1. Mechanical Properties
| Property | Q235NH | Q355NH |
|---|---|---|
| Yield Strength | ≥235 MPa | ≥355 MPa |
| Tensile Strength | 360–510 MPa | 490–630 MPa |
| Elongation | ≥24% | ≥22% |
| Impact Toughness | ≥27J (-40°C) | ≥34J (-40°C) |
Key Difference:
Q355NH has ~50% higher yield strength than Q235NH, making it suitable for heavier loads and larger structures.
Q355NH offers better low-temperature toughness.
2. Chemical Composition
| Element | Q235NH (Max %) | Q355NH (Max %) |
|---|---|---|
| C | ≤0.12 | ≤0.16 |
| Si | 0.25–0.75 | 0.20–0.60 |
| Mn | 0.50–1.20 | 0.90–1.50 |
| P | ≤0.030 | ≤0.030 |
| S | ≤0.025 | ≤0.025 |
| Cu | 0.25–0.55 | 0.25–0.55 |
| Cr | 0.30–1.25 | 0.30–1.25 |
| Ni | ≤0.65 | ≤0.65 |
Key Difference:
Q355NH has higher Mn and C content for increased strength, while maintaining similar corrosion-resistant elements (Cu, Cr, Ni).
3. Corrosion Resistance
Both steels form a protective rust layer (patina) when exposed to weather, reducing further corrosion.
Performance:
Q355NH's higher alloy content may offer marginally better long-term corrosion resistance in harsh environments (e.g., coastal or industrial areas).
4. Applications
| Q235NH | Q355NH |
|---|---|
| - Light structural components | - Heavy-duty bridges |
| - Small architectural façades | - High-rise buildings |
| - Guardrails, signage | - Transmission towers |
| - Low-stress outdoor furniture | - Railway vehicles, containers |
Key Difference:
Q355NH is used for critical load-bearing structures, while Q235NH is for lighter, decorative, or non-critical parts.
5. Standards & Equivalents
Chinese Standard: GB/T 4171-2008 (both grades).
International Equivalents:
Q235NH ≈ ASTM A606 Type 4 (weaker)
Q355NH ≈ ASTM A588 Grade A/B (closer in strength)
6. Cost & Availability
Q235NH: Lower cost, easier to weld (lower carbon equivalent).
Q355NH: 10–20% more expensive but provides higher strength-to-weight efficiency.
