|Picture 3.8 The chromium content protects stainless steel by forming an oxide layer.|| |
|How stainless steel resists corrosion|
| ||If iron and chromium are exposed to oxygen, it is the chromium that reacts to form an oxide. Due to its high chromium content, stainless steel forms a very thin layer of chromium(III) oxide as soon as the surface is exposed to the oxygen in the atmosphere. The layer of oxide is so thin that the metal can still shine through it, but it is thick enough to prevent the oxygen and water attacking the metal underneath and so no corrosion takes place. |
The protection is permanent because even if the protective layer is scratched, the chromium in the steel will react with oxygen in the air to immediately re-form the protective layer.