Weathering steel, often referred to by the*genericized 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 after several years' exposure to weather
U.S. Steel*holds the*registered trademark*on the name COR-TEN.*The name COR-TEN refers to the two distinguishing properties of this type of*steel:*corrosion*resistance and*tensile strength.*Although USS sold its discrete plate business to*International Steel Group*(now*ArcelorMittal) in 2003,*it still sells COR-TEN branded material in strip-mill plate and sheet forms.
The original COR-TEN received the standard designation A242 (COR-TEN A) from the*ASTM International*standards group. Newer ASTM grades are A588 (COR-TEN B) and A606 for thin sheet. All alloys are in common production and use.
The surface oxidation of weathering steel takes six months, but surface treatments can accelerate the oxidation to as little as two hours.
In 1933 the*United States Steel Corporationdeveloped and patented a steel with exceptional mechanical resistance, primarily for use in railroad*hopper cars, for the handling of heavy*bulk loadsincluding coal, metal*ores, other mineral products and*grain.*The controlled corrosion
for which this material is now best known was a welcome benefit discovered soon after, prompting USS to apply the trademarked name Cor-Ten. Because of its inherent toughness, this steel is still used extensively for bulk transport and storage
Railroad passenger cars were also being built with Cor-Ten, albeit painted, by*Pullman-Standard*for the*Southern Pacific*from 1936,*continuing through commuter coaches for the*Rock Island Line*in 1949.
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.
Weathering steel grade chemical composition (excl. iron) by weight (%)GradeCSiMnPSCrCuVNiASTM A2420.120.25–0.750.20–0.500.01–0.200.0300.50–1.250 .25–0.550.65ASTM A5880.160.30–0.500.80–1.250.0300.0300.40–0.650.25– 0.400.02–0.100.40
The mechanical properties of weathering steels depend on which alloy and how thick the material is.
The original A242 alloy has a*yield strength*of 50*kilopounds per square inch*(340*MPa) and*ultimate tensile strength*of 70*ksi (480*MPa) for light-medium rolled shapes and plates up to 0.75 inches (19*mm) thick. It has yield strength of 46*ksi (320*MPa) and ultimate strength of 67*ksi (460*MPa) for medium weight rolled shapes and plates from 0.75–1 inch (19–25*mm) thick. The thickest rolled sections and plates – from 1.5–4*in (38–102*mm) thick have yield strength of 42*ksi (290*MPa) and ultimate strength of 63*ksi (430*MPa). ASTM A 242 is available in Type 1 and Type 2. Both have different applications based on the thickness. Type 1 is often used in housing structures, construction industry and freight cars.The Type 2 steel which is also called Corten B is used majorly in urban furnishing, passenger ships or cranes.
A588 has a yield strength of at least 50*ksi (340*MPa), and ultimate tensile strength of 70*ksi (480*MPa) for all rolled*shapes*and plate thicknesses up to 4*in (100*mm) thick. Plates from 4–5*in (102–127*mm) have yield strength at least 46*ksi (320*MPa) and ultimate tensile strength at least 67*ksi (460*MPa), and plates from 5–8*in (127–203*mm) thick have yield strength at least 42*ksi (290*MPa) and ultimate tensile strength at least 63*ksi (430*MPa).