Corrosion of stainless steel

Normally, stainless steel is a very corrosion resistant material. Automatically, the steel is covered by an ultra-thin layer of oxides (chromium and iron), and despite being only a few nanometres thick, this invisible film protects the steel to such an extent that it stays “passive”. Sadly, this passive film is not invulnerable, and if it’s partially degraded or even removed completely, corrosion may take place. Depending upon the steel type and the conditions, five types of corrosion are possible: