Steel Q345B TMCP
Supply condition
GB Q345B
TMCP = thermomechanically controlled processed
Choose for heavy welded structures needing low carbon equivalent, high toughness and reduced preheat.
Values for the TMCP condition
Other Q345B tempers and conditions
Q345B is listed in 4 conditions; see the grade overview at Q345B.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Normalized | Pick for thick plate, pressure parts and anywhere uniform fine grain plus higher, more reliable impact energy is specified. | 360 | 505 | 26 | 155 HB | 8.6 % IACS |
HRDefault Hot rolled | Default stock condition for plate, H-beam, angle and hot-rolled coil; best price and full weldability. | 365 | 510 | 24 | 160 HB | — |
TMCPThis page Thermomechanically controlled processed | Choose for heavy welded structures needing low carbon equivalent, high toughness and reduced preheat. | 390 | 520 | 25 | 165 HB | 8.5 % IACS |
Cold rolled | Use for thin sheet needing tight thickness tolerance and a clean bright surface; strength is up, ductility and bend radius suffer. | 450 | 560 | 16 | 180 HB | — |
What is Q345B TMCP?
Q345B TMCP is Q345B supplied in the TMCP condition — choose for heavy welded structures needing low carbon equivalent, high toughness and reduced preheat. Q345B TMCP has a yield strength of 390 MPa (56.6 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 64% of steel grades. Elongation at break is 25% and the elastic modulus is 206 GPa (29.9 Msi). Q345B TMCP 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; TMCP is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 150 MPa·√m (136.5 ksi·√in), better than 96% of steel grades
- Readily welded — 90/100, better than 90% of steel grades
- Forms and bends easily — 70/100, better than 86% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
Q345B TMCP properties
Typical room-temperature values for Q345B TMCP; 23 are specific to this condition. Other listed values are Q345B reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Q345B TMCP 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 TMCP has a yield strength of 390 MPa (56.6 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 64% of steel grades. Elongation at break is 25% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
Q345B TMCP is rated for continuous service to 350°C (662 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q345B TMCP conducts electricity at 8.5 % IACS, better than 63% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of Q345B TMCP 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 TMCP's machinability is good (58/100, better than 75% of steel grades); weldability excellent (90/100); formability very good (70/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Q345B TMCP
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 TMCP — frequently asked
What is Q345B TMCP used for?
Q345B TMCP 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 TMCP?
Q345B TMCP has a typical yield strength of 390 MPa (56.6 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 64% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is Q345B TMCP easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% 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 TMCP be welded?
Yes — weldability is rated excellent (90/100). 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 TMCP?
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 TMCP 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 TMCP?
Q345B TMCP is rated for continuous use to about 350°C (662 °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 TMCP?
Yes — Q345B TMCP 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.