A572 Gr.50 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.
A572 Gr.50
Structural & HSLA Steel
ASTM A572 Grade 50 is the standard American HSLA structural steel — the 50 ksi yield grade that replaced A36 in most US bridge and heavy construction work. Strength comes from Nb/V microalloying and grain refinement rather than carbon, so weldability remains good.
Standards: DIN S355J2 (near) · AISI A572 Gr.50 · JIS SM520B (near) · GB Q355B (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 | A572 Gr.50 | Q345B / 16Mn |
|---|---|---|
| C | ≤0.23 | ≤0.20 |
| Si | ≤0.40 | ≤0.50 |
| Mn | ≤1.35 | 1.00–1.70 |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.045 | ≤0.035 |
| V | 0.01–0.15 (Type 2) | 0.02–0.15 (optional) |
| Nb | — | 0.01–0.06 (optional) |
Properties compared
| Property | A572 Gr.50 | Q345B / 16Mn |
|---|---|---|
| Yield strength | ≥345 MPa | ≥345 MPa (≤16 mm) |
| Tensile strength | ≥450 MPa | 470–630 MPa |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Impact | — | 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: A572 Gr.50 · Q345B / 16Mn. Substitution decisions for certified parts stay with the design authority.