Corten steel (or weathering steel) is a group of steel allows that finds frequent use in outdoor construction. Corten was originally designed to get rid of the need for painting if left outside and exposed to the elements. Corten A and Corten B develop a rusted appearance in just a few months, much quicker than standard steel. In this article, we outline the characteristics of Corten steel and the main differences between the A and B grades.
What is Weathering Steel
The most advantageous attribute of Corten A and Corten B is their corrosion resistance capacities. When this steel grade comes into contact with moisture it does not rust, unlike most of the low alloy steels available on the market.
For Corten A and Corten B, the steel forms a stable rust layer called a ‘patina’ which is a corrosion-resistant, protective barrier. This rust layer is different from that of standard steel which detaches from the surface and allows rust to penetrate deeper into the metal. The patina protects the steel beneath, ensuring its strength is maintained.
Key Features of Corten (or Cor-ten) Steel
All corten grades are weather-resistant, copper chromium alloy steels. They have a high level of resistance to atmospheric weathering, especially when compared to other unalloyed steels. Both Corten A and Corten B are aesthetically pleasing and have been used in a range of architectural applications such as sculptures and bridges.
Corten A Weathering Steel
Corten A is a blend of alloying copper, nickel, and chromium with added phosphorous. This blend of materials makes Corten A well-suited for gas flue applications. It is also frequently used for aesthetic fascias but is not recommended for applications that bear a heavy load.
Corten B Weathering Steel
Corten B is similar in composition to Corten A and is used for many structures due to its corrosion resistance. However, it is much more suitable for load-bearing structures than Corten A.
Here we can see a table of the mechanical properties of both grades:
| 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 | 2-13 | 6-40 | 345 | 485 | 19 |
Find Out More