Q460NH High Strength Weathering Steel Plate - GB/T 4171-2008
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Products Description
Q460NH is a premium-grade weathering steel plate engineered to withstand harsh atmospheric conditions while delivering exceptional structural integrity. Complying with GB/T 4171-2008 , this steel combines high strength (460 MPa yield) with inherent corrosion resistance, making it a cost-effective solution for long-term outdoor applications. Its unique alloy composition and microstructural design enable the formation of a stable rust layer (patina) that acts as a natural barrier against corrosion, eliminating the need for frequent painting or coating.
Chemical Composition (GB/T 4171-2008)
The alloying elements in Q460NH are precisely controlled to enhance corrosion resistance and mechanical properties:
| Element | Content (%) | Role |
|---|---|---|
| C | ≤0.12 | Maintains weldability and toughness. |
| Si | ≤0.65 | Strengthens the oxide layer stability. |
| Mn | ≤1.50 | Improves tensile strength and hardness. |
| P | ≤0.025 | Enhances atmospheric corrosion resistance in synergy with Cu. |
| S | ≤0.030 | Controls sulfide inclusions for improved ductility. |
| Cu | 0.20–0.55 | Promotes the formation of a dense, adherent rust layer. |
| Cr | 0.30–1.25 | Increases resistance to pitting and general corrosion. |
| Ni | 0.12–0.65 | Enhances toughness and corrosion resistance in chloride-rich environments. |
| Nb, V, Ti | trace addition | Refines grain structure for improved strength and weldability. |
The strategic addition of Cu, Cr, and P enables the formation of a dense, adherent α-FeO(OH)–γ-FeO(OH) oxide layer. This natural barrier significantly retards moisture, oxygen, and pollutant penetration, reducing corrosion rates to 1/5–1/3 of ordinary carbon steel and extending service life by 3–5 times in moderate-humidity environments.
Mechanical Properties (GB/T 4171-2008)
Q460NH provides robust mechanical performance across a range of thicknesses:
| Property | Value | Test Standard |
|---|---|---|
| Yield Strength (Re) | ≥460 MPa (for thickness ≤16mm) | GB/T 228 |
| Tensile Strength (Rm) | 570–730 MPa | GB/T 228 |
| Elongation (A) | ≥19% | GB/T 228 |
| Impact Toughness | ≥27 J at -40°C (for thickness ≥6mm) | GB/T 229 |
| Hardness | HB 180–240 | GB/T 231.1 |
These properties ensure Q460NH can withstand heavy loads and dynamic stresses in demanding environments.
Weathering Mechanism
Q460NH's corrosion resistance stems from its ability to form a stable, protective α-FeO(OH) rust layer when exposed to air and moisture. The alloying elements (Cu, P, Cr, Ni) accelerate the formation of this layer while preventing its exfoliation . This patina acts as a self-healing barrier, reducing corrosion rates to 1/8th of conventional carbon steel .
Applications
Q460NH is widely used in:
Bridges: Reduces maintenance costs for long-span structures in industrial or coastal zones.
Railway Carriages: Resists corrosion from moisture and salt in rail environments .
Coastal Infrastructure: Ideal for ports, offshore platforms, and marine equipment due to its salt fog resistance.
Architectural Design: Its natural rust aesthetic is popular in modern buildings and landscape design.
Industrial Equipment: Chimneys, storage tanks, and machinery exposed to corrosive gases.
Processing Recommendations
Welding: Use low-hydrogen electrodes (e.g., E5015-NH) and preheat to 100–150°C for thick sections to prevent hydrogen-induced cracking .
Surface Preparation: Avoid mechanical damage to the rust layer during fabrication. For painted applications, apply coatings after the patina stabilizes (3–6 months).
Forming: Cold or hot forming is feasible, but lubrication is recommended to prevent surface scratches.
Compliance and Sustainability
Q460NH meets GB/T 4171-2008 requirements and aligns with international standards like ISO 4952. Its reduced maintenance needs and extended lifespan (50+ years) contribute to sustainable construction practices by minimizing material waste and environmental impact.
Comparison with Conventional Steel
| Aspect | Q460NH | Q345B Carbon Steel |
|---|---|---|
| Corrosion Resistance | Excellent (2–8x better) | Poor (requires regular coating) |
| Yield Strength | 460 MPa | 345 MPa |
| Lifespan (Unpainted) | 50+ years | <20 years |
| Cost-Effectiveness | Higher initial cost, lower lifecycle cost | Lower initial cost, higher maintenance |
Conclusion
Q460NH High Strength Weathering Steel Plate (GB/T 4171-2008) offers a unique combination of high strength, corrosion resistance, and sustainability. Its performance in extreme environments and ease of fabrication make it a preferred choice for critical infrastructure projects worldwide. Always consult the latest standard and manufacturer guidelines for specific applications.
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