S355JR, Q355B and EN 10025-2: Steel Grades Across Regions
Key takeaways
- EN 10025-2 S355JR and GB/T 1591 Q355B are the usual pairing when drawings move between European and Chinese supply chains.
- Grade "equivalence" is a practical working assumption, not a legal identity — chemistry limits, impact testing and CEV requirements differ.
- The GB standard replaced Q345 with Q355 in the 2018 revision, so older drawings still say Q345.
- Always confirm the substitution in writing against your own drawing's requirements.
Why this comes up
A European drawing arrives specifying S355JR. The Chinese mill supplies Q355B. Someone has to decide whether that is acceptable — and "they are basically the same" is not an answer you want to defend after the fact.
The mapping we work from
| Item | European / EN | Chinese / GB |
|---|---|---|
| Structural steel grade | S355JR, S355J2 (EN 10025-2) | Q355B (GB/T 1591) |
| Welding procedure specification | EN ISO 15609-1:2019 | GB/T 19867.1-2005 (≡ ISO 15609-1:2004) |
| Procedure qualification | EN ISO 15614-1:2017 | GB/T 19869.1-2005 (≡ ISO 15614-1:2004) |
| Solid wire | EN ISO 14341 | GB/T 8110 (ER50-6) |
| Shielding gas | EN ISO 14175 (M21) | GB/T 39255-2020 (M21) |
| Imperfection quality levels | EN ISO 5817 (level C) | GB/T 19418-2003 (level C) |
| Visual testing | EN ISO 17637 | GB/T 32259-2015 |
| Magnetic particle testing | EN ISO 9934-1 | GB/T 15822.1 |
| Welder qualification | EN ISO 9606-1 | GB/T 15169-2003 |
| Preheat measurement | EN ISO 13916 | GB/T 18591-2001 |
| Process designation | EN ISO 4063 (135) | GB/T 5185-2005 (135) |
Note the pattern in that table: the GB equivalents generally correspond to earlier editions of the ISO standards. The numbering lines up, the family lines up, but the edition years do not — which is why a substitution should always be confirmed rather than assumed.
Three points to watch
- Impact testing. The suffix carries information. S355JR is tested at +20 °C; the J2 variant at −20 °C. Please check what your drawing actually requires before accepting a substitution that meets room-temperature toughness but not cold service.
- Chemistry limits. Permissible ranges for phosphorus, sulphur and alloying elements differ between the systems, and CEV limits may be specified differently. It matters when the part will be welded with preheat requirements set by CEV.
- Old drawings. If a drawing says Q345, it predates the 2018 revision of GB/T 1591. Confirm which grade you actually want — this comes up more often than you would expect.
How we handle it
If you supply drawings in one system and material in the other, we will state in writing what we are substituting and what standard it complies with, and ask you to confirm before cutting steel. Mill certificates accompany incoming material and are checked against physical markings on delivery.
SPEC BOX
| Field | Value |
|---|---|
| EN structural grade | S355JR / S355J2, EN 10025-2 |
| GB counterpart | Q355B, GB/T 1591 |
| Typical wire substitution | EN ISO 14341 ↔ GB/T 8110 ER50-6 |
| Typical gas designation | M21 in both systems |
| Incoming control | Mill certificate checked against marking |
FAQ
Can you build exactly to our specified grade? Yes. Where you specify the grade we buy to it and check the certificate on delivery.
What if our drawing names a grade unavailable locally? We will propose the closest counterpart, state the differences we are aware of, and wait for your written confirmation.
Do you check CEV on incoming material? Mill certificates accompany every incoming batch and are checked against the physical markings on delivery. If your project requires additional verification, tell us before ordering.
Internal links: insights/technical/preheat-and-interpass-s355-vs-hardox · insights/technical/how-to-read-a-wps · insights/cases/oem-programme-sample-to-repeat-order
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