Q355 is a Chinese structural steel grade that is comparable to Q345 but has better strength. It is sometimes referred to as Q355B or Q355D, based on its chemical makeup and mechanical qualities. Q355 steel is intended to have a minimum yield strength of 355 MPa, which is much greater than the 345 MPa yield strength of Q345 steel.
Q355 steel has increased performance and is often utilized in structural applications that demand more strength. It is used in the construction industry to fabricate beams, columns, and other load-bearing structures. Q355 steel is also appropriate for making equipment components, bridges, and offshore structures.
Grade of Q355 steel
Q355 steel is a high-strength structural steel grade that is commonly used in various industries and applications. However, it's important to note that there isn't a specific "grade" of Q355 steel as it is not classified using traditional grade designations like Q235 or Q345. Instead, Q355 is typically categorized based on its chemical composition and mechanical properties.
Different variations or types of Q355 steel exist, such as Q355B, Q355C, Q355D, and Q355E, each with its own specific composition and properties. These variations are distinguished by factors like carbon content, additional alloying elements, and specific heat treatment processes.
Q355B
This type of Q355 steel is characterized by a higher carbon content, typically ranging from 0.20% to 0.25%. It offers good weldability and formability, making it suitable for structural applications that require high strength and toughness. Q355B is commonly used in the construction of buildings, bridges, and machinery.
Q355C
Q355C steel has an increased carbon content, usually ranging from 0.18% to 0.22%. This variant provides improved strength and hardness compared to Q355B. Q355C is often utilized in applications that require higher load-bearing capacity, such as heavy machinery, cranes, and offshore structures.
Q355D
Q355D steel is a type of Q355 with enhanced mechanical properties. It typically has a higher carbon content and additional alloying elements like niobium, vanadium, or titanium. Q355D offers excellent strength, toughness, and impact resistance, making it suitable for demanding structural applications. It is commonly employed in the construction of bridges, high-rise buildings, and structural components subjected to dynamic loads.
Q355E
Q355E steel is another variant of Q355 that is designed to have enhanced properties. It frequently incorporates alloying metals like niobium, vanadium, or titanium to increase its strength and hardness. Q355E is commonly used in applications that require high strength and resistance to environmental conditions, such as offshore platforms, power transmission towers, and heavy-duty equipment.
Mechanical Properties of Q355 Steel
| Grade | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | Impact Temperature |
| Q355B | ≥355 | 470–630 | ≥22 | 20°C |
| Q355C | ≥355 | 470–630 | ≥22 | 0°C |
| Q355D | ≥355 | 470–630 | ≥22 | −20°C |
| Q355E | ≥355 | 470–630 | ≥22 | −40°C |
Q355 Chemical Composition (GB/T 1591)
Below is the chemical composition of Q355 according to GB/T 1591-2018 (for thickness ≤ 16 mm, maximum values unless noted):
| Element | Q355B | Q355C | Q355D | Q355E |
| C | ≤0.24% | ≤0.22% | ≤0.20% | ≤0.18% |
| Si | ≤0.55% | ≤0.55% | ≤0.55% | ≤0.55% |
| Mn | ≤1.60% | ≤1.60% | ≤1.60% | ≤1.60% |
| P | ≤0.035% | ≤0.035% | ≤0.030% | ≤0.025% |
| S | ≤0.035% | ≤0.035% | ≤0.030% | ≤0.020% |
| Nb+V+Ti | ≤0.12% | ≤0.12% | ≤0.12% | ≤0.12% |
Equivalent Standards of Q355 steel
Q355 is the successor to the widely known Q345 steel in the updated GB/T 1591 standard (2018 revision), offering slightly improved properties and better alignment with international standards.
European (EN): S355 series (e.g., S355J2 is roughly equivalent to Q355B; S355K2+N is roughly equivalent to Q355D). This is the closest equivalent
American (ASTM): A572 Grade 50 (Minimum Yield 50 ksi = ~345 MPa) is the most common equivalent, though strength differs slightly. ASTM A992 (for structural shapes) is also often comparable.
Primary Applications of Q355 HSLA Steel Plate
Structural frameworks for buildings (industrial, commercial, high-rise)
- Bridges
- Towers (transmission, communication)
- Cranes and lifting equipment
- Heavy machinery and mining equipment
- Construction vehicles
- Ships (hull structures requiring higher strength than ordinary hull plate)
- Pressure vessels (specific grades meeting additional standards)
- Pipe racks, platforms, and other structural steelwork.
How to Select Q355B/C/D/E
| Application Scenario | Recommended Grade |
|---|---|
| General construction | Q355B |
| Welding-focused structures | Q355C |
| Outdoor / cold regions | Q355D |
| Extremely low temperature | Q355E |
Key Differences
- E-grade used in low-temperature engineering & critical welded structures
- B → E indicates improved impact toughness
- The letter defines the temperature for Charpy V-notch impact test
- Composition is similar; toughness and service temperature differ
In Summary
Q355 is a versatile, high-strength structural steel from China, offering a good balance of strength, ductility, weldability, and impact toughness. Its specific properties (especially impact toughness at low temperatures) are defined by its grade (B, C, D, E). It's the cornerstone steel for demanding structural applications across various industries in China and is increasingly recognized globally through its equivalence to S355 steel.
What material is Q355?
Q355 steel is a Chinese low alloy high strength structural steel, which replaced Q345, the material density is 7.85 g/cm3. According to GB/T 1591 -2018, Q355 has 3 quality levels: Q355B, Q355C and Q355D.
What is Q355 steel equivalent to?
Q355 steel is generally considered equivalent to the EN S355 structural steel series in terms of yield strength and mechanical performance. The closest European equivalents are S355JR, S355J0, and S355J2, depending on impact test temperature requirements.
What is S355 British Standard?
S355 steel is a low carbon steel whose specifications offer high yield strength. The average minimum yield for S355 steel is 355 N/mm² giving its name: S355. BS EN 10025 S275 & S275JR supercedes BS4360 43A and 43B. S355 sheet/plate can also be flame cut to a profile on request.
What is the spec of Q355?
Q355 steel is a structural steel with a yield strength of 345 MPa and tensile strength of 450 MPa. It has terrific processing performance and compressive strength, which can be used to manufacture high-pressure gas pressure vessels containing less than 500 liters. Q355 also has a protective layer of rust resistance.
What is the difference between S355 and Q355?
Q355 and S355 are not identical standards, but they are functionally equivalent for most structural applications. Both have a minimum yield strength of 355 MPa and similar tensile strength ranges. The main differences lie in standard specifications, chemical composition limits, and delivery conditions
What standard is Q355B steel?
Production Standards
Q355B steel is manufactured under the provisions of the GB/T 1591-2018 standard, which governs the mechanical properties, chemical composition, and delivery conditions of high-strength low-alloy structural steels in China.
What is the difference between A36 and Q355B?
A36 and Q355B are both structural steel grades, but A36 is an older American standard (ASTM A36) while Q355B is a newer Chinese standard. Q355B generally offers higher strength and potentially better performance in some applications, particularly where higher yield strength is needed.
