Q355B is a new steel grade in latest version chinese steel standard GB/T1591-2018,before this version,Q355B steel called as Q345B in GB/T1591.
GB/T 700: This is the fundamental standard for "Carbon Structural Steels."
The designation Q355B follows a different logic:
- Q: Yield strength (Chinese: Qu fu dian)
- 355: Minimum yield strength in MPa (for thickness ≤ 16mm)
- B: Quality grade, primarily indicating a temperature for impact testing (in this case, +20°C). Grades A, B, C, D, E represent ascending levels of quality and lower test temperatures.
S355JR steels from European British steel standard BS EN10025-2 low alloy high strength steels.
S355JR steel grade can write as S355JR+AR,S355JR+N,S355JR+AR means S355jr steel materials rolled under As rolled,hot rolled.S355JR+N means S355JR steel materials rolled with heat treatment Normalized,Normalising.Normalized heat treating can approve uniformity in S355JR steel's grain size and microstructure.
EN 10025: This is a product standard for hot-rolled structural steel.
The designation S355JR is highly informative:
- S: Structural steel
- 355: Minimum yield strength in MPa (ReH ≥ 355 MPa for thicknesses ≤ 16mm)
- J: Impact energy of 27 Joules
- R: Room temperature (+20°C) test condition
Chemical Composition ( thickness ≤ 40mm)
|
Element |
EN 10025-2: S355JR |
GB/T 700: Q355B |
Analysis of Difference |
|
Carbon (C) |
0.24 |
0.24 |
/ |
|
Silicon (Si) |
≤ 0.55 |
≤ 0.55 |
/ |
|
Manganese (Mn) |
≤ 1.60 |
≤ 1.60 |
/ |
|
Phosphorus (P) |
≤ 0.045 |
≤ 0.045 |
/ |
|
Sulfur (S) |
≤ 0.045 |
≤ 0.040 |
Slightly stricter limit in Q355B (0.040% vs 0.045%). This can marginally improve weldability and hot-forming properties. |
|
Nitrogen (N) |
≤ 0.009 (if Al content not reported) |
Not typically specified as a core limit. |
EN 10025 controls N for aging prevention, linking it to Al content. GB/T 700 addresses this less explicitly in core requirements. |
|
Key Difference |
Limits are product of a detailed, product-specific standard. |
Limits are derived from a broader material standard; for modern applications, GB/T 1591 Q355B is the more direct comparator. |
For precise comparison, GB/T 1591 Q355B should be used against EN 10025 S355JR, as it is China's dedicated "high strength low alloy structural steel" standard. |
Mechanical Properties (thickness ≤ 16mm)
|
Property |
EN 10025-2: S355JR |
GB/T 700: Q355B |
Analysis of Difference |
|
Yield Strength (ReH/ Rp0.2) Min |
355 MPa |
355 MPa |
/ |
|
Tensile Strength (Rm) |
470 - 630 MPa |
470 - 630 MPa |
/ |
|
Elongation (A) Min |
22% |
22% |
/ |
|
Impact Toughness (Charpy V-Notch) |
27 J at +20°C (Mandatory) |
Tested at +20°C. Minimum value not universally mandated in GB/T 700 core text; often subject to purchase agreement. |
MAJOR DIFFERENCE. EN 10025 makes 27J at +20°C a mandatory, verifiable requirement for S355JR. In GB/T 700, "B" grade indicates the test temperature is +20°C, but the acceptance value is often negotiated. This creates potential for variability. |
|
Deoxidation Practice |
"R" indicates killed (deoxidized) with specified nitrogen control. |
Not explicitly defined in the grade designation. |
EN 10025 provides clearer guidance on steelmaking practice affecting internal soundness. |
Summary
In short, S355JR and Q355B are highly interchangeable international equivalent steel grades. Their chemical composition and mechanical properties are nearly identical, with the most critical difference being that Q355B offers better guaranteed low-temperature impact toughness. When selecting materials, engineers shall take the local climate conditions and structural service temperature of the project as the decisive factors.
💡 How to Get Professional Material Support?When facing complex international standard conversions and customized project requirements, accurate material selection is the key to ensuring engineering safety and cost control. If you are still uncertain about material selection for your specific application, or need authoritative material certification documents, our professional team is always ready to offer support.
👋 Contact our material engineers right now to get free professional consultation and precise quotations for S355JR / Q355B tailored to your project. Let professional expertise safeguard your engineering project.
What is the difference between S355 and Q355B?
Q355 and S355 are not identical standards, but they are functionally equivalent for most structural applications. Both have a minimum yield strength of 355 MPa and similar tensile strength ranges. The main differences lie in standard specifications, chemical composition limits, and delivery conditions
What is Q355B steel equivalent to?
Q355B is a Chinese low-alloy high-strength structural steel (355MPa yield strength) defined in GB/T 1591-2018, often considered the successor to Q345B. The closest international equivalents are European S355JR (EN 10025-2) and American ASTM A572 Grade 50. It is used for structural components requiring good welding and strength.
What is a steel grade S355JR equivalent to?
S355JR equivalent grades have very close chemical composition and mechanical properties to that of S355JR steel. Both the S355JR equivalent grades Q345B, A572 Gr 50, ST52-3, SM490B and S355JR steel are main products of GNEE steel.
What type of steel is S355JR?
Steel grade S355JR is used to manufacture hot-rolled flat and long products, which are subsequently used when producing steel building structures. Classification: Non-alloy structural steel. Products: Flat and long products, semi-finished products.
Is S355 equivalent to A36?
S355JR and A36 are not directly equivalent, as S355JR has higher strength (yield 355 MPa vs. A36's 250 MPa) and guaranteed impact toughness, making it closer to ASTM A572 Grade 50 than A36. A36 is often equivalent to S235JR (yield 235 MPa), a lower EN grade.
