Q345B Carbon Steel Flat Bar
Q345B is a Chinese standard low-alloy high-strength structural steel flat bar with minimum yield strength of 345 MPa, offering 50% higher strength than Q235B with excellent weldability. Width 20-500mm, thickness 3-100mm, ideal for bridges, heavy machinery, and structural fabrication.
| Material | Carbon Steel (Low Alloy High Strength) |
|---|---|
| Grade / Standard | GB Q345B |
| Diameter | Width: 20mm - 500mm, Thickness: 3mm - 100mm |
| Length | 6m / 12m (or cut to length) |
| Delivery Condition | hot_rolled / normalized / as_rolled |
| Surface Treatment | bare / shot_blasting / painting / coated |
| MOQ | 1 Ton |
| Delivery Time | 10-25 Days / In Stock |
| Loading Port | Tianjin / Shanghai / Qingdao |
Overview of Q345B Carbon Steel Flat Bar
Q345B is a widely used Chinese standard low-alloy high-strength structural steel flat bar specified under GB/T 1591 standard. With a minimum yield strength of 345 MPa and tensile strength of 470-630 MPa, Q345B offers significantly higher load-bearing capacity than common Q235B carbon steel while maintaining excellent weldability and good cold formability. The grade contains controlled additions of manganese, silicon, and microalloying elements to achieve enhanced mechanical properties through grain refinement.
Q345B flat bar is the preferred choice for medium to heavy-duty structural applications where higher strength-to-weight ratio is required. It is extensively used in construction, machinery manufacturing, bridge engineering, mining equipment, and general fabrication where Q235B does not meet load requirements. The Class B impact toughness rating ensures reliable performance at temperatures down to 20°C, making it suitable for outdoor and industrial environments.
Key Features and Manufacturing Methods
Q345B carbon steel flat bar is manufactured through hot rolling process from continuously cast slabs, providing uniform cross-sectional properties and consistent mechanical characteristics throughout the bar length. The flat bar is supplied in width range from 20mm to 500mm and thickness from 3mm to 100mm, with standard length of 6 meters and 12 meters. Custom cutting service is available for specific length requirements.
The surface conditions include hot rolled (mill scale), pickled and oiled, painted, and shot-blasted depending on application needs. The grade can be supplied as-rolled or normalized condition, with optional stress-relieving heat treatment for precision applications. Q345B flat bar offers excellent welding performance using SMAW, GMAW, FCAW, SAW, and GTAW processes without preheating requirements for sections under 25mm thickness, significantly reducing fabrication complexity and cost.
Main Applications of Q345B Flat Bar
Q345B carbon steel flat bar is extensively used in heavy structural fabrication including building frames, industrial workshop structures, mezzanine floor supports, and warehouse rack systems. In the bridge construction industry, it serves as gusset plates, connection plates, and reinforcement members for highway bridges, pedestrian bridges, and railway infrastructure. Mining and quarrying equipment manufacturers use Q345B flat bar for crusher frames, conveyor structural members, screening equipment frames, and material handling system supports.
The machinery manufacturing sector employs Q345B flat bar for crane components, lifting equipment frames, agricultural machinery chassis, construction equipment booms, and heavy vehicle structural parts. Other major applications include shipbuilding bulkhead stiffeners, offshore platform support structures, pressure vessel skirts and saddles, storage tank shell reinforcement, transmission tower components, and railway car body framework requiring higher strength than standard carbon steel grades.
Why Choose Us for Q345B Carbon Steel Flat Bar
Shandong Tanglu Metal Material Co., Ltd. supplies premium Q345B carbon steel flat bar sourced from major Chinese steel mills including HBIS, Shougang, Ansteel, and Baosteel with stable production capacity and consistent quality assurance. Our Q345B flat bar undergoes mandatory chemical analysis, mechanical property testing, and dimensional inspection per GB/T 1591 latest revision, with full traceability from heat number to finished product.
We offer flexible specification range covering width 20mm to 500mm and thickness 3mm to 100mm in hot rolled, pickled, painted, or shot-blasted surface conditions. With monthly supply capacity of 8,000 tons of structural steel bars and established export experience to over 50 countries, we support both small trial orders for product evaluation and large bulk shipments for ongoing project supply. Each shipment includes original mill test certificate (MTC) conforming to EN 10204 3.1 standard, with EN 10204 3.2 and third-party inspection (SGS, BV, ABS, DNV, LR) available for critical structural projects.
📐 Dimension & Size Table
| Width (mm) | Thickness (mm) | Length (m) | Weight (kg/m) |
|---|---|---|---|
| 20 | 3-10 | 6 / 12 | 0.471-1.570 |
| 25 | 3-12 | 6 / 12 | 0.589-2.355 |
| 30 | 3-16 | 6 / 12 | 0.706-3.768 |
| 40 | 4-20 | 6 / 12 | 1.256-6.280 |
| 50 | 4-25 | 6 / 12 | 1.570-9.813 |
| 60 | 5-30 | 6 / 12 | 2.355-14.130 |
| 80 | 5-40 | 6 / 12 | 3.140-25.120 |
| 100 | 6-50 | 6 / 12 | 4.710-39.250 |
| 120 | 8-60 | 6 / 12 | 7.536-56.520 |
| 150 | 10-70 | 6 / 12 | 11.775-82.425 |
| 180 | 10-80 | 6 / 12 | 14.130-113.040 |
| 200 | 12-90 | 6 / 12 | 18.840-141.300 |
| 250 | 15-100 | 6 / 12 | 29.438-196.250 |
| 300 | 20-100 | 6 / 12 | 47.100-235.500 |
| 400 | 20-100 | 6 / 12 | 62.800-314.000 |
| 500 | 25-100 | 6 / 12 | 98.125-392.500 |
* Custom sizes available upon request. Tolerances per relevant international standards.
🔬 Chemical Composition
| Element | Min | Max | Display Value | Note |
|---|---|---|---|---|
| C | - | 0.20 | ≤0.20 | Per GB/T 1591 |
| Mn | 1.00 | 1.60 | 1.00-1.60 | Strengthening element |
| Si | - | 0.55 | ≤0.55 | |
| P | - | 0.035 | ≤0.035 | |
| S | - | 0.035 | ≤0.035 | |
| V | - | 0.15 | ≤0.15 | Microalloying element |
| Nb | - | 0.07 | ≤0.07 | Microalloying element |
| Ti | - | 0.20 | ≤0.20 | Microalloying element |
| Cr | - | 0.30 | ≤0.30 | Residual element |
| Ni | - | 0.50 | ≤0.50 | Residual element |
* Chemical composition may vary by heat, thickness and specification. Please refer to the actual mill test certificate.
⚙️ Mechanical Properties
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (t≤16mm) | ≥345 | MPa | Per GB/T 1591 |
| Yield Strength (16<t≤40mm) | ≥325 | MPa | |
| Yield Strength (40<t≤63mm) | ≥295 | MPa | |
| Yield Strength (63<t≤80mm) | ≥275 | MPa | |
| Tensile Strength (t≤40mm) | 470-630 | MPa | |
| Tensile Strength (40<t≤63mm) | 470-630 | MPa | |
| Elongation (t≤40mm) | ≥21 | % | Gauge length 5.65√So |
| Elongation (40<t≤63mm) | ≥20 | % | |
| Impact Energy | ≥34 | J | Charpy V-notch at 20°C, longitudinal |
| Brinell Hardness | 150-180 | HBW | Typical hot rolled condition |
* Values shown are minimum requirements unless otherwise stated.
📦 Commercial Information
| Packaging | Standard seaworthy export packing. Q345B flat bars bundled with steel strapping (3-5 straps per bundle) based on size, typical bundle weight 2-5 tons. Bundles tagged with heat number, grade, dimensions, and length. Wooden separators provided between bundles to prevent damage during transport. Custom packaging including waterproof film wrapping and crating available for premium surface-treated bars. |
|---|---|
| Payment Terms | T/T (Telegraphic Transfer),L/C (Letter of Credit),D/P (Documents against Payment),Western Union,PayPal |
| Price Term | FOB,CFR,CIF,EXW |
| Supply Capacity | 8,000 Tons/Month (Carbon Steel Bars) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Why Choose Our Q345B Carbon Steel Flat Bar?
Mill Certified High Strength Grade
Q345B flat bar supplied with original mill test certificate EN 10204 3.1/3.2, including chemical composition analysis, mechanical test results with yield/tensile/elongation/impact data, and complete metallurgical traceability from heat to finished bar.
Comprehensive Specification Range
Width range from 20mm to 500mm and thickness from 3mm to 100mm, available in standard 6m and 12m lengths. Custom cut-to-length service supported for specific project requirements with precision dimensional tolerance per GB/T 702.
50% Higher Strength Than Q235B
With minimum yield strength of 345 MPa compared to Q235B's 235 MPa, Q345B enables material weight reduction in structural design while maintaining safety factors. Excellent for weight-sensitive structures including bridges, cranes, and transportation equipment.
Multiple Surface Treatment Options
Available in hot rolled (mill scale), pickled and oiled (clean surface), painted (red primer or custom color), and shot-blasted (Sa2.5) surface conditions. Anti-rust oil coating for extended outdoor storage and international shipping protection.
Reliable Stock and Production
Common specifications maintained in stock for 7-15 days dispatch. Custom dimensions production cycle 25-35 days. Container loading optimized for 20FT and 40FT containers with up to 27 tons payload capacity for standard size bars.
🏭 Applications of Q345B Carbon Steel Flat Bar
Q345B carbon steel flat bar is the preferred material for medium to heavy-duty structural applications requiring higher strength-to-weight ratio than standard Q235B. In construction industry, it is extensively used for building frames, industrial workshop structures, mezzanine floor supports, warehouse rack systems, and high-rise building reinforcement members. Bridge engineering applications include gusset plates, connection brackets, web stiffeners, and reinforcement members for highway bridges, pedestrian bridges, and railway infrastructure. The mining and quarrying industry uses Q345B flat bar for crusher frame structures, conveyor structural members, screening equipment frames, and heavy-duty material handling system components. Machinery manufacturing applications include crane component fabrication, lifting equipment frames, agricultural machinery chassis, construction equipment booms, and heavy vehicle structural parts. Other major applications cover shipbuilding bulkhead stiffeners, offshore platform support structures, pressure vessel skirts and saddles, storage tank reinforcement, transmission tower components, and railway car body framework.
📋 Quality & Certification
Our Certifications
- ✅ ISO 9001:2015
- ✅ CE Marking
- ✅ ABS
- ✅ DNV GL
- ✅ Lloyd's Register (LR)
- ✅ Bureau Veritas (BV)
- ✅ SGS Certified
- ✅ NK
- ✅ RINA
Mill Certificate Type
- 📋 EN 10204 3.1
- 📋 EN 10204 3.2
- 📋 Original Mill Certificate
- 📋 Third Party Inspection Available
- 📋 Certificate of Origin
❓ Frequently Asked Questions
What is Q345B carbon steel flat bar?
Q345B is a Chinese standard low-alloy high-strength structural steel flat bar specified under GB/T 1591 standard with minimum yield strength of 345 MPa. The 'Q' represents yield strength (Qu Fu Dian), '345' represents minimum yield value in MPa, and 'B' represents impact toughness rating tested at 20°C. Q345B offers approximately 50% higher strength than common Q235B carbon steel while maintaining excellent weldability and good cold formability, making it ideal for medium to heavy-duty structural applications.
What is the equivalent grade of Q345B?
Q345B has equivalent grades in multiple international standards: EN S355JR / 1.0045 (European standard EN 10025-2), ASTM A572 Grade 50 (American standard for high-strength low-alloy structural steel), JIS SM490A (Japanese standard JIS G3106 for welded structural steel), and DIN St52-3 (German standard DIN 17100). While these grades share similar yield strength of 345-355 MPa, exact substitution should be verified against project specifications considering chemical composition variations and impact test temperature requirements.
What is the difference between Q345B and Q235B flat bar?
The main difference is mechanical strength. Q345B has minimum yield strength of 345 MPa and tensile strength of 470-630 MPa, while Q235B has minimum yield strength of 235 MPa and tensile strength of 370-500 MPa. Q345B is achieved through higher manganese content (1.00-1.60%) and microalloying elements like vanadium and niobium for grain refinement strengthening. This results in approximately 50% higher load-bearing capacity, allowing structural designers to reduce material weight by 15-25% while maintaining safety factors. Q345B is preferred for bridges, heavy machinery, and high-rise construction, while Q235B remains the economical choice for general construction and light fabrication.
Can Q345B flat bar be welded without preheating?
Yes, Q345B has excellent weldability and can be welded without preheating for sections under 25mm thickness using common welding processes including SMAW, GMAW, FCAW, SAW, and GTAW. For sections over 25mm thickness or in cold ambient temperatures below 5°C, preheating to 100-150°C is recommended to prevent hydrogen-induced cold cracking in the heat-affected zone (HAZ). Recommended welding consumables include E50 series electrodes (E5015, E5016) or equivalent low-hydrogen electrodes. Post-weld heat treatment is typically not required except for thick sections or stress-critical applications.
What sizes and lengths are available for Q345B flat bar?
Q345B carbon steel flat bar is available in width range from 20mm to 500mm and thickness from 3mm to 100mm. Standard lengths are 6 meters and 12 meters, with custom cut-to-length service supported for specific project requirements. Dimensional tolerances comply with GB/T 702 standard or customer specification. For width over 200mm or thickness over 50mm, lead time may extend to 30-45 days depending on production scheduling. Special long lengths up to 18 meters and special dimensional combinations are available for project-specific orders.
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Q345B Carbon Steel Flat Bar
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