Stainless steels

Stainless steels are iron alloys whose defining feature is a chromium content of at least 10.5% by weight and a maximum carbon content of 1.2%. Chromium is the main alloying addition in stainless steel and can account for up to 26% by weight – steel of that kind is used in aggressive environments. The chromium in the steel blocks oxidation: the element reacts with oxygen and forms a protective layer of chromium oxide on the surface, which shields the steel from the agents that cause corrosion and makes the material as rust-resistant as it can be. That protective layer is known as the passive layer. It regenerates quickly after scratching and the surface returns to its proper form, keeping its bright finish. Whether the passive state forms at all depends mainly on the chromium concentration in the steel, although other elements – nickel among them – also increase corrosion resistance. Its anti-oxidation properties are what make stainless steel one of the most widely used materials there is. The same passivation can be observed in other metals, such as aluminium and titanium.