GB/T 1591 — High strength low alloy structural steels
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Scope
Chinese low-alloy structural steel: plate, strip, sections and bar in the Q355 to Q690 ladder, in quality classes B, C, D, E and F separated by the impact test temperature. Specifies chemical composition, carbon equivalent, yield and tensile by thickness, elongation and Charpy energy. The 2018 revision is the edition that replaced Q345 with Q355 and introduced the delivery-condition suffixes N and M alongside the as-rolled grades.
Grades covered by GB/T 1591
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Nearest equivalents |
|---|---|---|---|---|---|---|
| Q355 | — | High-strength low-alloy structural steel (Chinese national standard) | ≤ 0.24 | 355 | 470–630 | s355jr, s355j0, s355j2 |
Revision history and superseded standards
| Year | Change |
|---|---|
| 1988 | 16Mn and 15MnV replaced by the Q-number designation system |
| 1994 | Q295–Q460 ladder established |
| 2008 | Quality classes A–E; Q345 the dominant grade |
| 2018 | Current edition: Q345 → Q355, N and M delivery conditions added, quality class A withdrawn |
Supersedes: GB/T 1591-2008 (Q345, Q390, Q420, Q460); GB/T 1591-1994; GB/T 1591-1988.
Where to buy the standard
The full text is copyrighted by SAC (Standardization Administration of China) and is not reproduced here. Purchase the current edition from SAC / Chinese national standards bookshop or your national standards body. The values on this site are the normative limits as published; the standard's own tables, notes and test methods govern.
Related standards
The 2018 revision renamed the grade
GB/T 1591 is the Chinese low-alloy structural standard, and the most important fact about it is a date. The 2018 revision replaced Q345 with Q355, raising the guaranteed yield by 10 MPa and bringing the grade into line with the international 355 MPa class. It also withdrew quality class A — there is no Q355A.
Drawings, catalogues and stock lists across the industry still say Q345, and mills supply Q355B against them. A certificate issued after 2018 that names Q345 is working from a withdrawn edition.
Where it sits against EN 10025-2
The match is unusually clean. Q355 guarantees 355 MPa yield to 16 mm and a 470–630 MPa tensile band — the same band EN 10025-2 specifies for S355 — and its B, C and D classes map onto JR, J0 and J2 at +20, 0 and −20 °C.
Two differences deserve checking. The Chinese impact requirement is 34 J where the European is 27 J, so a conforming Q355 is tested slightly harder. And the yield ladders diverge above 63 mm, which means a substitution that is exact in thin plate is not exact in heavy section.