Difference between S355G7+M and S355G8+M steel plate

S355G7+M is a thermomechanical rolled (TMCP) offshore structural steel certified under EN 10225 for fixed offshore structures, wind turbine foundations, and oil/gas platforms . The "+M" suffix indicates the thermomechanical rolling process, which refines grain structure through controlled rolling and cooling without additional heat treatment . It has a minimum yield strength of 355 MPa (for thickness ≤25mm) and tensile strength ranging from 470 to 630 MPa, with a minimum elongation of 22% . Impact toughness is tested at -40°C with a minimum energy requirement of 50 Joules (longitudinal) . The chemical composition features carbon ≤0.12%, manganese 1.00-1.65%, and sulfur ≤0.005% .

S355G8+M is also a thermomechanical rolled offshore structural steel certified under EN 10225, sharing the same minimum yield strength of 355 MPa and tensile strength range of 470-630 MPa as G7 . Like G7, it is impact tested at -40°C with a minimum of 50 Joules . However, S355G8+M offers stricter chemical composition controls, including a lower sulfur limit (≤0.007% vs. ≤0.010%) and lower phosphorus (≤0.020%) . The higher "G" number (G8 vs. G7) signifies more stringent requirements for toughness and purity.

Both S355G7+M and S355G8+M are thermomechanical rolled offshore structural steels under EN 10225 with identical mechanical properties (minimum yield 355 MPa, tensile 470-630 MPa) and impact requirements (-40°C, 50J) . Their primary difference lies in chemical purity: S355G7+M is suitable for general offshore applications, while S355G8+M features stricter limits on sulfur (≤0.007%) and phosphorus, offering enhanced low-temperature toughness and weldability for more demanding offshore structures . Both grades maintain good weldability and are available up to 100mm thickness . The selection between them depends on whether the project requires standard offshore performance (G7) or enhanced purity and toughness for critical applications (G8).

Mechnical property for S355G7+M steel plate:
 

Mechnical property for S355G8+M steel plate:
 

Chemical composition for S355G7+M steel plate
 

Chemical composition for S355G8+M steel plate