Q235 steel is a widely used mild carbon structural steel with moderate strength, good bearing capacity, plasticity, toughness, and weldability. It is the most commonly used steel in general fabrication, construction, machinery, and structural applications.
The name "Q235" represents:
Q: Yield point
235: Nominal yield strength of ~235 MPa (decreases with increasing thickness)
Q235 Grades and Impact Temperature
Q235 is divided into four quality grades (A, B, C, D), mainly distinguished by impact performance at different temperatures:
| Grade | Impact Test Temperature | Notes |
|---|---|---|
| Q235A | Not tested | Basic grade, no impact test required |
| Q235B | 20 °C (room temperature) | Standard mechanical performance inspection |
| Q235C | 0 °C | Suitable for low-temperature applications |
| Q235D | −20 °C | Best low-temperature toughness, suitable for very cold environments |
Element trends across grades:
Sulfur content: decreases from A → D
Phosphorus content: A & B equal; C slightly lower; D lowest
Lower C, P, and S improve flexibility, weldability, and impact resistance.
Chemical Composition
| Grade | C (%) | Mn (%) | Si (%) | S (%) | P (%) | Notes |
|---|---|---|---|---|---|---|
| Q235A | 0.14–0.22 | 0.30–0.70 | ≤0.03 | ≤0.045 | 0.045 | Basic grade |
| Q235B | 0.12–0.20 | 0.30–0.70 | ≤0.03 | ≤0.045 | 0.045 | Includes some mechanical testing |
| Q235C | ≤0.18 | 0.35–0.70 | ≤0.03 | ≤0.040 | 0.040 | Full mechanical performance tested, includes impact test |
| Q235D | ≤0.17 | 0.35–0.70 | ≤0.03 | ≤0.035 | 0.035 | Best performance, full mechanical + impact testing |
Deoxidation Method:
Boiling Steel (F): Not fully deoxidized; plasticity and toughness are poorer; welded structures prone to cracking under dynamic load. Not suitable for low-temperature use.
Calm/Flat Steel (B/Z): Fully deoxidized; excellent uniformity, plasticity, and toughness; preferred for welded structures.
Mechanical Properties
| Property | Q235 (general) | Notes |
|---|---|---|
| Tensile Strength (Σb) | 375–500 MPa | Dependent on thickness/diameter |
| Elongation (δ5) | ≥26% (d ≤16 mm) ≥25% (16–40 mm) ≥24% (40–60 mm) ≥23% (60–100 mm) ≥22% (100–150 mm) ≥21% (d >150 mm) |
A = thickness or diameter |
| Yield Strength | ≥235 MPa | Decreases slightly with increasing thickness |
| Hardness | Medium | Good machinability |
Notes:
Q235A: only chemical inspection, mechanical properties not mandatory
Q235B: partial mechanical inspection
Q235C/D: full mechanical inspection, including impact tests
Products Applications
Q235 steel is widely used for:
Structural components: beams, columns, trusses
General construction: bridges, buildings, warehouses
Machinery and automotive parts
Roof structures, purlins, scaffolding
Steel plates, rods, and rebar for construction
Raw material for galvanized or coated steel
Q235 is a versatile, cost-effective, and widely available structural steel. Its grades (A–D) allow selection based on impact temperature requirements and mechanical performance testing.
The combination of moderate strength, good weldability, plasticity, and toughness makes it suitable for a wide range of industrial and construction applications.
