Q355NH Structural Steel with Enhanced Weather Resistance is a specialized low - alloy steel meticulously developed to meet the stringent requirements of GB/T 4171-2008. Engineered for critical structural applications, it provides an optimal balance of high mechanical strength, superior ductility, and significantly improved atmospheric corrosion resistance.
The steel's enhanced weather resistance is attributed to the strategic addition of Cu, Cr, and P. These elements facilitate the formation of a dense, adherent α - FeO(OH)–γ - FeO(OH) oxide layer. This protective layer acts as a natural barrier, reducing the corrosion rate to approximately 1/5–1/3 of that of conventional carbon steel, thereby extending the service life of structures.
Supplied in hot - rolled or normalized conditions, Q355NH exhibits excellent formability, making it suitable for complex structural designs. Its high strength - to - weight ratio enables the creation of lightweight yet robust structures, optimizing material usage and reducing construction costs.
Corrosion Resistance and Environmental Adaptability
In moderate - humidity environments (50 - 80% RH) with low salt and acid exposure, such as urban, rural, and mild industrial areas, Q355NH demonstrates stable corrosion resistance. The self - healing oxide layer eliminates the need for frequent protective coatings, reducing maintenance costs by up to 50% compared to standard structural steels. However, in high - salt coastal regions or areas with high - acidity levels (pH < 4), additional protective measures may be required.
Fabrication and Weldability
Q355NH supports a wide range of fabrication processes, including cold and hot forming, bending, and punching. For welding, low - hydrogen electrodes (such as E5015 - NH or E5515 - NH) are recommended to ensure that weld joints maintain the same level of corrosion resistance as the base metal. Preheating thick sections ( > 25mm) to 75–125°C helps prevent hydrogen - induced cracking, while post - weld cleaning ensures the integrity of the protective oxide layer.
FAQ
1. What standard does Q355NH Structural Steel comply with?
Answer: It complies with GB/T 4171-2008.
2. Which alloy elements improve its weather resistance?
Answer: Copper (Cu), chromium (Cr), and phosphorus (P) form a protective oxide layer.
3. How does Q355NH's corrosion rate compare to conventional carbon steel?
Answer: Its corrosion rate is 1/5–1/3 that of conventional carbon steel.
4. What are the environmental benefits of Q355NH in moderate-humidity areas?
Answer: It reduces maintenance costs by up to 50% by eliminating frequent protective coatings.
5. What welding recommendations apply to Q355NH?
Answer: Use low-hydrogen electrodes and preheat thick sections (>25mm) to 75–125°C to prevent cracking.
