Q420qD Bridge Steel Plate
High-strength structural steel specifically designed for heavy-load and long-span bridge construction, meeting GB/T 714-2015 standards for durability and reliability in low temperature conditions down to -20°C.
About Q420qD Steel
Q420qD is a Chinese standard (GB/T 714-2015) high-strength low alloy structural steel specifically developed for heavy-load and long-span 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 northern China and high-altitude regions.
It offers exceptional high strength (420MPa yield strength), excellent weldability, and superior low-temperature toughness, making it the premium choice for long-span, heavy-load and high-rise bridge infrastructure in cold environments.
Technical Specifications
Basic Information
Mechanical Properties
| Thickness (mm) | Yield Strength (MPa) ≥ | Tensile Strength (MPa) | Elongation (%) ≥ | Impact Energy (J) ≥ |
|---|---|---|---|---|
| ≤16 | 420 | 520-680 | 19 | 34 |
| >16-35 | 400 | 520-680 | 19 | 34 |
| >35-50 | 390 | 520-680 | 19 | 34 |
| >50-100 | 380 | 500-660 | 19 | 34 |
Chemical Composition (wt%)
| Element | C ≤ | Si ≤ | Mn | P ≤ | S ≤ | Nb ≤ | V ≤ | Ti ≤ | Ni ≤ | Cu ≤ |
|---|---|---|---|---|---|---|---|---|---|---|
| Content | 0.18 | 0.55 | 1.30-1.80 | 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%. The optimized chemical composition balances high strength (420MPa yield) with excellent low-temperature toughness at -20°C for heavy-load bridge applications.
International Standards Comparison
Mechanical Properties Comparison (≤16mm thickness)
| Property | Q420qD (GB/T 714-2015) | S420NL (EN 10025) | A709 Gr50W (ASTM A709) |
|---|---|---|---|
| Yield Strength (MPa) min | 420 | 420 | 345 (50 ksi) |
| Tensile Strength (MPa) | 520-680 | 500-630 | 485-655 (70-95 ksi) |
| Elongation (%) min | 19 | 20 | 21 |
| Impact Test Temperature (°C) | -20 | -50 | -29 (-20°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 | Q420qD (max/ range) | S420NL (EN 10025) (max/ range) | A709 Gr50W (ASTM A709) (max/ range) |
|---|---|---|---|
| Carbon (C) | ≤0.18% | ≤0.20% | ≤0.23% |
| Silicon (Si) | ≤0.55% | ≤0.55% | 0.15-0.40% |
| Manganese (Mn) | 1.30-1.80% | 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:
- Q420qD offers higher yield strength (420MPa) than standard international equivalents, ideal for long-span and heavy-load bridge applications in cold environments
- Optimized carbon content (≤0.18%) and strict P/S control (0.025/0.020%) ensure excellent low temperature toughness at -20°C
- Nickel allowance (0.30%) enhances low-temperature performance for cold regions without compromising weldability
- Impact test temperature of -20°C makes it suitable for cold regions in northern China and high-altitude areas
- Balanced carbon equivalent (0.48%) maintains good weldability while achieving high strength
- Higher manganese content (1.30-1.80%) optimizes strength-toughness balance for heavy-load applications
Application Cases
Beijing Grand Bridge Project
Used in the main girders of a 3.8km long long-span highway bridge in Beijing, supporting high traffic loads in cold winter conditions down to -20°C.
- Plate thickness: 40mm-80mm
- Total usage: 28,500 metric tons
- Service life: Designed for 100 years in cold climate
Shanxi High-Speed Railway Bridge
Applied in a high-speed railway bridge project in Shanxi province, providing exceptional fatigue resistance and low temperature performance at -20°C.
- Plate thickness: 30mm-70mm
- Total usage: 31,200 metric tons
- Operates at altitudes over 1500m, -20°C
Gansu Expressway Bridge
Utilized in a heavy-duty expressway bridge in Gansu province, designed to withstand heavy truck loads and cold climate conditions down to -18°C.
- Plate thickness: 35mm-85mm
- Total usage: 24,800 metric tons
- Special anti-corrosion coating for cold, dry environment
Other Typical Applications
Frequently Asked Questions (FAQ)
What is the difference between Q420qD and Q420qE steel?
The main differences between Q420qD and Q420qE bridge steel plates are:
- Impact test temperature: Q420qD (-20°C) vs Q420qE (-40°C)
- Carbon content: Q420qD (≤0.18%) vs Q420qE (≤0.16%)
- Phosphorus/Sulfur limits: Q420qD (0.025/0.020%) vs Q420qE (0.020/0.015%)
- Nickel allowance: Q420qD (0.30%) vs Q420qE (0.50%)
- Carbon equivalent: Q420qD (0.48%) vs Q420qE (0.45%)
- Applications: Q420qD for cold regions (-20°C), Q420qE for extreme cold (-40°C)
What welding precautions are needed for Q420qD in cold weather?
Q420qD 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 (lower than Q420qE)
- Preheat to 80-120°C for plates >40mm thick or when temperature < -10°C
- Use low hydrogen welding electrodes (E5515-G/E5516-G) to prevent cold cracking
- Maintain interpass temperature ≥80°C during multi-pass welding in cold conditions
- Post-weld heat treatment recommended for thickness >50mm or critical components
- Welding should be performed in sheltered areas when ambient temperature < -10°C
Follow WPS specifically qualified for high-strength steels in cold environments.
What is the service temperature range for Q420qD steel?
Q420qD 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)
- Storage/transport temperature: No lower limit with proper handling
Q420qD is the standard cold temperature grade in the Q420q series, suitable for cold climate heavy-load applications in northern China and high-altitude regions.
What special treatments enhance Q420qD performance in cold regions?
Several specialized treatments optimize Q420qD for cold environment heavy-load applications:
- TMCP (Thermo-Mechanical Control Process) with accelerated cooling for refined grain structure
- Strict impurity control (P≤0.025%, S≤0.020%) to prevent brittle fracture at -20°C
- Normalized heat treatment with precise temperature control for uniform microstructure
- Niobium microalloying (up to 0.08%) for strength enhancement and grain refinement
- Stress relief annealing after welding for heavy-load components in cold conditions
- Special anti-corrosion coatings with low-temperature flexibility for -20°C environments
- Shot peening for critical components to improve fatigue resistance in cold conditions
These treatments ensure reliable heavy-load performance in cold climate conditions down to -20°C.
What quality certifications are provided for Q420qD steel plates?
We provide comprehensive certification for Q420qD 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 for cold temperature grades
- Low-temperature toughness test reports (-20°C Charpy V-notch)
- Third-party inspection (SGS, BV, TUV) for cold region projects
- Welding procedure qualification for high-strength steel applications
- ISO 9001 and CE certification (when required for export to cold climate countries)
- Special certification for high-altitude/cold region applications (when required)
All Q420qD plates undergo 100% ultrasonic testing and additional -20°C impact testing to ensure internal quality for cold-region heavy-load applications.
Key Advantages of Q420qD
Superior High-Strength Performance
420MPa yield strength provides exceptional load-bearing capacity for long-span and heavy-load bridge applications in cold regions.
Excellent Low Temperature Toughness
Maintains superior toughness at -20°C, ideal for cold climate regions in northern China and high-altitude areas.
Balanced Weldability
Optimized carbon equivalent (0.48%) ensures good welding performance while maintaining high strength in cold construction conditions.
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