1. The Role of Alloying Elements in Weathering Steel
Weathering steel exhibits superior resistance to atmospheric corrosion compared to ordinary carbon steel, with alloying elements playing a crucial role. These roles include:
- 1) Reducing the electrical conductivity of the rust layer, allowing it to precipitate and cover the steel surface;
- 2) Influencing the phase structure and types within the rust layer, hindering its growth;
- 3) Delaying rust crystallization;
- 4) Accelerating the uniform dissolution of the steel;
- 5) Accelerating the conversion of Fe2+ to Fe3+ and inhibiting the rapid growth of corrosion products;
- 6) Alloying elements and their compounds blocking cracks and defects. Further research indicates that the effects of different alloying elements on the atmospheric corrosion resistance of weathering steel vary.
2. Corrosion Resistance of Alloying Elements in Weathering Steel
- C: Carbon (C) is detrimental to the atmospheric corrosion resistance of steel. It also affects the weldability, cold brittleness, and stamping properties of steel. The C content in weathering steel is controlled below 0.12%.
- Cu: Adding 0.2%–0.4% Cu to steel results in superior corrosion resistance compared to ordinary carbon steel in rural, industrial, and marine atmospheres.
- P: P is one of the most effective alloying elements for improving the atmospheric corrosion resistance of steel. Generally, the best corrosion resistance is achieved when the phosphorus (P) content is between 0.08% and 0.15%. When P and Cu are added to steel together, a better combined effect is observed. Under atmospheric corrosion conditions, P in steel acts as an anodic depolarizer, accelerating the uniform dissolution of steel and the oxidation rate of Fe²⁺. This helps form a uniform FeOOH rust layer on the steel surface, promoting the formation of a dense protective film of amorphous iron hydroxyl oxide (FeOx(OH)₃-2x), thereby increasing resistivity and acting as a protective barrier against corrosive media penetrating the steel matrix, protecting the steel from atmospheric corrosion. When phosphorus forms PO₄⁻, it also acts as a corrosion inhibitor.
- Cr: It can form a dense oxide film on the steel surface, improving the passivation ability of the steel. The Cr content in weathering steel is generally 0.4% to 1% (maximum 1.3%). The effect is particularly pronounced when Cr and Cu are added to steel simultaneously.
- Ni: A relatively stable element. Adding Ni can shift the self-corrosion potential of steel in a positive direction, increasing its stability.
- Si: When used in combination with other elements such as Cu, Cr, P, and Ca, it can improve the weather resistance of steel.
- Ca: Recent studies have shown that adding trace amounts of Ca to weathering steel can not only significantly improve the overall atmospheric corrosion resistance of the steel, but also effectively prevent rust dripping during use.
- Mn: There is no consensus on its effect on corrosion resistance. Many scholars believe that Mn can improve the corrosion resistance of steel in marine atmospheres, but has little effect on corrosion resistance in industrial atmospheres. The Mn content in weathering steel is generally 0.5% to 2%.
- Mo: When steel contains 0.4% to 0.5% Mo, the corrosion rate of the steel in atmospheric corrosion environments (especially industrial atmospheres) may decrease by more than half.
- Co: Recent studies suggest that, like Ni, enriched Co in stabilizing rust layers can effectively inhibit Cl- ion intrusion and improve the corrosion resistance of steel in marine atmospheres.
- S: Has a negative effect on weather resistance; as a residual element, its content is controlled to less than 0.04%.Rare Earth Elements (RE): RE is one of the additive elements in Cr- and Ni-free weathering steels. Typically, the amount of RE added is less than or equal to 0.2%. RE is an extremely reactive element and a strong deoxidizer and desulfurizer, primarily purifying the steel.
The characteristic of corrosion-resistant alloying elements in atmospheric corrosion-resistant steel is that their significant corrosion resistance effect only becomes apparent after long-term use. Studies also show that alloying elements that can improve the atmospheric corrosion resistance of steel should meet the following conditions:
1) Solubility in iron is greater than solubility in rust layers;
2) Ability to form a solid solution with iron;
3) Ability to increase the potential of the steel.
Company profile
Founded in 2008, Gnee (Tianjin) Supply Chain Group Co., Ltd. specializes in the global trade and processing of Corten steel products.
• We handle all kinds of Corten engineering projects, such as bridges, gardens, hotels, and facade systems.
• Compliant with ASTM, EN, and other international standards; third-party inspection supported.
• Exported to over 200 countries and regions worldwide.
• 8 subsidiaries across China and overseas, ensuring global service coverage.
Application Fields: Architecture, landscaping, gardening, cladding, and urban infrastructure.
