Revised hot rolled steel standards: their strength within the manufacturing sector

For the first time since 2004, five parts of the EN 10025 series have been revised – this is the series of standards on the topic of hot rolled products of structural steels.

The general construction market in the UK is reliant on hot rolled steel.Every year, approximately 1 million tonnes are used in the UK, and a further 6 million tonnes in Europe.

Hot rolled steel consumption in the 10 largest steel-consuming economies, including Europe, rose by 7.5% in the first 3 months of 2018 compared with the previous year, while OECD figures suggest that prices are on a downward trend.[1]

What is the purpose of this material and why does it matter to the construction and manufacturing industries?

The importance of hot rolled steel as a material

Hot rolled steel is all around us, holding up our infrastructure and keeping the world moving, but it is often hidden from sight.

In its most well-known form, I-beams (beams with a distinctive 'I' cross-section), also known as rolled steel joists, keep buildings standing by carrying bending and shear loads.

In the form of sheet metal, hot rolled steel is used to make automotive bodies and roofs for buildings.

Its robustness makes it ideal for agricultural equipment, such as tractors and harvesters, and it's also a common choice for components, such as for water heaters and storage tanks.

Its rough, non-shiny surface means it's less likely to be chosen for applications where aesthetics matter, though it can be descaled, painted and polished.

It is also used, perhaps surprisingly, for art sculptures. The variations in colour provide character, and it's robust enough to withstand display out in the open.[2]

What is the difference between hot and cold rolled steel?

Essentially, the difference between these two common types of steel product is in the process of manufacture.[3]

Both types are made from steel billets passed through two or four rolls, which squeeze them into the desired shape – for example tubes, bars or sheets.

Hot rolled steel is roll-pressed at a heat above 1,700 degrees Fahrenheit, which is higher than its recrystallization temperature.

That makes it easier to shape than cold rolled steel, so more shapes and larger sizes are available to purchase. It's also generally cheaper, as the manufacturing process is simpler.

After the roll-pressing process, it's allowed to cool at room temperature. This keeps it free of the internal stresses that can arise during the finishing processes used for cold rolled steel.

However, hot rolled steel shrinks as it cools and therefore its final shape and size are less predictable than cold rolled steel, rendering it less suitable for precision engineering.

It also has a lower yield and tensile strength, so it is more liable to fracture under pressure.

Both hot and cold rolled steel is available in a range of grades and specifications.

An overview of the revised standards

Parts 2, 3, 4, 5 and 6 have all been updated and are now stand-alone standards covering technical delivery conditions, including the preparation of samples and test pieces, test methods, marking, labelling and packaging, and drawings.

The standards set out the requirements for using steels of differing strength, toughness, ductility, weldability and durability. Changes to the updated standards in the series include editorial revisions, the deletion of certain appendices and the inclusion of new steel grades.

BS EN 10025-2:2019, Hot rolled products of structural steels – Technical delivery conditions for non-alloy structural steels, covers flat and long products, or those intended to be processed into such products, in the grades and qualities specified. Three engineering steels are also specified.

The revisions include the addition of one option and the deletion of two others. 

BS EN 10025-3:2019, Hot rolled products of structural steels – Technical delivery conditions for normalized/normalized rolled weldable fine grain structural steels, covers flat and long products of specific grades with a thickness of ≤250 mm. These steels have a high resistance to brittle fracture and are used in manufacturing highly stressed welded structures – for example bridges. They are designated with the letter 'N'.

In this revised version, certain options have been added, renumbered or deleted.

BS EN 10025-4:2019, Hot rolled products of structural steels – Technical delivery conditions for thermomechanical rolled weldable fine grain structural steels, covers flat and long products with a thickness of ≤150 mm. These steels are mechanically strong, tough, and easy to weld and form. They are frequently used in heavily loaded parts of welded structures such as bridges, flood gates, and water supply tanks that are in service at ambient and low temperatures. They are designated with the letter 'M'.

This standard now covers steel grade S500M.

BS EN 10025-5:2019, Hot rolled products of structural steels – Technical delivery conditions for structural steels with improved atmospheric corrosion resistance,applies to flat and long products of what are also known as hot rolled 'weathering steels' or 'corten steels', which have an enhanced resistance to rusting. They are commonly used to make bridges.[4] They are designated with the letter 'W'.

In this revised version, several steel grades have been added to Tables 1 to 5.

BS EN 10025-6:2019, Hot rolled products of structural steels – Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition, applies to flat products with a minimal nominal thickness of 3–125 mm, depending on the grade. They have a minimum yield strength of 460 MPa to 960 MPa after quenching and tempering. Such steels are designated 'Q'.

Changes include extending the values in Tables 3 and 4 for thicknesses up to 200 mm.

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The revised standards are available to buy from the BSI shop:  

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