Q355GNH Atmospheric Corrosion Resistant Weathering Steel Plate
GB/T 4171 | High Weathering Steel with 355 MPa Minimum Yield Strength
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), meaning "high weathering resistance". Compared to standard Q355NH, Q355GNH features enhanced phosphorus content (0.07-0.15%) which significantly improves atmospheric corrosion resistance. This steel forms a dense, stable, and adherent protective patina layer when exposed to cyclic wet/dry atmospheric conditions, providing superior corrosion resistance while maintaining excellent strength and good weldability.
Decoding the Grade: Q355GNH
The naming follows the Chinese steel grade system, where each part reveals key performance characteristics:
Q Yield Strength Designator — Structural steel where "Q" stands for "Qu" (屈), representing Yield Point.
355 Minimum Yield Strength — Guarantees a minimum yield strength of 355 MPa (for thickness ≤16mm).
G High Weathering — "Gao" (高) indicates enhanced weathering resistance with higher phosphorus content.
NH Weathering Quality Grade — "Nai Hou" (耐候) indicates atmospheric corrosion resistance with alloying elements (Cu, Cr, Ni, P) enabling patina formation.
Domestic Grades Comparison
Q295GNH
Yield Strength: ≥295 MPa
P Content: 0.07-0.12%
Application: Medium-load weathering structures
Key Alloy Elements (GB/T 4171)
Cu: 0.20-0.45% | Cr: 0.30-0.65% | Ni: 0.25-0.50%
Cu: 0.20-0.45% | Cr: 0.30-0.65% | Ni: 0.25-0.50%
Q355GNH
Yield Strength: ≥355 MPa
P Content: 0.07-0.15% (enhanced)
Application: Heavy-load weathering structures
Key Alloy Elements (GB/T 4171)
Cu: 0.25-0.55% | Cr: 0.30-1.25% | Ni: ≤0.65%
Cu: 0.25-0.55% | Cr: 0.30-1.25% | Ni: ≤0.65%
Q355NH
Yield Strength: ≥355 MPa
P Content: ≤0.030%
Application: Heavy-load general structures
Key Alloy Elements (GB/T 4171)
Cu: 0.25-0.55% | Cr: 0.40-0.80% | Ni: ≤0.65%
Cu: 0.25-0.55% | Cr: 0.40-0.80% | Ni: ≤0.65%
Core Characteristics:
✔ Q355GNH features enhanced phosphorus content (0.07-0.15%) for superior atmospheric corrosion resistance.
✔ The "G" designation indicates "Gao Nai Hou" (高耐候) meaning high weathering resistance.
✔ Q355GNH offers higher strength than Q295GNH with improved weathering performance.
International Equivalent Grades
ISO 4952:2006
S355WP
Chemical elements (typical):
C ≤0.12% | Si 0.10-0.50% | Mn ≤1.00%
P 0.07-0.15% | S ≤0.030%
Cu 0.25-0.55% | Cr 0.30-1.25% | Ni ≤0.65%
ISO 5952:2005
HSA355W1
Chemical elements (typical):
C ≤0.12% | Si 0.10-0.50% | Mn ≤1.00%
P 0.07-0.15% | S ≤0.030%
Cu 0.25-0.55% | Cr 0.30-1.25% | Ni ≤0.65%
EN 10025-5:2004
S355J0WP / S355J2WP
Chemical elements (typical):
C ≤0.12% | Si ≤0.50% | Mn ≤1.00%
P 0.06-0.15% | S ≤0.030%
Cu 0.25-0.55% | Cr 0.30-1.25% | Ni ≤0.65%
JIS G3125:2004
SPA-H
Chemical elements (typical):
C ≤0.12% | Si 0.25-0.75% | Mn ≤1.00%
P 0.07-0.15% | S ≤0.025%
Cu 0.25-0.55% | Cr 0.30-1.25% | Ni ≤0.65%
ASTM A242M-04
Type 1
Chemical elements (typical):
C ≤0.15% | Si ≤0.40% | Mn ≤1.00%
P 0.07-0.15% | S ≤0.050%
Cu 0.20-0.50% | Cr 0.30-1.25% | Ni ≤0.65%
Chemical Composition (GB/T 4171)
| Grade | C | Si | Mn | P | S | Cu | Cr | Ni | Others* |
|---|---|---|---|---|---|---|---|---|---|
| Q355GNH | ≤0.12 | 0.25-0.75 | ≤1.00 | 0.07-0.15 | ≤0.020 | 0.25-0.55 | 0.30-1.25 | ≤0.65 | ①,② |
📌 Notes on chemical composition:
① Micro-alloying: may contain Nb (0.015-0.060%), V (0.02-0.12%), Ti (0.02-0.10%), Alt ≥0.020%. At least one element meets lower limit; total Nb+V+Ti ≤0.22%.
② Optional: Mo ≤0.30%, Zr ≤0.15% may be added by agreement.
③ Permissible deviations for product analysis according to GB/T 222. Sulphur can be agreed ≤0.008%.
④ Through negotiation, Ni lower limit may be waived, or C ≤0.15% upon request.
⑤ Smelting: converter or electric furnace, fully killed steel. Delivery states: hot-rolled / controlled-rolled / normalized.
① Micro-alloying: may contain Nb (0.015-0.060%), V (0.02-0.12%), Ti (0.02-0.10%), Alt ≥0.020%. At least one element meets lower limit; total Nb+V+Ti ≤0.22%.
② Optional: Mo ≤0.30%, Zr ≤0.15% may be added by agreement.
③ Permissible deviations for product analysis according to GB/T 222. Sulphur can be agreed ≤0.008%.
④ Through negotiation, Ni lower limit may be waived, or C ≤0.15% upon request.
⑤ Smelting: converter or electric furnace, fully killed steel. Delivery states: hot-rolled / controlled-rolled / normalized.
Mechanical Properties & Bending Test
| Grade | Lower yield strength ReL (≥ MPa) | Tensile strength Rm (MPa) | Elongation after fracture A/% ≥ | 180° Bending mandrel diameter |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤16 | >16-40 | >40-60 | >60 | N/mm² | ≤16 | >16-40 | >40-60 | >60 | ≤6 | >6-16 | >16 | |||
| Q355GNH | 355 | 345 | — | — | 490 – 630 | 22 | 22 | — | — | a | 2a | 3a | ||
| 355/345 = Yield strength by thickness (MPa) — = not applicable for >40mm 490-630 = Tensile strength range (MPa) a/2a/3a = Bending mandrel diameter (a = specimen thickness) | ||||||||||||||
Note: 'a' = specimen thickness. Rp0.2 applies if no yield plateau. Bending specimen width b=35mm for arbitration. "—" indicates the property is not specified for that thickness range.
355
Min Yield (MPa) ≤16mm
490-630
Tensile Rm (MPa)
22%
Elongation A (≤40mm)
0.07-0.15
Phosphorus P %
Available Supply Range
Thickness Range
- Hot-rolled plates: 2mm - 40mm
- Sheets / Coils: 1.5mm - 20mm
- Custom thickness: Available upon request
Width & Length
- Width: 900mm - 4000mm
- Length: 2000mm - 18000mm
- Custom sizes: Cut-to-length available
Product Forms
- Steel Plates (hot-rolled, normalized)
- Steel Sheets & Coils
- Sections: H-beams, I-beams, Channels, Angles
- Flat bars & Round bars
Surface & Edge Options
- As-rolled surface / Shot blasted
- Primer coated (optional)
- Mill edge / Trimmed edge
- Beveled edge for welding
Stock availability: Regular sizes in stock for quick delivery | Mill order: Custom sizes available with 20-35 days lead time
Custom Dimensions & Processing
Custom Sizes
Non-standard dimensions
Laser/Plasma Cutting
CNC precision cutting
Edge Beveling
Single/double bevel
Drilling & Punching
Custom hole patterns
Bending & Forming
Plate rolling, profiling
Surface Treatment
Shot blasting, priming
Engineering Support: Free CAD assistance, nesting optimization, technical consultation
Advantages & Typical Applications
Key Advantages
- Enhanced phosphorus content for superior weathering resistance
- Higher strength than Q295GNH for demanding applications
- Excellent atmospheric corrosion resistance (2-8x carbon steel)
- Good weldability and formability
- No painting required, reduces lifecycle costs
- Wide international equivalents for global projects
Typical Applications
- Railway rolling stock & heavy containers
- Bridges & highway structures
- Industrial buildings & transmission towers
- Outdoor sculptures & architectural facades
- Heavy engineering machinery & vehicle frames
Frequently Asked Questions (FAQ)
1. What does "GNH" mean in Q355GNH?
2. What is the difference between Q355GNH and Q295GNH?
3. What are the international equivalents of Q355GNH?
4. Does Q355GNH require painting?
5. Is Q355GNH weldable?
Supply Information
Available Forms
- Plates & Sheets
- Hot-rolled Coils
- Sections (H-beams, Channels, Angles)
- Bars
Delivery Condition
- Hot-rolled: As-rolled, controlled-rolled, or normalized
- Cold-rolled: Annealed condition
- Mill test certificate (EN 10204 3.1) available
MOQ & Lead Time
- Standard MOQ: 5 tons
- Stock items: 30-35 days
- Custom production: 35-45 days
Start Your Q355GNH Project
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