Q355B is a new type of Q345B steel under GB/T1591-2018 low alloy structural steel standard. It is equivalent to Q345B in GB/T1591-2008 version and S355JR in EN 10025-2:2004 version.
Chemical composition(%) comparison of Q345B and Q355B:
| Material | C max. | Si max. | Mn max. | P max. | S max. | Cr max. | Ni max. | Cu max. | N max. | Nb max. | V max. | Ti max. | Mo max. |
| Q345B | 0.20 | 0.50 | 1.70 | 0.035 | 0.035 | 0.30 | 0.50 | 0.30 | 0.012 | 0.07 | 0.15 | 0.20 | 0.10 |
| Q355B | 0.20 | 0.55 | 1.60 | 0.030 | 0.030 | 0.30 | 0.30 | 0.40 | 0.012 | - | - | - | - |
Mechanical properties comparison of Q345B and Q355B steel:
| Grade | Yield strength MPa in different thickness mm | ||||||||
| ≤16 | 16-40 | 40-63 | 63-80 | 80-100 | 100-150 | 150-200 | 200-250 | 250-400 | |
| Q345B | ≥345 | ≥335 | ≥325 | ≥315 | ≥305 | ≥285 | ≥275 | ≥265 | - |
| Q355B | ≥355 | ≥345 | ≥335 | ≥325 | ≥315 | ≥295 | ≥285 | ≥275 | - |
| Grade | Tensile strength MPa in different thickness mm | ||||||
| ≤40 | 40-63 | 63-80 | 80-100 | 100-150 | 150-250 | 250-400 | |
| Q345B | 470-630 | 470-630 | 470-630 | 470-630 | 450-600 | 450-600 | - |
| Q355B | 470-630 | 470-630 | 470-630 | 470-630 | 450-600 | 450-600 | - |