What is Q235 Steel?
Q235 is a carbon structural steel grade widely used in China. The "Q" stands for the Chinese word "屈" (qu), meaning yield strength, and the number 235 indicates a yield strength of 235 MPa.
Q235 was previously known as A3; since the GB 700-88 standard, A3 has been reclassified as Q235, equivalent to Q235A. This steel is mild carbon, meaning it does not require heat treatment for most applications, and it has good plasticity, toughness, and weldability.
Grades of Q235 Steel
Q235 is divided into four grades according to GB/T 700-2006, based on metallurgical quality: Q235A, Q235B, Q235C, and Q235D.
| Grade | Carbon (%) | Manganese (%) | Silicon (%) | Sulfur (%) | Phosphorus (%) | Impact Test Temperature |
|---|---|---|---|---|---|---|
| Q235A | ≤0.22 | ≤1.40 | ≤0.35 | ≤0.050 | ≤0.045 | Not required |
| Q235B | ≤0.20 | ≤1.40 | ≤0.35 | ≤0.045 | ≤0.045 | ≥20℃ |
| Q235C | ≤0.17 | ≤1.40 | ≤0.35 | ≤0.040 | ≤0.040 | ≥0℃ |
| Q235D | ≤0.17 | ≤1.40 | ≤0.35 | ≤0.035 | ≤0.035 | ≥-20℃ |
Q235A is the standard quality, suitable for general construction.
Q235B, C, D have progressively lower impurity contents (S and P), improving toughness, weldability, and strength consistency.
Additional letters, like Q235AF or Q235AZ, indicate manufacturing methods (rimmed steel or killed steel) affecting uniformity and toughness.
Physical and Mechanical Properties of Q235 Steel
Density: 7.85 g/cm³
Melting Point: 1420–1460°C
Thermal Conductivity: 51.9 W/(m·K)
Coefficient of Linear Expansion: 11.7 µm/m·K (20°C)
Mechanical Properties:
Yield Strength: ≥ 235 MPa (thickness ≤16 mm)
Tensile Strength: 370–500 MPa
Elongation at Break: ≥ 26% (thickness ≤40 mm)
Impact Toughness: ≥ 27 J
Hardness: ≤ 201 HB
Characteristics:
Moderate strength and good toughness.
Easy to weld due to low carbon and low harmful elements (S, P).
Moderate corrosion resistance; prone to rust in chloride environments.
Applications of Q235 Steel
Construction Formwork and Temporary Structures
Hot-rolled plates for reinforced concrete formwork (2.5–6 mm thick).
Scaffolding, support frameworks, tower supports.
Structural and Non-Critical Components
Factory buildings, lightweight steel frameworks, secondary structural elements.
Mechanical and Agricultural Parts
Bolts, nuts, shafts, agricultural machinery components (tractor frames, plow parts).
Automotive and Transportation
Vehicle frames, brackets, substructures, and train carriage components.
Pressure Vessels and Pipelines (Low Pressure)
Water/steam tanks and pipelines, where moderate strength is acceptable.
Furniture and Everyday Metal Products
Chairs, tables, shelves, kitchen utensils.
Marine and Shipbuilding (Non-Critical Components)
Secondary components; not for primary hull structures.
Q235 Steel and H-Beams
Q235 is commonly used in H-beams for construction, industrial buildings, and temporary structures due to its good weldability, ductility, and moderate strength.
For projects requiring higher strength, like heavy industrial frames or long-span bridges, higher-grade steel such as Q345 or S355 may be more suitable.
