In metallurgy, stainless steel is defined as a steel alloy with a minimum of a 10% chrome content in mass. Other metals which it may contain are for example molybdenum and nickel.
Stainless steel is a steel of high resistence to corrosion, because of the chromium and other alloys materials it contained, have possess high affinity to oxygen and reacts with it forming a layer passive, preventing the corrosion of iron. (The only pure stainless materials which don´t react to oxygen are gold and platinum).However, this layer can be affected by some acids, causing the iron to be attacked and oxidized by intergranular mechanism or generalized stains.
Some types of stainless steel contain also other alloy elements, but the main ones are nickel and molybdenum.
The most common stainless steels are the 304 and 316, being this last used in marine environments or corrosive vapors.