Corten Weathering Steel Grades & Specifications
In the construction industry, builders, architects, and contractors rely on various materials to ensure strength and aesthetic appeal in their projects. Metal components have become a significant part of modern building designs, with cladding being one of the most common elements. Manufacturers offer several cladding options like aluminum panels, steel siding, and copper sheets. However, weathering steel, especially CORTEN, stands out for its distinctive properties and durability.
In this guide, we’ll explore the different grades of CORTEN weathering steel and the specifications that make it a preferred choice in many construction projects.
What is Weathering Steel or CORTEN Steel?
CORTEN Steel, also known as weathering steel, is a popular material in the construction industry, valued for its unique look and durability. Corten metal develops a natural, rust-like finish with orange hues over time, making it a favorite choice for architectural projects.
CORTEN Steel consists of steel alloys designed to help architects and designers create long-lasting, visually appealing structures. Its key advantage is its high resistance to corrosion, which comes from a protective layer of rust that forms when exposed to air and moisture. This protective layer makes CORTEN more durable than other steel alloys.
Another benefit of CORTEN weathering steel is its low maintenance. It doesn’t require painting or upkeep, even over a lifespan of 40 years or more. As the steel rusts, it forms a protective coating that enhances both the appearance and performance of your cladding system.
Corten Weathering Steel Grades & Specifications
Weathering steels fall under a group of ASTM standards and several trademarked specifications known for their corrosion resistance. The most common ASTM specifications include A588, A242, A606-4, A847, A871-65, and A709-50W. The main trademarked product is Cor-Ten®.
Cor-Ten® Steel Specifications
Cor-Ten® is the trade name developed by the United States Steel Corporation for a corrosion-resistant steel designed for high strength and long lifespan. This steel forms a protective rust layer when exposed to different weather conditions, which shields it from further corrosion. Over time, other manufacturers created their own corrosion-resistant steel types, leading to ASTM creating equivalent standards.Â
The Corten Steel ASTM specifications are ASTM A588, A242, A606-4, A847, and A709-50W.
ASTM A588
ASTM A588 is a high-strength, low-alloy steel with enhanced corrosion resistance. It’s commonly used for structural shapes like beams, channels, and steel plates. A588 is mainly used in welded bridges and other structures where durability and weight savings are crucial. ASTM A588 has a minimum yield strength of 50 ksi and a tensile strength of 70 ksi.
ASTM A242
ASTM A242 is also a high-strength, low-alloy steel specification with improved atmospheric corrosion resistance, commonly used in steel plates up to half an inch thick. It is ideal for unpainted structures and has similar strength properties as A588, with a yield strength of 50 ksi and a tensile strength of 70 ksi.
ASTM A606-4
ASTM A606-4 covers both hot and cold-rolled steel sheet, strip, and coil. It is known for its enhanced corrosion resistance and is used in many structural and miscellaneous applications. Like A588 and A242, ASTM A606-4 has a minimum yield strength of 50 ksi and a tensile strength of 70 ksi.
ASTM A847
ASTM A847 specifies high-strength, low-alloy steel for cold-formed, welded square and rectangular tubing. This steel is used in bridge construction and other applications where both strength and corrosion resistance are needed. It can be used bare without painting.
ASTM A709-50W
ASTM A709-50W is a standard for structural steel in bridge construction. It has an atmospheric corrosion index of 6.00 or higher, making it suitable for unpainted applications. It offers high strength and corrosion resistance in structural shapes, plates, and bars.
ASTM A871-65
ASTM A709-50W is a standard for structural steel in bridge construction. It has an atmospheric corrosion index of 6.00 or higher, making it suitable for unpainted applications. It offers high strength and corrosion resistance in structural shapes, plates, and bars.
ASTM A572-65
ASTM A572-65 is a high-strength, low-alloy steel, primarily used for galvanized transmission and lighting poles. ASTM A572-65 has a minimum yield strength of 65 ksi and a tensile strength of 80 ksi, with a Charpy V-Notch test of 15 ft-lb at -20°F.
Corten Steel Grades
- Corten A
- Corten B
Corten A Weathering Steel
Corten A is a weather-resistant steel made by combining copper, chromium, and nickel, with added phosphorus. This makes it ideal for gas flue applications and aesthetic facades. However, it’s not suitable for heavy load-bearing uses—Corten B or S355J2W are better options for those purposes.
The top layer of Corten A reacts with the atmosphere to form a rust-colored protective coating, giving it a maintenance-free finish while also offering an attractive, uniform appearance.
Chemical Composition of Corten A
| C | 0.15 |
|---|---|
| Si | >0.25/0.75 |
| Mn | 0.20/0.50 |
| P | 0.07/0.15 |
| S | 0.030 |
| Al | 0.015/0.06 |
| Cu | 0.25/0.55 |
| Cr | 0.50/1.25 |
| Ni | 0.65 |
Corten A Mechanical Properties
| Grade | Thickness (mm) Strip Products | Plate Products | Yield Strength Rel N/mm² Minimum | Tensile Strength Rm N/mm² Minimum | Elongation A50 % Minimum |
|---|---|---|---|---|---|
| Corten A | 2-12 | 6-12 | 345 | 485 | 20 |
Corten B Weathering Steel
Corten B is a weather-resistant steel designed for heavy and load-bearing structures. It forms a protective layer when exposed to the elements, as the outer surface rusts, shielding the steel underneath. This natural finish typically requires no maintenance, making it a cost-effective choice compared to other structural steels.
However, if the structure is consistently exposed to moisture (e.g., near the ground or submerged), the protective layer won’t form, and painting or maintenance will be necessary.
Please refer to the technical specifications for more details.
Corten B Grades & Equivalents
| Corten | EN 10025-5:2004 |
|---|---|
| Corten B | S355J2W |
Chemical Composition of Corten B
| C | 0.19 |
|---|---|
| Si | 0.30/0.65 |
| Mn | 0.80/1.25 |
| P | 0.035 |
| S | 0.030 |
| Al | 0.020/0.06 |
| V | 0.02/0.10 |
| Cu | 0.25/0.40 |
| Cr | 0.40/0.65 |
| Ni | 0.40 |
Corten B Mechanical Properties
| Grade | Thickness (mm) Strip Products | Plate Products | Yield Strength Rel N/mm² Minimum | Tensile Strength Rm N/mm² Minimum | Elongation A50 % Minimum |
|---|---|---|---|---|---|
| Corten B | 2-13 | 6-40 | 345 | 485 | 19 |
Can You Weld Weathering Steel Grades?
If you’re working with CORTEN Weathering Steel for complex designs, you might wonder if it can be welded. The answer is yes—weathering steel tubes, pipes, or panels can be welded using the proper techniques.
To weld CORTEN steel, manufacturers use a flux combination that matches the steel’s grade. This ensures the tensile strength of the welding rod or wire aligns with the strength of the weathering steel. Typically, the tensile strength of these grades ranges between 68 to 78 KSI. For best results, it’s recommended to weld A606-4 or A588 weathering steel grades together.
Note: Welding weathering steel with other types of metal may result in different reactions.
Can You Apply a Clear Coat to CORTEN Weathering Steel Grades?
Yes, you can apply a clear coat to weathering steel panels, but it’s best to do so after A606-4 and A588 have developed their natural rust or patina finish. If you apply a clear coat before the patina forms, it may strip away the rustic appearance.
Keep in mind that applying a clear coat will likely change the color of the steel surface due to the additives in the coating.
We don’t have specific recommendations for clear coating materials, so it’s a good idea to consult your local paint store for expert advice on the right products.
How Long Does It Take to Develop the Rustic Finish on CORTEN Steel?
The time it takes for CORTEN steel to develop its orange-brown patina varies based on several factors, including the environment, moisture, weather, and humidity.
A606-4 weathering steel forms the patina faster due to its ability to go through wet and dry cycles. When exposed to moisture, it begins to oxidize, and as it dries, the rust develops into the characteristic finish.
Note: To speed up the process, you can apply natural solutions. For example, rinsing your steel panels with water on a sunny day can increase humidity and accelerate the patina formation.
How Long Will CORTEN Steel Last?
CORTEN steel is known for its long-lasting durability, but its lifespan can vary based on environmental factors and installation methods. For instance, sealing CORTEN steel can either extend or shorten its lifespan.
Generally, bare cold-rolled weathering steel panels can last over forty years without issues. Modern CORTEN steel panels can even last longer.
For increased durability, consider using thicker gauge sheets, as these can enhance the lifespan of your CORTEN panels.
Does CORTEN Steel Rusting Stop?
CORTEN Weathering Steel doesn’t completely stop rusting or developing patina. After installation, the steel begins to form a patina, which eventually creates a protective layer on the surface. This layer helps shield the underlying metal from further corrosion.
Studies have shown that the rust film on weathering steel contains alloying elements that form compounds blocking the pores in the steel. As a result, the rusting process continues, but the steel’s corrosion is controlled.
Can You Use CORTEN Weathering Steel for Decorative Applications?
Yes, CORTEN Weathering Steel is a great choice for decorative applications. Its corrosion resistance, durability, and attractive rust finish make it ideal for creating stylish and long-lasting elements.
You can use CORTEN steel for various decorative features, such as gates, privacy screens, and ornamental fence panels. Modern manufacturers offer beautiful options for gardens, driveways, and gates made from weathering steel, adding both beauty and safety to your home.
Corten Steel Supplier
When it comes to sourcing high-quality Corten steel for various applications, including decorative and structural uses, Corten Steel Tube stands out as a leading corten steel supplier in India. We offer a comprehensive range of Corten steel products, including tubes, plates, and panels, catering to both aesthetic and functional needs.
Corten Steel Tube provides top-notch Corten steel options that align with the specifications discussed in this blog. Whether you’re looking to enhance your project with weather-resistant steel for architectural features or structural components, their wide selection ensures you’ll find the right product for your requirements. By choosing our Corten products, you’re investing in durability and timeless beauty for your construction or design projects.
For more details on their full range of Corten steel products –Contact us!