The Slow Burn

Rust is iron corrosion - a flaky mixture of hydrated iron oxides and iron oxyhydroxides, often simplified as Fe2O3.xH2O. It forms when iron reacts with oxygen in the presence of water. It is technically a form of oxidation, just incredibly slow. A fire turns fuel into oxide in seconds; rust turns iron into oxide over months or years.

Water makes rust possible — dry iron barely rusts. Add water and it becomes a medium for electron transfer between iron and oxygen. Salt water speeds up rusting dramatically because dissolved sodium chloride raises the water's electrical conductivity.