18 May FAQ: What is COR-TEN® Steel?
You know how “Kleenex” is used when referring to a “tissue?” Or “Chapstick” is used when referring to “lip balm?” Similarly, the terms “COR-TEN®,” “cor-ten,” “corten” and “weathering steel” are used interchangeably when referring to atmospheric, corrosion-resistant steel, which can be a tad confusing… Let’s be clear: COR-TEN® is the U.S. Steel’s trade name for atmospheric, corrosion resistant steel while weathering steel and corrosion-resistant steel are the generic terms.
The history of COR-TEN® steelBack in the 1930s, U.S. Steel developed COR-TEN® steel primarily to construct hopper cars, passenger rail cars and shipping containers. Its high strength, weather-resistant properties and extended lifecycle were ideal for these applications. In 1933, the USS patented atmospheric corrosion-resistant steel under the trade name COR-TEN®. The name is a combination of its two main features: “cor-rosion resistance” and “ten-sile strength.” Today, while the terms “corten” and “weathering steel” are used interchangeably, COR-TEN® remains a trademarked product of U.S. Steel, but is now only produced in Europe under a license agreement with U.S. Steel.
Weathering steels: A family of ASTM equivalents to COR-TEN®As COR-TEN® steel became increasingly popular, other producing mills began to develop their own weathering steels. This is when ASTM International stepped in to establish what are now considered equivalent specifications to Cor-Ten® in most applications:
The weathering processThe fundamental benefit of cor-ten steel is its ability to resist corrosion. The atmospheric corrosion resistance of weathering steel enables it to be used unpainted in many structural and architectural applications for structures, including bridges, open-frame buildings, transmission towers, sculptures and more. In the presence of moisture, air and other elements, most low alloy steels have the tendency to rust. Overtime, the rust layer becomes porous and detaches from the metal surface. With weathering steel, the rusting process occurs in the same way, but the steel produces a stable rust layer called the “patina,” which adheres to the base metal and is much less porous. This naturally-developed patina regenerates continuously as it is exposed to weather and produces a protective barrier that impedes further access of oxygen, moisture and pollutants. Essentially, weathering steel is allowed to rust in order to form the protective patina coating, which results in a much lower corrosion rate compared to other steels.
Common COR-TEN® and weathering steel applicationsIt wasn’t until the 1960s that architects began discovering new ways to use cor-ten steel. Since then, the high-strength, corrosion-resistant, aesthetically-pleasing, and cost saving benefits of weathering steel have increased in popularity. Today, weathering steels are used around the world for a variety of applications, including:
- Bridge construction
- Roofing, siding and building facades
- Transmission towers
- Landscape and garden design