The corrosion resistance of ASTM A606‑2 weathering steel directly comes from its carefully designed chemical composition, which promotes the formation of a dense, stable, and self‑protective surface patina that stops further atmospheric corrosion.
1. Copper (Cu): min 0.20%
Copper is the most critical element for weathering performance.
It accelerates the formation of a fine, protective oxide layer, inhibits the penetration of moisture and corrosive ions, and prevents the rust layer from becoming loose or flaking. Without sufficient copper, the steel cannot develop effective weathering resistance.
2. Chromium (Cr): 0.40–0.65%
Chromium strengthens and stabilizes the patina.
It improves the adhesion and compactness of the oxide film, making it more resistant to rain, humidity, and mild atmospheric pollutants. It also slows down the corrosion rate in urban and industrial environments.
3. Silicon (Si): 0.30–0.65%
Silicon aids deoxidation during steelmaking and refines the microstructure of the surface patina.
A finer, denser patina provides a more effective barrier against oxygen and moisture, greatly improving long‑term atmospheric corrosion resistance.
4. Nickel (Ni): up to 0.40%
Nickel enhances both toughness and corrosion resistance.
It helps the patina remain stable under changing weather conditions and improves resistance to mildly corrosive industrial atmospheres.
5. Low Carbon (C): max 0.22%
Low carbon ensures good weldability and formability without reducing corrosion resistance.
Excessively high carbon would cause uneven corrosion and reduce the stability of the protective patina.
6. Manganese (Mn): max 1.25%
Manganese provides strength while maintaining ductility, and supports a uniform microstructure that allows even patina formation across the entire surface.
