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Why Is Weathering Steel Resistant To Atmospheric Corrosion

What’s Weathering Steel?

Weathering steel, often referred to by the genericized trademark COR-TEN steel and sometimes written without the hyphen as corten steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years exposure to weather.
As we know, weathering steel is also called corten steel. Simply put, you would find this kind of a steel to be a trademark of the United States Steel Corporation. The thing with building materials is that you would often find a layer of rust to form over it during the course of time. No matter how much you would try to prevent it, it would definitely creep in. That is why United States Steel Corporation has come up with this idea. By giving a striking material, they would be able to prevent that layer of dust from being formed. Not only that, but it would also eliminate the steel from deteriorating more. As a result, you would not have to worry about getting it painted from time to time.
So, while all this might sound too good to be true, you would also have to look at things from a realistic point of view. This is because while the rust would continue to grow thicker, the steel would become thicker with no intention of becoming stabilized. After it would reach its breaking point, the steel would become perforated and would then need to be replaced. That is why it would be important to keep the difference in environmental conditions in mind when you would be choosing this steel.

Why Is Weathering Steel Resistant To Atmospheric Corrosion?

With air and moisture being present, all or majority of low alloy steels would have a tendency to rust. The rate at which that would happen would depend on its access to moisture, oxygen, and atmospheric contaminants that would hit the surface. As the process would progress, the rust layer would form a barrier that would prevent the contaminants, moisture, and oxygen from flowing through. This would also then help to delay the rusting process to some extent. After some time, this rusted layer would also separate itself from the metal. As you would be able to understand, this would be a cycle that would repeat itself over and over again.
However, in the case of weathering steel, things would work in a slightly different way. While the rusting process would definitely start off in the same way, the progression would be slightly different. This is because the alloying elements in the steel would produce a rust layer that would be stable and adhere to the base metal. This would then help to form a protective barrier that would prevent further access of moisture, oxygen, and pollutants. As such, you would be able to experience a corrosion rate at a much lower level than what you would normally find on ordinary structural steel.When is Weathering Steel Used?
Weathering steel mainly used in railway building, Auto-mobile, Bridge buildings, tower building, Photovoltaic power station and high way buildings, where need to material that exposed in the atmospheric. It also used in container making, oil and gas, sea port construction and drilling rigs, and the vessel parts that containing H2S.

Weathering Steel Grades

ASTM A242 Weathering Steel

Also known as the original A 242 alloy, this would have a yield strength of 50 ksi (340 Mpa) and the ultimate tensile strength would be of 70 ksi (480 Mpa) for light-medium rolled shapes. As for the plates, that would be up to 0.75 inches thick. In addition, it would have ultimate strength of 67 ksi and yield strength of 46 ksi, with the plates ranging from 0.75-1 inch in terms of thickness.
The ASTM A 242 rolled plates and sections which would be the most thickly rolled would have ultimate strength of 63 ksi and yield strength of 42 ksi.
As for its categories, you would be able to find it in Types 1 and 2. Just like the name suggests, both of them would be used for different applications, depending upon its thickness. In the case of Type 1, it would most normally be used in the construction industry, housing structures, and freight cars. As for Type 2 steel, also known as Corten B, this ASTM A 242 plates would mostly be used in passenger cranes or ships, and urban furnishings.
ASTM A588 Weathering Steel
With ultimate tensile strength of 70 ksi and a yield strength of at least 50 ksi, you would be able to find this kind of weathered steel in all rolled shapes. In terms of plate thickness, that would be up to 4 inches thick. As for plates that would be at least 4 to 5 inches, the ultimate tensile strength would be at least 67 ksi. For ASTM A588 plates that would range between 5 and 8 inches, the ultimate tensile strength would be at least 63 ksi and yield strength would be at least 42 ksi.