Difference between S355G9+M and S355G10+M - Knowledge

S355G9+M and S355G10+M are thermomechanically rolled, fine-grain structural steel plates for low-temperature service, conforming to the European standard EN 10025-4. The designation indicates a minimum yield strength of 355 MPa. The suffix "G9+M" and "G10+M" defines their key characteristics: the "G" number specifies impact toughness (G9 tested at -60°C, G10 at -70°C), and "+M" denotes the Thermomechanically Controlled Processed (TMCP) delivery condition. These grades are engineered for the most severe Arctic and cryogenic applications, such as LNG carrier containment systems, offshore platforms in extreme climates, and specialized infrastructure where maximum toughness at ultra-low temperatures is non-negotiable.

Key Differences:

The defining distinction is their minimum service temperature and corresponding toughness. S355G9+M is tested at -60°C with a minimum impact energy of 27 Joules. S355G10+M is tested at an even lower temperature of -70°C with the same 27 Joules minimum. This makes S355G10+M suitable for the absolute most extreme low-temperature environments, providing a critical safety margin against brittle fracture where S355G9+M may be at its limit.

Achieving guaranteed toughness at -70°C requires a more advanced metallurgical approach for S355G10+M. While both grades rely on TMCP for grain refinement, S355G10+M necessitates an exceptionally clean steel chemistry with ultra-low levels of impurities (sulfur, phosphorus) and precise control of micro-alloying elements (like Niobium) during rolling and accelerated cooling to achieve an optimal microstructure. Consequently, the welding and fabrication of S355G10+M are substantially more demanding and restrictive than for S355G9+M. It mandates the use of specifically qualified, ultra-low-temperature welding consumables, extremely strict control of heat input, precise preheating procedures, and often post-weld heat treatment to ensure the weld zone's toughness matches the extreme performance of the base material.

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	25	40	63	100	%
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	25	40	63	100	%
S355G10+M	470/630	–	355	355	345	335	325	–	22