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What is stainless steel?

Stainless steel is the term applied to identify the steel families that contain at least 11% of chromium, which is the chemical element that affords the material a high resistance to corrosion.
Stainless steels are resistant to corrosion due to the passivation phenomenon. The alloy elements present in stainless steels react very easily with the environment and one of them in particular, chromium, helps to form a thin and adherent film that protects the material from subsequent corrosive attacks. This film is known as passive film. The passive film of stainless steel results from the reaction between the material and water that is always present in the environment (air humidity condensates over the metal cold surface). The product resulting from this reaction is iron and chromium oxide-hydroxide. The oxide content is higher at the region closer to the metallic surface and the hydroxide at the region closer to the environment. As time passes, the oxide layer increases, but the same does not happen with the hydroxide layer and, apparently, an enrichment of the passive film occurs. Although invisible, stable and extremely thin, this film is highly adhering to stainless steel and the more chromium is added to the mixture the more resistant the steel becomes. Other elements such as nickel, molybdenum and titanium, for example, allow the stainless steel to be bent, welded, deep-drawn and worked on in such a way to be applied to various different products. The selection of the correct stainless steel grade and relevant surface finish is very important to afford the material a long life. The main stainless steel families are: Austenitic - Ferritic - Martensiti
 
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