③ 标准/对比页
Q345B Equivalent Grades Across GB and EN Systems
Q345B no longer exists in the current Chinese standard — GB/T 1591-2018 folded it into the Q355 series — yet the grade still appears on legacy drawings worldwide. The practical mappings are Q355B at home and EN S355JR in Europe, each with a nominal yield note that reviewers will want to see.
Home Mapping: Q355BWithin GB/T 1591-2018, Q345B maps to Q355B: minimum yield moves 345 → 355 MPa (≤16 mm) while the tensile band stays 470–630 MPa. The carbon cap loosens from 0.20 % to 0.24 % in the B quality. For Chinese design institutes this is a designation update, not a re-engineering exercise.
European Mapping: S355JREN 10025-2 S355JR is the customary EN-side counterpart, with a nominal yield 10 MPa higher at 355 MPa and a different impact system — 27 J versus the 34 J known from the GB grades. The two standards are similar in strength class but not paper-identical, so substitution rides on the design review.
What Carries OverTensile 470–630 MPa and a 34 J Charpy expectation at +20 ℃ for the B quality carry across the GB mapping. Welding consumables and procedure qualifications set for Q345B structures generally re-qualify to Q355B without changes; just note the updated carbon limit on the WPS records.
Paperwork That Settles ItAsk for the mill test certificate to state the delivered designation and standard edition explicitly. When a reviewer pushes back on a Q345B line item, an MTC showing Q355B to GB/T 1591-2018 with the mechanical table placed beside the old values usually closes the comment in one round.
Supply NoteYunhao supplies the Q355 series — which covers legacy Q345B call-offs — in 8–100 mm thickness, widths 1500–3200 mm, MOQ 25 t, 15–30 days from Tianjin or Qingdao. Send the legacy drawing reference and we mark the equivalence clearly on both the quote and the certificate.
| Item | Q345B (legacy) | Q355B (current) | EN S355JR |
|---|---|---|---|
| Standard | GB/T 1591-2008 | GB/T 1591-2018 | EN 10025-2 |
| Yield (≤16 mm) | ≥345 MPa | ≥355 MPa | ≥355 MPa |
| Tensile Rm | 470–630 MPa | 470–630 MPa | 470–630 MPa |
| Charpy | 34 J at +20 ℃ | 34 J at +20 ℃ | 27 J (JR, +20 ℃) |
| Carbon cap (B) | ≤0.20 % | ≤0.24 % | ≤0.24 % |