Weathered steel, also known as corten steel, is an alloy of steel commonly used outdoors. Corten steel was designed to eliminate the need to paint. If left outside in the elements, it will develop a rusty appearance within just a few months. Manufacturers in America in the 1930's noticed certain steel alloys developed a layer of rust that instead of corroding the steel, protected it.
COR-TEN is a trademark owned by U.S. Steel. COR-TEN refers to two of this type of steel's distinguishing properties: corrosion resistance and tensile strength. The 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) and A606 for thin sheets. All alloys are in common production and use.
Why is Corten Steel popular? CorTen is popular with architects and sculptors because of the exterior layer of rust that forms on its surface when conditions are right. The mute-reddish brown color of CorTen makes it stand out like the red rock faces of Utah, Texas, and South America. These naturalistic steel patinas look stunning on large, imposing surfaces.