Difference between S420G2+QT and S460G2+QT

S420G2+QT and S460G2+QT are high-strength steel plates for low-temperature service, manufactured to the European standard EN 10025-4. The designation specifies their minimum yield strength (420 MPa and 460 MPa respectively). The critical suffix, "G2+QT", combines two key characteristics: "G2" indicates guaranteed impact toughness tested at -20°C with a minimum energy of 27 Joules, and "+QT" specifies the Quenched and Tempered delivery condition. These grades are engineered for critical, heavily loaded welded structures operating in cold environments, such as offshore platforms, Arctic vessels, and high-performance bridges, where a superior combination of strength, toughness, and weldability is required.

Key Differences:

The fundamental distinction is their strength level. S420G2+QT provides a yield strength of 420 MPa, while S460G2+QT offers a higher yield strength of 460 MPa. This increment allows S460G2+QT to withstand greater loads, offering potential for weight reduction or increased structural capacity in low-temperature designs.

To achieve the higher strength while maintaining the identical low-temperature toughness ("G2") requirement, S460G2+QT necessitates a more precisely balanced chemical composition and stricter control during the quenching and tempering process. It typically involves optimized additions of micro-alloying elements (like Niobium and Vanadium) and adjusted levels of carbon and manganese. Consequently, S460G2+QT will have a higher carbon equivalent (Ceq) compared to S420G2+QT. This results in more demanding fabrication requirements. Welding S460G2+QT demands stricter procedural controls: mandatory use of qualified low-hydrogen, high-toughness consumables, precise management of higher preheating temperatures, careful limitation of heat input, and often post-weld heat treatment (PWHT) to mitigate the risk of hydrogen-induced cracking and to preserve the base material's toughness in the weld zone.

Mechnical property for S420G2+QT steel plate
 

Mechnical property for S460G2+QT steel plate
 

Chemical composition for S420G2+QT steel plate
 

Chemical composition for S460G2+QT steel plate