Q235NH Atmospheric Corrosion Resistant Weathering Steel Plate
🛡️ Patina-Forming Steel with 235 MPa Minimum Yield Strength & Enhanced Durability
What is Q235NH Weathering Steel?
Q235NH is a Chinese-grade structural weathering steel standardized under GB/T 4171. The "NH" stands for "Nai Hou" (耐候), directly translating to "weather resistance". Unlike ordinary steel, Q235NH forms a dense, stable, and adherent rust layer (the patina) when exposed to cyclic wet/dry atmospheric conditions. This self-protecting patina dramatically slows down further corrosion, offering 2 to 8 times the atmospheric corrosion resistance of standard carbon steel. It's the smart choice for structures where longevity and minimal maintenance are paramount, often eliminating the need for paint systems altogether.
Decoding the Grade: Q235NH
The naming follows the Chinese steel grade system, where each part reveals key performance characteristics:
Core Value Proposition
Q235NH delivers exceptional lifecycle cost savings by merging structural integrity with built-in corrosion protection. It's engineered for projects where aesthetics meet endurance, providing a robust, low-maintenance material solution.
Your Partner for Weathering Steel Supply
We are a professional Chinese supplier offering Q235NH 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 Q235NH Project
We offer flexible procurement options for Q235NH, 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
✓ Full technical data & mill certificates
✓ Export documentation support
Standards & International Comparisons
Q235NH 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, Q235NH is functionally comparable to several internationally recognized weathering steel grades, offering similar performance characteristics for atmospheric corrosion resistance.
Comparison with Key International Standards
| Standard | Comparable Grade | Key Similarity | Note |
|---|---|---|---|
| GB/T 4171 (China) | Q235NH | Primary reference grade. | Defines chemical composition & mechanical properties. |
| DIN EN 10025-5 (Europe) | S235J0W / S235J2W | Similar yield strength (235 MPa) and weathering principle. | Specific alloying content (Cu, Cr) may differ. J0/J2 indicates impact toughness temperature. |
| ASTM A588 (USA) | Grade A (~245 MPa) | Comparable strength & corrosion resistance profile for structural use. | A common US specification for painted and unpainted weathering steel structures. |
| JIS G3125 (Japan) | SMA400AW, SMA400BW | Similar weathering performance and application scope. | Japanese high-performance weathering steel for welded structures. |
Important Note: The table indicates functional comparability, not chemical identity. For any project requiring material substitution or governed by specific regional codes (e.g., Eurocodes, AISC), engineers must verify the suitability of Q235NH against the project's specified standard, considering all mechanical properties, weldability, and design requirements.
Chemical Composition (GB/T 4171)
The specific alloying elements (notably Copper, Chromium, and Nickel) are key to forming the protective patina. The following table details the mandatory and optional composition requirements for Q235NH.
| Grade | Chemical Composition(Quality Fraction)/% | |||||||||
| C | Si | Mn | P | S | Cu | Cr | Ni | others | ||
| Q235NH | ≤0.13 | 0.1 ~ 0.4 |
0.2~0.6 | ≤0.03 | ≤0.03 | 0.25 ~ 0.55 | 0.4 ~0.8 | ≤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 by the buyer, the smelting method shall be selected by the supplier.
Delivery Status: Hot-rolled steel is delivered in hot-rolled, controlled-rolled, or normalized condition. Cold-rolled steel is generally delivered in annealed condition.
Permissible Deviations: The permissible deviations in the chemical composition of finished steel products shall comply with the provisions of GB/T 222.
Mechanical & Processing Properties
Q235NH provides reliable structural strength 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/%≥ | ||||||||||||
| ≤16mm | >16~40mm | >40~60mm | >60mm | ≤16mm | >16~40mm | >40~60mm | >60mm | ≤6mm | >6~16mm | >16mm | ||||
| Q235NH | 235 | 225 | 215 | 215 | 360 ~ 510 | 25 | 25 | 24 | 23 | a | a | 2a | ||
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
- Superior Corrosion Resistance: Patina layer provides long-term protection, 2-8x better than carbon steel.
- Low Maintenance & Lifecycle Cost: Eliminates or reduces painting needs, saving on long-term upkeep.
- Aesthetic Appeal: Develops a unique, stable russet-brown patina that blends with natural surroundings.
- Good Weldability & Fabrication: Can be welded, cut, and formed using standard methods.
- Sustainable Choice: Long service life and reduced use of coatings contribute to greener construction.
Typical Applications
- Architectural Structures: Building facades, roofs, canopies, and decorative elements.
- Bridges & Highway Structures: Guardrails, sound barriers, and bridge components.
- Outdoor Sculptures & Art Installations.
- Containers, Railway Cars, and Transmission Towers.
- Industrial & Agricultural Structures exposed to the atmosphere.
Frequently Asked Questions (FAQ)
Find quick answers to the most common questions about Q235NH weathering steel. For more detailed inquiries, please don't hesitate to contact us.
"NH" stands for "Nai Hou" (耐候), which is the Chinese term for "weathering resistance" or "atmospheric corrosion resistance." In the context of steel grades like Q235NH under the GB/T 4171 standard, it specifically designates the steel as a weathering steel, meaning it contains alloying elements (primarily Copper, Chromium, and Nickel) that allow it to form a protective, self-healing rust layer (patina) when exposed to the atmosphere.
One of the primary advantages of Q235NH weathering steel is that painting is generally not required for corrosion protection. The steel is designed to form a dense, adherent patina that significantly slows down further corrosion. Painting may be applied for purely aesthetic reasons or in environments with exceptional contamination (e.g., high chloride from sea spray, industrial pollutants), but it is not necessary for its core function. This leads to substantial savings in initial and long-term maintenance costs.
There is no direct, chemically identical equivalent due to different national standards. However, Q235NH is most closely comparable to S235J0W or S235J2W as specified in DIN EN 10025-5. These European grades share the same minimum yield strength (235 MPa for S235) and are designed as weathering steels ("W"). The "J0" or "J2" indicates the impact toughness testing temperature. For project specifications requiring DIN material, engineers should conduct a detailed comparison of chemical composition, mechanical properties, and applicable design codes before substitution.
The patina formation is a natural process that depends on the local atmospheric conditions (cycles of wetting and drying). Typically, the initial rust layer develops within the first few months of exposure. However, it takes approximately 1.5 to 3 years for the patina to stabilize fully into the dense, protective layer that gives weathering steel its characteristic appearance and long-term corrosion resistance. The process can be accelerated in industrial or marine environments.
Yes, Q235NH has good weldability. Standard welding processes such as Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW/MIG), and Flux-Cored Arc Welding (FCAW) can be used. It is recommended to use welding consumables that match or exceed the strength and corrosion resistance of the base metal. Standard pre-heating and post-weld heat treatment practices for low-alloy steels should be followed, especially for thicker sections, to avoid hydrogen-induced cracking. Consulting the specific welding procedure specification for weathering steel is always advised for critical applications.
We offer flexible MOQ options to accommodate both small and large projects. For standard grades and sizes, typical MOQ starts from 5 metric tons, but we can discuss smaller quantities for trial orders. Lead time depends on the product form, size, quantity, and delivery condition:
- Hot-rolled plates/sheets from stock: 7-14 days.
- Custom production (hot-rolled): 20-35 days from order confirmation.
- Normalized or special treatment: Additional 10-15 days may be required.
Supply Information
Available Forms
We can supply Q235NH weathering steel in the following forms, subject to mill capability and order quantity:
- Plates & Sheets
- Hot-rolled Coils
- Sections (H-beams, I-beams, Channels, Angles)
- Bars
Delivery Condition
As per GB/T 4171:
- Hot-rolled: As-rolled, controlled-rolled, or normalized.
- Cold-rolled: Generally delivered in annealed condition.
ℹ️ All technical data is based on the standard GB/T 4171 and is for reference. Final specifications for your order are subject to negotiation and confirmation. Contact our sales team for a detailed technical consultation and quotation tailored to your project.
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