Iron is the fourth most common element in the Earth’s crust and, by mass, the most common element. It is a wonderful material, famed for its strength and mystery. Iron oxides give soils their red and yellow hues. They are nature’s foil to the often-garish colours of flowers and vivid greens of foliage. But gardeners associate iron with one of their enemies (rust) and coat it with expensive paints. Instead, they should learn to love the rich colours of iron oxide on Corten Steel.
Wrought iron has a low carbon content. Mild steel has a higher carbon content. Cast iron has an even higher carbon content (above 2.1%). Corten steel (patented as Cor-Ten) is an alloy of mild steel with copper and chromium. It oxidises to create a protective outer layer which stops corosion: it rusts a little and rusts no more. One can therefore enjoy the beauty of the iron oxide without worrying about the rusting destroying the steel. Having all the tensile strengh of steel, Corten garden planters are completely frost resistent and impact resistent. Since they are not mass produced, they can be supplied to order (eg by Crinklecrankle.com in the UK).
See also: corten steel in garden and landscape design