Difference between S460QL1 and S690QL1

S460QL1 and S690QL1 are quenched and tempered structural steel plates per EN 10025-6. The designation specifies minimum yield strength (460 MPa and 690 MPa) and the "QL1" suffix denotes Quenched (Q) and Tempered (T) condition with guaranteed longitudinal (L1) impact toughness at low temperatures (e.g., -40°C or -60°C). These grades are engineered for highly stressed, critical welded structures requiring superior strength and fracture resistance, such as in heavy construction and mining machinery, offshore installations, and advanced transportation systems.

Key Differences:

The primary distinction is the substantial difference in strength. S460QL1 offers a yield strength of 460 MPa, while S690QL1 provides a yield strength of 690 MPa-a 50% increase. This makes S690QL1 suitable for applications where extreme load-bearing capacity and maximum weight reduction are paramount.

Achieving this ultra-high strength while retaining the stringent "QL1" toughness necessitates a fundamentally more advanced metallurgical approach for S690QL1. Its chemical composition involves significantly higher levels of carbon, manganese, and alloying elements like chromium, nickel, molybdenum, and boron. Consequently, S690QL1 has a dramatically higher carbon equivalent (Ceq) and crack susceptibility index compared to S460QL1. This translates to an exponential increase in fabrication complexity. Welding S690QL1 is exceptionally restrictive: it demands specially developed ultra-high-strength consumables, meticulous preheating (often >150°C), extremely low heat input, strict interpass temperature control, and is almost always followed by mandatory post-weld heat treatment (PWHT) to restore toughness and prevent hydrogen cracking in the heat-affected zone. 

Chemical Composition

Mechanical Property