S500QL and S620QL are ultra-high-strength, quenched and tempered (Q+T) alloy special structural steels specified under EN 10025-6, designed for demanding welded structures requiring superior strength combined with excellent low-temperature toughness . The "Q" denotes quenched and tempered delivery condition, while "L" signifies low-temperature impact testing at -50°C (minimum 30J longitudinal), which is a critical distinction from non-L grades tested at -20°C . Both grades are fully killed, fine-grain treated, and supplied exclusively in the quenched and tempered condition.
Key Differences:
Strength Level: S620QL provides approximately 24% higher minimum yield strength (620 vs 500 MPa for ≤50mm), enabling significant weight reduction in highly stressed designs .
Ductility: S500QL offers superior formability with 17% elongation versus 15% for S620QL, an important consideration for cold-forming operations .
Carbon Equivalent (CEV): S620QL has markedly higher CEV (0.65% vs 0.47% for ≤50mm), reflecting increased hardenability requirements but also demanding more stringent welding precautions (higher preheat, stricter interpass temperature control) .
Identical Toughness: Both grades maintain identical low-temperature impact performance (-50°C/30J longitudinal), despite their strength差异 .
Applications: S500QL suits high-strength applications with balanced weldability and formability requirements-commonly used in hydraulic supports, heavy vehicles, construction machinery, and port equipment . S620QL is preferred for maximum strength-to-weight optimization in mobile cranes, concrete pumps, mining equipment, and critical structural components where every kilogram reduction justifies higher-strength selection .
Cost Efficiency: S500QL offers better economic efficiency and weldability when design stresses do not fully utilize S620QL's capabilities.
Mechnical property for S500QL steel plate:
| Thickness (mm) | |||
| S500QL | ≥ 3 ≤ 50 | > 50 ≤ 100 | > 100 |
| Yield strength (≥Mpa) | 500 | 480 | 440 |
| Tensile strength (Mpa) | 590-770 | 590-770 | 540-720 |
Mechnical property for S620QL steel plate:
| Thickness (mm) | |||
| S620QL | ≥ 3 ≤ 50 | > 50 ≤ 100 | > 100 |
| Yield strength (≥Mpa) | 620 | 580 | 560 |
| Tensile strength (Mpa) | 700-890 | 700-890 | 650-830 |
Chemical composition for S500QL steel plate
| Main chemical elements composition of S500QL steel plate | |||||||
| C | Si | Mn | P | S | N | B | Cr |
| 0.20 | 0.80 | 1.70 | 0.020 | 0.010 | 0.015 | 0.005 | 1.50 |
| Cu | Mo | Nb | Ni | Ti | V | Zr | |
| 0.50 | 0.70 | 0.06 | 2.0 | 0.05 | 0.12 | 0.15 | |
Chemical composition for S620QL steel plate
| Main chemical elements composition of S620QL steel plate | |||||||
| C | Si | Mn | P | S | N | B | Cr |
| 0.20 | 0.80 | 1.70 | 0.020 | 0.010 | 0.015 | 0.005 | 1.50 |
| Cu | Mo | Nb | Ni | Ti | V | Zr | |
| 0.50 | 0.70 | 0.06 | 2.0 | 0.05 | 0.12 | 0.15 | |
