Chemically speaking, rust is an iron oxide that is formed in the presence of water or air moisture. When you have too much rust then the metal will eventually break down and disintegrate. Corrosion usually occurs in steel and iron when it is exposed to water and oxygen over a long period of time. What happens is that the oxygen bonds with the metal on a molecular level and creates oxide, which weakens the bonds of the metal itself. The presence of saltwater makes the process of oxidation faster, this is why you’ll often see lots of rust on metal parts near the sea. Rust can be removed and treated to prevent further damage.