SM490A 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.
SM490A
Structural & HSLA Steel
SM490A is the weldable structural steel of JIS G3106 — rolled steel for welded structures with controlled chemistry (C ≤0.20%, Mn ≤1.60%) and a 490–610 MPa tensile range. It is the Japanese counterpart class to Q345B and A572 Gr.50 and the default upgrade from SS400 for welded primary structures.
Standards: DIN 1.0570 (S355J2, near) · AISI A572 Gr.50 (near) · JIS SM490A (JIS G3106) · GB Q345B (near)
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 | SM490A | Q345B / 16Mn |
|---|---|---|
| C | ≤0.20 | ≤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 | SM490A | Q345B / 16Mn |
|---|---|---|
| Tensile strength | 490–610 MPa | 470–630 MPa |
| Yield strength | ≥325 MPa (≤16 mm) | ≥345 MPa (≤16 mm) |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Impact | A grade: no mandatory Charpy (B/C grades add impact requirements) | B grade: 20 °C, ≥34 J |
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: SM490A · Q345B / 16Mn. Substitution decisions for certified parts stay with the design authority.