Q345E Low-Alloy High-Strength Structural Steel Plate
Q345E Low-Alloy High-Strength Structural Steel Plate | GB/T 1591 Analysis & Equivalent Grades
Comprehensive technical data for Q345E steel according to GB/T 1591: chemical composition, mechanical properties, thermal and electrical properties, international equivalents, and application guide.
Hot rolling, controlled rolling, normalizing, or thermo-mechanical controlled processing (TMCP); suitable for cutting, welding, bending, and cold forming
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Q345E Low-Alloy High-Strength Structural Steel Plate Introduction
Q345E is a low-alloy high-strength structural steel grade specified in Chinese standard GB/T 1591. It is characterized by a minimum yield strength of 345 MPa and good low-temperature impact toughness (guaranteed down to -40°C). The steel offers excellent weldability, formability, and corrosion resistance, making it suitable for welded structures in building, bridges, and heavy machinery.
- High strength-to-weight ratio compared to plain carbon steel
- Reliable notch toughness at sub-zero temperatures
- Widely used in structural engineering and construction
Q345E Low-Alloy High-Strength Structural Steel Plate Chemical Composition
The chemical composition complies with GB/T 1591-2008 for grade Q345E. Maximum limits are given unless a range is specified. The steel is fully killed and contains fine grain forming elements (Nb, V, Ti, Al). Note: The composition may be adjusted within limits to achieve the required mechanical properties.
- Low carbon content ensures good weldability.
- Microalloying elements provide grain refinement and precipitation strengthening.
| Element | Specified Value (max, %) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.18 | CEV ≤ 0.45% for thickness ≤ 40 mm |
| Silicon (Si) | ≤ 0.50 | For killed steel |
| Manganese (Mn) | ≤ 1.70 | May be increased to 1.80% for thickness > 40 mm |
| Phosphorus (P) | ≤ 0.020 | |
| Sulfur (S) | ≤ 0.020 | |
| Niobium (Nb) | ≤ 0.07 | Grain refiner |
| Vanadium (V) | ≤ 0.15 | |
| Titanium (Ti) | ≤ 0.20 | |
| Chromium (Cr) | ≤ 0.30 | |
| Nickel (Ni) | ≤ 0.50 | |
| Copper (Cu) | ≤ 0.30 | |
| Nitrogen (N) | ≤ 0.012 | Aluminium is added to bind nitrogen |
| Molybdenum (Mo) | ≤ 0.10 | |
| Aluminium (Alt) | ≥ 0.015 | Acid-soluble, for grain refinement |
Q345E Low-Alloy High-Strength Structural Steel Plate Thermal and Electrical Physical Properties
Typical physical properties for low-alloy steel of similar composition. Values are approximate and apply at room temperature unless specified. Note: Actual properties may vary slightly depending on processing and exact composition.
- Density is virtually constant for structural steels.
- Thermal expansion coefficient and thermal conductivity are temperature-dependent.
| Property | Reference Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | at 20°C |
| Elastic modulus (E) | 206 | GPa | at 20°C; decreases with temperature |
| Shear modulus (G) | 79.3 | GPa | calculated from E and Poisson's ratio |
| Poisson's ratio (ν) | 0.30 | — | elastic range |
| Thermal expansion coefficient (α) | 11.8 × 10⁻⁶ | K⁻¹ | between 20°C and 100°C |
| Thermal expansion coefficient (α) | 12.8 × 10⁻⁶ | K⁻¹ | between 20°C and 200°C |
| Thermal expansion coefficient (α) | 13.5 × 10⁻⁶ | K⁻¹ | between 20°C and 300°C |
| Thermal conductivity (λ) | 52 | W/(m·K) | at 20°C |
| Thermal conductivity (λ) | 48 | W/(m·K) | at 200°C |
| Specific heat capacity (cp) | 470 | J/(kg·K) | at 20°C |
| Specific heat capacity (cp) | 510 | J/(kg·K) | at 200°C |
| Electrical resistivity (ρe) | 0.16 – 0.20 | μΩ·m | at 20°C; depending on exact composition |
Q345E Low-Alloy High-Strength Structural Steel Plate Mechanical Properties
Tensile and impact properties according to GB/T 1591-2008 for grade Q345E. Values are for transverse test pieces unless otherwise specified. Impact test temperature is -40°C. The yield strength varies with plate thickness.
- Elongation is measured on a gauge length of 5.65√So (proportional test piece).
- 1 MPa = 1 N/mm².
| Property | Specified Requirement | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield strength (ReH) | ≥ 345 | MPa | thickness ≤ 16 mm |
| Yield strength (ReH) | ≥ 335 | MPa | 16 mm < thickness ≤ 40 mm |
| Yield strength (ReH) | ≥ 325 | MPa | 40 mm < thickness ≤ 63 mm |
| Yield strength (ReH) | ≥ 315 | MPa | 63 mm < thickness ≤ 80 mm |
| Yield strength (ReH) | ≥ 305 | MPa | 80 mm < thickness ≤ 100 mm |
| Tensile strength (Rm) | 470 – 630 | MPa | All thicknesses |
| Elongation after fracture (A) | ≥ 20 | % | Longitudinal, thickness ≤ 40 mm (5.65√So) |
| Elongation after fracture (A) | ≥ 19 | % | Longitudinal, 40 mm < thickness ≤ 63 mm |
| Elongation after fracture (A) | ≥ 19 | % | Longitudinal, 63 mm < thickness ≤ 100 mm |
| Bend test (mandrel diameter) | d = 2a (t ≤ 16 mm); d = 3a (t > 16 mm) | 180° bend, a = specimen thickness, no cracks | |
| Charpy V-notch impact energy (KV₂) | ≥ 34 | J | at -40°C, longitudinal, average of 3 tests |
Q345E Low-Alloy High-Strength Structural Steel Plate Fully Equivalent Material Standards and Substitute Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2008 | Q345E | Original grade; replaced by Q355E in GB/T 1591-2018 |
| China | GB/T 1591-2018 | Q355E | Current standard; yield strength 355 MPa, otherwise similar |
| European Union | EN 10025-2 | S355K2 (+N) | Impact at -20°C standard; requires supplementary -40°C impact test |
| European Union | EN 10025-3 | S355NL | Normalized fine-grain steel; CVN ≥27 J at -50°C; very close but more stringent |
| United States | ASTM A572/A572M | Grade 50 [345] with supplementary S5 | Requires Charpy V-notch test at -40°C; strength range similar |
| Japan | JIS G 3106 | SM490YB (modified) | May need additional low-temperature toughness verification |
| International | ISO 4950-2 | E355DD | High yield strength flat products; impact at -20°C, may be ordered with -40°C test |
Q345E Low-Alloy High-Strength Structural Steel Plate Application Introduction
Q345E steel is extensively used in welded structures that require high strength, good toughness at low temperatures, and reliable weldability. It is suitable for heavy plate fabrications, space frames, bridge girders, and offshore structures.
- The guaranteed impact toughness at -40°C makes it ideal for cold regions and low-temperature service.
- Typical processing includes flame cutting, cold forming (with appropriate bend radii), and all common arc welding methods.
Product Applications: Welded H-beams, box columns, and trusses for building frameworks, Highway and railway bridge main girders and crossframes, Offshore platform decks, legs, and bracings, Tower crane booms, excavator arms, dump truck bodies, Penstocks and spiral cases for hydropower projects, Wind turbine tubular towers and foundations
Processed into products: Structural steel plates cut to shape for base plates and stiffeners, Built-up I-sections and plate girders for long-span structures, Bracket plates and node connections in steel frames, Rolled angles, channels, and square hollow sections for secondary framing, Flanges and webs for crane runway beams, Plate-welded bearing pedestals and machine frames
Application industries: Civil engineering and construction (high-rise buildings, stadiums, bridges), Offshore engineering (platform structures, wind turbine towers), Heavy machinery and mining equipment, Railway and transportation (wagon frames, crane booms), Shipbuilding (for certain secondary structural parts), Pressure vessel manufacturing (with additional requirements)
Q345E Low-Alloy High-Strength Structural Steel Plate Closely Related / Similar Substitute Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2008 | Q345D | Same strength, guaranteed impact at -20°C; less low-temperature toughness |
| European Union | EN 10025-2 | S355J2 (+N) | Impact at -20°C; commonly used as equivalent but does not meet -40°C requirement |
| United States | ASTM A572/A572M | Grade 50 [345] | Typical structural steel; impact testing optional; must specify -40°C requirement |
| Russia | GOST 19281 | 09G2S-12 | Similar strength and -40°C toughness; used in CIS countries |
| India | IS 2062 | E350BR/E350C | E350C has guaranteed impact at -20°C; supplementary low-temperature option needed |
Notes:
Note: While Q345E was withdrawn in the 2018 revision of GB/T 1591 and replaced by Q355E, many projects still specify the grade according to the older standard. When ordering, it is essential to confirm the applicable standard edition. For critical structures, additional through-thickness (Z-direction) tensile requirements may be imposed. Welding consumables should be selected to match the base metal's strength and toughness (e.g., AWS E7018 or equivalent low-hydrogen electrodes).
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