③ 标准/对比页
Q235B vs Q355B: Where the Extra 120 MPa Pays Off
Q235B (GB/T 700) and Q355B (GB/T 1591) are the two default structural plates out of China, and the choice between them is a load question. Q355B brings 355 MPa minimum yield against 235 MPa, a different tensile band and a tougher impact requirement. Here is how the two differ on paper and in the yard.
The Strength StepQ235B guarantees 235 MPa minimum yield and 370–500 MPa tensile; Q355B guarantees 355 MPa and 470–630 MPa. That is a 50 % yield step within the same class of per-ton material budgets, which is why weight-sensitive frames, booms and long spans default to Q355B while base frames and secondary supports stay with Q235B.
Toughness Rules Differ TooQ355B requires Charpy KV2 of at least 34 J at +20 ℃ in the B quality; Q235B impact requirements follow GB/T 700 at a lower energy class. If the structure sees cold winters, remember the Q355 side offers higher quality letters — C, D and E — that move the test temperature down to −40 ℃.
Welding and FabricationBoth weld readily with common consumables; the practical difference shows in preheat for thick Q355B sections and in springback during forming, since 355 MPa class material is noticeably stiffer. Q235B remains the easier grade for bending, rolling and on-site correction — one reason equipment bases keep specifying it.
Cost Logic Without AdjectivesPer ton, Q235B is cheaper; per unit of carried load, Q355B often wins because members slim down and dead weight drops. Run the connection design both ways when loads are moderate — the crossover point is project-specific, and a single comparison sheet usually settles it.
Supply From One Mill LineYunhao rolls both grades in 8–100 mm thickness and 1500–3200 mm widths, MOQ 25 t, 15–30 days from Tianjin or Qingdao, mill test certificate per heat declaring grade and standard. Mixed-grade orders ship together, so a Q355B frame with Q235B attachments lands as one consignment.
| Item | Q235B | Q355B |
|---|---|---|
| Governing standard | GB/T 700 | GB/T 1591-2018 |
| Minimum yield (≤16 mm) | ≥235 MPa | ≥355 MPa |
| Tensile Rm | 370–500 MPa | 470–630 MPa |
| Charpy KV2 (B, +20 ℃) | per GB/T 700 | ≥34 J |
| Typical fit | bases, supports, general work | frames, booms, long spans |