Resistance to Corrosion
Stainless steels’ resistance to corrosion is mainly due to the presence of Chromium. This element, in relatively low quantities (2 to 5%) improves mechanical resistance, but it is only with the addition of a minimum of 12% chromium that we may say that steel is truly stainless.
According to classic theories, the action of Chromium is due to an extremely thin layer of Chromium oxide on the metal surface, which is impermeable to and insoluble in the corrosive environment. We understand that this layer can only be formed in oxidising environments.
The addition of Nickel increases resistance in slightly oxidising or reducing environments. Besides, its presence modifies steel structure, endowing it with other mechanical characteristics.
Other additives are also used, with the purpose of increasing resistance to different types of corrosion. For example: Molybdenum, Copper, Silica, Aluminium, Nitrogen, Titanium and Niobium.