Wood is decomposed under the influence of climate and bacteria, and plastics age, brittle and deteriorate under the influence of sunlight, temperature and atmosphere. Concerning metals and metallic materials we say that they corrode, or rust.
Iron and other metals are extracted from naturally existing minerals that are more stable composites that the metals, and therefore the corrosion processes transform the metals into products much alike the minerals. Iron reverts to the oxides FeO, Fe2O3 and Fe3O4 under the influence of oxygen. What oxides and in what amounts are mainly decided by the oxygen availability and the surrounding temperature. If water is available a hydrating process will begin.
In order to reduce or stop steel corrosion the steel has to be protected, which can be done in many different ways and with many types of corrosion protecting products. One alternative is to create a dense layer preventing the steel from reacting with the surrounding media (oxygen or electrolyte). Another way is to apply one or more substances on or in contact with the steel that is less precious than the steel, and therefore corrode instead. The substance act as a sacrificing anode.
Other ways to protect the steel can be to raise the electrical transmission resistance in the corrosion cell, e.g. by creating an environment that does not fulfil the corrosion criteria, but most by shaping the structures adequately, e.g. by avoiding narrow cavities, moisture storages or direct contact between different metals.
The new steel can be protected in short term by a thin oil layer. Later on the most steel products get a durable cathodic protection by a thin layer application of zinc or mixtures of zinc and aluminium (also zinc and titanium). Up on this you can thereafter put any of the many types of protecting painting systems in one or many layers. What system to choose depend on where the end-product is to be used. The painting system is a composition of adhesives, pigments, additives and water or solvents.
If you want to avoid corrosion protecting coatings but still want an excellent protection, stainless steels are preferable. These create an invisible layer of chromium oxide that protects very well against further attack. Another alternative is weathering steel, where the obviously visible corrosion product gives a good protection against further corrosion.