S235 / S355 steel properties: yield and tensile strength

S355 steel up to 16 mm thick has a minimum yield strength ReH of 355 MPa and a tensile strength Rm of 470–630 MPa; S235 has 235 MPa and 360–510 MPa. The number in the grade name is the yield strength of the thinnest product: from 16 mm it steps down, so a 50 mm S355 plate only guarantees 335 MPa. Below are the EN 10025-2 tables by thickness, impact energy, CEV and the stainless grades of EN 10088-2.

Short answer

S235: ReH ≥ 235 MPa, Rm 360–510 MPa; S355: ReH ≥ 355 MPa, Rm 470–630 MPa (up to 16 mm thick, EN 10025-2). S275 sits in between: 275 MPa and 410–560 MPa. Over 16 mm the yield strength is lower: 40 mm S355 gives 345 MPa, 80 mm 325 MPa. The letters after the number (JR, J0, J2, K2) are not about strength but toughness: the temperature at which 27 or 40 J is guaranteed. The full table by thickness is below.

Yield strength ReH by thickness, MPa

EN 10025-2 guarantees a minimum upper yield strength ReH, and the guarantee falls as the product gets thicker: heavy plate cools more slowly during rolling and ends up with a coarser grain. Thickness in mm, values in MPa (N/mm²):

In the 2019 edition of EN 10025-2, S460 covers long products only (sections and bars); for 80–100 mm our sources disagree, so that cell is left empty. There is no S420 in EN 10025-2: S420 is supplied to EN 10025-3 (normalised, S420N/NL) or EN 10025-4 (thermomechanically rolled, S420M/ML) — check the certificate against that standard.

Tensile strength Rm and elongation A

Rm is given as a range — a minimum and a maximum. Very thin product (under 3 mm) has a higher range. Elongation A is measured on a proportional test piece:

For 40–63 and 63–100 mm the minimum elongation is one and two points lower (S355: 21 and 20 %). On wide plate (600 mm and over) the test piece is taken across the rolling direction and the minima are lower still — the certificate says which direction was tested. For S355K2 the sources give 20–22 %; the certificate decides.

Impact energy KV: JR, J0, J2, K2

The letters after the number tell you at what temperature the Charpy V-notch test was done and how much energy it had to absorb. JR and J2 have the same strength — only the toughness guarantee differs.

For structures that work outdoors in frost or under dynamic load, the designer specifies J2 or K2; JR (+20 °C) only tells you the steel is not brittle at room temperature.

Carbon equivalent CEV — maximum values

CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 is calculated from the ladle analysis. EN 10025-2 caps it by thickness (mm), in %:

These are maxima; the actual CEV of the heat is on the 3.1 certificate and is usually lower. That figure, not the table, goes into the carbon equivalent calculator and then into the preheat calculator: CEV, the combined thickness of the joint, hydrogen from the consumable and the heat input decide whether to preheat and how far. Why — see steel weldability.

How to read S355J2+N

The full designation to EN 10027-1 is built from parts, and each one has its own job:

So a plate marked S355J2+N guarantees 355 MPa up to 16 mm, 27 J at −20 °C and a normalised condition, while the 3.1 certificate (EN 10204) shows the actual values for that heat. More on the letters and on substitutes in the steel grade equivalents table.

What these numbers mean for welding

• The weld must not be weaker than the plate. Pick a consumable whose weld-metal yield strength is not below the ReH of the parent metal; the strength class is part of the wire or electrode designation.
• Toughness at the same temperature. On J2 steel the weld metal must also pass an impact test at −20 °C — check the impact temperature symbol of the consumable.
• Thicker means more preheat. Over 30 mm, S355 may have a CEV of up to 0.47 instead of 0.45, and the joint draws heat away faster — work it out in the preheat calculator.
• Fillet size follows strength. The throat of a fillet weld is sized from the load and the steel grade — fillet weld size calculator.

Stainless steels to EN 10088-2: Rp0.2, Rm, A

Stainless steels have no pronounced yield point, so the 0.2 % proof strength Rp0.2 is quoted instead. Values for the solution-annealed condition: C — cold-rolled strip and sheet up to 8 mm, P — hot-rolled plate up to 75 mm:

The austenitic grades have a proof strength close to S235 (200–240 MPa) but an elongation of 40–45 % instead of 26 %. Duplex 1.4462 has roughly twice the proof strength of the austenitics. How to weld them — in welding stainless steel.

Where next

EN, GOST, AISI and PN equivalents — steel grade equivalents table. Carbon equivalent from the certificate — CE calculator, preheat temperature — preheat calculator, weld size — fillet weld size calculator.

Author: Dmitry Frolov, welder and metal fabricator Updated: 24 October 2026