Corrosion resistant metals are defined as the class of metals that are inherently resilient to degradation caused by corrosion. A metal that is not naturally corrosion resistant can be made so by combining it with small amounts of another metal in a process known as alloying. The main characteristic responsible for a metal’s ability to resist corrosion is its passive or protective layer.
When metals are exposed to air and moisture, a series of chemical reactions occur that cause a thin oxide layer to form on the surface of the metal. This layer acts as a protective barrier that prevents further air and moisture from coming into contact with the underlying steel substrate. The oxide layer is tighter and stronger in some metals than in others, thus making some metals better able to resist corrosion.
Common alloying elements used to increase the corrosion resistance of metals include titanium, chromium, nickel and molybdenum. Stainless steel, for example, contains at least 10.5% of chromium. This addition of chromium allows stainless steel to generate a thin and stable chromium oxide layer, which limits the intrusion of water and oxygen, thus preventing further corrosion.