The minimum specified yield strength of S355J0 is 355 MPa, as indicated by the 355 in its designation. However, the exact guaranteed value depends on the thickness of the product, because the yield strength of structural steel decreases as material thickness increases due to less effective through-thickness hardening during rolling. This thickness dependence is defined precisely in EN 10025-2:2004, the governing standard for S355J0, and it is a critical factor in structural design.
What Is S355J0 Steel?
S355J0 is a European standard non-alloy structural steel per EN 10025-2, with a minimum yield strength of 355 MPa and guaranteed impact toughness at 0 degrees Celsius, indicated by the J0 suffix. It is a low-carbon manganese steel, easily weldable and formable, often supplied in the normalized or untreated condition. It is suitable for general construction, bridges, ships, power plant equipment, and lifting and transport machinery in mild climates, and it is similar in strength to ASTM A572 Grade 50, although it adds a mandatory 0 degree Celsius impact requirement that A572 Grade 50 does not include.
Thickness-Dependent Yield Strength
The minimum yield strength of S355J0 according to EN 10025-2:2004 is as follows:
Thickness up to 16 mm: 355 MPa
16-40 mm: 345 MPa
40-63 mm: 335 MPa
63-80 mm: 325 MPa
80-100 mm: 315 MPa
100-150 mm: 295 MPa (for flats)
150-250 mm: 285 MPa (for flats)
For long products such as sections, the thickness refers to the nominal thickness of the flange. The actual yield strength from a mill test certificate will almost always be higher than the minimum, with a surplus of 30-100 MPa being common, but engineers must use the minimum values to ensure safety and consistency.
Related Mechanical Properties
The tensile strength of S355J0 also varies with thickness. For the common range up to 40 mm, it is 470-630 MPa, with slightly reduced ranges for thicker material. The minimum elongation at failure is typically 21-24% depending on thickness and test specimen, indicating good ductility. The J0 designation guarantees a minimum Charpy V-notch impact energy of 27 J at 0 degrees Celsius. The composition is a low-carbon manganese steel with carbon limited to about 0.20-0.24% depending on thickness, manganese up to about 1.60%, and controlled phosphorus and sulfur, which keeps the steel readily weldable.
Design Implications
When designing a structure with S355J0, the yield strength value corresponding to the thickest element in the design load path must be used. For example, a 20 mm thick plate has a minimum yield of 345 MPa, and a beam with a 45 mm thick flange must be designed using 335 MPa, not the 355 MPa value for the thin range. Using the thin-range value for thicker members is non-conservative and unsafe. The same principle applies to procurement: the purchase order should state both the grade and the thickness range so that the correct strength guarantee is supplied.
Applications and Grade Selection
S355J0 is commonly used in bridges, building frames, ships, power plant equipment, and heavy machinery in temperate climates where temperatures may approach freezing. Because the J0 grade is certified for 0 degrees Celsius only, structures with sustained service below freezing should use S355J2, tested at -20 degrees Celsius, or S355K2, which offers higher impact energy at -20 degrees Celsius. S355JR, tested at +20 degrees Celsius, is the room-temperature alternative for mild environments.
Frequently Asked Questions
What is the yield strength of S355J0? The minimum yield strength is 355 MPa for thicknesses up to 16 mm, decreasing stepwise with thickness per EN 10025-2: 345 MPa for 16-40 mm, 335 MPa for 40-63 mm, 325 MPa for 63-80 mm, 315 MPa for 80-100 mm, and 295/285 MPa for thicker flats.
What does J0 mean in S355J0? J0 indicates Charpy V-notch impact testing at 0 degrees Celsius with a minimum absorbed energy of 27 J, ensuring reliable performance in cold conditions.
What is the difference between S355JR and S355J0? S355JR is impact tested at +20 degrees Celsius, while S355J0 is tested at 0 degrees Celsius, making J0 suitable for applications exposed to near-freezing temperatures.
Is S355J0 equivalent to ASTM A572 Grade 50? Not directly. The strength is similar, but S355J0 includes a mandatory impact toughness requirement at 0 degrees Celsius that standard A572 Grade 50 does not have.
Can S355J0 be welded? Yes, S355J0 has good weldability. Proper procedures should be followed, including potential preheating for thick sections or cold environments, per the applicable welding procedure specification.
Can S355J0 be used for sustained service below 0 degrees Celsius? No. S355J0 is certified only for 0 degrees Celsius. For sustained service below freezing, use S355J2 (-20 degrees Celsius) or S355K2 (higher impact energy at -20 degrees Celsius).