Q355 is a Chinese low-alloy, high-strength structural steel that replaced Q345. It has a material density of 7.85 g/cm³. According to GB/T 1591-2018, Q355 is divided into three quality levels: Q355B, Q355C, and Q355D.
"Q" = Yield strength (from Chinese Pinyin "qu fu dian")
"355" = Minimum yield strength of 355 MPa (for thickness ≤16mm)
Tensile strength: 470–630 MPa
1. Chemical Composition (Hot Rolled)
| Steel Grade | Quality Grade | C % (≤) | Si % (≤) | Mn % (≤) | P % (≤) | S % (≤) | Cr % (≤) | Ni % (≤) | Cu % (≤) | N % (≤) |
|---|---|---|---|---|---|---|---|---|---|---|
| Q355 | Q355B | 0.24 | 0.55 | 1.6 | 0.035 | 0.035 | 0.30 | 0.30 | 0.40 | 0.012 |
| Q355 | Q355C | 0.20 | – | – | 0.030 | 0.030 | – | – | – | 0.012 |
| Q355 | Q355D | 0.20 | – | – | 0.025 | 0.025 | – | – | – | – |
2. Carbon Equivalent (CEV, Hot Rolled)
Based on smelting analysis; steel delivered in hot-rolled state.
| Steel Grade | Quality Grade | ≤30 mm | 30 < d ≤ 63 mm | 63 < d ≤ 150 mm | 150 < d ≤ 250 mm | 250 < d ≤ 400 mm |
|---|---|---|---|---|---|---|
| Q355 | Q355B | 0.45 | 0.47 | 0.47 | 0.49 | – |
| Q355 | Q355C | – | – | – | – | – |
| Q355 | Q355D | – | – | – | – | 0.49 |
3. Mechanical Properties (Hot Rolled)
Yield Strength (ReH, ≥ MPa)
| Steel Grade | Quality Level | d ≤ 16 mm | 16 < d ≤ 40 | 40 < d ≤ 63 | 63 < d ≤ 80 | 80 < d ≤ 100 | 100 < d ≤ 150 | 150 < d ≤ 200 | 200 < d ≤ 250 | 250 < d ≤ 400 |
|---|---|---|---|---|---|---|---|---|---|---|
| Q355 | Q355B | 355 | 345 | 335 | 325 | 315 | 295 | 285 | 275 | – |
| Q355 | Q355C | – | – | – | – | – | – | – | – | – |
| Q355 | Q355D | – | – | – | – | – | – | – | – | 265 |
Tensile Strength (Rm, MPa)
| Steel Grade | Quality Level | d ≤ 100 mm | 100 < d ≤ 150 mm | 150 < d ≤ 250 mm | 250 < d ≤ 400 mm |
|---|---|---|---|---|---|
| Q355 | Q355B | 470–630 | 450–600 | 450–600 | – |
| Q355 | Q355C | – | – | – | – |
| Q355 | Q355D | 450–600 | – | – | – |
Notes:
1 MPa = 1 N/mm²; 1 GPa = 1 kN/mm²
Mechanical properties vary with thickness and quality grade
Q355 steel grades are often selected based on specific project requirements, impact toughness, and operating temperature
