The oxygen-depleted region is anodic relative to the well-aerated boldly exposed surface, possibly resulting in the corrosion of the covered region. For example, covering a portion of the surface-for example, by biofouling, painting or installing a gasket-produces an oxygen-depleted region under the covered region. If passivity is destroyed under conditions that do not permit restoration of the passive film, then stainless steel will corrode much like a carbon or low-alloy steel. It is generally assumed that stainless steel has a very good resistance to atmospheric corrosion and yet, when analyzing the effect of general corrosion on. Corrosion resistance is greatest when the steel is boldly exposed and the surface is maintained free of deposits.
(For more on chromium, see The Role of Chromium in Intergranular Corrosion.) Other elements such as nickel, manganese and molybdenum can be added to enhance stainless steel corrosion resistance.Īnother requirement for the formation and maintenance of the passive layer is that the steel surface must be exposed to oxygen. The more chromium that is added, the more stable the passive layer becomes, and the better the corrosion resistance. Stainless steel must have at least 10.5% chromium in order for the passive layer to form. In most cases it should not affect the mechanical properties of the stainless steel but it will show brown rust stains which can effect the attractiveness of. The passive layer forms because of the chromium added to stainless steel.