Overview
Q345B is a low-alloy high-strength structural steel standardized under the Chinese GB/T 1591-2018 standard.
The designation breaks down as follows:
- Q: Stands for "Qu" , meaning "yield strength" in Chinese.
- 345: Minimum yield strength of 345 MPa (≈50 ksi) at room temperature.
- B: Indicates the quality grade (impact toughness tested at 20°C).
Widely used in construction, bridges, machinery, and heavy equipment, Q345B balances strength, weldability, and cost-effectiveness.
Key Material Properties
A. Mechanical Properties
| Thickness (mm) | ||||
| Q345B | ≤ 16 | > 16 ≤ 35 | > 35 ≤ 50 | >50 |
| Yield strength (≥Mpa) | 345 | 325 | 295 | 275 |
| Tensile strength (Mpa) | 470-630 | |||
B. Chemical Composition (Typical)
| Main chemical elements composition of Q345B | |||||||
| C | Si | Mn | P | S | V | Nb | Ti |
| 0.20 | 0.55 | 1.00-1.60 | 0.040 | 0.040 | 0.02-0.15 | 0.015-0.060 | 0.02-0.20 |
C. Fabrication Properties
- Weldability: Good, but requires preheating (100–150°C) for thick sections to avoid cracking. Low-hydrogen electrodes recommended.
- Formability: Moderate; avoid sharp bends due to higher strength compared to mild steel (e.g., Q235).
- Machinability: Fair; use carbide tools for optimal results.
Applications
- Construction: Beams, columns, and trusses in buildings and bridges.
- Heavy Machinery: Excavators, cranes, and mining equipment.
- Pressure Vessels: Non-corrosive, low-temperature pressure systems.
- Transportation: Shipbuilding, railcar components.
Comparisons
- Q345B vs. Q235: Q345B offers 50% higher yield strength than Q235 (235 MPa), making it better for load-bearing structures.
- Q345B vs. ASTM A572 Gr.50: Similar yield strength (345 MPa vs. 345 MPa), but Q345B is more cost-effective in China.
- Q345B vs. Q345C/D/E: Higher grades (C, D, E) offer better low-temperature toughness (impact tested at 0°C, -20°C, -40°C).
Standards and Availability
- Standard: GB/T 1591-2018 (equivalent to EN 10025-2 S355JR).
- Forms: Available as plates, sheets, structural sections (I-beams, angles), pipes, and bars.
- Surface: Hot-rolled or normalized; often galvanized or painted for corrosion protection.
Conclusion
Q345B steel is a versatile, cost-effective material for structural applications requiring moderate strength and weldability. Its balance of mechanical properties and ease of fabrication makes it a staple in Chinese industrial and construction projects. Proper pre/post-weld treatments and environmental protections (e.g., coatings) maximize its performance.
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FAQ
Q: What is Q345B steel?
A: Q345B steel is a Chinese standardized low alloy, medium tensile strength steel made with a hot-rolling process, and is used for a number of manufacturing purposes.
Q: What is material grade Q345B?
A: Q345B Description. Q345 is a kind of steel material. It is carbon alloy steel (C <0.2%), good overall performance, good low temperature performance, good cold stamping performance, good welding performance and good machinability. Widely used in Bridges, vehicles, ships, buildings, pressure vessels, etc.
Q: Is Q345B equivalent to s355?
A: These two steel materials Q345B steel plate and S355JR+AR steel plate are totally equivalent in chemical composition and mechincal properties from the following comparasion data table.
Q: What is Q345 steel equivalent to?
A: Q345 can also be replaced with equivalent materials, including A572 Grade 50 USA ASTM, Q355 China GB/T, and SPFC 590 Vietnam/Japanese JIS. The yield strength of Q345 is where the material begins to deform plastically. Before hitting deformation, it will return to its original shape when stress is removed.
| Other steel plate | ||||
| Name | Material | Specification (mm) | Tons | Remark |
| Low Alloy | Q345A, Q345B, Q345C, Q345D, Q345E, Q390, Q420, Q460C, ST52-3, S355J2+N, SS400, SA302GrC, S275NL, 35CrMo | 6 - 350 | 5788.56 | Normalizing, tempered ,controlled rolling, hot rolling , Hot rolling,1st inspection, 2nd inspection, 3rd inspection |
| Pressure Vessel Plate | Q245R, Q345R, Q370R, 16MnDR, 09MnNiDR, 15CrMoR, 14Cr1MoR, 12Cr2Mo1R, SA516Gr60, SA516Gr70, SA516Gr485, SA285, SA387Gr11, SA387Gr12, SA387Gr22, P265,P295,P355GH,Q245R(R-HIC),Q345R(R-HIC) | 3 - 300 | 8650 | Normalizing, tempered ,controlled rolling, hot rolling , Hot rolling,1st inspection, 2nd inspection, 3rd inspection |
| High-Strength Plate | WH785D/E,Q960D/E, Q890D/E,WH60D/E,WH70B,Q550D,Q590D,Q690D/E | 8 - 120 | 3086.352 | Quenched and tempered |
| Wear-Resistant Plate | NM360, NM400, NM450, NM500 | 6 - 150 | 3866.297 | Quenched and tempered |
| Bridge Plate | Q235qC, Q345qC, Q370qC, Q420qC, Q345qDNH, Q370qDNH, A709 - 50F - 2, A709 - 50T - 2 | 8 - 200 | 2853.621 | Hot rolling, normalized ,hot rolling controlled rolling, quenched and tempered + toughness and brittleness |
