Weathering steel, best-known under the trademark COR-TEN steel and sometimes written without the hyphen as "Corten steel", is a group of steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 alloys which were developed to eliminate the need for painting, and form a stable rust

Rust

Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

-like appearance if exposed to the weather for several years.

United States Steel Corporation (USS) holds the registered trademark

Trademark

A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

 on the name COR-TEN. Although USS sold its discrete plate business to International Steel Group

International Steel Group

International Steel Group was a steel company headquartered in Cleveland, Ohio. In 2004 it was ranked #426 on the Fortune 500. It was created after the turn around fund, WL Ross & Co. LLC, purchased LTV Steel in February 2002...

 (now Arcelor-Mittal

Arcelor-Mittal

ArcelorMittal S.A. is a global steel company headquartered in Avenue de la Liberté, Luxembourg, Luxembourg. It is the largest steel producing company in the world and is the market leader in steel for use in automotive, construction, household appliances and packaging. It holds sizeable captive...

) in 2003, it still sells COR-TEN branded material in strip-mill plate and sheet forms.

The original COR-TEN received the standard designation A 242 ("COR-TEN A") from the ASTM International

ASTM International

ASTM International, known until 2001 as the American Society for Testing and Materials , is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services...

 standards group. Newer ASTM grades are A 588 ("COR-TEN B") and A 606 for thin sheet. All alloys are in common production and use.

Properties

"Weathering" means that due to their chemical compositions, these steels 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.

Chemical composition of Cor-ten grades

Grade	%C Carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...	%Si Silicon Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...	%Mn Manganese Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...	%P Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...	%S Sulfur Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...	%Cr Chromium Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...	%Cu Copper Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...	%V Vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...	%Ni Nickel Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
Cor-ten A	0.12	0.25-0.75	0.20-0.50	0.07-0.15	0.030	0.50-1.25	0.25-0.55		0.65
Cor-ten B	0.16	0.30-0.50	0.80-1.25	0.030	0.030	0.40-0.65	0.25-0.40	0.02-0.10	0.40

The mechanical properties of weathering steels depend on which alloy and how thick the material is.

ASTM A 242

The original A 242 alloy has a yield strength of 50000 pound per square inches (344,737,864.7 Pa) and ultimate tensile strength of 70000 psi (482,633,010.5 Pa) for light-medium rolled shapes and plates up to 0.75 inches (1.9 cm) thick. It has yield strength of 46000 psi (317,158,835.5 Pa) and ultimate strength of 67000 psi (461,948,738.6 Pa) for medium weight rolled shapes and plates from 0.75–1 in (1.9–2.5 ) thick. The thickest rolled sections and plates – from 1.5–4 in (3.8–10.2 ) thick have yield strength of 42000 psi (289,579,806.3 Pa) and ultimate strength of 63000 psi (434,369,709.5 Pa).

ASTM A 588

A 588 has a yield strength of at least 50000 psi (344,737,864.7 Pa), and ultimate tensile strength of 70000 psi (482,633,010.5 Pa) for all rolled shapes

I-beam

-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...

 and plate thicknesses up to 4 in (10.2 cm) thick. Plates from 4–5 in (10.2–12.7 ) have yield strength at least 46000 psi (317,158,835.5 Pa) and ultimate tensile strength at least 67000 psi (461,948,738.6 Pa), and plates from 5–8 in (12.7–20.3 ) thick have yield strength at least 42000 psi (289,579,806.3 Pa) and ultimate tensile strength at least 63000 psi (434,369,709.5 Pa).

Use

Weathering steel is popularly used in outdoor sculptures, such as in the large Chicago Picasso

Chicago Picasso

The Chicago Picasso is an untitled monumental sculpture by Pablo Picasso in Chicago, Illinois. The sculpture, dedicated on August 15, 1967, in Daley Plaza in the Chicago Loop, is tall and weighs 162 tons...

 sculpture, and as exterior facades, for its rustic antique appearance. Examples include The Angel of the North

Angel of the North

The Angel of the North is a contemporary sculpture, designed by Antony Gormley, which is located in Gateshead,formerly County Durham, England.It is a steel sculpture of an angel, standing tall, with wings measuring across...

, Gateshead

Gateshead

Gateshead is a town in Tyne and Wear, England and is the main settlement in the Metropolitan Borough of Gateshead. Historically a part of County Durham, it lies on the southern bank of the River Tyne opposite Newcastle upon Tyne and together they form the urban core of Tyneside...

, UK and the Humanities and Arts complex at Leeds Metropolitan University

Leeds Metropolitan University

Leeds Metropolitan University is a British University with three campuses. Two are situated in Leeds, West Yorkshire, England while the third is situated in Bhopal, India...

 - Broadcasting Place - Leeds

Leeds

Leeds is a city and metropolitan borough in West Yorkshire, England. In 2001 Leeds' main urban subdivision had a population of 443,247, while the entire city has a population of 798,800 , making it the 30th-most populous city in the European Union.Leeds is the cultural, financial and commercial...

, UK

It has also been used in bridge and other large structural applications such as the New River Gorge Bridge

New River Gorge Bridge

The New River Gorge Bridge is a steel arch bridge long over the New River Gorge near Fayetteville, West Virginia, in the Appalachian Mountains of the eastern United States. With an arch long, the New River Gorge Bridge was for many years the world's longest arch bridge; it is now the third...

, the newer span of the Newburgh–Beacon Bridge, and the creation of the Australian Centre for Contemporary Art (ACCA)

Australian Centre for Contemporary Art

The Australian Centre For Contemporary Art is a contemporary art gallery in Melbourne, Australia. The gallery is located on Sturt Street in the Melbourne Arts Precinct, in the inner suburb of Southbank....

.

It is very widely used in marine transportation, in the construction of Intermodal container

Intermodal container

An intermodal container is a standardized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system...

s.

The first use of COR-TEN for architectural applications was the John Deere World Headquarters

John Deere World Headquarters

The John Deere World Headquarters is a complex of four buildings located on 1,400 acres of land in Moline, Illinois, United States. The complex serves as corporate headquarters for John Deere.- History :...

 in Moline, Illinois

Moline, Illinois

Moline is a city located in Rock Island County, Illinois, United States, with a population of 45,792 in 2010. Moline is one of the Quad Cities, along with neighboring East Moline and Rock Island in Illinois and the cities of Davenport and Bettendorf in Iowa. The Quad Cities has a population of...

. The building was designed by architect Eero Saarinen

Eero Saarinen

Eero Saarinen was a Finnish American architect and industrial designer of the 20th century famous for varying his style according to the demands of the project: simple, sweeping, arching structural curves or machine-like rationalism.-Biography:Eero Saarinen shared the same birthday as his father,...

, and completed in 1964. In 1977, Robert Indiana

Robert Indiana

Robert Indiana is an American artist associated with the Pop Art movement.-Life and work:Robert Indiana was born Robert Clark in New Castle, Indiana. His family relocated to Indianapolis, where he graduated from Arsenal Technical High School...

 created a Hebrew version of the Love sculpture

LOVE (Sculpture)

LOVE is a sculpture by American artist Robert Indiana. It consists of the letters LO over the letters VE.The image was originally designed as a Christmas card for the Museum of Modern Art in 1964...

 using the four-letter word ahava

Ahava

Ahava is an Israeli cosmetics company that manufactures skin care products made of mud and mineral-based compounds from the Dead Sea. The company's administrative headquarters are located in Holon but the main manufacturing plant and showroom are in Mitzpe Shalem, an Israeli settlement located on...

 (אהבה "love" in Hebrew) made from COR-TEN, for the Israel Museum

Israel Museum

The Israel Museum, Jerusalem was founded in 1965 as Israel's national museum. It is situated on a hill in the Givat Ram neighborhood of Jerusalem, near the Bible Lands Museum, the Knesset, the Israeli Supreme Court, and the Hebrew University of Jerusalem....

 Art Garden in Jerusalem, Israel

Israel

The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

.

COR-TEN was used in 1971 for an order of electric railcars built by the St. Louis Car Company for Illinois Central Railroad. The use of COR-TEN was seen as a cost-cutting move in comparison with the contemporary railcar standard of stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

. A subsequent order in 1979 was built to similar specs, including COR-TEN bodies, by Bombardier. The cars were painted, a standard practice for COR-TEN railcars. However, the durability of COR-TEN did not live up to expectations, with rust holes appearing in the railcars. Ironically, painting may have contributed to the problem, as painted weathering steel is no more corrosion-resistant than conventional steel, because the protective patina

Patina

Patina is a tarnish that forms on the surface of bronze and similar metals ; a sheen on wooden furniture produced by age, wear, and polishing; or any such acquired change of a surface through age and exposure...

 will not form in time to prevent corrosion over a localized area of attack such as a small paint failure. Most of these railcars still operate out of Chicago.

Disadvantages

Using weathering steel in construction presents several challenges. Ensuring that weld-points weather at the same rate as the other materials may require special welding techniques or material. Weathering steel is not rustproof in itself. If water is allowed to accumulate in pockets, those areas will experience higher corrosion rates, so provision for drainage must be made. Weathering steel is sensitive to salt-laden air environments. In such environments, it is possible that the protective patina may not stabilize but instead continue to corrode. Hawaii's Aloha Stadium

Aloha Stadium

Aloha Stadium is a stadium located in the Halawa CDP, City and County of Honolulu, Hawaii, United States. Currently Aloha Stadium is home to the University of Hawaii Warriors football team...

, built in 1975, is one example of this. The former Omni Coliseum

Omni Coliseum

The Omni Coliseum, usually called The Omni, from the Latin for "all," or "every," was an indoor arena, located in Atlanta, Georgia, United States. Completed in 1972, the arena seated 16,378, for basketball and 15,278, for ice hockey...

, built in 1972 in Atlanta, Georgia, never stopped rusting, and eventually large holes appeared in the structure. This was a major factor in the decision to demolish it just 25 years after construction. Weathering steel's normal surface weathering can also lead to rust stains on nearby surfaces.

The U.S. Steel Tower

U.S. Steel Tower

U.S. Steel Tower, also known as the Steel Building , is the tallest skyscraper in Pittsburgh, the fourth tallest building in Pennsylvania, and the 37th tallest in the United States. Completed in 1970, the tower has 64 floors to and has of leasable space. Its original name was the U.S. Steel...

 in Pittsburgh, Pennsylvania was constructed by U.S. Steel

U.S. Steel

The United States Steel Corporation , more commonly known as U.S. Steel, is an integrated steel producer with major production operations in the United States, Canada, and Central Europe. The company is the world's tenth largest steel producer ranked by sales...

 in part to showcase COR-TEN steel. The initial weathering of the material resulted in a discoloration of the surrounding city sidewalks, as well as other nearby buildings. A cleanup effort was orchestrated by the corporation once weathering was complete to clean the markings. A few of the nearby sidewalks were left uncleaned, and remain a rust color. This problem has been reduced in newer formulations of weathering steel. Staining can be prevented if the structure can be designed so that water does not drain from the steel onto concrete where stains would be visible.

External links

• Report on Performance of Weathering Steel in Highway Bridges from the American Iron and Steel Institute
  American Iron and Steel Institute
  The American Iron and Steel Institute is an association of North American steel producers. Its predecessor organizations date back to 1855 making it one of the oldest trade associations in the United States. AISI assumed its present form in 1908, with Elbert H...
  
  
• Report on Weathering Steel in TxDOT Bridges from the Texas Department of Transportation
  Texas Department of Transportation
  The Texas Department of Transportation is a governmental agency in the U.S. state of Texas. Its stated mission is to "work cooperatively to provide safe, effective and efficient movement of people and goods" throughout the state...
  
   (4464 KB). Contains recommended details to avoid staining. Note: wrapping of piers was later found not to be cost-effective.
• Stadium rust to get $12.4M treatment an article from the Honolulu Advertiser
• A Primer on Weathering Steel: a white paper from the National Steel Bridge Alliance
• Corten FAQ from the American Institute of Steel Construction
  American Institute of Steel Construction
  The American Institute of Steel Construction, often abbreviated AISC, is a not-for-profit technical institute and trade association for the use of structural steel in the construction industry of the United States. It is headquartered in Chicago, IL. Their mission is to make structural steel the...
  
  
• Weathering steel: A technical overview of weathering steels for bridges and general construction