Q370qD Bridge Steel Plate
High-strength structural steel specifically designed for heavy-load bridge construction in cold regions, meeting GB/T 714-2015 standards for durability and reliability in low temperature conditions down to -20°C.
About Q370qD Steel
Q370qD is a Chinese standard (GB/T 714-2015) high-strength low alloy structural steel specifically developed for heavy-load bridge construction in cold climate zones.
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 in central and northern China.
It offers exceptional strength, excellent weldability, and superior formability, making it the premium choice for long-span and heavy-load bridge infrastructure in cold environments.
Technical Specifications
Basic Information
Mechanical Properties
| Thickness (mm) | Yield Strength (MPa) ≥ | Tensile Strength (MPa) | Elongation (%) ≥ | Impact Energy (J) ≥ |
|---|---|---|---|---|
| ≤16 | 370 | 490-650 | 20 | 34 |
| >16-35 | 350 | 490-650 | 20 | 34 |
| >35-50 | 340 | 490-650 | 20 | 34 |
| >50-100 | 320 | 470-630 | 20 | 34 |
Chemical Composition (wt%)
| Element | C ≤ | Si ≤ | Mn | P ≤ | S ≤ | Nb ≤ | V ≤ | Ti ≤ | Ni ≤ | Cu ≤ |
|---|---|---|---|---|---|---|---|---|---|---|
| Content | 0.18 | 0.55 | 1.20-1.80 | 0.025 | 0.020 | 0.08 | 0.15 | 0.02 | 0.30 | 0.30 |
Note: Carbon equivalent (Ceq) ≤ 0.48%, Weldability carbon equivalent (Pcm) ≤ 0.26%. Ni content can be increased to improve low-temperature toughness as required for extreme cold applications.
International Standards Comparison
Mechanical Properties Comparison (≤16mm thickness)
| Property | Q370qD (GB/T 714-2015) | S355NL (EN 10025) | A709 Gr50S (ASTM A709) |
|---|---|---|---|
| Yield Strength (MPa) min | 370 | 355 | 345 (50 ksi) |
| Tensile Strength (MPa) | 490-650 | 470-630 | 485-655 (70-95 ksi) |
| Elongation (%) min | 20 | 21 | 21 |
| Impact Test Temperature (°C) | -20 | -50 | -18 (0°F) |
| Impact Energy (J) min | 34 | 27 | 27 (20 ft-lb) |
| Carbon Equivalent (Ceq) max | 0.48% | 0.45% | 0.45% |
Chemical Composition Comparison (wt%)
| Element | Q370qD (max/ range) | S355NL (EN 10025) (max/ range) | A709 Gr50S (ASTM A709) (max/ range) |
|---|---|---|---|
| Carbon (C) | ≤0.18% | ≤0.20% | ≤0.23% |
| Silicon (Si) | ≤0.55% | ≤0.55% | 0.15-0.40% |
| Manganese (Mn) | 1.20-1.80% | 1.00-1.60% | 1.00-1.50% |
| Phosphorus (P) | ≤0.025% | ≤0.025% | ≤0.035% |
| Sulfur (S) | ≤0.020% | ≤0.020% | ≤0.040% |
| Niobium (Nb) | ≤0.08% | ≤0.06% | ≤0.05% |
| Vanadium (V) | ≤0.15% | ≤0.15% | ≤0.06% |
| Titanium (Ti) | ≤0.02% | ≤0.05% | ≤0.03% |
Key Differences Summary:
- Q370qD offers higher yield strength (370MPa) compared to international equivalents, making it ideal for heavy-load bridge applications
- Optimized manganese content (1.20-1.80%) enhances strength while maintaining good weldability and toughness
- Impact test temperature of -20°C makes it suitable for cold regions without the extreme cost of ultra-low temperature grades
- Higher niobium allowance (0.08%) allows for better grain refinement and strength development
- Carbon equivalent (0.48%) is slightly higher than international standards but still maintains excellent weldability
- Strict P/S control (0.025/0.020%) ensures good low-temperature toughness and resistance to lamellar tearing
Application Cases
Yangtze River Highway Bridge
Used in the main girders of a 1.8km long heavy-load highway bridge in central China, supporting high traffic loads in cold winter conditions down to -15°C.
- Plate thickness: 35mm-60mm
- Total usage: 12,800 metric tons
- Service life: Designed for 100 years
Beijing-Shanghai High-Speed Railway Bridge
Applied in a high-speed railway bridge project in eastern China, providing exceptional fatigue resistance and strength for heavy train loads in cold conditions.
- Plate thickness: 25mm-50mm
- Total usage: 15,600 metric tons
- Operates at temperatures down to -20°C
Qingdao Port Container Bridge
Utilized in a heavy-duty port container bridge in northern China, designed to withstand heavy lifting loads and cold coastal climate conditions.
- Plate thickness: 30mm-70mm
- Total usage: 8,900 metric tons
- Corrosion-resistant coating for marine environment
Other Typical Applications
Frequently Asked Questions (FAQ)
What is the difference between Q370qD and Q345qD steel?
The main differences between Q370qD and Q345qD bridge steel plates are:
- Yield strength: Q370qD (370MPa) vs Q345qD (345MPa) for ≤16mm thickness
- Tensile strength: Q370qD (490-650MPa) vs Q345qD (470-630MPa)
- Manganese content: Q370qD (1.20-1.80%) vs Q345qD (1.00-1.60%)
- Niobium allowance: Q370qD (0.08%) vs Q345qD (0.06%)
- Applications: Q370qD for heavy-load/high-strength requirements, Q345qD for standard applications
- Carbon equivalent: Q370qD (0.48%) vs Q345qD (0.45%)
What welding precautions are needed for Q370qD in cold weather?
Q370qD has good weldability (Ceq ≤ 0.48%), but special precautions apply for welding in cold weather:
- Preheat base metal to ≥10°C when ambient temperature < 0°C (higher than Q345qD)
- Preheat to 80-120°C for plates >40mm thick or when temperature < -10°C
- Use low-hydrogen welding electrodes (E5015/E5016) to prevent cold cracking
- Maintain interpass temperature ≥80°C during multi-pass welding
- Post-weld heat treatment recommended for thickness >50mm or critical components
Follow WPS specifically qualified for high-strength low alloy steels.
What is the service temperature range for Q370qD steel?
Q370qD is engineered for cold environments with the following temperature range:
- Minimum operating temperature: -20°C (meets impact energy requirements at this temperature)
- Recommended continuous service: -20°C to 200°C
- Maximum short-term service temperature: 300°C
- Optimal welding temperature: ≥10°C (preheating required below this)
Q370qD is the high-strength grade in the Q370q series, suitable for cold climate heavy-load applications in China.
What special treatments enhance Q370qD performance in cold regions?
Several specialized treatments optimize Q370qD for cold environment heavy-load applications:
- TMCP (Thermo-Mechanical Control Process) for refined grain structure and higher strength
- Strict impurity control (P≤0.025%, S≤0.020%) to prevent brittle fracture
- Normalized heat treatment for uniform microstructure and toughness
- Niobium microalloying (up to 0.08%) for grain refinement and strength
- Stress relief annealing after welding for heavy-load components
- Zinc-rich epoxy coatings with anti-corrosion properties for cold, humid environments
These treatments ensure reliable heavy-load performance in cold climate conditions.
What quality certifications are provided for Q370qD steel plates?
We provide comprehensive certification for Q370qD steel plates, including:
- Mill Test Certificate (MTC) EN 10204 3.1 / 3.2 with -20°C impact test results
- GB/T 714-2015 standard compliance certificate
- Low-temperature toughness test reports (-20°C Charpy V-notch)
- Third-party inspection (SGS, BV, TUV) for critical heavy-load projects
- Welding procedure qualification for high-strength steel applications
- ISO 9001 and CE certification (when required for export)
All Q370qD plates undergo 100% ultrasonic testing to ensure internal quality for heavy-load cold-region applications.
Key Advantages of Q370qD
Superior High-Strength Performance
370MPa yield strength provides exceptional load-bearing capacity for heavy-load bridge applications in cold regions.
Excellent Low-Temperature Toughness
Maintains superior toughness at -20°C, ideal for cold climate regions in central and northern China.
Optimized Weldability
Carefully balanced chemical composition ensures excellent welding performance with minimal preheating requirements.
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