There are many examples of European grades of structural steel – for example, S235, S275, S355 For the purposes of this article, we will focus on the chemical composition, mechanical properties, and applications of S235, S275, and S355, which are three common structural steel grades used in all manner of construction projects.
In line with the European Standard classifications, structural steels must be referenced using standard symbols including but not limited to S, 235, J2, JO, JR and K2 where:
'S' denotes the fact that it is structural steel;
'235' which relates to the minimum yield strength of the steel (tested at a thickness of 16mm);
'J2', 'K2', 'JR', and 'JO' all demonstrate the material toughness in relation to the Charpy impact or 'V' notch test methodology;
S symbol for structural steel
JR symbol 20 temperature impact test.
J0 symbol 0 temperature impact test
J2 symbol -20 temperature impact test
electing the right structural steel grade is critical for ensuring the safety, durability, and cost-effectiveness of construction and industrial projects. Three commonly compared grades-ASTM A36 (USA), S235JR (Europe), and SS400 (Japan)-are all mild steels used in structural applications. While they share similarities, their chemical compositions, mechanical properties, and regional standards differ significantly.
Overview of Each Grade
| Grade | Standard | Region | Key Characteristics |
|---|---|---|---|
| ASTM A36 | ASTM International | Americas | General-purpose structural steel |
| S235JR | EN 10025-2 | Europe | Non-alloy steel with guaranteed toughness |
| SS400 | JIS G3101 | Asia | Japanese standard for general structures |
Chemical Composition
| Element | ASTM A36 | S235JR | SS400 |
|---|---|---|---|
| Carbon (C) | ≤0.26% | ≤0.17% | ≤0.29% |
| Manganese (Mn) | ≥0.75% (no max) | ≤1.40% | ≤1.60% |
| Phosphorus (P) | ≤0.04% | ≤0.035% | ≤0.050% |
| Sulfur (S) | ≤0.05% | ≤0.035% | ≤0.050% |
| Silicon (Si) | ≤0.40% | ≤0.35% | ≤0.55% |
Key Differences:
S235JR has the lowest carbon content, improving weldability and toughness.
SS400 allows higher carbon and manganese, making it slightly stronger but less ductile.
ASTM A36 has no upper limit for manganese, offering flexibility in strength.
Mechanical Properties
| Property | ASTM A36 | S235JR | SS400 |
|---|---|---|---|
| Yield Strength | ≥250 MPa (36 ksi) | ≥235 MPa | ≥245 MPa |
| Tensile Strength | 400–550 MPa | 360–510 MPa | 400–510 MPa |
| Elongation | ≥20% (200mm gauge) | ≥26% (5.65√So) | ≥17% (50mm gauge) |
| Impact Toughness | Not required | ≥27 J at 20°C | Not required |
Why It Matters:
S235JR guarantees impact toughness (tested at room temperature), making it ideal for cold climates.
SS400 has lower elongation, indicating reduced ductility compared to S235JR.
ASTM A36 is versatile but lacks standardized toughness requirements.
Applications by Grade
| Grade | Typical Applications |
|---|---|
| ASTM A36 | Bridges, buildings, machinery frames (USA/CAN projects) |
| S235JR | European structural frameworks, platforms, welded components |
| SS400 | General construction in Asia (beams, brackets, supports) |
