Steel grades and mill certificates (EN 10204 3.1)

Reading a grade name

In the European system (EN 10025-2), S355J2 means: structural steel (S), minimum yield strength 355 MPa for the thinnest products, and an impact-toughness quality (J2 = 27 J at −20 °C). The yield strength drops slightly as thickness increases, so thick plates must be checked against the thickness band in the standard.

Other systems name grades differently: ASTM uses the yield in ksi (A572 Grade 50 ≈ 345 MPa), JIS uses the minimum tensile strength (SS400: 400–510 MPa tensile) and the Chinese GB/T 1591 uses the yield (Q355B).

Commonly compared grades

Grades from different standards are similar, not identical: chemistry, toughness and thickness limits differ. A substitution needs the approval of the designer and, where applicable, the client.

Mill certificates (EN 10204)

• Type 2.1 / 2.2: declaration of compliance by the manufacturer, without (2.1) or with (2.2) non-specific test results.
• Type 3.1: inspection certificate with the results of specific tests on the delivered product, validated by the manufacturer's inspection representative independent of production. It carries the heat (cast) number, chemistry and mechanical properties. Most structural specifications require 3.1 for main members.
• Type 3.2: as 3.1, but also validated by the purchaser's inspector or a third party named in the order.

Traceability in the shop

For higher execution classes, each main part must be traceable back to its certificate: the heat number is transferred when plates are cut, recorded on the cutting plan or the material requisition, and kept in the quality dossier.