Difference between S355G5+M and S355G6+M steel plate

S355G5+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 ≤16mm) and tensile strength ranging from 470 to 610 MPa, with a minimum elongation of 22% . Maximum plate thickness is 20 mm . Impact toughness is tested at -20°C with a minimum energy requirement of 50 Joules, making it suitable for moderate cold environments . The chemical composition features carbon ≤0.14% and manganese ≤1.65% .

S355G6+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 470-610 MPa as G5 . However, it offers enhanced low-temperature toughness, impact tested at -40°C with a minimum energy requirement of 50 Joules . Maximum plate thickness is 40 mm . Like G5, its chemical composition includes carbon ≤0.14% and manganese ≤1.65% . The improved low-temperature performance of S355G6+M is achieved through stricter process controls during thermomechanical rolling, making it ideal for more demanding offshore applications in colder environments .

Both S355G5+M and S355G6+M are thermomechanical rolled offshore structural steels under EN 10225 with identical mechanical properties (minimum yield 355 MPa, tensile 470-610 MPa) . Their primary difference lies in impact test temperature and maximum thickness: S355G5+M is tested at -20°C and limited to 20mm thickness, suitable for moderate cold environments and thinner plates ; while S355G6+M is tested at -40°C and available up to 40mm thickness, offering superior low-temperature toughness for more critical offshore applications . The thermomechanical rolling process of both grades provides excellent weldability and a favorable balance of strength and ductility.

Mechnical property for S355G5+M steel plate:
 

Mechnical property for S355G6+M steel plate:
 

Chemical composition for S355G5+M steel plate
 

Chemical composition for S355G6+M steel plate