As long as iron has been used, corrosion has been a problem. There are only a handful of metals that can be found in pure forms – gold, for example. These metals do not corrode, but iron naturally mixes with oxygen in the presence of water to form rust. It is neither the oxygen nor the water that creates corrosion, though.
Confusion about rust
The misconception that rust comes from water exposure stems from the observable phenomenon of iron rusting when exposed to moisture in “normal” conditions found in habitable areas of the planet. However, if you take away just one component from that equation (water or oxygen), corrosion slows, or even stops.
For instance, iron ships that sink within very deep parts of the ocean rust very slowly. This is because the water at those depths is oxygen-poor – there is very little reaction between the iron, oxygen and water. Likewise, iron exposed in an arid desert will form almost no rust because, while there is plentiful oxygen, there is very little water present to create the reaction.
Corrosion is natural
Corrosion is a natural phenomenon for all iron products. In fact, rust actually protects the iron. When corrosion forms over the top of an iron object, the metal below that layer is not affected. However, frequent cleaning of corrosion continually removes that protection and layers of metal, exposing more metal to oxygen and moisture, and creating an endless cycle that will eventually wear the iron implement out.
Why stainless steel is corrosion resistant
Stainless steel is one of the few metals that can resist the natural course of the oxygen/moisture corrosion cycle. Stainless steel is an alloy of iron (it contains at least 62% iron, with the balance being made up of chromium and other metals). However, because of the chromium within the mixture, corrosion can be controlled. The process is actually rather similar to the way in which rust is formed, though the results are markedly different. The chromium within stainless steel forms a passive layer to thin to see. This layer covers the stainless steel and prevents the iron within the alloy from reacting to the presence of water and oxygen, preventing rust from forming.