Q355D vs Q355B
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)
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)
Chemical composition compared (%)
| Element | Q355D | Q355B |
|---|---|---|
| C | ≤0.18 | ≤0.24 |
| Si | ≤0.50 | ≤0.55 |
| Mn | ≤1.60 | ≤1.60 |
| P | ≤0.025 | ≤0.035 |
| S | ≤0.020 | ≤0.035 |
Properties compared
| Property | Q355D | Q355B |
|---|---|---|
| Yield strength | ≥355 MPa (≤16 mm) | ≥355 MPa (≤16 mm) |
| Tensile strength | 470–630 MPa | 470–630 MPa |
| Impact | −20 °C, ≥34 J | B grade: 34 J at 20 °C |
| 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 · Q355B. Substitution decisions for certified parts stay with the design authority.