What is the ASTM equivalent of Q355B?

The closest ASTM equivalent is A572 Grade 50 (345 MPa min yield vs Q355B's 355 MPa). For EN, Q355B corresponds to S355JR. The old Chinese name Q345B appears on pre-2019 drawings — same grade, renamed when GB/T 1591-2018 aligned chemistry with EN.

Is Q355B the same as S355JR?

Practically yes for structural use: both specify 355 MPa minimum yield and 27 J impact at +20 °C, with similar chemistry (Q355B's carbon cap of 0.20% is even tighter than S355JR's). Code projects should still get engineer sign-off on the substitution.

What does the B in Q355B mean?

It is the impact quality class: B = 27 J Charpy at +20 °C. The ladder continues C (0 °C), D (−20 °C) and E (−40 °C), matching EN's JR/J0/J2/K2 system.

Why did Q345 change to Q355?

GB/T 1591-2018 raised the minimum yield of the old Q345 class to 355 MPa and aligned chemistry with EN 10025 — the grade was renamed Q355. Old drawings saying Q345B map directly to today's Q355B.

Q355B Steel: Equivalent, Properties, Chemistry & Applications

Quick Answer

Q355B is China's GB/T 1591 high-strength structural grade: 355 MPa minimum yield with 27 J impact at +20 °C — the direct equivalent of EN S355JR and ASTM A572 Gr50 (ex-grade Q345B, renamed 2019). Chemistry: C ≤ 0.20%, Mn ≤ 1.70%. Rolled as HW/HM/HN beams, plates, angles and hollow sections; supplied with EN 10204 3.1 MTC from 5 tons.

Q355B is the grade you meet on nearly every Chinese structural drawing: columns, rafters, plate girders, trailer frames. It replaced the old Q345B designation in 2019 (GB/T 1591-2018 aligned chemistry with EN) — drawings still show both names. Buyers outside China ask two questions: is it really S355JR, and will my engineer accept it. Here are the facts.

Chemistry (ladle, GB/T 1591, ≤16 mm)

C	Si	Mn	P	S	CEV (typ.)
≤ 0.20	≤ 0.50	≤ 1.70	≤ 0.035	≤ 0.035	≤ 0.45

Carbon cap 0.20% is tighter than S355JR's 0.24% (by thickness) — Q355B welds comfortably by all standard processes.

Mechanical Properties

Property	Value	Equivalent Grade Check
Min yield Rp0.2	355 MPa (≤16 mm)	S355JR: 355 · A572 Gr50: 345
Tensile Rm	470–630 MPa	S355JR: 470–630
Elongation A	≥ 22%	—
Impact KV (B class)	≥ 27 J at +20 °C	S355JR (JR): 27 J at +20 °C

Cold-climate projects step to Q355C (0 °C) or Q355D (−20 °C) — the B/C/D/E ladder mirrors JR/J0/J2/K2 exactly.

Equivalents Across Standards

GB/T 1591	EN 10025-2	ASTM	JIS	Old GB Name
Q355B	S355JR	A572 Gr50	SM490A/B	Q345B (pre-2019 drawings)
Q355C	S355J0	A572 + CVN 0 °C	SM490C	Q345C
Q355D	S355J2	A572 + CVN −20 °C	—	Q345D

Detailed comparison: S355JR vs Q355B substitution rules →

Where Q355B Is Used

Steel structures: columns, rafters, crane beams on Chinese drawings — the default "Q355B" call-out.
Plates: base plates, gussets, equipment frames, trailer main beams.
Hollow sections: lattice towers, booms, high-load trusses.
Export projects: Southeast Asian and African fabricators buying Chinese-drawn shop plans.

What Ships with Q355B Orders

Mill test certificate 3.1 naming "Q355B per GB/T 1591" with heat chemistry and mechanicals — plus our equivalence statement to S355JR/A572 Gr50 for your engineer.
Shapes: HW/HM/HN beams, plates 2–200 mm (Q235B plate page shows the size ladder), angles, channels, hollow sections.
Cut-to-length, drilling, blasting + primer — processing services.
MOQ 5 t; EN 10204 3.1 MTC; SGS/BV inspection on request.

Q355B is the mill's default — best price, shortest lead

Size list to [email protected] or WhatsApp +86 191 5745 8011 — quotation with equivalence documentation in one working day. MOQ 5 tons.

Request Q355B Quote