Stainless steel is an alloy of iron, carbon and chromium with minimum content of chromium at least 10,5 % by weight. Chromium creates an adherent, insoluble film on the surface of the steel that shields the metal substrate from uniform and localized attack. This protective film is called passive layer or passive film and constitutes a very fine layer on the surface of the steel (its thickness is 5-15 nm). Apart from chromium, stainless steels may contain and other alloying elements like nickel Ni, molybdenum Mo, manganese Mn etc (we examined them earlier).

They are widely used into several applications that require among others resistance to corrosion, effective relation between cost and life cycle, for their aesthetic or hygienic properties. Stainless steels apart from their resistance to corrosion, they also enjoy higher mechanical properties in comparison with other common types of steel. Yet, they are harder and more difficult to work with. An additional characteristic is their lower thermal conductivity.

Stainless steels are distinguished according to the dominant phase in their crystal lattice.