Corten

COR-TEN (known also as Weathering Steel) is a special Steel Alloy inclusive of copper, chromium and phosphorus. It forms a durable rust-like appearance when exposed to the weather for several months.
The “Weathering” term is used because, due to the chemical composition of COR-TEN, resistance to atmospheric corrosion is higher compared to other types of steels. COR-TEN forms a protective layer on its surface under the influence of the weather. This is not corrosion but simply an oxidation which has the same color of rust without being rust.
Being particularly resistant to corrosion and to tensile strength COR-TEN is widely used for the construction of bridges, guard-rails & containers