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.
Weathering refers to the chemical composition of these steels, allowing them to exhibit increased resistance to atmospheric corrosion compared to other steels. This is because the steel forms a protective layer on its surface under the influence of the weather.
The corrosion-retarding effect of the protective layer is produced by the particular distribution and concentration of alloying elements in it. The layer protecting the surface develops and regenerates continuously when subjected to the influence of the weather. In other words, the steel is allowed to rust in order to form the protective coating.
Usually used in heavy carpentry speeches or for the realization of sculptures. Thanks to the mechanical characteristics of the material, the high corrosion resistance and to the particular color tones, the COR-TEN has recently found application in architecture in the realization of profiles for door and window frames equipped with a thermal break technology.