Difference between S355G9+M and S355G10+M steel plate - Knowledge

S355G9+M is a thermomechanical rolled offshore structural steel certified under EN 10225 for fixed offshore structures, wind turbine foundations, and Arctic oil/gas platforms . The "+M" suffix indicates the thermomechanical controlled process (TMCP) , which refines grain structure through controlled rolling and accelerated cooling without additional heat treatment . It has a minimum yield strength of 355 MPa (for thickness ≤16mm) and tensile strength ranging from 470 to 630 MPa, with a minimum elongation of 22% . Maximum plate thickness is 100 mm . Impact toughness is tested at -60°C with a minimum energy requirement of 27 Joules . The chemical composition features carbon ≤0.12%, manganese ≤1.65%, and low sulfur ≤0.010% .

S355G10+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 G9 . However, S355G10+M offers superior low-temperature toughness, impact tested at -70°C with a minimum energy requirement of 27 Joules . To achieve this extreme performance, it employs stricter chemical composition controls, including a lower sulfur limit (≤0.005% vs. 0.010%) and lower phosphorus (≤0.015% vs. 0.020%) . Maximum plate thickness is also 100 mm .

Both S355G9+M and S355G10+M are thermomechanical rolled offshore structural steels under EN 10225 with identical mechanical properties (minimum yield 355 MPa, tensile 470-630 MPa) . Their primary difference lies in impact test temperature: S355G9+M is tested at -60°C, suitable for general Arctic offshore applications, while S355G10+M is tested at the extreme temperature of -70°C, offering superior low-temperature toughness for the most demanding cryogenic environments such as LNG carrier containment systems . Consequently, S355G10+M requires stricter chemical purity controls (especially lower sulfur and phosphorus) and more demanding welding procedures . Both grades are available up to 100mm thickness . The selection between them depends on whether the project requires standard Arctic performance (G9) or extreme low-temperature toughness (G10) for the most critical applications.

S355G9+M Steel plate Chemical Composition

C	Si	Mn	P	S	Cr	Mo	Ni	Al	Cu	N	Nb	Ti	V	Nb+V
0.12	0.15/0.55	1.65	0.02	0.01	0.20	0.08	0.7	0.015/0.055	0.3	0.01	0.03	0.025	0.06	0.06

S355G10+M Steel plate Chemical Composition

C	Si	Mn	P	S	Cr	Mo	Ni	Al	Cu	N	Nb	Ti	V	Nb+V
0.12	0.15/0.55	1.65	0.015	0.005	0.20	0.08	0.7	0.015/0.055	0.3	0.01	0.03	0.025	0.06	0.06

S355G9+M Steel plate Mechanical Properties

Grade	S355G9+M Steel plate Mechanical Properties (min) unless stated
	Tensile Strength		Yield Strength						Elongation A
	Thickness (mm)		Thickness t - mm						Elongation A
	≤100	>100	≤16	16<t≤25	25<t≤40	40<t≤63	63<t≤100	100<t≤150	%
S355G9+M	470/630	–	355	355	345	335	325	–	22

S355G10+M Steel plate Mechanical Properties

Grade	S355G10+M Steel plate Mechanical Properties (min)
	Tensile Strength		Yield Strength						Elongation A
	Thickness (mm)		Thickness t - mm						Elongation A
	≤100	>100	≤16	16<t≤25	25<t≤40	40<t≤63	63<t≤100	100<t≤150	%
S355G10+M	470/630	–	355	355	345	335	325	–	22