1. Classification of stainless steels

1.1 The basics

Stainless steels owe their resistance to corrosion to the formation, under their conditions of use, of a very thin passive layer (a few nanometers) made up of chromium compounds with a complex structure. The judicious choice of a stainless steel for a given application is designed to ensure that the chosen steel remains in this "passive" state, characterized by a very low dissolution or corrosion rate (generally less than 0.1 mm per year). These steels contain from 10 to 30% chromium by mass, as well as other elements chosen to improve their resistance to corrosion or their effect on their structure, such as molybdenum, nickel, nitrogen or titanium.

Chromium-alloyed steels also offer good resistance to high-temperature oxidation, thanks to the...