Steel Q345B · supply condition · default condition
Steel Q345B-HR
Properties of the HR condition, compared with the other Q345B tempers.
Default stock condition for plate, H-beam, angle and hot-rolled coil; best price and full weldability.
What is Q345B-HR?
Q345B-HR is Q345B supplied in the HR condition — default stock condition for plate, H-beam, angle and hot-rolled coil; best price and full weldability. Q345B-HR has a yield strength of 365 MPa (52.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 71% of steel grades. Elongation at break is 24% and the elastic modulus is 206 GPa (29.9 Msi). Q345B-HR 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).
Advantages
- Easy to machine — 60/100, better than 83% of steel grades
- Readily welded — 85/100, better than 83% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 80% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
Q345B-HR properties
Typical room-temperature values for Q345B-HR — 11 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-HR 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-HR has a yield strength of 365 MPa (52.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 71% of steel grades. Elongation at break is 24% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
Q345B-HR 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-HR 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-HR 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-HR's machinability is good (60/100, better than 83% of steel grades); weldability excellent (85/100); formability good (65/100).
Common Calculations5
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-HR
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-HR — frequently asked
What is Q345B-HR used for?
Q345B-HR 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-HR?
Q345B-HR has a typical yield strength of 365 MPa (52.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 71% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is Q345B-HR easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% 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-HR be welded?
Yes — weldability is rated excellent (85/100). 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-HR?
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-HR 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-HR?
Q345B-HR 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-HR?
Yes — Q345B-HR 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.