What are stainless steels?
Stainless steels are a family of alloys of Iron with a minimum of 10.5% Chromium. Chromium produces a thin layer of oxide on the surface of the steel known as the passive layer. This prevents any further corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion. Because of the passive layer stainless steels have a unique feature: they are self-healing. Even if the stainless steel surface is scratched or damaged otherwise, this passive layer, which is only a few atoms thick, instantaneously reforms under the influence of oxygen from air or water. This explains why stainless steel does not require any coating or other corrosion protection to remain bright and shiny even after decades of use.
Besides Chromium, stainless steels can also contain other elements like Nickel or Molybdenum.