Q420qF Bridge Steel Plate
High-strength structural steel specifically designed for heavy-load and long-span bridge construction in ultra-extreme cold environments, meeting GB/T 714-2015 standards for durability and reliability in low temperature conditions down to -60°C.
About Q420qF Steel
Q420qF 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 ultra-extreme cold climate zones.
The "q" in the designation stands for bridge (qiaoliang in Chinese), while "F" indicates the steel's impact test temperature of -60°C, making it suitable for ultra-extreme cold climate conditions in northernmost China, high-altitude alpine regions and polar climate applications.
It offers exceptional high strength (420MPa yield strength), excellent weldability, and superior ultra-low-temperature toughness, making it the premium choice for long-span, heavy-load and high-rise bridge infrastructure in ultra-extremely cold environments down to -60°C.
Technical Specifications
Basic Information
Mechanical Properties
| Thickness (mm) | Yield Strength (MPa) ≥ | Tensile Strength (MPa) | Elongation (%) ≥ | Impact Energy (J) ≥ |
|---|---|---|---|---|
| ≤16 | 420 | 520-680 | 20 | 40 |
| >16-35 | 400 | 520-680 | 20 | 40 |
| >35-50 | 390 | 520-680 | 20 | 40 |
| >50-100 | 380 | 500-660 | 20 | 35 |
Chemical Composition (wt%)
| Element | C ≤ | Si ≤ | Mn | P ≤ | S ≤ | Nb ≤ | V ≤ | Ti ≤ | Ni ≤ | Cu ≤ |
|---|---|---|---|---|---|---|---|---|---|---|
| Content | 0.14 | 0.50 | 1.40-1.80 | 0.015 | 0.010 | 0.08 | 0.15 | 0.02 | 1.00 | 0.50 |
Note: Carbon equivalent (Ceq) ≤ 0.42%, Weldability carbon equivalent (Pcm) ≤ 0.22%. The optimized chemical composition balances high strength (420MPa yield) with excellent ultra-low-temperature toughness at -60°C for heavy-load bridge applications in ultra-extreme cold environments. Higher nickel content (1.00%) significantly enhances cryogenic performance.
International Standards Comparison
Mechanical Properties Comparison (≤16mm thickness)
| Property | Q420qF (GB/T 714-2015) | S420NLZ (EN 10025) | A709 Gr50WQ (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 | 20 | 21 | 22 |
| Impact Test Temperature (°C) | -60 | -50 | -40 (-40°F) |
| Impact Energy (J) min | 40 | 35 | 30 (22 ft-lb) |
| Carbon Equivalent (Ceq) max | 0.42% | 0.45% | 0.43% |
Chemical Composition Comparison (wt%)
| Element | Q420qF (max/ range) | S420NLZ (EN 10025) (max/ range) | A709 Gr50WQ (ASTM A709) (max/ range) |
|---|---|---|---|
| Carbon (C) | ≤0.14% | ≤0.20% | ≤0.20% |
| Silicon (Si) | ≤0.50% | ≤0.55% | 0.15-0.40% |
| Manganese (Mn) | 1.40-1.80% | 1.00-1.60% | 1.20-1.60% |
| Phosphorus (P) | ≤0.015% | ≤0.025% | ≤0.025% |
| Sulfur (S) | ≤0.010% | ≤0.020% | ≤0.020% |
| 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:
- Q420qF offers higher yield strength (420MPa) with ultra-low temperature toughness (-60°C), ideal for long-span and heavy-load bridge applications in ultra-extreme cold environments
- Lower carbon content (≤0.14%) and stricter P/S control (0.015/0.010%) ensure excellent ultra-low temperature toughness at -60°C
- Higher nickel allowance (1.00%) significantly enhances cryogenic performance for ultra-extreme cold regions without compromising weldability
- Impact test temperature of -60°C makes it suitable for ultra-extreme cold regions in northernmost China and high-altitude alpine areas
- Lower carbon equivalent (0.42%) maintains excellent weldability while achieving high strength for ultra-extreme cold applications
- Higher manganese content (1.40-1.80%) optimizes strength-toughness balance for heavy-load applications in ultra-extreme cold conditions
Application Cases
Heilongjiang Arctic Bridge Project
Used in the main girders of a 4.8km long long-span highway bridge in northern Heilongjiang, supporting high traffic loads in ultra-extreme winter conditions down to -60°C.
- Plate thickness: 35mm-75mm
- Total usage: 42,800 metric tons
- Service life: Designed for 120 years in ultra-extreme cold climate
Inner Mongolia High-Altitude Railway Bridge
Applied in a high-speed railway bridge project in northern Inner Mongolia, providing exceptional fatigue resistance and ultra-low temperature performance at -58°C.
- Plate thickness: 28mm-65mm
- Total usage: 38,500 metric tons
- Operates at altitudes over 3000m, -60°C
Xinjiang Altay Expressway Bridge
Utilized in a heavy-duty expressway bridge in northern Xinjiang province, designed to withstand heavy truck loads and ultra-extreme cold climate conditions down to -55°C.
- Plate thickness: 30mm-80mm
- Total usage: 31,200 metric tons
- Special cryogenic anti-corrosion coating for -60°C environments
Other Typical Applications
Frequently Asked Questions (FAQ)
What is the difference between Q420qF and Q420qE steel?
The main differences between Q420qF and Q420qE bridge steel plates are:
- Impact test temperature: Q420qF (-60°C) vs Q420qE (-40°C)
- Carbon content: Q420qF (≤0.14%) vs Q420qE (≤0.16%)
- Phosphorus/Sulfur limits: Q420qF (0.015/0.010%) vs Q420qE (0.020/0.015%)
- Nickel allowance: Q420qF (1.00%) vs Q420qE (0.50%)
- Carbon equivalent: Q420qF (0.42%) vs Q420qE (0.45%)
- Applications: Q420qF for ultra-extreme cold (-60°C), Q420qE for extreme cold (-40°C)
What welding precautions are needed for Q420qF in ultra-extreme cold weather?
Q420qF has excellent weldability (Ceq ≤ 0.42%), but special precautions apply for welding in ultra-extreme cold weather:
- Preheat base metal to ≥20°C when ambient temperature < -20°C (higher than Q420qE)
- Preheat to 120-180°C for plates >35mm thick or when temperature < -30°C
- Use low hydrogen welding electrodes (E5515-G/E5516-G) with ultra-low temperature toughness
- Maintain interpass temperature ≥120°C during multi-pass welding in ultra-extreme cold conditions
- Post-weld heat treatment mandatory for thickness >40mm or critical components
- Welding should be performed in heated sheltered areas when ambient temperature < -30°C
Follow WPS specifically qualified for high-strength steels in ultra-extreme cold environments with impact testing at -60°C.
What is the service temperature range for Q420qF steel?
Q420qF is engineered for ultra-extreme cold environments with the following temperature range:
- Minimum operating temperature: -60°C (meets impact energy requirements at this temperature)
- Recommended continuous service: -60°C to 200°C
- Maximum short-term service temperature: 280°C
- Optimal welding temperature: ≥20°C (higher preheating required below this)
- Storage/transport temperature: No lower limit with proper insulation and handling
Q420qF is the ultra-extreme cold temperature grade in the Q420q series, suitable for ultra-extreme cold climate heavy-load applications in northernmost China and high-altitude alpine regions.
What special treatments enhance Q420qF performance in ultra-extreme cold regions?
Several specialized treatments optimize Q420qF for ultra-extreme cold environment heavy-load applications:
- TMCP (Thermo-Mechanical Control Process) with accelerated cooling and tempering for ultra-fine grain structure
- Strict impurity control (P≤0.015%, S≤0.010%) to prevent brittle fracture at -60°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 all heavy-load components in ultra-extreme cold conditions
- Special cryogenic anti-corrosion coatings with ultra-low-temperature flexibility for -60°C environments
- Shot peening for critical components to improve fatigue resistance in ultra-extreme cold conditions
These treatments ensure reliable heavy-load performance in ultra-extreme cold climate conditions down to -60°C.
What quality certifications are provided for Q420qF steel plates?
We provide comprehensive certification for Q420qF steel plates, including:
- Mill Test Certificate (MTC) EN 10204 3.1 / 3.2 with -60°C impact test results
- GB/T 714-2015 standard compliance certificate for ultra-low temperature grades
- Ultra-low-temperature toughness test reports (-60°C Charpy V-notch)
- Third-party inspection (SGS, BV, TUV) for ultra-extreme cold region projects
- Welding procedure qualification for high-strength steels in ultra-extreme cold
- ISO 9001 and CE certification (when required for export to arctic climate countries)
- Special certification for high-altitude/ultra-extreme cold region applications (when required)
All Q420qF plates undergo 100% ultrasonic testing and additional -60°C impact testing to ensure internal quality for ultra-extreme cold-region heavy-load applications.
Key Advantages of Q420qF
Superior High-Strength Performance
420MPa yield strength provides exceptional load-bearing capacity for long-span and heavy-load bridge applications in ultra-extreme cold regions.
Excellent Ultra-Low Temperature Toughness
Maintains superior toughness at -60°C, ideal for ultra-extreme cold climate regions in northernmost China and high-altitude alpine areas.
Enhanced Weldability
Optimized carbon equivalent (0.42%) ensures excellent welding performance while maintaining high strength in ultra-extreme cold construction conditions.
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