The term stainless steel is applied to a group of Fe-Cr alloys, with or without nickel, which offers a good resistance to chemical corrosion. Contrary to their name, stainless steels owe their "cleanliness" to a very thin superficial oxide layer, rich in chromium and oxygen.
This layer, which acts as a protective film (passivation), exists due to the chromium, which is an easily oxidised element. It is very thin and inert in a large number of environments.
This property of Fe-Cr alloys is valid for Cr contents of approximately 12%, the minimum for all stainless steels. Sometimes, it happens that this protective film is destroyed, either uniformly or locally a status known as general- or localised corrosion (pitting, crevice, stress corrosion).
This layer, which acts as a protective film (passivation), exists due to the chromium, which is an easily oxidised element. It is very thin and inert in a large number of environments.
This property of Fe-Cr alloys is valid for Cr contents of approximately 12%, the minimum for all stainless steels. Sometimes, it happens that this protective film is destroyed, either uniformly or locally a status known as general- or localised corrosion (pitting, crevice, stress corrosion).