Iron and steel are thermodynamically unstable and revert to their oxide form in the presence of oxygen and water - generally known as rust. Preventing the corrosion of steel requires a multi-disciplined approach and should be considered at the very beginning of a project.
Non-ferrous metals are not suitable for general structural purposes as they lack strength workability chemical resistance and cost-effectiveness of Iron and Steel, but are nonetheless used as coatings in their own right to afford cathodic protection to steel.