Q355NH Atmospheric Corrosion Resistant Weathering Steel Plate

GB/T 4171 | Patina-Forming Steel with 355 MPa Minimum Yield Strength

What is Q355NH Weathering Steel?

Q355NH is a high-strength Chinese-grade structural weathering steel standardized under GB/T 4171. The "NH" stands for "Nai Hou" (耐候), directly translating to "weather resistance". As a high-strength weathering steel, it delivers excellent mechanical performance while forming a dense, stable, and adherent protective patina layer in natural atmospheric environments. This self-protecting characteristic provides 2 to 8 times the corrosion resistance of conventional carbon steel, making it ideal for heavy-duty outdoor structures requiring high load-bearing capacity and long-term durability.

Decoding the Grade: Q355NH

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).
NH Weathering Quality Grade — "Nai Hou" (耐候) indicates atmospheric corrosion resistance with alloying elements (Cu, Cr, Ni) enabling patina formation.

Domestic Grades Comparison

Q295NH

Yield Strength: ≥295 MPa
Strength Level: Medium Strength
Application: Medium-load structures
Key Alloy Elements (GB/T 4171)
Cu: 0.25-0.55% | Cr: 0.40-0.80% | Ni: ≤0.65%

Q355NH

Yield Strength: ≥355 MPa
Strength Level: High Strength
Application: Heavy-load structures
Key Alloy Elements (GB/T 4171)
Cu: 0.25-0.55% | Cr: 0.40-0.80% | Ni: ≤0.65%

Q415NH

Yield Strength: ≥415 MPa
Strength Level: Ultra High Strength
Application: Ultra-heavy duty infrastructure
Key Alloy Elements (GB/T 4171)
Cu: 0.25-0.55% | Cr: 0.40-0.80% | Ni: ≤0.65%

Core Characteristics:
✔ All three grades share identical weathering alloy composition (Cu, Cr, Ni) for excellent corrosion resistance.
✔ Strength increases with grade number, while cost efficiency decreases slightly.
✔ Q355NH is the most widely used high-strength weathering steel grade for general engineering projects.

International Equivalent Grades

EN 10025-5 (Europe)
S355J0W / S355J2W / S355K2W
Chemical elements (typical):
C ≤0.16% | Si ≤0.50% | Mn 0.50-1.50%
Cu 0.25-0.55% | Cr 0.40-0.80% | Ni ≤0.65%
JIS G3114 (Japan)
SMA490AW / BW / CW
Chemical elements (typical):
C ≤0.18% | Si 0.30-0.65% | Mn ≤1.25%
Cu 0.20-0.50% | Cr 0.45-0.75% | Ni 0.05-0.30%
ASTM A588 (USA)
A588 Grade K
Chemical elements (typical):
C ≤0.17% | Si 0.25-0.50% | Mn 0.50-1.20%
Cu 0.20-0.40% | Cr 0.40-0.70% | Ni ≤0.40%
ISO 4952 / 5952
S355W / HSA355W2
Chemical elements (typical):
C ≤0.16% | Si 0.10-0.50% | Mn 0.50-1.50%
Cu 0.25-0.55% | Cr 0.40-0.80% | Ni ≤0.65%

Chemical Composition (GB/T 4171)

Grade C Si Mn P S Cu Cr Ni Others
Q355NH ≤0.16 ≤0.50 0.50-1.50 ≤0.030 ≤0.030 0.25-0.55 0.40-0.80 ≤0.65 Nb,V,Ti,Mo,Zr optional
Microalloying: Nb 0.015-0.060%, V 0.02-0.12%, Ti 0.02-0.10%, Alt ≥0.020%. V+Nb+Ti ≤0.22%. Mo ≤0.30%, Zr ≤0.15% (optional).

Mechanical & Processing Properties

Thickness (mm) Yield Strength (MPa) ≥ Tensile Strength (MPa) Elongation (%) ≥ 180° Bending
≤16 355 490-630 22 a
>16~40 345 22 2a
>40~60 335 21 3a
>60 325 20 3a

Note: a = specimen thickness; Bending test: mandrel diameter = a/2a/3a

Available Supply Range

Thickness Range

  • Hot-rolled plates: 3mm - 250mm
  • 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

  • High strength design, higher load capacity than Q295NH
  • Excellent weathering and corrosion resistance
  • 2-8x corrosion resistance vs carbon steel
  • Excellent weldability and cold forming properties
  • No painting required, reduces lifecycle costs
  • Wide international equivalent grades for global projects

Typical Applications

  • Heavy-duty bridges & steel structures
  • Railway rolling stock & large containers
  • Transmission towers & high-load infrastructure
  • Engineering machinery & vehicle frames
  • Architectural structures & outdoor heavy-duty facilities

Frequently Asked Questions (FAQ)

1. What does "NH" mean in Q355NH?
2. What is the difference between Q355NH and Q295NH?
3. What are the international equivalents of Q355NH?
4. Does Q355NH form a protective patina?
5. Is Q355NH suitable for heavy structural use?

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 Q355NH Project

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