S235JR
EN 10025-2 · 1.0038
S235JR is a structural steel (Carbon-Manganese family) to EN 10025-2 (1.0038). It has a specified 0.2 % proof stress of 235 MPa and a typical tensile strength of about 360 MPa, with a uniform elongation of 26 %. Nominal carbon content is around 0.17 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 487 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 = 26.0% · conservative analysis limit ½εu = 13.0%
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
Weldabilityexcellent
About as weldable as structural steel gets — low carbon and low CE mean no preheat in normal sections and no fuss with any common process.
Formabilitygood
Good cold formability for a hot-rolled structural steel; bends and rolls readily within sensible radii.
Machinabilitymoderate
Soft and a little gummy — sharp tooling and positive rake give the best finish. Not free-cutting.
Corrosion resistancepoor
None inherent — paint or galvanise for any exposed use.
Hardenabilitylow
Too little carbon to harden usefully. Supplied as-rolled.
Toughnessmoderate
JR guarantees 27 J at +20 °C only. Fine indoors and in mild climates; specify J0/J2 for cold or dynamic service.
Expert notes
S235 is “mild steel” in the everyday sense — the default when strength isn’t the governing factor and you just need something weldable, cheap and universally stocked. If a drawing says “mild steel” without a grade, S235 is the safe assumption.
The JR suffix only guarantees impact toughness at +20 °C. That’s fine for most indoor and temperate outdoor steelwork, but for anything cold, dynamically loaded, or safety-critical, step up to J0 (0 °C) or J2 (−20 °C) — the cost difference is trivial.
It’s so weldable that it’s forgiving of poor practice, which is a blessing and a trap: the base metal will tolerate a lot, but that’s no excuse for skipping preheat on thick, restrained joints.
For bolted connections S235 is often the connected material rather than the fastener. Watch bearing and edge-distance limits — the lower yield versus S275/S355 means the plate reaches bearing capacity sooner.
Mechanical properties
| Condition | Section | Yield (MPa) |
|---|---|---|
| S235 · as-rolled | t ≤ 16 mm | 235 |
| 16 < t ≤ 40 mm | 225 | |
| 40 < t ≤ 63 mm | 215 | |
| 63 < t ≤ 100 mm | 215 | |
| 100 < t ≤ 150 mm | 195 | |
| 150 < t ≤ 200 mm | 185 |
UTS 360–510 MPa · Impact 27 J @ +20 °C · Hardness ~120 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 | 53 | W/(m·K) |
| Specific heat | 470 | J/(kg·K) |
Chemical composition (wt %)
Available forms
Equivalent grades
| Standard | Grade | Note |
|---|---|---|
| BS 4360 | 40B | |
| ASTM | A283 Gr. C | Close; A36 is the nearest common US structural grade. |
| DIN 17100 | St 37-2 | |
| JIS | SS400 | Approximate — SS400 has a wider composition tolerance. |
| ISO 630 | E235B |
Historical designations
| Standard | Grade | Note |
|---|---|---|
| DIN 17100 | St 37-2 | The classic German designation — “37” = ~370 MPa tensile. |
| BS 4360:1990 | 40B | UK Grade 40; still on older drawings. |
| Euronorm 25 | Fe 360 B | Pre-EN 10025 designation. |
Common applications
- General structural steelwork and frames
- Brackets, base plates and non-critical connections
- Handrails, walkways and secondary steel
- General fabrication and weldments
- Agricultural and construction plant structures
History
S235 is the direct descendant of the ubiquitous St 37 / Grade 40 mild steels — the baseline structural steel that European harmonisation carried forward under EN 10025.
- 1949DIN 17100 codifies St 37 as the standard German structural steel
- 1968BS 4360 defines UK Grade 40
- 1990EN 10025 introduces the S235 designation (S = structural, 235 = min yield)
- 2004EN 10025-2:2004 — current form of S235JR