Overview
Q235 and Q345 are two widely used Chinese standardized carbon structural steels. Both can be produced as H Beams, plates, coils, sheets, or pipes.
They are favored for their mild temper, formability, and excellent welding capability, making them ideal for structural applications in construction, bridges, ships, automotive, steel tanks, and vessel containers.
While their chemical compositions are similar, the percentage of each element differs, which leads to different mechanical properties and recommended uses.
Chemical Composition Comparison
| Element | Q235B | Q345 |
|---|---|---|
| Carbon (C) | 0.12–0.20% | ≤0.20% |
| Manganese (Mn) | 0.30–0.70% | 1.00–1.60% |
| Silicon (Si) | ≤0.30% | ≤0.55% |
| Sulfur (S) | ≤0.045% | ≤0.045% |
| Phosphorus (P) | ≤0.045% | ≤0.045% |
| Vanadium (V) | – | 0.02–0.15% |
| Niobium (Nb) | – | 0.015–0.060% |
| Titanium (Ti) | – | 0.2% |
| Aluminum (Al) | – | ≥0.015% |
Key Difference: Q345 contains higher Mn and microalloying elements (V, Nb, Ti) which enhance strength, toughness, and low-temperature performance.
Mechanical Properties
| Property | Q235 | Q345 |
|---|---|---|
| Yield Strength | ≥235 MPa | ≥345 MPa |
| Tensile Strength | 375–500 MPa | 490–675 MPa |
| Elongation | ≥26% | ≥21% |
| Cold Temperature Performance | Suitable for mild environments | Can perform at -40℃ |
| Weldability | Excellent | Good, may require preheating for thick sections |
Implication: Q235 is more ductile, suitable for low-load structures, while Q345 provides higher strength and toughness for demanding applications.
Recommended Applications
Q235 – Moderate-strength, general-purpose structural steel
Tie rods, bolts, nuts, hooks/couplers, sleeves
Welding parts for frameworks
Light construction, low-load H Beams
General mechanical parts
Q345 – High-strength, heavy-duty structural steel
H Beams and pipes for heavy buildings, bridges, cranes, and power stations
Oil tanks, low-pressure vessels, mining machinery, and automotive frames
Structures requiring high load-bearing capacity, low-temperature performance, and durability
H-Beam Application Guidance
| Steel Grade | Typical H-Beam Use | Key Advantages |
|---|---|---|
| Q235 | Medium-load frameworks, light industrial buildings | Cost-effective, high ductility, easy fabrication and welding |
| Q345 | High-load frameworks, bridges, high-rise structures | High tensile/yield strength, good toughness, low-temperature performance, reliable under heavy dynamic loads |
Choose Q235 for projects where ductility, weldability, and cost-effectiveness are more important than high strength.
Choose Q345 for critical or heavy-load structures, harsh environments, or low-temperature conditions, ensuring safety and long-term performance.
