Drawings from Australia call for AS/NZS 3678 Grade 350. A Gulf consultant specifies S355J2. A US engineer writes A572 Gr.50. A Chinese mill certificate says Q355B. Are they the same steel? Close, but not always interchangeable.
This guide puts the common structural grades from GB/T 1591, EN 10025 and ASTM side by side, with yield, tensile, impact test temperature and carbon equivalent (CEV), and explains when a substitution is safe and when it needs the engineer’s approval.
- Equivalence chart
- Substitution map
- Five substitution checks
- Mill test certificates 3.1
- Grades we supply
- FAQ
Written by the Guiguan Steel Engineering Team. Published October 2026. Figures are typical values and are confirmed per project in our quotation.
Structural steel grade chart: GB vs EN vs ASTM
| Grade (standard) | Min. yield ReH MPa (≤16 mm) | Tensile Rm MPa | Impact test | Max CEV (≤30 mm) |
|---|---|---|---|---|
| Q235B (GB/T 700) | 235 | 370–500 | 27 J at +20 °C | not specified |
| S235JR (EN 10025-2) | 235 | 360–510 | 27 J at +20 °C | 0.35 |
| ASTM A36 | 250 | 400–550 | not required | not specified |
| Q355B (GB/T 1591) | 355 | 470–630 | 34 J at +20 °C | 0.45 |
| Q355C (GB/T 1591) | 355 | 470–630 | 34 J at 0 °C | 0.45 |
| Q355D (GB/T 1591) | 355 | 470–630 | 34 J at -20 °C | 0.45 |
| S355JR (EN 10025-2) | 355 | 470–630 | 27 J at +20 °C | 0.45 |
| S355J0 (EN 10025-2) | 355 | 470–630 | 27 J at 0 °C | 0.45 |
| S355J2 (EN 10025-2) | 355 | 470–630 | 27 J at -20 °C | 0.45 |
| ASTM A572 Gr.50 | 345 | ≥450 | supplementary (S5) | supplementary |
| ASTM A992 (W-shapes) | 345–450 | ≥450, Y/T ≤0.85 | supplementary | 0.45 (shapes) |
| Q390B/C/D (GB/T 1591) | 390 | 490–650 | 34 J at +20 / 0 / -20 °C | 0.45 |
| Q420GJC (GB/T 19879) | 420–550 (16–50 mm) | 520–680 | 47 J at 0 °C | 0.48 (≤50 mm) |
| S420M / ML (EN 10025-4) | 420 | 520–680 | 40 J at -20 °C / 27 J at -50 °C | 0.43 |
| ASTM A572 Gr.60 | 415 | ≥520 | supplementary | supplementary |
Minimum values per the referenced standards. Impact energies are the average of three Charpy V-notch specimens, longitudinal. GJ steels also limit yield ratio and offer Z15/Z25/Z35 through-thickness grades.
The key practical difference between “B”, “C” and “D” (or “JR”, “J0” and “J2”) is the Charpy test temperature, not strength. Strength is the same within each family.
Q355B vs S355JR vs A572 Gr.50: nearest equivalents
Grades are rarely exact equivalents because the standards test different things. This is the substitution map we use when an engineer approves alternatives.
| GB grade | Nearest EN grade | Nearest ASTM grade | Nearest AS/NZS grade | Notes |
|---|---|---|---|---|
| Q235B | S235JR | A36 | AS/NZS 3678 Gr.250 | A36 has slightly higher yield (250 vs 235) |
| Q355B | S355JR | A572 Gr.50 | AS/NZS 3678 Gr.350 | Most common structural grade |
| Q355C | S355J0 | A572 Gr.50 + S5 at 0 °C | Gr.350L0 | For outdoor or fatigue-loaded members |
| Q355D | S355J2 | A572 Gr.50 + S5 at -20 °C | Gr.350L15 (-15 °C) | Cold climates, thick plates |
| Q390C | between S355 and S420 | A572 Gr.55 | – | Use only with engineer approval |
| Q420GJC | S420M / S420N | A572 Gr.60 | Gr.400 | Thick plate for high-rise columns |
A572 Gr.50 has a minimum yield of 345 MPa, 10 MPa below Q355B. Q355B therefore satisfies a Gr.50 strength requirement. The reverse substitution is not automatic.
Five checks before substituting a grade
Strength and chemistry are not the only checks. Before replacing a specified grade, confirm these five points with the engineer of record.
1. Impact toughness at the right temperature
Q355B is tested at +20 °C. If the design asks for S355J2 (-20 °C), substitute Q355D, not Q355B. This matters for outdoor steel in cold regions, crane girders and dynamically loaded members.
2. Thickness bands
For Q355 and S355, minimum yield drops to 345 MPa above 16 mm, 335 MPa above 40 mm and 325 MPa above 63 mm. Designs using thick plate must use the reduced value for the actual thickness.
3. Carbon equivalent and weldability
CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Below about 0.42 most plate welds without preheat at normal thickness. Above 0.45, or for plate over 40 mm, our WPS specifies preheat. For thick-plate CJP welds this is checked per heat.
4. Through-thickness (Z) properties
Thick plates loaded across their thickness, such as column flanges at beam-to-column CJP welds, need Z15, Z25 or Z35 properties to resist lamellar tearing. Q420GJC and S355J2+Z35 are typical for box columns and multi-cavity nodes.
5. Section availability
ASTM W-shapes are not rolled in China. When a US design calls for A992 W-shapes, we either supply the nearest GB H-section in Q355B or build up a welded section to the same dimensions. Both need the engineer’s sign-off. See H-beams and plate girders and our H-beam vs I-beam guide.
Reading a mill test certificate (EN 10204 3.1)
Every heat of steel we use is traceable to a mill test certificate to EN 10204 type 3.1. “3.1” means the certificate is issued by the mill’s own inspection department, independent of production, and is based on tests of the actual product supplied.
| MTC field | What to check |
|---|---|
| Standard and grade | Matches the drawing, for example GB/T 1591 Q355D or EN 10025-2 S355J2 |
| Heat number | Matches the stamp on the plate and our traceability record |
| Thickness and dimensions | Covers the plate thickness used in the member |
| Chemical composition | C, Si, Mn, P, S, plus micro-alloys; CEV calculated and within the limit |
| Tensile test | ReH, Rm and elongation at or above minimum |
| Charpy V-notch | Test temperature and average energy meet the sub-grade |
| Z-test (if ordered) | Reduction of area ≥15 / 25 / 35% |
| Signature and stamp | Mill inspection department, not the sales office |
Where the specification asks for 3.2 certificates, the test is witnessed by a third party (for example SGS, BV or TUV) and co-signed. We arrange this at cost. A 3.1 certificate pack ships with every order, cross-referenced to piece marks in the final BOM. More on our quality, NDT and shipping process and certifications.
Which grades we use, and for what
Most of our structural steel is Q355B, the default grade for frames, girders and trusses. These are the grades we stock and fabricate most often.
| Use | Typical grade we supply | Equivalent on export drawings |
|---|---|---|
| Purlins, girts, secondary steel | Q235B or Q355B; G550 for cold-formed | S235JR / A36 |
| PEB frames, beams, trusses | Q355B | S355JR / A572 Gr.50 |
| Outdoor, crane girders, fatigue | Q355C or Q355D | S355J0 / S355J2 |
| High-rise box columns, thick plate | Q355D-Z25 or Q420GJC | S355J2+Z25 / S420M |
| Mega columns and nodes | Q420GJC, Q390GJC | S420M / A572 Gr.60 |
The 241 m Zengcheng New World tower used about 7,000 t of Q420GJC plate for its columns, and the CGN Headquarters used thick-plate multi-cavity mega columns. For lighter work, see steel warehouse buildings and structural steel fabrication.
Questions engineers ask about this topic
Need a project-specific answer? Our engineers reply within 24 hours.
Is Q355B the same as S355JR?
They have the same minimum yield (355 MPa) and tensile range (470–630 MPa) and are accepted as equivalents on most projects. Q355B is impact-tested at 34 J at +20 °C versus 27 J for S355JR, so it meets the JR requirement. Final substitution is the engineer’s decision.
Can Q355B replace ASTM A572 Gr.50?
For strength, yes: Q355B has 355 MPa minimum yield versus 345 MPa. Check any supplementary requirements in the specification, such as CVN toughness or CE limits, and get the engineer of record’s approval.
What replaced Q345B?
GB/T 1591-2018 replaced Q345 with Q355. The new grade has a 10 MPa higher yield and is the grade on current Chinese mill certificates.
What does S355NH mean?
S355NH is a hot-finished hollow section to EN 10210, normalized, with 40 J at -20 °C. For fabricated box members we usually use S355J2 or Q355D plate with matching toughness.
