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What Exactly Is Weathering Steel And What Are Its Application?

Weathering steel is a type of low carbon steel that incorporates additional alloying elements in addition to carbon and iron atoms. Weathering steel has greater strength and corrosion resistance than normal low carbon steel grades owing to the inclusion of these alloying components. As a result, weathering steel is often used in outdoor installations or areas where regular steel will rust.


Weathering steel, as a low carbon steel, usually absorbs less than 0.3 percent carbon by weight. The low amount of carbon allows it to remain hard and malleable. Corrosion resistance, high strength are the important alloying elements of these steel types. Nickel, Copper and Chromium are the 3 important alloying materials in installations weathering steel.

How does Weathering Steel work?

Weathering steel is not the same as other corrosion-resistant steels, such as austenitic stainless steel, which resists the accumulation of rust. Weathering steel can rust, but only on the outer surface. If the exterior coating of rust has grown, the rust does not reach further into the weathering steel. The rusty surface coating serves as a shield, shielding the steel from further corrosion. The rust layer formed in the plain carbon steel is porous and breaks off, so it allows another layer to form deeper into the material. The cycle goes on till the steel is useless. The first layer rust on the metal forms to hold on to the steel because of contribution of alloys. Hence there is no need to coat the metal with protective layer.

Grade of weathering steel

Weathering steel is from a low carbon alloy steel that consists of various grades. Some classes, such as CORTEN A and CORTEN B, are proprietary. Patinax weathering steels are a different kind of patented grade. Many of these patented ratings refer to ASTM classifications A 242 and A 588.

What are the applications of Weathering Steel?

Weathering steel is widely used for exposed steel buildings because it outlasts plain carbon steel under outdoor environments. This eliminates the need for steel repainting and recoating on a regular basis. Building and bridge design are two examples. The defensive rust coating reduces the corrosion rate to the point that, by the time the level of corrosion becomes dangerous, the structure has already outlived its design life for other reasons.

Weathering steel can not be used in such situations because the corrosion resistance is inadequate to survive the conditions. Weathering steel can not be used in areas containing elevated levels of chlorine so the defensive corrosion coating would be unable to tolerate the high levels of corrosives current. As a result, the system will fail prematurely. Weathering steel should not be used in applications that could result in galvanic corrosion or corrosion caused by extreme pH levels.

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