Q345 is a low-alloy, high-strength structural steel widely used in motor vehicles, bridges, ships, and construction projects. It is standardized under GB/T 1591, where "Q" indicates the yield point, and "345" represents the minimum yield strength in MPa. Note that the yield strength decreases slightly as the material thickness increases.
Equivalent Materials
Q345 steel can be substituted with equivalent international grades, such as:
A572 Grade 50 (USA, ASTM)
Q355 (China, GB/T)
SPFC 590 (Vietnam/Japan, JIS)
Key Characteristics
Yield Strength: 345 MPa – the stress at which the material begins to deform plastically. Before reaching this point, it will return to its original shape.
Tensile Strength: 470–660 MPa – able to withstand heavy-duty loads before failure.
Elongation: ~20% – allowing for significant deformation before rupture.
Weldability: Excellent, due to optimized chemical composition and improved production technology.
Durability: High-pressure and cold-temperature resistance, suitable for structures exposed to -40°C or under heavy loads.
Typical Applications
Q345 steel is highly versatile and widely applied in:
Building structures and cranes
Bridges and ships
Petroleum storage tanks and lifting machinery
Power stations and mining machinery
General mechanical parts and structural components exposed to low temperatures or heavy loads
Physical Properties
| Property | Metric | US/Imperial |
|---|---|---|
| Density | 7.80 g/cc | 0.282 lb/in³ |
| Bulk Modulus | 160 GPa | 23,200 ksi |
| Shear Modulus | 80.0 GPa | 11,600 ksi |
Mechanical Properties
| Property | Metric | US/Imperial |
|---|---|---|
| Brinell Hardness | 135 | 135 |
| Rockwell B Hardness | 74 | 74 |
| Yield Strength | 345 MPa | – |
| Tensile Strength, Ultimate | 450 MPa | – |
| Elongation at Break | 18–21 % | 18–21 % |
Chemical Composition
| Element | Max / Range |
|---|---|
| Carbon (C) | ≤ 0.23% |
| Iron (Fe) | 98% |
| Manganese (Mn) | 1.35% |
| Phosphorus (P) | ≤ 0.040% |
| Silicon (Si) | 0.15–0.55% |
| Sulfur (S) | ≤ 0.050% |
Q345 steel combines high strength, excellent weldability, and cold-weather performance, making it an ideal choice for demanding structural and mechanical applications.
