S420G1+QT and S460G1+QT are quenched and tempered structural steel plates for low-temperature service, manufactured to the European standard EN 10025-4. The designation indicates their minimum yield strength (420 MPa and 460 MPa). The suffix "G1+QT" defines two key properties: "G1" specifies guaranteed impact toughness at 0°C with a minimum energy of 27 Joules, and "+QT" denotes the Quenched and Tempered delivery condition. These grades are engineered for high-strength, welded steel structures operating in moderate low-temperature environments, such as bridges, offshore equipment, and heavy machinery in temperate or cool climates.
Key Differences:
The primary difference is their strength level. S420G1+QT offers a yield strength of 420 MPa, while S460G1+QT provides a higher yield strength of 460 MPa. This allows S460G1+QT to support greater static loads or enable weight reduction in structural designs operating at or near 0°C.
To achieve the higher strength while maintaining the specified "G1" toughness at 0°C, S460G1+QT requires a more refined chemical composition and precise control during the quenching and tempering process. This involves optimized additions of micro-alloying elements (such as Niobium and Vanadium) and careful balancing of carbon and manganese content. Consequently, S460G1+QT has a marginally higher carbon equivalent (Ceq) compared to S420G1+QT. This results in slightly more stringent fabrication requirements for welding S460G1+QT. It demands stricter control of preheating temperatures, the use of qualified low-hydrogen consumables, and careful management of heat input to preserve the base material's toughness in the weld heat-affected zone and mitigate the risk of cold cracking.
Mechnical property for S420G1+QT steel plate:
| Thickness (mm) | |||||
| S420G1+QT steel plate | ≤ 16 | > 16 ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 |
| Yield strength (≥Mpa) | 420 | 400 | 390 | 380 | 380 |
| ≤ 40 | > 40 | ||||
| Tensile strength (Mpa) | 500-660 | 480-640 | |||
Mechnical property for S460G1+QT steel plate:
| Thickness (mm) | ||||||
| S460G1+QT steel plate | ≤ 16 | > 16 ≤ 25 | > 25 ≤ 40 | > 40 ≤ 63 | > 63 ≤ 80 | > 80 |
| Yield strength (≥Mpa) | 460 | 440 | 420 | 415 | 405 | 400 |
| Tensile strength (Mpa) | 540-700 | 530-690 | 520-680 | 515-675 | 505-665 | 500-660 |
Chemical composition for S420G1+QT steel plate
| Main chemical elements composition of S420G1+QT steel plate | ||||||||
| C | Si | Mn | P | S | Cr | Mo | Nb+V | Nb+V+Ti |
| 0.14 | 0.15-0.55 | 1.65 | 0.020 | 0.010 | 0.25 | 0.25 | 0.09 | 0.11 |
| Ni | Alt | Cu | N | Nb | Ti | V | Cr+Mo+Ni+Cu | |
| 0.70 | 0.015-0.055 | 0.30 | 0.010 | 0.040 | 0.025 | 0.080 | 0.90 | |
Chemical composition for S460G1+QT steel plate
| Main chemical elements composition of S460G1+QT steel plate | ||||||||
| C | Si | Mn | P | S | Cr | Mo | Nb+V | Nb+V+Ti |
| 0.14 | 0.15-0.55 | 1.65 | 0.020 | 0.010 | 0.25 | 0.25 | 0.09 | 0.11 |
| Ni | Alt | Cu | N | Nb | Ti | V | Cr+Mo+Ni+Cu | |
| 0.70 | 0.015-0.055 | 0.30 | 0.010 | 0.040 | 0.025 | 0.080 | 0.90 | |
