Q355B
Data under reviewQ355B is the current GB/T 1591 designation that replaced Q345B in the 2018 revision, with the yield class raised from 345 to 355 MPa to align with international S355 practice. It is now the standard Chinese HSLA for structures, machinery and pipe.
Chemical composition
| Element | Content (%) |
|---|---|
| C | ≤0.24 |
| Si | ≤0.55 |
| Mn | ≤1.60 |
| P | ≤0.035 |
| S | ≤0.035 |
Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.
Properties
| Yield strength | ≥355 MPa (≤16 mm) |
| Tensile strength | 470–630 MPa |
| Impact | B grade: 34 J at 20 °C |
| Density | 7.85 g/cm³ |
Heat treatment
Supplied hot rolled, normalized or TMCP depending on thickness and order.
Equivalent grades
| Standard | Designation |
|---|---|
| din | S355J2 (near) |
| aisi | A572 Gr.50 (near) |
| jis | SM490B (near) |
| gb | Q355B (GB/T 1591) |
Compare side by side: Q355B vs S355J2 · Q355B vs Q345B / 16Mn · Q355B vs A572 Gr.50
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Structures, cranes, machinery, structural pipe and tube.
Processing: Good weldability; the natural successor grade when older drawings still call Q345B — confirm with the design authority before substituting.
FAQ
- Q355B vs Q345B?
- Q355B (GB/T 1591-2018) supersedes Q345B with a slightly higher yield floor (355 vs 345 MPa) and similar chemistry; most mills now certify to Q355B.
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Ask for a quotationVisit NasteelSource: GB/T 1591 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.