S355J2W
EN 10025-5 · 1.8965
S355J2W is a structural steel (Weathering family) to EN 10025-5 (1.8965). It has a specified 0.2 % proof stress of 355 MPa and a typical tensile strength of about 510 MPa, with a uniform elongation of 22 %. Nominal carbon content is around 0.16 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 717 MPa above it. It develops a stable protective patina in the open air, often allowing use without paint.
Bilinear material model — nonlinear FEA
Uniform elongation εu = 22.0% · conservative analysis limit ½εu = 11.0%
Bilinear (BISO) approximation. Elastic modulus E up to the 0.2% proof stress R_p0.2, then a single tangent slope Eₜ to the ultimate tensile strength: Eₜ = (Rₘ − R_p0.2) / (εu − R_p0.2/E − 0.002), where εu is the uniform elongation and Rₘ is a typical (nominal) UTS within the specified band. The half-εu figure is a conservative strain limit for the analysis. Treat these as guidance for first-pass models; for critical work use a measured true stress–strain curve for the actual product and condition.
Ratings — engineering judgement
Weldabilitygood
Welds like S355 with matching or weathering-grade consumables so the joint patinas with the parent metal; normal preheat rules for thick sections.
Formabilitymoderate
As S355 — good structural cold forming within sensible radii.
Machinabilitymoderate
Machines like a structural C-Mn steel.
Corrosion resistancemoderate
The copper/chromium additions form a dense, adherent rust patina that slows further corrosion — but only under alternating wet/dry conditions. In permanently wet, buried or salt-laden service it corrodes like ordinary steel.
Hardenabilitylow
Not a hardening steel; supplied as-rolled.
Toughnessgood
J2 sub-quality guarantees 27 J at −20 °C — good for exposed outdoor structures.
Expert notes
S355J2W is weathering steel — “Cor-Ten” in everyday speech. Small additions of copper and chromium change how it rusts: instead of loose, flaking scale it grows a dense, tightly-adherent patina that seals the surface and dramatically slows further corrosion, so it can be used bare. Structurally it is S355 — same strength, same weldability, design to the same numbers.
The patina only forms if the steel is allowed to cycle wet and dry. In situations that stay permanently wet, are buried, sit under sheltered condensation, or are exposed to chlorides (marine spray, de-icing salt), the protective layer never stabilises and it corrodes like ordinary carbon steel. That single condition decides whether weathering steel is genius or a mistake on a given job — it is not a universal “paint-free” fix.
Detail for the run-off: during the first few years the patina sheds rust-coloured staining, which will mark concrete, glazing and paving below. Design the drainage and drip details, and keep bearings and connection crevices from trapping water.
For welding, use consumables that weather with the parent metal, and account for a small corrosion (thickness) allowance in the design life just as you would with any exposed steel.
Mechanical properties
| Condition | Section | Yield (MPa) |
|---|---|---|
| S355J2W · as-rolled | t ≤ 16 mm | 355 |
| 16 < t ≤ 40 mm | 345 | |
| 40 < t ≤ 63 mm | 335 | |
| 63 < t ≤ 80 mm | 325 |
UTS 470–630 MPa · Impact 27 J @ −20 °C · Hardness ~160 HB
Physical properties
| Density | 7850 | kg/m³ |
| Elastic modulus | 210 | GPa |
| Shear modulus | 81 | GPa |
| Poisson's ratio | 0.30 | |
| Thermal expansion | 12.0 | ×10⁻⁶/°C |
| Thermal conductivity | 50 | W/(m·K) |
| Specific heat | 470 | J/(kg·K) |
Chemical composition (wt %)
Available forms
Equivalent grades
| Standard | Grade | Note |
|---|---|---|
| ASTM | A588 / A242 | The US weathering grades. |
| Trade | COR-TEN A/B | The original US Steel trade name. |
| EN 10025-5 | 1.8965 |
Historical designations
| Standard | Grade | Note |
|---|---|---|
| Trade | COR-TEN | US Steel’s 1930s weathering steel — the name that stuck. |
| BS 4360 | WR50 | Old UK weathering-steel designation. |
Common applications
- Weathering-steel bridges and viaducts
- Architectural facades, canopies and sculpture
- Shipping-container and transport structures
- Exposed steelwork designed to run unpainted
History
Weathering steels were invented by US Steel in the 1930s (COR-TEN) to shed maintenance painting; EN 10025-5 carries the family as the S…W grades.
- 1933US Steel patents COR-TEN weathering steel
- 1960Weathering steel adopted for bridges and architecture
- 2004EN 10025-5 harmonises the S…W weathering grades