DIN EN 10025: Structural Steel, Grades and Strength

An order for structural steel plate specified simply as "per DIN EN 10025" can't actually be filled that way. Without an exact grade designation such as S235JR or S355J2, it stays unclear what strength and toughness the material must actually deliver. Both designations come from DIN EN 10025, the central European standard series for hot-rolled structural steel. Skip that precision, and the supplier may well deliver a part that's technically "structural steel" but doesn't meet the required properties.

In brief: DIN EN 10025 is the European standard series for hot-rolled structural steel. It spans six parts, from general delivery conditions (Part 1) to quenched-and-tempered fine-grain steels (Part 6). Part 2 covers the most common non-alloy structural steels, such as S235JR (1.0038) and S355J2 (1.0577). The designation encodes yield strength and impact toughness; actual strength also depends on plate thickness.

What does DIN EN 10025 cover?

DIN EN 10025 sets the technical delivery conditions for hot-rolled structural steel products (plates, sections, and bars) used mainly in welded, bolted, or riveted structures. The standard defines binding values for chemical composition, mechanical properties, and permissible tolerances.

It's issued by the European Committee for Standardization (CEN) and published in Germany via DIN Media as a national standard. For buyers, this matters because an order "per DIN EN 10025" only becomes unambiguous once the exact part number and grade are specified. Citing the standard by name alone fixes neither strength nor toughness.

For parts that go into a building structure, the EU Construction Products Regulation also comes into play. Structural steel per this standard falls under a harmonised European standard in that case. It needs a declaration of performance plus CE marking before it can be used on a construction site in the EU. That requirement doesn't apply to pure mechanical or plant engineering outside of construction, though.

What parts does the standard have?

DIN EN 10025 splits into six parts, each covering a distinct steel group. Part 1 sets the general delivery conditions that apply across all other parts, covering test methods and certificate types. Part 2 is by far the most frequently requested part, since it governs the non-alloy structural steels used throughout general steel and mechanical engineering.

Parts 3 and 4 differ mainly in the rolling process. Normalized/normalized-rolled fine grain steels (Part 3) get a separate normalizing heat treatment afterward. Thermomechanically rolled grades (Part 4), by contrast, reach their fine-grained structure directly through a controlled rolling temperature. Part 5 covers weathering structural steel, whose alloyed surface deliberately forms a protective rust layer, for example for uncoated facades or bridges. Part 6 covers quenched and tempered fine-grain steels with particularly high yield strength, used in crane construction or heavy machinery.

What do designations like S235JR or S355J2 mean?

The short designation follows a fixed scheme: the "S" stands for structural steel. The number that follows states the minimum yield strength in N/mm² at a reference thickness of 16 mm. S355J2 therefore has a minimum yield strength of 355 N/mm², S235JR correspondingly 235 N/mm².

The letter code afterward describes impact toughness. JR stands for 27 joules at room temperature (20°C). J0 stands for 27 joules at 0°C. J2 stands for 27 joules at minus 20°C. The lower the test temperature, the tougher the steel has to stay in cold conditions. That matters for structural steel used outdoors or in cold climates. Additional suffixes such as +N (normalized) or +AR (as rolled, no heat treatment) state the delivery condition.

This steel designation shouldn't be confused with the numeric material number (1.xxxx format) under DIN EN 10027. DIN EN 10025 fixes the short designation and properties, while the material number comes from its own separate numbering system.

In our sourcing projects, we always have suppliers confirm the full designation, not just "S355" or "structural steel per EN 10025". That includes the toughness code and the delivery condition. Especially with suppliers in the Far East, this has paid off repeatedly. Without it, a cheaper grade with lower impact toughness otherwise gets delivered on a regular basis.

How does strength depend on plate thickness?

The yield strength stated in the designation only applies up to a certain reference thickness, usually 16 mm. As plate thickness increases, yield strength drops noticeably, since thicker material cools more slowly and forms a coarser structure. Committing to a strength value for a specific part without accounting for the actual thickness is risky. In the worst case, it means calculating with too high a value.

Source: DIN EN 10025-2:2019-10, yield strength values by thickness range (excerpt).

For a 90 mm thick S355J2 plate, the guaranteed yield strength is therefore 315 rather than 355 N/mm², a difference of over 10 percent. When sizing a part, this table should always be read against the thickness actually ordered, not the nominal value implied by the short designation.

What evidence should buyers request when sourcing?

The short designation alone isn't enough for an order. Contractually, buyers should also fix the required delivery condition, the reference thickness, and the type of test certificate. According to Dillinger's customer information on EN 10025:2019, the current edition of Part 2 raised the maximum nominal thickness for the JR and J0 grades. It now stands at 400 mm, up from 250 mm previously. It also made CE marking the default for delivery unless otherwise agreed. That shows even established standards keep evolving.

In our experience, buyers rarely ask for the chemical composition proactively, even though it should be included in the test certificate. For safety-relevant structural steel parts especially, it's worth checking for an inspection certificate 3.1. It documents the actual heat analysis of the delivered batch, rather than relying on a general declaration of conformity.

An incoming goods inspection with material verification additionally protects against the wrong grade getting built in unnoticed. For welded steel assemblies, it's also worth checking the applicable general tolerances per ISO 2768. Dimensional deviations add up quickly on larger structural steel parts. Anyone also considering higher-alloy alternatives can start with our article on what sets stainless steel apart from structural steel.

When sourcing from the Far East, it's also worth checking availability and lead time early. Standard grades such as S235JR and S355J2 are usually available at short notice in common dimensions. Fine-grain steels per Parts 3 or 4 and quenched-and-tempered grades per Part 6, by contrast, are often rolled to order. That means correspondingly longer lead times.

Frequently asked questions about DIN EN 10025

What does DIN EN 10025 cover?

The standard sets the technical delivery conditions for hot-rolled structural steel, including chemical composition, mechanical properties, and test methods. These are split across six parts for different steel groups.

What does the designation S235JR mean?

The S stands for structural steel, and 235 for the minimum yield strength in N/mm² at 16 mm thickness. JR stands for an impact toughness of 27 joules at room temperature.

Is there an ASTM equivalent to S235JR or S355J2?

There's no exact 1:1 equivalent, since the test systems differ. In practice, S235JR is most often compared to ASTM A36, and S355J2 to ASTM A572 Grade 50, each with slightly different limits.

Is structural steel per DIN EN 10025 the same as stainless steel?

No. The standard covers non-alloy and low-alloy structural steels, while stainless steel achieves significantly higher corrosion resistance through a high chromium content.

Why does yield strength drop for thicker plates?

Thicker material cools more slowly during rolling and forms a coarser structure, which lowers the achievable yield strength. The standard accounts for this with staggered limits per thickness range.

Conclusion: DIN EN 10025 as a reliable basis for sourcing structural steel

DIN EN 10025 isn't a single rulebook but a six-part standard series that offers a matching structural steel group for whatever the requirement calls for. Anyone sourcing should specify not just the short designation, but also the part number, delivery condition, and reference thickness. That's how you get a part with exactly the strength the design actually needs.

As process specialists, we at Line Up support our clients from the material selection stage onward. We match grade, delivery condition, and test evidence to the specific part. 👉 Book a no-obligation consultation and we'll help you find the right structural steel grade for your next project.

Sources:

• DIN Media: DIN EN 10025-1 – General technical delivery conditions

• DIN Media: DIN EN 10025-2 – Technical delivery conditions for non-alloy structural steels

• Dillinger: Customer information on EN 10025:2019

• European Commission: Construction Products Regulation (CPR)