Q355D 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.
Q355D
Structural & HSLA Steel
Q355D is the low-temperature quality of China’s Q355 HSLA series to GB/T 1591 — the successor designation to Q345D. It guarantees impact toughness at −20 °C with tightened P/S limits, and is the standard Chinese plate for bridges and structures that see real winters.
Standards: DIN S355J2 (near) · AISI A572 Gr.50 (near) · JIS SM520C (near) · GB Q355D (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 | Q355D | Q345B / 16Mn |
|---|---|---|
| C | ≤0.18 | ≤0.20 |
| Si | ≤0.50 | ≤0.50 |
| Mn | ≤1.60 | 1.00–1.70 |
| P | ≤0.025 | ≤0.035 |
| S | ≤0.020 | ≤0.035 |
| V | — | 0.02–0.15 (optional) |
| Nb | — | 0.01–0.06 (optional) |
Properties compared
| Property | Q355D | Q345B / 16Mn |
|---|---|---|
| Yield strength | ≥355 MPa (≤16 mm) | ≥345 MPa (≤16 mm) |
| Tensile strength | 470–630 MPa | 470–630 MPa |
| Impact | −20 °C, ≥34 J | 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: Q355D · Q345B / 16Mn. Substitution decisions for certified parts stay with the design authority.