Difference between S620QL1 and S690QL1 steel plate

S620QL1 and S690QL1 are ultra-high-strength, quenched and tempered (Q+T) alloy special structural steels specified under EN 10025-6, designed for demanding welded structures requiring exceptional strength combined with extremely low-temperature toughness . The "QL1" suffix signifies the highest toughness grade, with mandatory Charpy V-notch impact testing at -60°C (minimum 30J longitudinal), compared to -40°C for QL and -20°C for Q grades . Both grades are fully killed, fine-grain treated, and supplied exclusively in the quenched and tempered condition .

Key Differences:

Strength Level: S690QL1 provides approximately 11% higher minimum yield strength (690 vs 620 MPa for ≤50mm), enabling further weight reduction in highly stressed designs .

Ductility: S620QL1 offers superior formability with 15% elongation versus 14% for S690QL1 .

Thickness-Derating: Both grades show similar strength reduction patterns in thicker sections, but S690QL1 maintains a higher absolute strength advantage throughout all thickness ranges .

Application Nuance: S620QL1 suits very high-strength applications with balanced formability requirements; S690QL1 is preferred for maximum strength-to-weight optimization in cranes, heavy machinery, offshore platforms, mining equipment, and pressure vessels where every kilogram reduction justifies the higher-strength selection .

Cost Efficiency: S620QL1 may offer better economic efficiency when the design's maximum required strength does not fully utilize S690QL1's capabilities.

Chemical Composition

Mechanical Property