Q345qD Bridge Steel Plate
High-performance structural steel specifically designed for bridge construction, meeting national and international standards for durability and reliability.
About Q345qD Steel
Q345qD is a Chinese standard (GB/T 714-2015) low alloy high strength structural steel specifically developed for bridge construction applications.
The "q" in the designation stands for bridge (qiaoliang in Chinese), while "D" indicates the steel's impact test temperature of -20°C, making it suitable for cold climate conditions.
It offers excellent weldability, formability, and toughness, making it the preferred material for medium to large span bridges, overpasses, and other heavy infrastructure projects.
Technical Specifications
Basic Information
Mechanical Properties
| Thickness (mm) | Yield Strength (MPa) ≥ | Tensile Strength (MPa) | Elongation (%) ≥ | Impact Energy (J) ≥ |
|---|---|---|---|---|
| ≤16 | 345 | 470-630 | 21 | 34 |
| >16-35 | 325 | 470-630 | 21 | 34 |
| >35-50 | 315 | 470-630 | 21 | 34 |
| >50-100 | 295 | 450-600 | 21 | 34 |
Chemical Composition (wt%)
| Element | C ≤ | Si ≤ | Mn | P ≤ | S ≤ | Nb ≤ | V ≤ | Ti ≤ | Ni ≤ | Cu ≤ |
|---|---|---|---|---|---|---|---|---|---|---|
| Content | 0.18 | 0.55 | 1.00-1.60 | 0.025 | 0.020 | 0.06 | 0.15 | 0.02 | 0.30 | 0.30 |
Note: Carbon equivalent (Ceq) ≤ 0.45%, Weldability carbon equivalent (Pcm) ≤ 0.24%
International Standards Comparison
Mechanical Properties Comparison (≤16mm thickness)
| Property | Q345qD (GB/T 714-2015) | S355J2 (EN 10025) | A709 Gr50 (ASTM A709) |
|---|---|---|---|
| Yield Strength (MPa) min | 345 | 355 | 345 (50 ksi) |
| Tensile Strength (MPa) | 470-630 | 470-630 | 485-655 (70-95 ksi) |
| Elongation (%) min | 21 | 21 | 21 |
| Impact Test Temperature (°C) | -20 | -20 | -18 (0°F) |
| Impact Energy (J) min | 34 | 27 | 27 (20 ft-lb) |
| Carbon Equivalent (Ceq) max | 0.45% | 0.45% | 0.45% |
Chemical Composition Comparison (wt%)
| Element | Q345qD (max/ range) | S355J2 (EN 10025) (max/ range) | A709 Gr50 (ASTM A709) (max/ range) |
|---|---|---|---|
| Carbon (C) | ≤0.18% | ≤0.20% | ≤0.23% |
| Silicon (Si) | ≤0.55% | ≤0.55% | 0.15-0.40% |
| Manganese (Mn) | 1.00-1.60% | 1.00-1.60% | 1.00-1.50% |
| Phosphorus (P) | ≤0.025% | ≤0.030% | ≤0.035% |
| Sulfur (S) | ≤0.020% | ≤0.025% | ≤0.040% |
| Niobium (Nb) | ≤0.06% | ≤0.06% | ≤0.05% |
| Vanadium (V) | ≤0.15% | ≤0.15% | ≤0.06% |
| Titanium (Ti) | ≤0.02% | ≤0.05% | ≤0.03% |
Key Differences Summary:
- Q345qD has stricter P/S limits (0.025/0.020%) compared to international standards, improving weldability and toughness
- S355J2 (EN standard) has slightly higher minimum yield strength (355MPa vs 345MPa)
- A709 Grade 50 (ASTM standard) has more flexible chemical composition requirements for broader manufacturing adaptability
- Q345qD requires higher impact energy (34J vs 27J) at -20°C, making it more suitable for cold regions
- All three grades maintain excellent weldability with carbon equivalent ≤0.45%
Application Cases
Highway Bridge Construction
Used in the main structure of a 1.2km long highway bridge in Northern China, withstanding extreme weather conditions and heavy traffic loads.
- Plate thickness: 25mm-40mm
- Total usage: 3,500 metric tons
- Service life: Designed for 100 years
Railway Bridge Construction
Applied in a railway bridge overpass project, providing excellent fatigue resistance for train load cycles.
- Plate thickness: 16mm-50mm
- Total usage: 5,200 metric tons
- Complies with high-speed rail standards
Urban Viaduct System
Utilized in a large urban viaduct system, combining high strength with excellent fabrication properties.
- Plate thickness: 12mm-30mm
- Total usage: 2,800 metric tons
- Corrosion protection treatment applied
Other Typical Applications
Frequently Asked Questions (FAQ)
What is the difference between Q345qD and Q345D steel?
Q345qD is specifically formulated and produced for bridge construction applications (the "q" stands for bridge in Chinese), while Q345D is a general structural steel. Key differences include:
- Q345qD has stricter requirements for toughness and fatigue resistance
- Lower impurity content (P, S) for better weldability and durability
- Special rolling process to ensure uniform mechanical properties across the plate
- Complies with bridge-specific standard GB/T 714-2015 instead of general structural steel standard
What welding methods are suitable for Q345qD steel?
Q345qD has excellent weldability due to its low carbon equivalent (≤0.45%). Recommended welding methods include:
- Submerged Arc Welding (SAW) - ideal for thick plate welding in bridge fabrication
- Gas Metal Arc Welding (GMAW/MIG) - suitable for on-site construction
- Shielded Metal Arc Welding (SMAW/MMA) - versatile for field welding
- Gas Tungsten Arc Welding (GTAW/TIG) - for high-quality, precision welds
No preheating is required for plates ≤30mm thick under normal temperature conditions (≥5°C).
What is the maximum service temperature for Q345qD steel?
Q345qD is designed to perform reliably in the following temperature range:
- Minimum operating temperature: -20°C (meets impact energy requirements at this temperature)
- Maximum operating temperature: 300°C (for short-term service)
- Continuous service temperature: Up to 200°C
For applications in extremely cold regions (-30°C and below), we recommend Q345qE grade steel with -40°C impact test requirement.
What surface treatments are recommended for Q345qD bridge steel?
To ensure long service life (typically 50-100 years for bridges), we recommend these surface treatments:
- Zinc-rich epoxy primer (dry film thickness: 60-80μm) + intermediate coat + finish coat
- Hot-dip galvanizing for structural components (minimum zinc thickness: 85μm)
- Weathering steel treatment (if using Q345qDNH grade) - no painting required after initial patina formation
- Cathodic protection for marine bridge applications in coastal areas
Regular inspection and maintenance (every 5-10 years) is recommended to maintain protective coatings.
What certifications do you provide for Q345qD steel plates?
We provide comprehensive certification documentation for all Q345qD steel plates:
- Mill Test Certificate (MTC) EN 10204 3.1 / 3.2
- GB/T 714-2015 standard compliance certificate
- Third-party inspection reports (SGS, BV, TUV as required)
- Welding procedure specification (WPS) and procedure qualification record (PQR)
- ISO 9001 quality management system certification
- CE certification (if required for EU projects)
All certificates are traceable with unique heat numbers for each steel plate.
Key Advantages of Q345qD
Excellent Low-Temperature Toughness
Maintains high toughness at -20°C, suitable for cold climate regions and winter construction.
Superior Weldability
Low carbon equivalent ensures excellent welding performance without preheating requirements.
High Structural Reliability
Consistent mechanical properties and strict quality control ensure long-term structural safety.
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