Steel Q355B · heat-treated state
Steel Q355B-N
Properties of the N condition, compared with the other Q355B tempers.
Choose for thick plate or when finer grain, uniform properties through thickness and better low-temperature toughness are needed.
What is Q355B-N?
Q355B-N is Q355B heat treated to N — choose for thick plate or when finer grain, uniform properties through thickness and better low-temperature toughness are needed. Q355B-N has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 69% of steel grades. Elongation at break is 27% and the elastic modulus is 206 GPa (29.9 Msi). Q355B-N has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F). HR is the default condition FabDigit quotes; N is available on request or by drawing note.
Advantages
- Readily welded — 88/100, better than 87% of steel grades
- Ductile — tolerates forming and impact — 27%, better than 85% of steel grades
- Forms and bends easily — 70/100, better than 85% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
Q355B-N properties
Typical room-temperature values for Q355B-N — 9 properties are specific to this condition; the rest are grade-level values shared by every Q355B temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
Q355B-N has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F).
Mechanical16
Q355B-N has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 69% of steel grades. Elongation at break is 27% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
Q355B-N is rated for continuous service to 400°C (752 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q355B-N conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of Q355B-N takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 22%.
Manufacturability6
Q355B-N's machinability is good (58/100, better than 75% of steel grades); weldability excellent (88/100); formability very good (70/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Q355B tempers and conditions
Q355B is also supplied in 3 other conditions. The full side-by-side table is on the Q355B overview.
- HRDefaultDefault stock form: hot-rolled plate, sections, coil and bar for general structural fabrication.380 MPa yield · 155 HB
- CRPick for thin gauge (<3 mm) parts needing tight thickness tolerance, clean scale-free surface and direct painting.420 MPa yield · 172 HB
- GalvanizedUse where the structure is outdoors or humid and painting maintenance is undesirable; zinc gives sacrificial protection.375 MPa yield · 155 HB
- NChoose for thick plate or when finer grain, uniform properties through thickness and better low-temperature toughness are needed.375 MPa yield · 148 HB
Working with Q355B-N
Is Q355B easy to machine?
Machines like a 0.2 %C low-alloy steel — use carbide at ~120–180 m/min, expect stringy chips and moderate tool life; ~60 % of AISI 1212 rating.
Can Q355B be welded?
Readily weldable by SMAW/GMAW/SAW with E50xx (ER50-6) consumables; preheat 75–150 °C for plate above ~30 mm or under restraint, and avoid welding through zinc on galvanized stock.
Can Q355B be formed, bent or molded?
Cold bends to 2× thickness inner radius per GB/T 1591; hot forming 900–1150 °C, and re-normalize heavy sections after severe hot work.
What surface finishes work on Q355B?
No inherent corrosion protection — shot blast to Sa2.5 then epoxy/zinc-rich primer, or hot-dip galvanize; not suitable for decorative polished exposure.
Q355B chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CGB/T 1591-2018, AR delivery | ≤ 0.24 | 0.18 |
| Si | ≤ 0.55 | 0.3 |
| Mn | ≤ 1.6 | 1.35 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.04 | 0.02 |
| Nbmicroalloying, optional | ≤ 0.05 | 0.02 |
| Vmicroalloying, optional | ≤ 0.12 | — |
| Timicroalloying, optional | ≤ 0.2 | — |
| Crresidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.4 | — |
| Moresidual | ≤ 0.1 | — |
| N | ≤ 0.01 | — |
| Altotal Al, when Nb/V/Ti not added | ≥ 0.02 | 0.03 |
| Fe | balance | — |
Q355B-N — frequently asked
What is Q355B-N used for?
Q355B-N is typically used for bridges, building frames and crane jibs. In short: high-strength structural plate.
What is the yield strength of Q355B-N?
Q355B-N has a typical yield strength of 375 MPa (54.4 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 69% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is Q355B-N easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machines like a 0.2 %C low-alloy steel — use carbide at ~120–180 m/min, expect stringy chips and moderate tool life; ~60 % of AISI 1212 rating.
Can Q355B-N be welded?
Yes — weldability is rated excellent (88/100). Readily weldable by SMAW/GMAW/SAW with E50xx (ER50-6) consumables; preheat 75–150 °C for plate above ~30 mm or under restraint, and avoid welding through zinc on galvanized stock.
What surface finishes work on Q355B-N?
No inherent corrosion protection — shot blast to Sa2.5 then epoxy/zinc-rich primer, or hot-dip galvanize; not suitable for decorative polished exposure.
Can Q355B-N be formed, bent or molded?
Cold bends to 2× thickness inner radius per GB/T 1591; hot forming 900–1150 °C, and re-normalize heavy sections after severe hot work.
What is the maximum service temperature of Q355B-N?
Q355B-N is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Q355B-HR and Q355B-CR?
HR is the default condition — default stock form: hot-rolled plate, sections, coil and bar for general structural fabrication. CR: pick for thin gauge (<3 mm) parts needing tight thickness tolerance, clean scale-free surface and direct painting. Yield strength is 380 MPa in HR versus 420 MPa in CR.
Can FabDigit make parts in Q355B-N?
Yes — Q355B-N is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- GB/T 700 / GB 50017 (elastic constants, CTE) — MOHURD (2017)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- EN 10025-2 S355JR (comparison grade) — CEN (2019)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.