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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 (USS) held the original Registered Trademark on the name COR-TEN, which passed to International Steel Group (now Arcelor-Mittal ) with the purchase of USS's heavy steel plate business. http://www.uss.com/corp/products/plate.htm , Accessed Sept 21, 2006 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 The mechanical properties of weathering steels depend on which alloy and how thick the material is. http://www.chapelsteel.com/A588.html , accessed Sept 21, 2006 http://www.mittalsteel.com/documents/en/Inlandflats/ProductBrochure/weathering.pdf , Accessed December 28, 2006 Manual of Steel Construction, 8th Edition, Second Revised Printing, American Institute of Steel Construction, Chicago, 1987; chapter 1 page 1-5 ASTM A 588 (now withdrawn) A 588 has a Yield Strength of at least 50 Ksi (50,000 Psi , 345 MPa ), and Ultimate Tensile Strength of 70 ksi (480 MPa) for all rolled Shapes and plate thicknesses up to 4.0 inches thick. Plates from 4.0 to 5.0 inches have yield strength at least 46 ksi (320 MPa) and ultimate tensile strength at least 67 ksi (460 MPa), and plates from 5.0 to 8.0 inches thick have yield strength at least 42 ksi (290 MPa) and ultimate tensile strength at least 63 ksi (435 MPa). ASTM A 242 (now withdrawn) The older A 242 alloy has a yield strength of 50 ksi (345 MPa) and ultimate tensile strength of 70 ksi (480 MPa) for light-medium rolled shapes and plates up to 0.75 inch thickness. 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 to 1.50 inch thick. The thickest rolled sections and plates from 1.50 to 4.0 inches thick have yield strength of 42 ksi (290 MPa) and ultimate strength of 63 ksi (435 MPa). 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. 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. 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 Cor-ten. It's also worth noting that the IC painted their Cor-ten railcars, a strange practice for a steel designed to remain exposed. See pictures in the "external links" section. USAGE CHALLENGES The use of weathering steel in construction presents several challenges: ;Weld-area corrosion Ensuring that weld-points weather at the same rate as the other materials may require special welding techniques or material. ;Trapped water corrosion It is not a rustproof material. If water is allowed to accumulate in pockets, those areas will experience higher corrosion rates, so provision for drainage must be made. ;Salt-Laden Air Environments 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. ;Discoloration 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 Cor-Ten steel. REFERENCES EXTERNAL LINKS
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