The corrosion resistance of stainless steel is due to a "passive" film complex oxide rich in chromium, spontaneously formed on the surface of steel. This is the normal state of the surfaces of stainless steel and is known as 'passive state' or 'passive condition'. Stainless steels autopasivarán spontaneously when a clean surface is exposed to an environment that can provide enough oxygen to form the surface layer of chromium-rich oxide. This occurs automatically and instantaneously, provided there is sufficient oxygen available on the surface of steel. Chromium stainless steels is primarily responsible for the mechanisms of self-passivation. Stainless steels can not be considered as corrosion resistant in all working conditions. Depending on the type (composition) steel, there will be certain conditions under which the "passive state" is lost and can not regroup. In this case the surface becomes "active", and the corrosion occurs.
There may be active conditions in small private areas of oxygen stainless steels, such as mechanical bonds, compact corners in the bad welds incomplete finished. El resultado puede ser formas «localizadas» de grietas o Stings.
Passive layer
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