Weathering steel

Weathering steel

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Weathering steel

Cor-Ten steel - Fulcrum (1987) by Richard Serra

Weathering steel, best-known under the trademark COR-TEN steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years.

United States Steel Corporation (USS) holds the registered trademark on the name COR-TEN.^[1] Although USS sold its discrete plate business to International Steel Group (now Arcelor-Mittal) in 2003,^[2] it still sells COR-TEN branded material in strip-mill plate and sheet forms.

In some areas it may be known without the hyphen as "Corten steel".

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

ASTM A 242
ASTM A 588

Usage
Usage challenges
References
External links

Properties

"Weathering" means that due to their chemical compositions, these steels exhibit increased resistance to atmospheric corrosion compared to unalloyed 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.

The mechanical properties of weathering steels depend on which alloy and how thick the material is. ^[3] ^[4] ^[5]

ASTM A 242

The original A 242 alloy has a yield strength of and ultimate tensile strength of for light-medium rolled shapes and plates up to thick. It has yield strength of and ultimate strength of for medium weight rolled shapes and plates from thick. The thickest rolled sections and plates - from thick have yield strength of and ultimate strength of .

ASTM A 588

A 588 has a yield strength of at least , and ultimate tensile strength of for all rolled shapes and plate thicknesses up to thick. Plates from have yield strength at least and ultimate tensile strength at least , and plates from thick have yield strength at least and ultimate tensile strength at least .

Usage

Weathering steel is popularly used in outdoor sculptures, such as in the large Chicago Picasso sculpture, and as exterior facades, for its rustic antique appearance.

One of the most popular applications of Corten steel in art is by Belgian artist Wim Delvoye. He creates full scale sculptures lasercutting the Corten steel in a gothic ornamental style.

It has also been used in bridge and other large structural applications such as the New River Gorge Bridge, the newer span of the Newburgh-Beacon Bridge, and the creation of the Australian Centre for Contemporary Art (ACCA).

It is very widely used in marine transportation, in the construction of shipping containers.

The first use of COR-TEN for architectural applications was the John Deere World Headquarters in Moline, Illinois. The building was designed by architect Eero Saarinen, and completed in 1964.

COR-TEN was used by St. Louis Car Company to build an order of electric railcars for Illinois Central Railroad in 1971. For uniformity, the next order was built to similar specs, including COR-TEN bodies, by Bombardier in 1979. The use of COR-TEN was seen as a cost-cutting move in comparison with the railcar standard of stainless steel. The durability of COR-TEN railcars did not live up to expectations, and rust holes are appearing in the Illinois Central railcars. Most of these railcars still operate out of Chicago. No other orders of railcars have been made of weathering steel. It's also worth noting that the IC painted their COR-TEN railcars, an unusual practice for a steel designed to remain exposed. See pictures in the "external links" section. Painted weathering steel is no more corrosion-resistant than painted conventional steel, because the protective patina will not form in time to prevent corrosion over a localized area of attack such as a small paint failure.

Usage challenges

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 like Hawaii. In such environments, it is possible that the protective patina may not stabilize but instead continue to corrode. An example of such a structure would be the Aloha Stadium built in 1975 in Hawaii. Weathering steel's normal surface weathering can lead to rust stains on nearby surfaces.

The U.S. Steel Tower in Pittsburgh, Pennsylvania was constructed by U.S. Steel 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 undo this damage, but the sidewalks still have a decidedly rusty tinge. This problem has been reduced in newer formulations of weathering steel. Staining can be prevented if the structure can be detailed so that water does not drain from the steel onto concrete where stains would be visible.