Q355NHB is a high-strength, low-alloy (HSLA) weather-resistant structural steel plate produced according to the Chinese national standard
GB/T 4171. It is designed to resist atmospheric corrosion by forming a stable, protective oxide "patina" on its surface when exposed to the elements.
Meaning of the Designation
Q: Represents "Qu" (yield), indicating the steel's yield strength.
355: Specifies a minimum yield strength of 355 MPa (for thicknesses ≤16mm).
NH: Abbreviation for "Nai Hou" (weather-resistant).
B: Refers to the quality grade (Grade B), which typically defines specific low-temperature impact test requirements.
| Feature | Technical Details |
|---|---|
| Atmospheric Resistance | 2–8 times higher than ordinary carbon steel. |
| Tensile Strength | 490–630 MPa. |
| Alloying Elements | Contains Copper (Cu), Chromium (Cr), Nickel (Ni), and Phosphorus (P) to catalyze the protective layer. |
| Workability | Excellent weldability, ductility, and low-temperature impact toughness. |
| Equivalents | Comparable to ASTM A588 (US) and EN S355J2WP (European). |
Chemical Composition
The excellent performance of Q355NHB mainly relies on its scientifically formulated chemical composition. The key elements and their functions are as follows (mass fraction, wt.%):
| Element | Content Range | Core Function |
|---|---|---|
| Carbon (C) | ≤0.12% | Controls content to ensure good weldability and toughness, avoiding excessive brittleness. |
| Silicon (Si) | 0.15%-0.50% | Strengthens the ferrite structure and improves the stability of the protective rust layer. |
| Manganese (Mn) | 0.90%-1.50% | Enhances solid solution strengthening and improves hot working performance. |
| Phosphorus (P) | ≤0.020% | Strictly controlled as a harmful element to prevent brittleness; trace amounts can enhance corrosion resistance. |
| Sulfur (S) | ≤0.008% | Minimized to reduce hot brittleness and avoid defects during processing. |
| Copper (Cu) | 0.25%-0.55% | The core anti-corrosion element; forms a dense oxide film on the surface to block corrosion spread. |
| Chromium (Cr) | 0.40%-0.80% | Improves the passivation ability of the rust layer and enhances resistance to acidic atmospheric corrosion. |
| Nickel (Ni) | ≤0.65% | Optimizes the structure of the protective rust layer and improves low-temperature toughness. |
| Micro-alloys (Nb/V/Ti) | Trace amounts (e.g., V: 0.02%-0.10%) | Refines grain structure, improves strength and toughness through precipitation strengthening. |
Mechanical Properties
Q355NHB balances high strength and good processability, meeting the load-bearing and forming requirements of engineering structures:
- Tensile Strength: 470-630 MPa, providing sufficient resistance to external tensile forces.
- Elongation: ≥22% (≥21% for thickness ≤6mm), ensuring good ductility during bending, stamping, and other processing.
- Impact Toughness: At 20℃, the longitudinal impact energy Akv ≥47 J; optional low-temperature impact testing (-20℃, Akv ≥27 J) for cold-region applications.
- Cold Bending Performance: Passes the 180° cold bending test (bending radius = 2×plate thickness) without cracks, suitable for complex component forming.
Key Characteristics
Weather Resistance: Forms a protective rust layer (patina) that prevents deeper corrosion, reducing maintenance.
High Strength: Good tensile strength (typically 490-630 MPa) and yield strength (≥355 MPa for <16mm thickness).
Good Formability: Exhibits toughness, ductility, and good weldability, allowing for easy cutting, forming, and welding.
Alloy Composition: Contains small amounts of copper (Cu), chromium (Cr), nickel (Ni), and phosphorus (P) to enhance corrosion resistance and toughness.
Common Applications
Infrastructure: Bridges, towers, pylons, and structural components.
Transportation: Railway vehicles, shipping containers, and vehicle frames.
Industrial: Oil derricks, seaport buildings, and offshore platforms.
Architectural: Building facades, where its natural rusted look is desired.
If you want to learn more about GNEE's products, you can send an email to alloy@gneesteelgroup.com. We are more than happy to assist you.
Q: What is Q355NHB steel plate?
A: Q355NHB is a high-performance low-alloy high-strength weather-resistant steel plate for engineering structures, complying with the Chinese national standard GB/T 4171-2008.
Q: What is the impact toughness of Q355NHB?
A: Q355NHB has a longitudinal impact energy of ≥47 J at 20℃, and optional low-temperature impact testing allows its use in cold regions.
Q: Does the performance of Q355NHB change with plate thickness?
A: Yes, the yield strength and elongation of Q355NHB slightly decrease as the plate thickness increases, while tensile strength remains stable.
Q: What quality inspection reports are provided with Q355NHB?
A: Q355NHB is accompanied by quality inspection reports such as material certificates, performance test reports, and optional non-destructive testing reports.
