Steel Q345B · heat-treated state
Steel Q345B-N
Properties of the N condition, compared with the other Q345B tempers.
Pick for thick plate, pressure parts and anywhere uniform fine grain plus higher, more reliable impact energy is specified.
What is Q345B-N?
Q345B-N is Q345B heat treated to N — pick for thick plate, pressure parts and anywhere uniform fine grain plus higher, more reliable impact energy is specified. Q345B-N has a yield strength of 360 MPa (52.2 ksi) and a tensile strength of 505 MPa (73.2 ksi) — weaker than 72% of steel grades. Elongation at break is 26% and the elastic modulus is 206 GPa (29.9 Msi). Q345B-N has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,460°C (2,660 °F). HR is the default condition FabDigit quotes; N is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 135 MPa·√m (122.9 ksi·√in), better than 93% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
- Readily welded — 87/100, better than 85% of steel grades
- Ductile — tolerates forming and impact — 26%, better than 82% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
Q345B-N properties
Typical room-temperature values for Q345B-N — 9 properties are specific to this condition; the rest are grade-level values shared by every Q345B temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
Q345B-N has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,460°C (2,660 °F).
Mechanical16
Q345B-N has a yield strength of 360 MPa (52.2 ksi) and a tensile strength of 505 MPa (73.2 ksi) — weaker than 72% of steel grades. Elongation at break is 26% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
Q345B-N is rated for continuous service to 400°C (752 °F). It conducts heat at 47 W/m·K (27.2 BTU/hr·ft·°F), better than 75% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q345B-N conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of Q345B-N takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability6
Q345B-N's machinability is good (62/100, better than 89% of steel grades); weldability excellent (87/100); formability good (65/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Q345B tempers and conditions
Q345B is also supplied in 4 other conditions. The full side-by-side table is on the Q345B overview.
- HRDefaultDefault stock condition for plate, H-beam, angle and hot-rolled coil; best price and full weldability.365 MPa yield · 160 HB
- CRUse for thin sheet needing tight thickness tolerance and a clean bright surface; strength is up, ductility and bend radius suffer.450 MPa yield · 180 HB
- GalvanizedPick when the part stays outdoors unpainted; zinc gives sacrificial protection but caps service temperature and complicates welding.360 MPa yield · 158 HB
- NPick for thick plate, pressure parts and anywhere uniform fine grain plus higher, more reliable impact energy is specified.360 MPa yield · 155 HB
Working with Q345B-N
Is Q345B easy to machine?
Machines like a tough C-Mn steel at roughly 55–65 % of AISI 1212 rates; use rigid setups, coated carbide and generous feed to avoid the gummy chip of the as-rolled ferrite-pearlite structure.
Can Q345B be welded?
Readily welded by SMAW/GMAW/SAW with E50xx-class consumables (ER50-6, J507); CEV ≈ 0.40 so preheat 80–120 °C only for thick section, high restraint or damp conditions.
Can Q345B be formed, bent or molded?
Cold-bends to 2t–3t inner radius per GB/T 1591 in the rolling direction; hot forming 900–1050 °C followed by normalizing restores toughness after heavy strain.
What surface finishes work on Q345B?
Must be protected — shot-blast Sa2.5 then epoxy/PU paint, or hot-dip galvanize (silicon content controls coating thickness); phosphating and powder coating also standard.
Q345B 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 1591-2008; ≤0.18 for some thin products | ≤ 0.2 | 0.17 |
| Si | ≤ 0.5 | 0.3 |
| Mn | ≤ 1.7 | 1.45 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.04 | 0.02 |
| Vmicroalloying, optional single or combined with Nb/Ti | 0.02 – 0.15 | — |
| Nbmicroalloying | 0.02 – 0.06 | — |
| Timicroalloying | 0.02 – 0.2 | — |
| Alacid-soluble Al, grain refinement | ≥ 0.02 | 0.03 |
| Crresidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.5 | — |
| Curesidual | ≤ 0.3 | — |
| Moresidual | ≤ 0.1 | — |
| N | ≤ 0.01 | — |
| Fe | balance | — |
Q345B-N — frequently asked
What is Q345B-N used for?
Q345B-N is typically used for bridge girders and gussets, building and plant structural frames, crane booms and gantry structures, pressure-bearing frames and skids, heavy machinery bases and weldments and galvanized structural sections. In short: workhorse Chinese HSLA plate.
What is the yield strength of Q345B-N?
Q345B-N has a typical yield strength of 360 MPa (52.2 ksi) and a tensile strength of 505 MPa (73.2 ksi) — weaker than 72% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is Q345B-N easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines like a tough C-Mn steel at roughly 55–65 % of AISI 1212 rates; use rigid setups, coated carbide and generous feed to avoid the gummy chip of the as-rolled ferrite-pearlite structure.
Can Q345B-N be welded?
Yes — weldability is rated excellent (87/100). Readily welded by SMAW/GMAW/SAW with E50xx-class consumables (ER50-6, J507); CEV ≈ 0.40 so preheat 80–120 °C only for thick section, high restraint or damp conditions.
What surface finishes work on Q345B-N?
Must be protected — shot-blast Sa2.5 then epoxy/PU paint, or hot-dip galvanize (silicon content controls coating thickness); phosphating and powder coating also standard.
Can Q345B-N be formed, bent or molded?
Cold-bends to 2t–3t inner radius per GB/T 1591 in the rolling direction; hot forming 900–1050 °C followed by normalizing restores toughness after heavy strain.
What is the maximum service temperature of Q345B-N?
Q345B-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 Q345B-HR and Q345B-CR?
HR is the default condition — default stock condition for plate, H-beam, angle and hot-rolled coil; best price and full weldability. CR: use for thin sheet needing tight thickness tolerance and a clean bright surface; strength is up, ductility and bend radius suffer. Yield strength is 365 MPa in HR versus 450 MPa in CR.
Can FabDigit make parts in Q345B-N?
Yes — Q345B-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 1591-2008 (Q345B edition) — SAC (China) (2008)
- ASM Handbook Vol.1: Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.13: Corrosion — ASM International (2005)
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.