent corrosion resistance properties (particularly to stress corrosion cracking). They tend to be divided in three sub groups: Grade 1.4462 which has been the grade initially developed. and reperesents the "mid-range" of properties and is perhaps the most used today