Key Technical Details:
Standard Compliance:
GB/T 4171-2008 (Weathering Structural Steels) explicitly specifies that for thicknesses ≤16 mm, the yield strength must be ≥355 MPa.
Mechanical Properties for Thickness ≤16 mm:
Yield Strength (ReH): ≥355 MPa
Tensile Strength (Rm): 470–630 MPa
Elongation (A5): ≥22% (ensures ductility for structural forming).
Comparison with Thicker Sections:
| Thickness Range (mm) | Minimum Yield Strength (MPa) |
|---|---|
| ≤16 | ≥355 |
| 16–40 | ≥345 |
| 40–60 | ≥335 |
| 60–100 | ≥325 |
International Equivalents:
EN Standard: S355J0W (EN 10025-5) requires ≥355 MPa for t ≤16 mm.
ASTM Standard: ASTM A588 Grade A specifies ≥345 MPa for thicknesses ≤50 mm.
Material Certification:
Mill Test Certificates (MTC) must verify compliance with GB/T 4171-2008, including chemical composition (e.g., Cu, Cr, P alloys for weathering resistance) and mechanical properties.
Practical Implications:
Structural Design: Engineers use the 355 MPa yield strength value for load calculations in applications like bridges, building frames, and containers.
Corrosion Resistance: While mechanical strength is critical, Q355NH's primary advantage lies in its weathering durability (alloying elements like Cu/Cr/P form a protective patina).
Quality Control: Thinner sections (≤16 mm) are commonly used in façades or lightweight structures, where consistent strength is essential to avoid buckling or deformation.
Note: Properties may vary slightly based on manufacturing (e.g., thermo-mechanical control process, TMCP). For critical projects, request third-party testing to confirm yield strength and impact toughness (e.g., at -20°C per GB/T 4171).
