1. Core material equivalence
| A572 Grade | Yield Strength(MPa) | GB | EN | JIS |
|---|---|---|---|---|
| Gr42 | ≥290 | Q295B | S275JR | SM400B |
| Gr50 | ≥345 | Q355B | S355JR | SM490YB |
| Gr55 | ≥380 | Q390B | S355J2 | SM520 |
| Gr60 | ≥415 | Q420B | S420ML | SM570 |
| Gr65 | ≥450 | Q460C | S460ML | - |
2. Key points for substitution
Composition difference
A572 is strengthened by microalloying with niobium (Nb) and vanadium (V) (e.g. Gr50 requires Nb+V: 0.05-0.15%), while the national standard Q355B relies on manganese (Mn) content to improve strength (Mn: 1.00-1.60%), and the control of trace elements is relatively loose. When directly replacing, the low-temperature toughness index needs to be verified, especially in an environment below -20℃.
Strength deviation compensation
When Q355B is used to replace A572Gr50:
Pressure-bearing parts need to increase wall thickness by about 3-5% to compensate for the strength gap
Dynamic load scenarios require additional fatigue life verification (refer to GB/T 3075)
Welding process adaptation
A572 welded pipes are recommended to use ER70S-6 welding wire (AWS A5.18 standard), while the corresponding national standard material needs to be switched to CHW-50C6 welding wire (GB/T 8110), and the preheating temperature needs to be increased by 10-15℃ to suppress cold cracks.
3. Special scenario recommendations
Bridges and high-pressure pipelines: The original standard A572Gr60/Gr65 is preferred, and its 415-450MPa yield strength and strict impact toughness requirements (-40℃≥27J) are difficult to be fully covered by the national standard.
Building structure: Q355B/S355JR can replace A572Gr50, but the strength of the connection nodes needs to be recalculated (the bolt hole weakening rate increases by about 2%).
