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GB/T 1591 Q345C is a low-alloy high-strength structural steel (HSLA) — the grade that gives roughly 95 MPa more yield than plain carbon structural steel while still welding with ordinary consumables. The name is a specification, not a marketing line: Q is the Chinese abbreviation for yield strength (qu fu), 345 is the minimum yield strength in MPa, and C is the quality grade — the letter that tells you the steel carries a guaranteed Charpy V-notch impact test at 0 °C (≥ 34 J). It sits in the middle of the Q345 family, one step tougher than Q345B.
Q345C is hot-rolled plate, sheet, section and bar for welded and bolted structures — bridges, building frames, transmission towers, crane and mining equipment, ships and general heavy fabrication. The strength comes from small additions of niobium (Nb) and vanadium (V) (plus aluminium grain refinement), not from high carbon, so it stays formable and readily weldable. One naming note worth keeping straight: GB/T 1591 was revised in 2018 and the grade was renamed Q355 (Q355C, Q355B and so on); Q345C is the legacy 2008 designation and is still specified every day, so both names reach the same steel — we supply and certify against whichever your drawing cites.
470-630 MPaTensile Strengthmin-max band, not a single value
345 MPa minYield Strengthup to 16 mm; steps down with thickness
0 °CImpact Test Temperature≥ 34 J (the 'C' grade)
Q355C2018 Renamed GradeGB/T 1591 legacy = Q345C
02Technical Specifications
What this page publishes, and what must be confirmed on the mill certificate when you enquire.
Item
Specification
Executive Standard
GB/T 1591 (Chinese standard for hot-rolled low-alloy high-strength structural steel). The 2008 edition calls the grade Q345C; the 2018 revision renamed it Q355C with slightly tightened chemistry and a stated carbon-equivalent. Both are the same product family.
Low-alloy high-strength structural steel (HSLA), micro-alloyed with Nb / V
Product Forms Covered
Steel PlateSheetSectionBarhot-rolled plate and sheet on this page
Thickness Range
6 – 200 mm (published mechanical brackets cover up to 200 mm; thinner coil and heavier plate confirmed per rolling programme)
Width Range
1 000 – 4 000 mm
Length Range
4 000 – 12 000 mm
Production Way
Hot rolled — the usual supply route; TMCP and normalizing available by agreement
Delivery Condition
Hot rolled / as rolled (usual) — see section 07 for what the order can add
Impact Requirement
0 °C, ≥ 34 J longitudinal Charpy V-notch — this is what the “C” grade guarantees, beyond Q345B
MOQ
1 tmixed sizes negotiable
Lead Time by Quantity
1 – 10 t: 5 days · 10 – 50 t: 10 days · > 50 t: negotiable
Payment Terms
L/CT/TD/PWestern UnionPaypalMoney Gram
Processing Services
Cutting to length and width, profiling, bevelling, bending, drilling, welding, shot blasting and painting
Certification
Mill Test Certificate to EN 10204 3.1, or 3.2 with third-party endorsement; heat analysis and mechanical test report
Two things worth clearing up about this table. First, Q345C is a low-alloy high-strength steel, not plain carbon — some older listings and the site category label call it “carbon structural steel”, which is imprecise. Its strength comes from Nb/V micro-alloying, so it is heavier in manganese and carries alloying limits the plain-carbon grades do not. Second, the grade name changed: Q345C (2008) = Q355C (2018). The 2018 edition also publishes a carbon-equivalent requirement; if your project cites the newer edition, name it so the MTC and the Ceq match.
03How to Read the Grade
Every part of Q345C is a specification, not a marketing name.
Part
Meaning
Q
The Chinese abbreviation for yield strength (“qu fu”). It tells you the first number is a yield value, not a tensile one.
345
The specified minimum yield strength in MPa — the whole reason the grade is called “345”. Tensile and elongation come with it, impact does not (it is set by the quality letter).
C
The quality grade: it fixes the Charpy V-notch impact temperature at 0 °C with a minimum absorbed energy of ≥ 34 J (longitudinal), and tightens phosphorus and sulphur to ≤ 0.035 % each. A, B, C, D, E step up the impact temperature and tighten cleanliness.
GB/T 1591
The Chinese national standard for hot-rolled low-alloy high-strength structural steel. Revised in 2018; the grade was then renamed Q355C — same steel family, tighter chemistry.
The Q345 / Q355 quality ladder — the letter is the impact temperature.
Pick the letter by the coldest service temperature. Q345C is the default for outdoor and dynamic-load structures in temperate to cold climates because it guarantees 0 °C toughness. If the structure sits in a reliably warm environment, Q345B (+20 °C) is enough and slightly cheaper; if it sees hard cold, step up to Q345D (−20 °C) or Q345E (−40 °C). The yield and tensile values are the same across the letters — only the impact and the P/S cleanliness change.
04Equivalent Grades
Q345C is the 345 MPa yield level of the Chinese low-alloy structural family. The table maps it to its closest international grades — a similar yield figure is not a licence to substitute; check chemistry, toughness and thickness brackets before swapping. Every linked grade opens its own page.
Standard
Grade
Min. Yield
What to check before substituting
GB/T 1591 (this page)
Q345C / Q355C
345 MPa
The Chinese grade — 0 °C impact, P/S ≤ 0.035 % (this page)
Below Q345C by 20 MPa — do not read "490" as stronger than "345"; the JIS SM number is a tensile value, the Q/A572 number is a yield value.
AS/NZS 3678
Grade 350
350 MPa
Approximate match, often accepted on Australia / New Zealand projects.
BS 4360
50B / 50C
—
Legacy British designations still cited on older Commonwealth drawings.
ASTM A36 / A283
A36
250 MPa
Not an equivalent — plain carbon structural steel ~95 MPa below Q345C. Only relevant where the design genuinely needs no more strength.
Strength proximity is not interchangeability. Chemistry limits, toughness classes, thickness brackets and delivery conditions all differ between these standards, and a substitution has to be signed off by the designer against the governing code. The two traps to name: JIS SM490A / SM490YA specify 325 MPa minimum yield, 20 MPa below Q345C, so "490 versus 345" is not the comparison it looks like; and A572 / A709 Gr.50 give no guaranteed impact unless you order it, whereas Q345C’s 0 °C / 34 J is built into the grade. Where a European project needs the cold-toughness match, specify S355J0 or S355J2 rather than S355JR.
05Chemical Composition
Ladle (cast) analysis limits in weight percent, per GB/T 1591 Q345C (2008 edition). The residual elements the old product sheet omitted are included here — product-analysis tolerances apply when ordered.
Element
Limit (% by mass)
Carbon, C
≤ 0.20
Silicon, Si
≤ 0.50
Manganese, Mn
1.00 – 1.70
Phosphorus, P
≤ 0.035
Sulphur, S
≤ 0.035
Niobium, Nb
0.015 – 0.060
Vanadium, V
0.020 – 0.150
Titanium, Ti
0.020 – 0.200
Aluminium (total), Al
≥ 0.015
Chromium, Cr
≤ 0.30
Nickel, Ni
≤ 0.30
Copper, Cu
≤ 0.30
Molybdenum, Mo
≤ 0.10
Nitrogen, N
≤ 0.012
Read the certificate against this table, not against a one-line data sheet. Q345C is a micro-alloyed grade — the Nb, V and Ti rows are what deliver the 345 MPa yield without raising carbon, and they will appear on the MTC. Two notes: the 2018 edition (Q355C) tightens several limits and adds a maximum carbon-equivalent, so if your drawing cites GB/T 1591-2018, expect a slightly cleaner chemistry; and the Mn range widens with thickness in the standard, so the 1.00–1.70 figure is the as-rolled band, confirmed on the certificate of the heat you buy.
06Mechanical Properties
Minimum room-temperature values, read against nominal thickness. The old product sheet listed only four brackets; the full GB/T 1591 ladder is below. Every figure is a floor the heat is tested against — not a prediction of your certificate.
Thickness (mm)
Yield ReH min (MPa)
Tensile Rm (MPa)
Elongation A min (%)
≤ 16
345
470 – 630
21
> 16 – 35
325
470 – 630
21
> 35 – 50
295
470 – 630
21
> 50 – 100
275
470 – 630
21
> 100 – 150
265
450 – 600
21
> 150 – 200
255
450 – 600
21
Impact — the property that defines the “C” grade.
Test
Requirement
Charpy V-notch, longitudinal
0 °C, ≥ 34 J (the Q345C / Q355C requirement)
Three corrections / completions against the old page. First, the yield is given in thickness bands (345 MPa up to 16 mm, stepping down to 255 MPa at 150–200 mm), not a single value — the old listing showed only four of the six brackets. Second, the old sheet gave no elongation or impact; the standard requires ≥ 21 % elongation and the 0 °C / ≥ 34 J impact that the “C” letter guarantees. Third, for the thickest brackets (above 100 mm) the tensile band also narrows to 450–600 MPa. Treat the table as the GB/T 1591 reference and confirm the exact band for your thickness on the certificate.
Q345C reaches its strength through Nb/V micro-alloying and controlled rolling — the order, not the grade, fixes the rest.
Item
Options
Delivery Condition
AR — As hot rolled (usual)TMCPN — Normalized
Additional Conditions
UTCharpy V-notchZ15 / Z25 / Z35Third-party test (SGS)Coated or shot blasted and painting
Surface Treatment
As rolledShot blastedPrimedPainted
What the specification sets, and what has to be added by the order.
Item
Status in GB/T 1591
How it is obtained
Delivery condition
As rolled is the usual route
Normalizing or TMCP can be agreed for thick plate or for a tighter microstructure.
Heat treatment
Not required by the grade
Strength comes from micro-alloying and controlled rolling, not heat treatment. Quenching and tempering is a different product family.
Impact toughness
0 °C / ≥ 34 J at the “C” grade
Built into the grade; third-party witnessed impact on request.
Ultrasonic testing
Not specified
GB/T 2970 or EN 10160 at an agreed acceptance level, by agreement.
Through-thickness (Z) properties
Not specified
Z15 / Z25 / Z35 by agreement where the joint pulls through the plate thickness.
Third-party inspection
Not specified
SGS, BV, TUV or Intertek at the mill before shipment.
Certificate
MTC per the specification
EN 10204 3.1 as standard, 3.2 with third-party endorsement on request.
Keep the condition and the code edition in the enquiry. Q345C is normally delivered hot rolled and tested per heat; anything beyond that — normalized, TMCP, UT, Z-direction, third-party inspection — has to be written into the order before rolling, not added afterwards. And if the project cites GB/T 1591-2018, say so: the certificate should then read Q355C and meet the 2018 chemistry and carbon-equivalent limits.
08Typical Applications
Where a low-alloy 345 MPa structural steel carries the load.
Bridge Girders & Structural Plates
Plate girders, cross-frames, gussets and splice plates on riveted, bolted or welded bridges — the 0 °C impact of Q345C is what lets it serve in colder-climate bridgework where Q345B would not.
Building Frames & High-Rise
Columns, beams, bracing and moment-frame members in multi-storey commercial and industrial buildings, where 345 MPa yield cuts section size and weight against plain carbon steel.
Transmission & Telecom Towers
Lattice towers, substation structures and lighting poles — applications where strength-to-weight and fatigue resistance matter more than corrosion resistance.
Construction & Mining Equipment
Excavator booms, mining truck bodies, crane jibs and outrigger pads — impact-tolerant, weldable plate that takes repeated dynamic loading.
Ship & Offshore Structures
Deckhouses, superstructure and non-critical hull members where a low-alloy 345 MPa grade gives weight savings; for primary hull plate use a dedicated shipbuilding grade.
Why this grade is chosen when the design needs more than plain carbon steel: it gives roughly 95 MPa more yield than Q235 / A36 for a modest price step, it does it with micro-alloying rather than carbon so it still welds with ordinary consumables, and the C letter adds 0 °C toughness for outdoor and cold-climate service. What it does not give you is weathering (atmospheric-corrosion) resistance or a guaranteed thicker-section yield floor beyond the published bands — those are different specifications or need the order to add them.
09Processing, Testing & Supply
From mill plate to a cut, certified, ready-to-fit structural item.
1
Cutting & Profiling
Plate and sheet cut to length and width, profiled to drawing and bevelled for weld preparation on flame, plasma or laser equipment.
2
Forming, Bending & Welding
Bending and rolling to radius, cold forming to the radius the thickness allows, plus welded assemblies built under a qualified procedure — preheat is generally not required up to about 25 mm, and thicker or highly restrained joints call for 100 – 150 °C with low-hydrogen consumables.
3
Surface Treatment
Shot blasting to remove mill scale, then shop primer or full paint system, followed by export marking and seaworthy packing.
4
Inspection & Certified Delivery
Chemical analysis and tensile testing per heat, 0 °C Charpy, UT and Z-direction testing when specified, then the MTC carrying the grade, the GB/T 1591 edition and any third-party report.
Mill Test Certificate to EN 10204 3.1, or 3.2 with third-party endorsement
MTC stating the grade (Q345C or Q355C) and the GB/T 1591 edition cited
Heat analysis and mechanical test report (yield, tensile, elongation, 0 °C Charpy)
Nb / V / Ti micro-alloy content recorded against the grade ordered
Ultrasonic testing report to the agreed acceptance level (GB/T 2970 / EN 10160)
Z-direction (through-thickness) test report where Z15/Z25/Z35 is ordered
Third-party inspection by SGS, BV, Intertek or another nominated agency
Export packing, marking and loading supervision
Quote checklist — you get a faster, comparable price if you send: thickness × width × length, quantity, product form (plate, sheet, section or bar), delivery condition, whether the material is for GB/T 1591-2008 (Q345C) or GB/T 1591-2018 (Q355C), required mechanical values plus the 0 °C impact, UT acceptance level and any Z-direction requirement, surface treatment, MTC type, destination port and payment terms. MOQ is 1 t.
10Frequently Asked Questions
Q1What does GB/T 1591 Q345C actually mean?
Q345C is a Chinese low-alloy high-strength structural steel. Q is the abbreviation for yield strength, 345 is the minimum yield in MPa, and C is the quality grade that fixes a guaranteed Charpy V-notch impact of 0 °C, ≥ 34 J and tightens P/S to ≤ 0.035 %. It is the 0 °C-toughness step above Q345B and the grade standard is GB/T 1591 (renamed Q355C in the 2018 revision).
Q2Is Q345C the same as Q355C?
Effectively yes for procurement. Q345C is the old GB/T 1591-2008 designation and Q355C is the same steel under GB/T 1591-2018 (the revision renamed the whole Q345 family to Q355 and tightened chemistry and added a carbon-equivalent limit). They reach the same 345 MPa yield; the 2018 edition is a slightly cleaner heat. Most new enquiries and many old drawings both appear, and both names reach the same material — just state which edition your certificate must show.
Q3What is Q345C equivalent to in EN / ASTM / JIS?
The exact impact match in Europe is EN 10025-2 S355J0 (0 °C); S355J2 (−20 °C) is a conservative upgrade and S355JR (+20 °C) gives no cold-toughness margin over Q345C. In the US the nearest is ASTM A572 Grade 50 (or A709 Grade 50 for bridges), but those carry no mandatory impact unless you order it. In Japan it is JIS G3106 SM490YA / SM490B — note their minimum yield is 325 MPa, 20 MPa below Q345C. All are procurement mappings; confirm the actual values against your governing code.
Q4Is Q345C a weathering or “carbon” steel?
Neither label is quite right, and both appear on older listings. Q345C is a low-alloy high-strength steel — micro-alloyed with Nb/V, not plain carbon, and not a weathering steel (it gives no atmospheric-corrosion guarantee). If bare, unpainted outdoor exposure is the design condition, that is a different specification; ask us for a weathering grade rather than assuming Q345C will patina-protect itself.
Q5Can I substitute S355JR or A572 Gr.50 for Q345C?
Only with the designer’s sign-off against the governing code. Similar yield is not interchangeability: chemistry limits, toughness classes, thickness brackets and delivery conditions all differ. In particular, A572 / A709 Gr.50 carry no guaranteed impact unless you order Charpy, while Q345C’s 0 °C / 34 J is built in — so a direct swap can quietly remove the cold-toughness you specified. For a European cold-toughness match, specify S355J0 or S355J2. Also note the frequently cited JIS alternatives are weaker, not equivalent: SM490YA specifies 325 MPa minimum yield, 20 MPa below Q345C.
Q6How thick, how fast, what paperwork, and is the old page’s data right?
From 1 t, with typical lead times of about 5 days for 1–10 t, about 10 days for 10–50 t and negotiable above 50 t. Each heat ships with an EN 10204 3.1 mill test certificate. The figures on this page correct / complete the older listing: Q345C is a low-alloy high-strength steel (not plain carbon), the mechanical table now shows the full six thickness brackets (the old sheet stopped at four) plus elongation and the 0 °C impact, the chemistry now includes the residual limits, and we publish the Q345 → Q355 (2018) rename and the Q345A/B/C/D/E family — none of which the old page stated. Each change is flagged in a note box above.
Sources and limits: the figures on this page are reference information drawn from GB/T 1591 (Q345C, the 2008 edition; the 2018 edition renamed the grade Q355C) and published steel data sheets. Q345C is a low-alloy high-strength structural steel; the chemistry limits and the tensile / yield / elongation / 0 °C impact floors are the standard requirements, while actual heat values are recorded on the EN 10204 certificate of the lot supplied. Older listings of this grade called it “carbon structural steel” and omitted the residual chemistry, the full thickness ladder, the Q345 → Q355 rename and the Q345A/B/C/D/E family — we have corrected those against the standard. BBN supplies, cuts and processes the plate.
Get Your GB/T 1591 Q345C Quotation Now
Send us your standard and edition (GB/T 1591-2008 Q345C ), thickness, width and length, quantity, product form, delivery condition, the 0 °C impact requirement and any UT / Z-direction requirement. We will reply with what the mill can roll and certify at that thickness, plate or cut-length options, mill price and production lead time — and tell you plainly if a thinner-section A36 / Q345B would do, or if a colder-climate duty should step up to Q345D / Q345E or an EN S355J0 / S355J2 equivalent.
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