Difference between S355G3+N and S355G9+N steel plate - Knowledge

S355G3+N and S355G9+N are normalized fine-grain structural steel plates conforming to the European standard EN 10025-4. The designation indicates a minimum yield strength of 355 MPa, with the "+N" suffix specifying the Normalized delivery condition. The critical "G" component designates these grades for use at Low (sub-zero) temperatures, with the following numbers specifying the guaranteed minimum Charpy V-notch impact energy (in Joules) at specific test temperatures. These grades are engineered for critical welded structures in demanding cold environments, such as offshore platforms, Arctic vessels, cryogenic storage, and infrastructure in cold climates.

Key Differences:

The core distinction lies in their low-temperature toughness specifications. S355G3+N is tested at -20°C with a guaranteed minimum impact energy of 40 Joules. In contrast, S355G9+N is tested at the much lower temperature of -60°C while guaranteeing a minimum of 27 Joules. This represents a fundamental divergence in application: S355G3+N is suited for moderately cold service, whereas S355G9+N is engineered for extremely severe Arctic or deep-cryogenic conditions.

Achieving toughness at -60°C for S355G9+N necessitates a far more stringent metallurgical approach compared to S355G3+N. It requires an exceptionally clean steel composition with very low levels of impurities (sulfur, phosphorus) and precise control of micro-alloying elements (like Niobium) during normalizing to ensure an ultra-fine, homogeneous grain structure that resists brittle fracture at extreme cold. Consequently, the welding and fabrication of S355G9+N are substantially more demanding. It mandates the use of specifically qualified welding consumables, strict control of heat input, and often preheating to prevent any degradation of the heat-affected zone's toughness.

S355G3+N Chemical Composition

S355G3+N	The Element Max (%)
	C	Si	Mn	P	S	Nb	V	Ti	Al	Cr	Ni	Mo	Cu	N
	0.18	0.50	0.90-1.65	0.030	0.025	0.060	0.12	0.030	0.020	0.30	0.50	0.10	0.35	0.015

S355G9+N Chemical Composition

Grade	C	Si	Mn	P	S	Ni	Cr	Mo	Cu
S355G9+N	≤0.12	0.15-0.55	≤1.65	≤0.02	≤0.010	≤0.7	≤0.2	≤0.08	≤0.3
Nb	V	Ti	Alt	N	B	Ca	Pb	Ceq Max	Pcm Max
≤0.03	≤0.06	≤0.025	0.015-0.055	≤0.010	≤0.0005	≤0.005	≤0.010	≤0.43	≤0.22

S355G3+N Steel plate Mechanical Property

S355G3+N	Yield Strength mm Min(Mpa)		Tensile Strength mm Min(Mpa)						Elongation Min,%
	Yield Strength mm Min(Mpa)		Tensile Strength mm Min(Mpa)
	≤ 100	＞100	≤16	＞ 16 ≤ 25	＞ 25 ≤ 40	＞ 40≤ 63	＞ 63 ≤ 100	＞ 100 ≤ 150	22
	470-630	–	355	345	345	–	–	–	22

S355G9+N Steel plate Mechanical Property

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