Stainless steel comprises a group of iron-based alloys, characterized by a chromium content of at least 10%, usually above 12%. Unlike ordinary steels, stainless steel exhibits excellent resistance to corrosion in humid air and oxygenated water, thanks to the thin protective oxide layer, mainly consisting of chromium oxide, that forms on its surface in ordinary air.
Many varieties of stainless steel also contain nickel, and other alloying additions such as molybdenum, copper, nitrogen or titanium may be present. Generally speaking, corrosion resistance increases with increased alloy content, and highly alloyed stainless steels can resist attack from aggressive chemicals such as acids, as well as be used in extremely corrosive environments, such as seawater.
