What Is Corten Steel?

In the 1930’s, U.S. Steel developed a commodity that they named Corten Steel. The product was originally designed to help build railroad coal wagons. The success of the coal wagons led to it being a prominent material for outdoor art projects during the 1960’s. In America, you can still find some early examples of the delicacy of Corten Steel structures.

U.S. Steel holds the registered trademark on the name COR-TEN. COR-TEN refers to corrosion resistance and tensile strength. USS sold its discrete plate business to International Steel Group, USS still sells branded material in strip-mill plate and sheet forms. So to get back to your question, no, COR-TEN is not available. What is available is steel in an ASTM A606-4, A588, and A847 finish. If somebody tells you that they are supplying you COR-TEN they are almost certainly unaware of their own product. When someone needs COR-TEN they are usually referring to A606 Type 4, A588, or A847.

Weathering steels, such as ASTM A847, A588, A242, A606 and COR-TEN exhibit superior corrosion resistance over regular carbon steel as a result of the development of a protective oxide film on the metals surface which slows down future corrosion. A606-4 steel is available in metal roofing/siding panels, standing seam panels, flat sheets, and coil form. If you are looking for a panel that will give you a rustic look the two best options are bare cold rolled finish and A606. A606-4 will cost more, but it definitely will last longer. 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”) which is normally heavier gauge plates and A606 for lighter gauge flat sheets. ASTM A847 is used for pipe and tube. All alloys are in common production and use.

Just like anything else, there will always be advantages and disadvantages. Using weathering steel in construction can present several challenges. One challenge can be the weld-points that weather at the same rate as the other materials may require special welding techniques. Also, weathering steel is not 100% rustproof, if water is allowed to accumulate in pockets, those areas may experience higher corrosion rates, but as long as provisions for drainage are made you will be in business. Besides that, the increased resistance of Corten Steel to atmospheric corrosion makes this product a great choice for the builder. The layer protecting the surface develops and regenerates continuously when subjected to the influence of weather; the steel is allowed to rust in order to form the protective coating.