Steel Grade Selection: S235, S275 and S355 Explained

One of the first decisions in steel structure design is the choice of steel grade. Under European standards, structural steels are specified according to EN 10025 (hot-rolled products) and EN 10210/EN 10219 (hollow sections). The most widely used grades are S235, S275, and S355 — but what do these designations mean, and how do you choose the right grade for your structure?

Steel Grade Designations: What Do S235, S275, S355 Mean?

In the designation, S stands for “structural steel” and the following number indicates the minimum yield strength in megapascals (MPa) — measured on products up to 16 mm thick. For example:

• S235 — yield strength ≥ 235 MPa, tensile strength 360–510 MPa
• S275 — yield strength ≥ 275 MPa, tensile strength 410–560 MPa
• S355 — yield strength ≥ 355 MPa, tensile strength 470–630 MPa

Importantly, yield strength decreases as material thickness increases. For S355, yield strength on 16–40 mm products is ≥ 345 MPa, and on products over 63 mm it is ≥ 315 MPa.

What Do the Suffixes Mean: JR, J0, J2, K2?

The suffix after the grade designation describes the impact toughness requirement (CVN — Charpy V-notch test). This is critical for structures used in cold environments, where the material must retain ductility at low temperatures:

• JR — 27 J impact energy at +20 °C
• J0 — 27 J impact energy at 0 °C
• J2 — 27 J impact energy at −20 °C
• K2 — 40 J impact energy at −20 °C

In Estonia, where winter temperatures can fall below −20 °C, J2 or K2 grade materials are commonly specified for external structures. JR is generally sufficient for structures operating indoors.

S235 vs S275 vs S355 — When to Use Which?

S235 is best suited for:

• Non-load-bearing or minor structures
• Stairs, ladders, access platforms
• Situations where dimensions are constrained by other factors (e.g. architectural) and load-bearing capacity is not critical

S275 is a mid-range option used for secondary structures, façade and roof systems.

S355 is today the preferred choice for main structures in industrial buildings, bridges, and crane girders. Its higher yield strength allows smaller cross-sections, which means:

• Lower structural weight and therefore reduced fabrication and transport costs
• Less weld filler material consumption
• The ability to achieve longer spans without adding intermediate supports

Weldability and Steel Grade

Higher-strength steels (S355 and above) demand stricter welding controls: preheating for thicker sections, heat input limitations, and the use of compatible filler materials. S235 and S275 are generally readily weldable without additional requirements at standard thicknesses (up to 25–30 mm).

Material Certificates — EN 10204 3.1 and 3.2

Every steel used in a CE-marked structure must be supplied with a material test report (mill certificate). Under EN 10204, there are two principal certificate types:

• 3.1 — certificate issued by the manufacturer’s own inspection representative
• 3.2 — certificate issued by an independent third party (required for EXC3–EXC4 structures and most bridge projects)

Steel Element OÜ retains all material certificates as part of the order documentation and provides them together with the finished structures. Learn more about our production capabilities and services, or request a quote.