Q345C steel is a Chinese structural steel grade (per GB/T 1591 standard) commonly used in construction, bridges, machinery, and pressure vessels.
There is no perfect "equivalent" across all international standards, but it aligns closely with several grades in European (EN) and American (ASTM/SAE) standards based on key properties:
Yield Strength: Minimum 345 MPa (Megapascals) or ~50 ksi (kips per square inch).
Tensile Strength: Typically 470-630 MPa.
Key Distinguishing Feature: Impact toughness (Charpy V-notch) tested at 0°C (32°F) with a minimum requirement.
Here are the most relevant counterparts:
| Standard | Closest Equivalent Grades | Key Properties |
|---|---|---|
| EN (European) | S355J2 or S355J2+N (EN 10025-2) | • Yield: ≥355 MPa (thickness dependent) • Tensile: 470-630 MPa • Impact: Tested at -20°C |
| S355JR (EN 10025-2) | • Similar strength • Tested at ambient temperature |
|
| ASTM/SAE (American) | ASTM A572 Grade 50 | • Yield: ≥345 MPa (50 ksi) • Tensile: ≥450 MPa • Similar applications |
| ASTM A992 (For structural shapes) | • Yield: 50-65 ksi • More stringent limits |
|
| Comparison | Differences to note | • Direct equivalents don't consider trace elements • Thickness affects properties • Welding characteristics vary |
Why these are the closest equivalents:
S355J2 (EN):
Matches Q345C's yield strength requirement (S355 = min 355 MPa yield, similar to Q345's nominal 345 MPa in practice).
Has an impact toughness requirement at -20°C, which is similar to (and slightly more stringent than) Q345C's requirement at 0°C. S355J2+N (normalized) offers slightly better toughness/thicker section performance.
S355JR (EN):More readily available but impact tested only at ambient temperature (+20°C). Suitable if the low-temperature toughness of Q345C is not critical for the application.
ASTM A572 Gr 50:
Matches the yield strength requirement exactly (min 50 ksi = 345 MPa).
Widely used for similar structural applications (buildings, bridges).
Crucial Difference: A572 Gr 50 does NOT mandate impact toughness testing unless specifically ordered with Supplementary Requirements (e.g., S3 for testing at 0°F / -18°C). Q345C always includes the 0°C impact requirement.
ASTM A992:
Used for rolled structural shapes (W-beams, I-beams). Has tighter chemistry controls than A572 Gr 50 and yield strength between 50-65 ksi. Like A572, impact testing is not standard unless supplementary requirements are specified.
Important Considerations When Choosing an "Equivalent":
Impact Toughness: If the Q345C specification is driven by its guaranteed toughness at 0°C, S355J2 is the closest direct match in terms of mandated properties. A572 Gr 50 or A992 would require supplementary ordering for impact testing to meet this. S355JR is not suitable if low-temperature toughness is needed.
Standard & Application: The governing design code or standard (e.g., Eurocode vs. AISC) will dictate which material standard (EN or ASTM) is acceptable. You can't simply substitute one standard for another without engineering review.
Specific Properties: Trace element limits (like Carbon Equivalent for weldability), exact tensile ranges, and elongation requirements can vary slightly between grades. Always consult the detailed material data sheets.
Thickness: Mechanical properties (especially yield strength) decrease with increasing material thickness in all these grades. Ensure the thickness range matches.
Processing: "N" in S355J2+N/NL indicates normalized or normalized-rolled delivery condition, which Q345C often is. This affects grain structure and properties, particularly for thicker sections.In summary:
The closest overall equivalent considering strength and mandated toughness is European grade S355J2 (EN 10025-2).
The closest strength equivalent in US standards is ASTM A572 Grade 50 or ASTM A992 for shapes. However, remember impact testing is not standard for these ASTM grades. Specify supplementary requirements if impact toughness is needed.
Always consult the relevant design specifications and material standards, and involve engineers when substituting materials across different standards. Never assume a direct 1-to-1 equivalence.
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