Product Details. Design: Plain. Weathering steel, best-known under the trademark COR-TEN steel and sometimes written without the hyphen as "Corten steel", is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years. Despite the corrosion on the surface of CORTEN Steel, the material still contains twice the tensile strength to that of mild steel making it an ideal structural building material as well. Look out for our Corten cladding and Corten screenings on major commercial buildings along with residential projects throughout Australia. I don't think raw sheet metal will weather the same, and if it does weather, it probably won't be as structurally sound as cor-ten. Contrary to most cases where you would think rust decreases the structural integrity of the material, Cor-ten is designed to become even stronger after weathering. Rusted metal roofing offers a rustic or modern approach to weathering steel designed to naturally rust and protect the inner metal layers. A588 is the generic grade that meets the cor-ten spec, ought to be around $1.10 per lb in full sheets at least from a supplier that wants your business. Its been a few years since we bought any but we regularly by A656 and A514 at that price, they differ from A588 only slightly in chemistry and market distribution.