S355K2
EN 10025-2 · 1.0596
S355K2 is a structural steel (Carbon-Manganese family) to EN 10025-2 (1.0596). 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 0.23 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 717 MPa above it. A plain-carbon steel: economical and predictable, strengthened by carbon content and heat treatment rather than alloying.
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
Weldabilitymoderate
Medium carbon (~0.23%) — preheat and hydrogen-controlled consumables advisable, especially in thicker sections.
Machinabilitymoderate
Soft and gummy at low carbon — sharp tooling helps surface finish.
Corrosion resistancepoor
No inherent corrosion resistance — protect by paint, galvanising or plating in exposed use.
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 carbon-manganese steel — use the mill certificate for the specific product.
Chemical composition (wt %)
Typical composition per EN 10025-2 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
The non-alloy structural steels are the direct heirs of the St 37 / St 52 / Grade 40–55 mild and medium-strength steels; EN 10025-2 unified them under the S-plus-yield designation that is now the European default for hot-rolled structural steel. The number, 355, is the minimum yield strength in MPa. This is the K2 sub-quality (40 J at −20 °C).
- 1949DIN 17100 codifies the St 37 / St 52 structural steels
- 1968BS 4360 defines the UK Grade 40–55 structural steels
- 1990EN 10025 introduces the S-designation (S = structural, number = min yield)
- 2004EN 10025-2:2004 — current form of the non-alloy structural 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.