Stainless steel are iron, chromium and carbon based alloy that may contain other alements such as Ni, Mo, Si, etc, whose main characteristic is their resistance to corrosion.

This characteristic is due to the property of these steels to passivate in the presence of an oxidizing environment (therefore also in air). Passivation consists in the formation of an invisible layer of oxide, which varies according to the chemical composition of the steel, the type of heat treatment and the type of oxidizing environment and which forms a protective barrier to continuation of oxidation and therefore corrosion and which is reformed immediately if removed.

A chromium content of at least 11% is necessary for the formation of the protective layer.

Stainless steels are divided into various grades according to their chemical composition and therefore the possibility, or not, to modify their structure through heat treatments. The grades of stainless steels are:

 
1 Austenitic Steels
2 Heat Resistant
3 Martensitic steels
4 Ferritic steels
5 Duplex / Super Duplex Steels