Understanding Steel Quality & Terminology
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Structural Steel
Structural steel is a basic construction material, made from specific grades of steel and manufactured in a variety of industry standard cross-sectional shapes or sections.
Structural Steel Grades
Structural steel grades are engineered with specific chemical compositions and mechanical properties formulated for speficic applications.
European Standard
In Europe, structural steel must adhere to European Standard EN-10025, governed by the European Committee for iron and steel standardisation (ECISS), a subset of CEN (European Committee for Standardisation).
- S – denotes the fact that it is structural steel
- 235 – related to the minimum yield strength of the steel (tested at a thickness of 16 mm)
- J2/K2/JR/JO – material toughness in relation to the Charpy impact or ‘V’notch test methodology
- W – Weathering steel (atmospheric corrosion resistant)
- Z – Structural steel with improved strength perpendicular to the surface
- C – Cold-formed
Based on the manufacturing process, chemical composition and applicable application, further letters and classifications might be used to reference particular grades/products of structural steel.
Chemical Composition of Structural Steels – S235 and S355
The chemical composition of structural steel is very important and highly regulated. It is a central factor which defines the mechanical properties of the steel material. In the following table, one can see the maximum % levels of certain regulated elements present in European structural steel grades S235, S275 and S355.
| Grade | C% | Mn% | P% | S% | Si% |
|---|---|---|---|---|---|
| S235 | 0.22 max | 1.60 max | 0.05 max | 0.05 max | 0.05 max |
| S355 | 0.23 max | 1.60 max | 0.05 max | 0.05 max | 0.05 max |
The chemical composition of structural steel is extremely important to the engineer and will change with specific grades based on their intended use. For instance; S355K2W is a structural steel that has been hardened (K2) and has been designed with a chemical composition to endure increased weathering (W). Thus, this grade of structural steel will have a marginally different chemical composition to the standard S355 grade.
If you have any questions about the mechanical properties of our structural steel, feel free to contact us antime.
Mechanical Properties of Structural Steel – S235, S355
The mechanical properties of structural steel are central to its classification and hence, application. Although, chemical composition is a governing factor of the mechanical properties of steel, it is also very important to understand the minimum standards for the mechanical properties (performance characteristics) such as tensile strength and yield strength.
Yield Strength
The structural steel’s yield strength measures the minimum force needed to create a permanent deformation in the steel. The naming convention used in European Standard EN10025 relates to the minimum yield strength of the steel grade tested at 16 mm thick.
| Structural Steel Grade at 16 mm | Minimum Yield Strength at nominal thickness 16 mm | |
|---|---|---|
| ksi | N/mm2 (MPa) | |
| S235 | 33 000 ksi | 235 N/mm2 |
| S355 | 50 000 ksi | 355 N/mm2 |
