Steel grade designation (EN, ASTM, AISI, JIS, GB)
Steels carry different names in different standard systems. In the European system (EN 10027) a letter shows the use and a number the minimum yield strength: S235JR is a structural steel with 235 MPa and impact tested at 20 °C, while S355J2 is tested at –20 °C. Approximate equivalents are ASTM A36 or A572 Gr.50, JIS SS400 in Japan and GB Q235/Q355 in China; for stainless, AISI 304 ≈ EN 1.4301. Equivalents are not identical, so chemistry and mechanical values should be checked on the certificate.
Related terms
Yield strength, tensile strength and elongation
The basic mechanical properties measured in a tensile test (EN ISO 6892-1, ASTM E8). Yield strength (ReH or Rp0.2, MPa) is the stress at which the material starts to deform permanently and is the basis of design; tensile strength (Rm) is the maximum stress before fracture; elongation (A %) is the stretch up to fracture and indicates formability. For rebar the Rm/ReH ratio and elongation are critical for earthquake resistance (e.g. Rm/Re ≥ 1.15 for B500C).
EN 10204 mill test certificate (2.2, 3.1, 3.2)
The European standard defining types of inspection documents for metallic products – plate, pipe, sections, castings and forgings – used worldwide under the name “mill test certificate” (MTC). Type 2.2 gives the manufacturer’s non-specific test results; Type 3.1 gives chemical and mechanical results specific to the delivered lot, validated by the manufacturer’s independent inspection representative; Type 3.2 additionally includes tests witnessed by the purchaser or an independent body such as a classification society. Pressure vessels, shipbuilding and energy projects usually require 3.1 or 3.2.
Flat steel: hot-rolled (HRC), cold-rolled (CRC) and galvanised (HDG)
HRC is made by rolling slab at around 1,100 °C to 1.2–25 mm; its surface carries scale, and it is used for pipe, sections, ships and structures and is the main benchmark of global steel prices. Pickling HRC and reducing it at room temperature to 0.2–3 mm gives CRC, with a smoother surface and tighter tolerances for appliances and automotive. Hot-dip zinc coating of CRC gives galvanised sheet (GI, DX51D+Z), aluminium-zinc gives Galvalume (AZ), and painting gives pre-painted steel (PPGI).