Q345R is a Chinese low-alloy steel grade specified under the GB 713 standard, primarily used for pressure vessels and boilers. Below is a detailed overview of its material specification, including chemical composition, mechanical properties, and other relevant details.
Chemical Composition
The chemical composition of Q345R (per GB 713 standard) is as follows:
Carbon (C): ≤0.20% (≤0.22% for plates >60mm thick)
Manganese (Mn): 1.20-1.60%
Silicon (Si): ≤0.55%
Phosphorus (P): ≤0.025%
Sulfur (S): ≤0.015%
Aluminum (Al) (total): ≥0.020% (for deoxidation)
Other Elements: Trace amounts of Cr, Ni, Mo, or Cu may be present but are not typically specified unless required for specific applications.
Carbon Equivalent (Ceq): Typically ~0.47% (calculated as C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15), which impacts weldability.
Note: The exact composition may vary slightly depending on plate thickness or manufacturer, but it must comply with GB 713.
Mechanical Properties
The mechanical properties of Q345R vary based on plate thickness:
| Thickness (mm) | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | Impact Test Temp (°C) | Min. Absorbed Energy (J) |
|---|---|---|---|---|---|
| ≤16 | ≥345 | 510-640 | ≥21 | 0 | ≥41 (longitudinal) |
| >16-36 | ≥325 | 500-630 | ≥21 | 0 | ≥41 |
| >36-60 | ≥315 | 490-620 | ≥21 | 0 | ≥41 |
| >60-100 | ≥305 | 490-620 | ≥20 | 0 | ≥41 |
| >100-150 | ≥295 | 480-610 | ≥20 | 0 | ≥41 |
| >150-250 | ≥285 | 470-600 | ≥20 | 0 | ≥41 |
Impact Toughness: Q345R is tested at 0°C with a minimum absorbed energy of 41 J (longitudinal) to ensure low-temperature performance.
Bend Test: Must pass a 180° bend test (d=2a for transverse, where d is bend diameter and a is plate thickness).
Physical Properties
Density: ~7.85 g/cm³ (typical for low-alloy steel)
Thermal Conductivity: ~40-50 W/(m·K) at room temperature
Specific Heat: ~460-500 J/(kg·K)
Key Characteristics
Weldability: Moderate due to higher carbon equivalent (~0.47%) compared to Q245R (~0.37%). Requires precautions like preheating and low-hydrogen electrodes to prevent weld imperfections.
Strength: Higher yield and tensile strength than Q245R, making it suitable for high-pressure and high-temperature applications.
Corrosion Resistance: Less resistant to stress corrosion cracking (e.g., in wet H2S environments) compared to Q245R due to higher manganese content, which can form non-metallic inclusions like manganese sulfide.
Temperature Range: Suitable for service temperatures up to ~500°C, depending on design conditions.
Applications
Pressure Vessels: Used in manufacturing boilers, storage tanks, and heat exchangers.
Industrial Equipment: Common in petrochemical, oil and gas, and power generation industries where higher strength is required.
Typical Uses: Reactors, separators, and other equipment under high pressure or temperature.
Processing and Fabrication
Hot Forming: Can be hot-formed at 850-1100°C, followed by controlled cooling.
Welding: Compatible with common welding methods (e.g., SMAW, GTAW, SAW), but requires careful control to avoid cracking due to higher Ceq.
Heat Treatment: Typically supplied in normalized condition (heated to 880-940°C and air-cooled) to improve toughness and relieve stresses.
Equivalent Standards
ASTM Equivalent: Closest match is ASTM A516 Grade 70 or ASME SA516 Grade 70 due to similar yield strength (≥265-345 MPa) and tensile strength (485-620 MPa).
EN Equivalent: P355GH (EN 10028) is often cited as a close match, though slight differences in composition and properties exist.
Notes
Always refer to the GB 713 standard for precise specifications and verify with the material certificate for specific batches.
Selection of Q345R vs. Q245R depends on strength requirements, weldability, and environmental conditions (e.g., Q245R is preferred for better corrosion resistance in H2S environments).
For detailed design or application-specific requirements, consult with engineers and consider factors like service temperature, pressure, and corrosion risks.
If you need further details or comparisons (e.g., with Q245R or specific ASTM grades), let me know!
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