What is weathering steel

Weathering steel refers to the chemical composition of these steels, allowing them to exhibit increased resistance to atmospheric corrosion compared to other steels. This is because the weathering steel forms a protective rust patina on its surface under the influence of the weather. The corrosion-retarding effect of the protective layer is produced by the distribution and concentration of alloying elements in the steel chemistry. The layer protecting the surface develops when subjected to the influence of weather. In other words, the weathering steel is required to rust to form the protective layer.

Weathering steel, often referred to by the genericized trademark Cor-ten steel. It is a group of steel alloys developed to form a stable corrosion-resistant surface after several years exposure to weather, potentially eliminating the need for painting in many environments.

U.S. Steel (USS) holds the registered trademark on the name Cor-ten, which refers to the two distinguishing properties of this type of weathering steel: corrosion resistance and tensile strength. The original Cor-ten received the standard designation A242 (Cor-ten A) from ASTM International. Newer ASTM grades are A588 (Cor-ten B) and A606 for thin sheet.