Steel is sold by grade, and the grade designation carries a surprising amount of information. Reading it correctly is the first step to comparing offers properly — and to avoiding material that looks right on paper but fails an inspection or a weld procedure.
Structural steel: S235, S275 and S355
In Europe, hot-rolled structural steels are specified under EN 10025-2. The number in the designation is the minimum yield strength in megapascals for the thinnest thickness range: S235 has a minimum yield strength of 235 MPa, S275 of 275 MPa, and S355 of 355 MPa. Minimum yield strength reduces as thickness increases, so the standard's tables matter for heavy plate.
The letters that follow describe impact toughness, measured by a Charpy V-notch test:
- JR — 27 J at +20 °C
- J0 — 27 J at 0 °C
- J2 — 27 J at −20 °C
- K2 — 40 J at −20 °C
S355J2 is therefore a 355 MPa steel with guaranteed toughness at −20 °C, which is why it is common in structures exposed to low temperatures or dynamic loads. Specify the full designation, not just “S355”.
International equivalents
Buyers often ask for equivalents such as ASTM A36 (minimum yield of 36 ksi, about 250 MPa) or ASTM A572 Grade 50 (about 345 MPa). These are broadly comparable to S235 and S355 but are not identical: chemistry limits, toughness requirements and testing differ. Substituting one standard for another should be approved by the responsible engineer, not assumed by the supplier.
Stainless steel: 304, 316 and their low-carbon versions
- 304 (EN 1.4301) — the general-purpose austenitic stainless steel, roughly 18% chromium and 8% nickel. Widely used in food equipment, kitchens and architecture.
- 304L (EN 1.4307) — a low-carbon version that reduces the risk of corrosion at welds.
- 316 (EN 1.4401) — adds about 2% molybdenum for better resistance to chlorides, such as coastal air, de-icing salts and some chemicals.
- 316L (EN 1.4404) — low-carbon 316, the usual choice for welded fabrications in corrosive environments.
- Duplex 2205 (EN 1.4462) — higher strength and resistance to stress-corrosion cracking, used in process and marine applications.
The price difference between 304 and 316 is mainly driven by nickel and molybdenum content, so it moves with those markets. Surface finish (for example 2B, BA or No. 4) should also be specified, because it affects both appearance and cleanability.
Mill certificates: EN 10204 types
EN 10204 defines the inspection documents that accompany metallic products:
- Type 2.1 — declaration of compliance with the order, without test results.
- Type 2.2 — test report with results from non-specific inspection (typical production results, not necessarily from your batch).
- Type 3.1 — inspection certificate with results from specific inspection of the supplied products, validated by the manufacturer's authorised inspection representative, independent of manufacturing.
- Type 3.2 — as 3.1, but also validated by the purchaser's representative or an inspector designated by official regulations.
For structural, pressure and traceability-critical applications, 3.1 is the usual minimum. Check that the heat number on the certificate matches the marking on the material — this is the link that makes the certificate meaningful.
Practical checklist
- State the full grade and the governing standard.
- Specify toughness requirements (JR, J0, J2) for structural steel.
- Choose 304/316 and L-grades based on environment and welding.
- Define surface finish for stainless products.
- Require EN 10204 3.1 certificates where traceability matters, and check heat numbers on delivery.
Echo Core Ltd sources carbon and stainless steel against the full designation and requests mill certificates appropriate to the application.