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Why is weathering steel resistant to corrosion?

2021-05-06 10:31:15
Weathering steel (WS), also known as low alloy steel, has a carbon content of less than 0.2 wt. % Steel. Mainly add copper, chromium, nickel, phosphorus, silicon and manganese as alloying elements. The chemical composition of these weathering steel alloys is specially formulated to quickly form an anti-rust iron layer, thereby providing a weatherproof coating for the basic steel.
Weathering steel does not require paint, which means it will not release volatile organic compounds into the atmosphere and speed up construction. Now, this has been particularly sought after by some architects, and has decorated many famous buildings and monuments.
For example, China's Vanke Center and Shanghai's Australia Pavilion. The patina on weathering steel not only has higher corrosion resistance than mild steel, but also has its attractive appearance and self-healing ability.
The steel is allowed to rust, and due to its alloy composition, the rust rate is slower than that of traditional steel, and the rust forms a protective coating, which slows down the future corrosion rate. Studies have shown that repeated dry/wet cycles are critical to the formation of the best dense and adherent anti-rust layer.
Rainwater can wash the surface of weathering steel well, is easy to drain water, and has a fast drying effect. The oxidation process of weathering steel can last for several years, and then the surface reaches a steady state "stable" through a tightly bonded coating. This largely depends on the current atmospheric conditions.