Weathering steel

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A high strength, Low carbon steel. Weathering steels contain 0.2-0.5 % Copper and Phosphorus. When exposed to a cycle of wet and dry outdoor conditions, weathering steels form a thin protective patina composed of metal oxyhydroxides. The oxyhydroxide film is initially a dull red, but as the crystals grown the color can change to a reflective blue (Gallagher 2000). First sold in 1933 by U.S. Steel under the name of Cor-Ten and this name is now generically used for weathering steels. Weathering steels have been used for structural and design elements in buildings. They work exceptionally well in high sulfur pollution regions. Chlorides from adjacent materials (polyurethanes, polyvinyl chlorides, etc.) or from marine environments can accelerate degradation. Patina products may slowly wash from the surface staining materials (Concrete, Stucco, Stone, Wood, Brick, etc.) in its drainage path.

Synonyms and Related Terms

weathering steel; copper steel; aço patinável (Port.); Cor-Ten; Mayari R; River-Ten; Wetterstahl (Deut.)


  • Corrodes rapidly when kept wet.

Physical and Chemical Properties

  • Patina is slightly soluble in water.

Resources and Citations

  • J.Scott, C.Searles, "Weathering Steel", in Twentieth-Century Building Materials, T. Jester (ed.), McGraw-Hill: New York, 1995.
  • W.P.Gallagher, "The Appearance of Weathering Steel Sculpture" from abstract in WAAC Newsletter Vol 22(1):13, 2000.
  • Thomas C. Jester (ed.), Twentieth-Century Building Materials, McGraw-Hill Companies, Washington DC, 1995 Comment: J.Scott, C.Searles, "Weathering Steel"

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