SM520B vs Q390B
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.
SM520B
Structural & HSLA Steel
SM520B is the 520 MPa tensile class of JIS G3106 weldable structural steel, with yield of at least 365 MPa in thin sections and the same controlled C/Si/Mn chemistry window as SM490. The B suffix adds a Charpy impact requirement that the A grades do not carry.
Standards: DIN S355J2 / S420 type (near) · AISI A572 Gr.50–60 type (near) · JIS SM520B (JIS G3106) · GB Q390B (near)
Q390B
Structural & HSLA Steel
Q390B is the 390 MPa step in the GB/T 1591 HSLA ladder, microalloyed with Nb/V/Ti for strength without a carbon increase. It fills the gap between Q355 and Q420 in Chinese machinery and construction design.
Standards: AISI A572 Gr.60 (near) · JIS SM570 (near) · GB Q390B (GB/T 1591)
Chemical composition compared (%)
| Element | SM520B | Q390B |
|---|---|---|
| C | ≤0.20 | ≤0.20 |
| Si | ≤0.55 | ≤0.50 |
| Mn | ≤1.60 | ≤1.70 |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.035 | ≤0.035 |
| Nb | — | 0.015–0.06 |
| V | — | 0.02–0.15 |
Properties compared
| Property | SM520B | Q390B |
|---|---|---|
| Tensile strength | 520–640 MPa | 490–650 MPa |
| Yield strength | ≥365 MPa (≤16 mm) | ≥390 MPa (≤16 mm) |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Impact | B grade: Charpy requirement applies per JIS G3106 | B grade: 34 J at 20 °C |
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: SM520B · Q390B. Substitution decisions for certified parts stay with the design authority.