No products in basket

Understanding Steel Quality & Terminology

iSteel work hard to source reliable suppliers,
only using the finest grades of steel


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.

Domestic, Manchester

Make a bold statement. Make it luxurious. Make it Steel. Discover the epitome of luxury with our stunning black steel doors featuring elegant bronze handles. Just imagine… abstract art on your...

Domestic, Brighton

Featuring beautiful reeded glass panels, our doors not only ensure privacy but also add a touch of timeless charm. And for those looking to maximize space and style, our sliding door options are the...

Domestic, Manchester

Seeing is believing! Exclusively from iSteel: 30-minute fire-rated black glazed steel doors. The perfect blend of timeless elegance and robust fire safety. 🔥 E30 Fire Rating - 30 minutes of reliable...

Domestic, Watford

Elevate your interiors with the sleek, contemporary elegance of iSteel Fire Rated Super Slim Framed Doors, where innovation meets design excellence. The Super Slim Framed E30 Fire Rated Steel Glass...

Domestic, Cambridge

Introducing our striking Arched E30 Fire-Rated Glazed Steel Door, an impeccable blend of form and function designed to elevate safety without compromising style. Crafted from robust steel, this door...

Domestic, London

Make a statement of elegance and style to your homes interior with iSteel’s glazed steel slimline doors available in Fire Rated and Non Fire Rated options. Our internal doors are completely...

Domestic, London

iSteel doors are a true timeless classic, look impressive and last a lifetime! Finchley, London based client was looking for a way to divide the sitting and TV room without loosing light and open...

Domestic, Surrey

Want timeless design? Master craftmanship? Precision installation? Look no further than iSteel, the UK’s number one choice for glazed steel internal and fire rated doors. Unlike other companies, All...

Domestic, Notton

Fantastic Fire Rated Doors Luxury Home builders Whitshaw Builders, have recently completed an impressive development in Notton Wakefield and chose iSteel to design, fabricate and install bespoke...

Domestic, Northallerton

Exposed Brick, Beautiful Stone and Steel doors. What more could a Barn Conversion ask for? A lot of thought had gone into the look and feel of the space to maintain character. Our glazed steel...

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