1. Thanks to the addition of chromium (and sometimes other additional elements), stainless steel resists corrosion. Carbon steel corrodes when the iron in it is allowed to combine with the oxygen in the surrounding environment. The chromium in it prevents this because it combines with oxygen and forms a passive layer of chromium oxide.
  2. This layer of chromium oxide prevents the formation of iron oxide, (also known as rust), in many cases, provided the chromium content of the steel is sufficiently large. The different grades of stainless steel specify and determine the amount of chromium and other alloying elements required, which helps indicate the level of corrosion resistance.