Q355B is a newly defined steel grade introduced in the latest Chinese steel standard GB/T 1591-2018.
Before the 2018 revision, this grade was named Q345B in the older version of GB/T 1591.
On the other hand, S355JR belongs to the European/British standard EN 10025-2, which defines low-alloy high-strength structural steels.
Based on chemical composition and mechanical properties, Q355B and S355JR are fully equivalent grades, offering comparable performance and applications in structural engineering, construction, and machinery manufacturing.
Rolling Conditions of S355JR
S355JR steel may be supplied in different delivery conditions:
S355JR+AR – As Rolled / Hot Rolled
S355JR+N – Normalized / Normalizing Rolled
Normalized (+N) treatment improves the steel's microstructure uniformity and refines the grain size, resulting in better toughness and mechanical stability.
International Equivalents of S355JR
S355JR is also equivalent to several well-known global structural steel grades, including:
ASTM A572 Grade 50 (USA)
DIN 17100 St50-2 (Germany)
JIS G3101 SS540 (Japan)
Chemical Composition Comparison (Max % – Heat Analysis)
| Standard | Grade | C | Mn | P | S | Si | N | Cu |
|---|---|---|---|---|---|---|---|---|
| EN 10025-2 | S355JR | 0.24 | 1.60 | 0.035 | 0.035 | 0.55 | 0.012 | 0.55 |
| GB/T 1591 | Q355B | 0.24 | 1.60 | 0.035 | 0.035 | 0.55 | 0.012 | 0.40 |
Conclusion:
Both grades have nearly identical chemistry, with only slight variation in copper (Cu) content, which does not affect material equivalency.
Mechanical Properties Comparison
For Thickness T ≤ 16 mm
| Standard | Grade | Yield Strength (Min, MPa) | Tensile Strength (MPa) |
|---|---|---|---|
| EN 10025-2 | S355JR | 355 | 470–630 |
| GB/T 1591 | Q355B | 355 | 470–630 |
Mechanical properties are completely matched, confirming their interchangeability in engineering applications.
Q355B ≈ S355JR in both chemical composition and mechanical performance.
Q355B is the new Chinese grade, replacing the older Q345B in GB/T1591-2018.
S355JR has several international equivalents such as A572 Gr.50, St50-2, SS540.
Both materials are widely used in bridges, buildings, machinery, structural parts, and other load-bearing applications.
