Quick facts - GB/T 1591-2018 · Yield ≥355 MPa · Tensile 470–630 MPa · Quality grades A / B / C / D / E at +20 / 0 / −20 / −40 °C · Plate, coil, section and tube · EN 10204 3.1 MTR · Quote in 24 hours

Q355 Steel Plate

Q355 is a Chinese low-alloy high-strength structural steel specified in GB/T 1591-2018, with a minimum yield strength of 355 MPa. It replaced Q345 when the standard was revised in 2018 to align Chinese structural steel with the European S355 series - same strength band, tighter chemical tolerances, better international interchangeability.

The letter after "355" is not cosmetic: it sets the Charpy V-notch impact test temperature, which is the temperature at which the steel is proven not to fracture brittlely. Choosing B when your project needs D is a safety decision, not a paperwork one.

1.Q355 quality grades

Grade	Impact test temperature	Min. impact energy	Typical application
Q355A	Not required	Not required	Non-critical, non-welded, ambient-only parts
Q355B	+ 20 °C	≥ 34 J	General construction, standard welded structures
Q355C	0 °C	≥ 34 J	Welded structures, moderate climates
Q355D	− 20 °C	≥ 34 J	Outdoor and cold-region structures, bridges
Q355E	− 40 °C	≥ 34 J	Cold regions, offshore, energy projects

A high impact value at +20 °C does not qualify the material for service at −20 °C. Impact energy is non-linear with temperature: specify the grade from your lowest expected service temperature.

2.Chemical composition (max %, thickness ≤ 16 mm)

Element	Q355B	Q355C	Q355D	Q355E
C	≤ 0.24	≤ 0.22	≤ 0.20	≤ 0.18
Si	≤ 0.55	≤ 0.55	≤ 0.55	≤ 0.55
Mn	≤ 1.60	≤ 1.60	≤ 1.60	≤ 1.60
P	≤ 0.035	≤ 0.035	≤ 0.030	≤ 0.025
S	≤ 0.035	≤ 0.035	≤ 0.030	≤ 0.020
Nb + V + Ti	≤ 0.12	≤ 0.12	≤ 0.12	≤ 0.12

Carbon, phosphorus and sulfur drop as the grade rises - that is how low-temperature toughness is bought. Micro-alloying (Nb, V, Ti) plus TMCP refines the grain; grades D and E are frequently supplied normalised or normalising-rolled (often marked Q355NE).

3.Mechanical properties

Property	Value	Note
Yield strength ReH	≥ 355 MPa	Thickness ≤ 16 mm; decreases with thickness (see below)
Tensile strength Rm	470 – 630 MPa	Thickness-dependent
Elongation A	≥ 21 %	Thickness ≤ 40 mm; check thicker sections
Impact energy	≥ 34 J	At the temperature set by the grade letter
Density	7.85 g/cm³	Standard for carbon steel
Weldability	Good	Arc, gas and resistance welding; preheat for thick sections

4.Yield strength decreases with thickness

Thickness (mm)	≤ 16	16 – 40	40 – 63	63 – 80	80 – 100	100 – 150	150 – 200
Min. yield (MPa)	355	345	335	325	315	295	285

A 60 mm plate is not a 355 MPa plate. If your calculation assumed 355 MPa on a thick section, re-run it before ordering.

5.Q355 equivalent grades

Region	Standard	Grade	Relationship
Europe	EN 10025-2	S355JR	Match for Q355B (+20 °C)
Europe	EN 10025-2	S355J0	Match for Q355C (0 °C)
Europe	EN 10025-2	S355J2	Match for Q355D (−20 °C)
Europe	EN 10025-2	S355K2 / S355NL	Nearest to Q355E (−40 °C / −50 °C); S355NL is normalised with stricter chemistry
USA	ASTM A572	Grade 50	Closest common US grade - but 345 MPa minimum yield, 10 MPa below Q355. Not a free substitution where the design uses 355 MPa.
USA	ASTM A709	Grade 50	Bridge steel counterpart
Japan	JIS G 3106	SM490B / SM490C	Approximate match by strength; check impact requirements

*Note: weathering resistance is a separate specification. If you need atmospheric corrosion-resistant steel, the grade is Q355NH (GB/T 4171), not Q355E. The letter on Q355B–Q355E sets impact temperature, not weathering.*

6.Q355 vs Q345

	Q345 (GB/T 1591-2008)	Q355 (GB/T 1591-2018)
Min. yield	345 MPa	355 MPa
Tensile	470 – 630 MPa	470 – 630 MPa
Chemical tolerances	Looser	Tighter
International alignment	Weaker	Aligned with EN S355

The 2018 revision folded the old multi-grade family (16Mn, 12MnV, 14MnNb) into a single performance-based series and raised the nominal yield by 10 MPa. For new designs, specify Q355 and name the quality letter.

7.Applications

Building frames, beams and columns · bridges and flyovers · offshore platforms and marine structures · heavy machinery and equipment frames · transmission towers and poles · pressure vessels and piping (with the appropriate grade) · cold-region and energy projects (D and E grades).

What is Q355 steel?

Q355 is a Chinese structural steel grade that is comparable to Q345 but has better strength. It is sometimes referred to as Q355B or Q355D, based on its chemical makeup and mechanical qualities. Q355 steel is intended to have a minimum yield strength of 355 MPa, which is much greater than the 345 MPa yield strength of Q345 steel.

Q355 steel has increased performance and is often utilized in structural applications that demand more strength. It is used in the construction industry to fabricate beams, columns, and other load-bearing structures. Q355 steel is also appropriate for making equipment components, bridges, and offshore structures.

Good Ductility

Q355 steel has strong ductility, which allows it to be deformed without fracture. This feature is significant for structural materials because it allows steel to be bent, stretched, or molded while maintaining its integrity.

Impact Resistance

Q355 steel has good impact resistance, making it appropriate for applications involving sudden and high impact loads. It can bear rapid stresses and absorb energy without failing, which is critical in constructions that may encounter dynamic loads or vibrations.

Weather Resistance

Some varieties of Q355 steel, such as Q355E, may have improved weather resistance due to the addition of alloying components. This feature allows the steel to tolerate corrosive environments, making it appropriate for use in outdoor constructions or marine situations.

FAQ

Q1. What is Q355 equivalent to in ASTM?

The closest common US grade is ASTM A572 Grade 50, but its minimum yield is 345 MPa - 10 MPa below Q355. It is an equivalent only where the design accepts that. For bridge work, A709 Grade 50 is the counterpart.

Q2. Is Q355 the same as S355?

Functionally very close: Q355B ≈ S355JR, Q355C ≈ S355J0, Q355D ≈ S355J2. Match the impact temperature, then get the substitution approved by the design authority.

Q3. Which grade letter do I need?

Take your lowest expected service temperature: above 0 °C → Q355B; down to −20 °C → Q355D; down to −40 °C → Q355E. Do not substitute a higher impact test result at +20 °C for a colder grade.

Q4. Can Q355 replace Q345 in an existing design?

Usually yes, and it is the direction the standard moved in - the yield floor is 10 MPa higher and chemistry is tighter. Confirm with the design authority before swapping on a certified structure.

Q5. Does the yield strength change with thickness?

Yes. 355 MPa applies up to 16 mm; at 40–63 mm it drops to 335 MPa and at 100–150 mm to 295 MPa. Always specify the thickness when you calculate.

Q6. Is Q355E a weathering grade?

No. On Q355B–Q355E the letter sets the impact test temperature. Weathering steel is a separate series - Q355NH under GB/T 4171. Ordering Q355E and expecting weathering performance is a costly misunderstanding.

Q7. What certificate ships with the order?

EN 10204 3.1 mill certificate with heat analysis, tensile results and Charpy impact results at the specified temperature. Third-party inspection can be arranged.

Q8. How fast can you deliver and what is the MOQ?

MOQ is 200 kg. Ex-stock sizes ship in 5–10 days; production and cut-to-length orders take 15–30 days.

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