S235, S275, S355 steel: yield strength, tensile strength and designation
Published October 4, 2026 — EN 10025-2 values by thickness range, the JR, J0, J2 and K2 qualities, how to read a full designation, and equivalences with old French and American grades.
In short: in a designation such as S355J2, S means structural steel, the number is the minimum yield strength in MPa for thicknesses up to 16 mm, and the following letters give the guaranteed impact toughness (J2: 27 J at −20 °C). The thicker the plate, the lower the guaranteed yield: a 50 mm S355 plate only ensures 335 MPa. All three grades share the same elastic modulus: moving to S355 adds strength, not stiffness.
1. Minimum yield strength ReH by thickness
Minimum values in MPa (N/mm²) per EN 10025-2, by nominal thickness range: up to and including 16 mm, then over … up to and including ….
Above 80 mm, values keep decreasing (for S355: 315 MPa up to 100 mm, 295 MPa up to 150 mm): refer to the standard or the material certificate.
2. Tensile strength Rm
Rm is given as a range (min – max) in MPa. To weigh parts, the density of these steels is about 7,850 kg/m³: see the mass calculator.
3. JR, J0, J2, K2 qualities: impact toughness
The letters after the number guarantee a minimum energy in the Charpy impact test at a given temperature. The lower the test temperature, the better the steel resists brittle fracture: the criterion for outdoor structures, thick welded parts or impact loads.
For a welded structure, the quality is chosen with thickness and service temperature; weld symbols are read with the ISO 2553 welding symbols memo.
4. Reading a full designation, and equivalents
Example: S355J2C+N, part by part.
Old French designations (NF A 35-501) still appear on many drawings. American grades are close but not equivalent: check the guaranteed values before any substitution.
5. Calculator: guaranteed Re and Rm for your plate
Choose the grade and thickness: you get the EN 10025-2 minimum yield strength and tensile strength, and the load a bar of given section carries before yielding.
Order of magnitude, not design: the force at Re is the tension that brings the section to its yield strength, without any safety factor. A structural calculation applies the Eurocode 3 partial factors and also checks buckling, deflection and connections.
6. FAQ
What does S355J2 mean?
S: structural steel; 355: minimum yield strength of 355 MPa for thicknesses up to 16 mm; J2: at least 27 J impact energy at −20 °C in the Charpy test. A +N suffix means delivered normalized, +AR as rolled.
What is the difference between S235 and S355?
Yield strength: 235 versus 355 MPa up to 16 mm thick, about 50 % more for S355. Tensile strength goes from 360–510 to 470–630 MPa (3 to 100 mm thick). The elastic modulus is the same: about 210,000 MPa.
Is S355 stiffer than S235?
No. Both have the same elastic modulus (about 210,000 MPa): with the same section they deflect the same under the same load. S355 takes a higher stress before permanent deformation, but it does not reduce deflection.
What is the equivalent of E24 steel?
The old French designation E24 corresponds to S235 in EN 10025-2, E28 to S275 and E36 to S355. These names still appear on many older drawings.
Why does yield strength decrease with thickness?
A thick plate gets less rolling reduction and cools more slowly, giving a coarser structure. The standard accounts for this with minimum values per thickness range: a 50 mm S355 plate only guarantees 335 MPa.