S355K2W
EN 10025-5 · 1.8967
S355K2W is a structural steel (Weathering family) to EN 10025-5 (1.8967). 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
Low carbon (~0.16%) gives good weldability by all common processes; preheat rarely needed in thin sections.
Machinabilitymoderate
Soft and gummy at low carbon — sharp tooling helps surface finish.
Corrosion resistancemoderate
Forms a protective patina in the open air (weathering steel); still needs protection where wet/salt persists.
Hardenabilitylow
Limited hardenability at low carbon — surface hardening is possible but through-hardening is not.
Toughnessmoderate
Adequate toughness for general use at ambient temperature.
Indicative ratings derived from composition and family — engineering guidance, not specification values.
Physical properties
| Density | 7850 | kg/m³ |
| Elastic modulus | 210 | GPa |
| Shear modulus | 80.8 | GPa |
| Poisson's ratio | 0.30 | |
| Thermal expansion | 12.0 | ×10⁻⁶/°C |
| Thermal conductivity | 48 | W/(m·K) |
| Specific heat | 470 | J/(kg·K) |
| Magnetic | Yes |
Typical values for weathering steel — use the mill certificate for the specific product.
Chemical composition (wt %)
Typical composition per EN 10025-5 for this grade — confirm exact limits (thickness-dependent) against the standard.
Available forms
Common applications
- Building and bridge steelwork
- Platforms, frames and support structures
- Crane and lifting structures
- General heavy fabrication
History
Weathering steels — US Steel’s 1930s COR-TEN — carry small copper and chromium additions that turn ordinary rust into a dense, self-protecting patina, letting exposed steel run unpainted. EN 10025-5 holds the European S…W grades. The number, 355, is the minimum yield strength in MPa. This is the K2 sub-quality (40 J at −20 °C). The W marks it as a weathering grade.
- 1933US Steel patents COR-TEN weathering steel
- 1964Weathering steel adopted widely for bridges and architecture
- 2004EN 10025-5 harmonises the S…W / WP weathering grades
This profile is generated from the grade's core data and family. Composition is decoded from the designation where its naming system defines it; physical properties are family-typical and ratings are indicative. Confirm critical values against the governing standard or the mill certificate. Equivalents, historical designations and hand-written expert notes are added per grade over time.