Q355B vs Q345B / 16Mn
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
Q355B
Structural & HSLA Steel
Q355B 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.
Standards: DIN S355J2 (near) · AISI A572 Gr.50 (near) · JIS SM490B (near) · GB Q355B (GB/T 1591)
Q345B / 16Mn
Pipe & Tube Steel
Q345B is China’s HSLA structural steel (successor of 16Mn) for welded structures, pressure equipment and seamless pipe — the volume grade behind much of China’s pipe and fabrication exports.
Standards: DIN 1.0570 (S355J2, near) · AISI A572 Gr.50 (near) · JIS SM490 (near) · GB Q345B (GB/T 1591); 16Mn legacy
Chemical composition compared (%)
| Element | Q355B | Q345B / 16Mn |
|---|---|---|
| C | ≤0.24 | ≤0.20 |
| Si | ≤0.55 | ≤0.50 |
| Mn | ≤1.60 | 1.00–1.70 |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.035 | ≤0.035 |
| V | — | 0.02–0.15 (optional) |
| Nb | — | 0.01–0.06 (optional) |
Properties compared
| Property | Q355B | Q345B / 16Mn |
|---|---|---|
| Yield strength | ≥355 MPa (≤16 mm) | ≥345 MPa (≤16 mm) |
| Tensile strength | 470–630 MPa | 470–630 MPa |
| Impact | B grade: 34 J at 20 °C | B grade: 20 °C, ≥34 J |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: Q355B · Q345B / 16Mn. Substitution decisions for certified parts stay with the design authority.