Mechanical Properties and Chemical Composition of Structural Steel

Structural steel is a standard construction material, manufactured from specific grades of steel and formed in a variety of industry standard cross-sectional shapes (or ‘Sections’). Structural steel grades are designed with particular mechanical properties and chemical compositions formulated for specific applications.

In Europe, the structural steel must conform to the European Standard EN 10025 governed by the ECISS (European Committee for Iron and Steel Standardization), which is a subset of CEN (European Committee for Standardization).

Some examples of European grades of structural steel are S195, S235, S275, S355, S420, S460 etc. However, the scope of this article is to focus on the Mechanical Properties, Chemical Composition, and Applications of S235, S275, S355, which are the three regular structural steel grades used in every aspect of construction projects across the EU.

Inline with the European Standard classifications, structural steels should be referenced using standard symbols including but not limited to: "S"235"J2’‘K2’’C’’Z’’W’’JR’’JO’’

Where:

  • 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 relevant application, additional letters and classifications might be used to reference specific grades/products of structural steel.

As the EU Standard classifications are inherently not a global standard, several corresponding grades with the same Mechanical and Chemical properties may be used in other parts of the globe. For instance, Structural Steels manufactured for the US market must be specified according to the ASTM (American Society for Testing and Materials) international guidelines and will be referenced with an ‘A’, followed by the relevant Grade such as A36, A53 etc.

US Equivalent Grades

EU US
S235 A283C
S275 A570Gr40
S355 A572Gr50

 

In most countries, Structural Steel is regulated and it is essential that it meets a minimum specific criterion for size, shape, strength, chemical composition, etc.

Chemical Composition of Structural Steels - S235, S275 and S355

Structural steel’s chemical composition is very important and highly regulated. It is a fundamental factor that defines the Mechanical properties of the steel material. In the table given below, one can see the Max % 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
S275 0.25 max 1.60 max 0.04 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 paramount to the engineer and will change with specific grades based on their intended use. For instance, the structural steel S355K2W has been hardened (K2) and designed with a chemical composition to endure increased weathering (W). Hence, the chemical composition of this grade of structural steel will be slightly different from that of the standard S355 grade.

Mechanical Properties of Structural Steel - S235, S275, S355

The Mechanical Properties of Structural Steel are fundamental to its classification and thus, application. While Chemical Composition is a major factor of the steel’s the mechanical properties, understanding the minimum standards for the Mechanical Properties (performance characteristics) such as yield strength and tensile strength is also vital.

Yield Strength

The yield strength of structural steel determines the minimum force needed to create a permanent deformation in the steel. The naming convention used in European Standard EN10025 indicates the Minimum Yield strength of the steel grade tested at a thickness of 16 mm.

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
S275 36 000 ksi 275 N/mm2
S355 50 000 ksi 355 N/mm2

 

Tensile Strength

The Tensile Strength of Structural Steel relates to the point at which permanent deformation occurs on pulling or stretching the material laterally along its length.

Structural Steel Grade Tensile Strength MPa at
Nom thickness between 3 mm and 16 mm
S235 360 – 510 MPa
S275 370 – 530 MPa
S355 470 – 630 MPa

 

Typical Structural Steel ‘Sections’ / Cross-Sectional Shapes

Structural steel is available in several Grades but is usually sold pre-formed with a defined cross-sectional shape, designed for particular applications. For instance, it is not unusual to find Structural Steel sold in: Z-beams, I-Beams, HSS (Hollow Structural Section), L-shaped, Box Lintels, Steel Plate etc.

Based on the preferred application, an engineer will specify a grade of steel (mostly to meet minimum strength, maximum weight and/or weathering requirements) and the sectional shape, relative to the desired location and expected load to be performed or job to be carried out.

Applications of Structural Steel

Structural steels are used in various ways and have diverse applications. They are especially valuable as they provide the unique combination of good welding properties with assured strengths. Structural steel is an exceptionally versatile product and is generally preferred by the engineer trying to maximize strength or structure while minimizing its weight.

Unsurprisingly, the construction industry is the largest consumer of Structural Steel, where it is used for every purpose and employed at diverse scales. Whether a vast I-beam is bolted in place to hold the road surface on a bridge or a small box lintel is used to carry the load of a structural wall in a residential property, structural steel can be specified, designed, and fabricated for the job.

  • Houses
  • High Rise Buildings / Skyscrapers
  • Offices
  • Factories
  • Train Tracks
  • Shopping Malls
  • Bridges
  • Road barriers

References

  • S275 - Leeco Steel
  • S235 - Masteel
  • Structural Steels - SteelStrip
  • Tata Steel Europe

Masteel UK Ltd

This information has been sourced, reviewed and adapted from materials provided by Masteel UK Ltd.

For more information on this source, please visit Masteel UK Ltd.

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