Q355GNH Atmospheric Corrosion Resistant Weathering Steel Plate
🛡️ Patina-Forming Steel with 355 MPa Minimum Yield Strength & Enhanced Durability
What is Q355GNH Weathering Steel?
Q355GNH is a Chinese-grade structural weathering steel standardized under GB/T 4171. The "GNH" stands for "Gao Nai Hou" (高耐候), directly translating to "high weather resistance". With a minimum yield strength of 355 MPa, Q355GNH is a high-performance weathering steel that offers an excellent balance of strength, formability and corrosion resistance. It forms a dense, stable, and adherent rust layer (the patina) under cyclic wet/dry conditions, providing 2 to 8 times the atmospheric corrosion resistance of standard carbon steel. This grade is widely used in demanding structural applications where both higher strength and long-term, low-maintenance durability are required.
Decoding the Grade: Q355GNH
The naming follows the Chinese steel grade system, where each part reveals key performance characteristics:
Core Value Proposition
Q355GNH delivers exceptional lifecycle cost savings by merging high structural strength with built-in corrosion protection. It is engineered for projects requiring superior load-bearing capacity without sacrificing longevity, providing a robust, low-maintenance material solution for the most demanding applications.
Your Partner for Weathering Steel Supply
We are a professional Chinese supplier offering Q355GNH weathering steel plates, sheets, and sections for global projects. We provide mill-direct ordering with full traceability and support the entire export process, ensuring you receive material that meets both GB/T 4171 and your specific project requirements.
Start Your Q355GNH Project
We offer flexible procurement options for Q355GNH, from technical consultation to reliable delivery. Benefit from competitive pricing, strict quality adherence to GB/T 4171, and dedicated support for your international project needs.
✓ Formal quotation within 8-12 hours
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✓ Export documentation support
Standards & International Comparisons
Q355GNH is specified under the Chinese National Standard GB/T 4171 "Weathering Structural Steels". While direct, chemically identical equivalents in other standards are rare due to differing numbering systems, Q355GNH is functionally comparable to several internationally recognized high-strength weathering steel grades, offering similar performance characteristics for atmospheric corrosion resistance with enhanced yield strength.
Comparison with Key International Standards
| Standard | Comparable Grade | Key Similarity | Note |
|---|---|---|---|
| GB/T 4171 (China) | Q355GNH | Primary reference grade. | Defines chemical composition & mechanical properties. |
| DIN EN 10025-5 (Europe) | S355J0W / S355J2W | Similar yield strength (355 MPa) and weathering principle. | J0/J2 indicates impact toughness temperature. Widely used European weathering steel. |
| ASTM A588 (USA) | Grade A (~345 MPa) | Comparable weathering performance for structural use. | A588 has slightly lower min yield (345 MPa). Common US weathering steel spec. |
| JIS G3125 (Japan) | SMA490W | Similar weathering and strength level. | Japanese high-performance weathering steel for welded structures. |
Important Note: The table indicates functional comparability, not chemical identity. Q355GNH features higher phosphorus content for enhanced weathering performance. For any project requiring material substitution or governed by specific regional codes, engineers must verify suitability.
Chemical Composition (GB/T 4171)
The specific alloying elements (notably Copper, Chromium, Nickel, and Phosphorus) are key to forming the protective patina. The following table details the mandatory and optional composition requirements for Q355GNH.
| Grade | Chemical Composition (Quality Fraction)/% | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| C | Si | Mn | P | S | Cu | Cr | Ni | others | ||
| Q355GNH | ≤0.12 | 0.25 ~ 0.75 | ≤1.0 | 0.07 ~ 0.15 | ≤0.020 | 0.25 ~ 0.55 | 0.30 ~ 1.25 | ≤0.65 | a , b | |
| Notes: ᵃ To improve the properties of steel, one or more trace alloying elements may be added: Nb 0.015%~0.060%, V 0.02%~0.12%, Ti 0.02%~0.10%, Alt ≥0.020%. When the above elements are used in combination, at least one element should be ensured to meet the lower limit of the above chemical composition. ᵇ The following alloying elements can be added: Mo≤0.30%, Zr≤0.15%. ᶜ The total amount of the three alloying elements Nb, V, and Ti added should not exceed 0.22%. ᵈ Through negotiation between the supplier and the buyer, the sulfur content may not exceed 0.008%. ᵉ Through negotiation between the supply and demand parties, a lower limit for Ni content may not be required. ᶠ Through negotiation between the supply and demand parties, the content of C may not exceed 0.15%. |
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Production & Delivery (Based on GB/T 4171)
Smelting Methods: The steel is smelted in a converter or electric furnace and is killed steel. Unless otherwise specified, the smelting method shall be selected by the supplier.
Delivery Status: Hot-rolled steel is delivered in hot-rolled, controlled-rolled, or normalized condition. Steel grades Q460NH, Q500NH, and Q550NH can be delivered in quenched and tempered condition. Cold-rolled steel is generally delivered in annealed condition.
Permissible Deviations: Shall comply with GB/T 222.
Mechanical & Processing Properties
Q355GNH provides high structural strength (355 MPa min yield) combined with good formability and weldability. The mechanical properties vary slightly with plate thickness as detailed below.
| Grade | Tensile Test a | 180° Bending test mandrel diameter | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Lower yield strength ReL ≥ (MPa) | Tensile Strength Rm (MPa) |
Elongation after fracture A/% ≥ | ||||||||||||
| ≤16 | >16~40 | >40~60 | >60 | ≤16 | >16~40 | >40~60 | >60 | ≤6 | >6~16 | >16 | ||||
| Q355GNH | 355 | 345 | - | - | 490 ~ 630 | 22 | 22 | - | - | a | 2a | 3a | ||
Note: 'a' represents the steel thickness (in mm). When a yield plateau is not evident, Rp0.2 may be used.
Advantages & Typical Applications
Key Advantages
- High Strength (355 MPa): Excellent load-bearing capacity, enabling lighter and more efficient structural designs.
- Superior Corrosion Resistance: 2-8x better than carbon steel, reducing maintenance.
- Low Lifecycle Cost: Eliminates or reduces painting requirements.
- Aesthetic Patina: Develops a stable, attractive russet-brown appearance.
- Good Weldability & Fabrication: Suitable for standard welding and forming processes.
- Sustainable Choice: Extended service life and reduced coating use.
Typical Applications
- High-load structural components (bridges, high-rise buildings).
- Steel bridges, highway guardrails, sound barriers.
- Transmission towers, telecommunication masts.
- Railway rolling stock, containers, and frames.
- Heavy industrial equipment and mining structures.
- Offshore and port facilities (in suitable atmospheric zones).
Frequently Asked Questions (FAQ)
Find quick answers to the most common questions about Q355GNH weathering steel. For more detailed inquiries, please don't hesitate to contact us.
Q355GNH has a minimum yield strength of 355 MPa for thicknesses up to 16mm. This high strength makes it suitable for heavy-load structural applications, often allowing for reduced material thickness compared to lower-strength grades like Q295GNH.
Like all weathering steels, Q355GNH is designed to form a protective patina, so painting is generally not required for corrosion protection in most atmospheric environments. This leads to significant long-term maintenance savings. Painting is only necessary for aesthetic reasons or in exceptionally aggressive environments.
The most comparable international grades are S355J0W/J2W (EN 10025-5) and SMA490W (JIS G3125). They share similar minimum yield strength (355 MPa) and are specifically designed as weathering steels. However, Q355GNH features higher phosphorus content (0.07-0.15%) for enhanced weathering performance. Always verify specific properties before substitution.
Yes, Q355GNH has good weldability. Standard welding processes (SMAW, GMAW, FCAW) can be used. It is recommended to use low-hydrogen consumables that match the strength and corrosion resistance of the base metal. Due to the phosphorus content, proper welding procedures should be followed to avoid hot cracking.
For standard sizes, MOQ starts from 5 tons. Stock items can ship in 7-14 days. Custom mill production typically requires 20-35 days. Please contact us with your specific requirements for an accurate lead time and quotation.
Supply Information
Available Forms
- Plates & Sheets
- Hot-rolled Coils
- Sections (H-beams, I-beams, Channels, Angles)
- Bars
Delivery Condition
- Hot-rolled: As-rolled, controlled-rolled, or normalized.
- Cold-rolled: Generally delivered in annealed condition.
ℹ️ All technical data is based on GB/T 4171 and is for reference. Contact our sales team for a detailed technical consultation.
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