European Steel Properties — EN 10025 Structural Steel Grades S235 to S460

Complete reference for EN 10025 structural steel mechanical properties used in Eurocode 3 (EN 1993-1-1) design. Nominal (characteristic) values for yield strength Fy, tensile strength Fu, Charpy V-notch impact subgrades, carbon equivalent value (CEV), and delivery conditions for hot-rolled structural sections and plates.

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EN 10025 Structural Steel Grade System

EN 10025 is the harmonised European standard for hot-rolled structural steel products. It is divided into six parts covering different steel types. The grade designation follows the pattern:

S[Fy] [Subgrade] [Delivery Condition]

• S = Structural steel
• Fy = Minimum yield strength in MPa for t <= 16 mm
• Subgrade = Charpy impact toughness designation (JR, J0, J2, K2)
• Delivery Condition = +AR, +N, +M, +QT (optional suffix)

For example, S355J2+N is structural steel with Fy = 355 MPa, Charpy 27 J at -20C, delivered in the normalised condition.

Primary Structural Grades

Complete Fy and Fu Table — EN 10025-2 (Non-Alloy Structural Steels)

Yield strength reduces with increasing thickness due to the coarser grain microstructure that develops during slower cooling of thicker products. Always use the Fy value for the actual element thickness per EN 1993-1-1 Table 3.1.

Notes: S235 and S275 are non-alloy structural steels to EN 10025-2. S355 is available in both non-alloy (Part 2) and fine-grain (Part 3) forms. S450 is covered in EN 10025-2 up to 80 mm. S420 and S460 are fine-grain steels to EN 10025-3 (normalised) or EN 10025-4 (thermomechanical rolled).

Fine-Grain Structural Steels — EN 10025-3 and EN 10025-4

For higher-strength applications where enhanced toughness and improved weldability are required:

The fine-grain designation (N or M) provides guaranteed through-thickness properties and lower CEV limits compared to the non-alloy S355JR from Part 2. For critical welded connections and thick sections, S355NL (EN 10025-3) is preferred.

Charpy V-Notch Subgrades — Toughness Classification

The subgrade suffix after the strength grade specifies the minimum Charpy V-notch impact energy at a given test temperature. This is critical for fracture toughness selection per EN 1993-1-10.

For UK practice: S355J2 is the default subgrade for most building structures. S355J0 is acceptable for internal members in heated buildings (consequence class CC1). S355K2 should be specified for bridges, crane girders, and structures in cold regions (e.g., northern Scotland).

Chemical Composition Limits — EN 10025-2

The chemical composition determines weldability, toughness, and mechanical properties. The Carbon Equivalent Value (CEV) is the primary weldability index.

CEV is calculated per the International Institute of Welding (IIW) formula:

CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

For CEV <= 0.45, no preheat is generally required for sections up to approximately 30 mm thickness, assuming low-hydrogen welding processes.

Through-Thickness Properties — EN 10164 Z-Quality

When welded connections subject the steel to through-thickness tension (e.g., full-penetration welds in moment connections, stiff column base plates), lamellar tearing is a risk. EN 10164 defines improved through-thickness properties:

Specify S355J2+Z25 for thick end plates in moment connections and for column base plates with high through-thickness stress. The +Z25 suffix guarantees a minimum 25% reduction of area in through-thickness tensile testing.

Delivery Conditions

The delivery condition affects residual stress state, which in turn influences buckling behaviour (EN 1993-1-1 buckling curves):

For S355, the default delivery condition for standard sections is +AR (as-rolled) for members up to ~40 mm flange thickness and +N (normalised) for thicker sections. S460 is typically supplied as +M (TMCP, EN 10025-4) with a CEV <= 0.39 and excellent weldability.

EN 1993-1-1 Design Values — Partial Factors

When using the characteristic (nominal) steel properties above for design resistance calculations:

Note: Unlike AISC (phi factors 0.75-0.90) and AS 4100 (phi = 0.80-0.90), EN 1993 uses gamma_M0 = gamma_M1 = 1.00. The conservatism is embedded in the buckling curves (a0 through d), not in the partial factors.

Cross-Reference to International Steel Grades

Direct substitution is not permitted without re-check. The three standards have different fu/fy ratios, different Charpy requirements, and different thickness derating tables. If substituting S355 for A992, recalculate all design resistances with the tabulated Fy and Fu per EN 1993-1-1 for the actual element thickness.

Frequently Asked Questions

What is the yield strength of S355 steel per EN 10025? The minimum yield strength (Fy) of S355 is 355 MPa for thicknesses up to 16 mm. This reduces to 345 MPa for 16 < t <= 40 mm, 335 MPa for 40 < t <= 63 mm, 325 MPa for 63 < t <= 80 mm, and 315 MPa for 80 < t <= 100 mm, per EN 1993-1-1 Table 3.1. The tensile strength (Fu) is 470-630 MPa for t <= 40 mm and 450-600 MPa for 40 < t <= 100 mm. Always use the thickness-corrected Fy value for the actual element flange or web thickness in design calculations.

What do S355JR, S355J0, and S355J2 mean? The suffix indicates Charpy V-notch impact toughness: JR = 27 Joules at +20C, J0 = 27 J at 0C, J2 = 27 J at -20C, and K2 = 40 J at -20C. S355J2 is the standard specification for UK and Northern European building structures because it guarantees adequate toughness at winter temperatures. For Southern Europe, J0 is often sufficient. For bridges and fatigue-loaded structures, K2 is typically required.

How does EN S355 compare to US A992 steel? S355J2 has a minimum Fy of 355 MPa (for t <= 16 mm) compared to A992 with Fy = 345 MPa (50 ksi). The fu/fy ratio is approximately 1.32 for S355 vs 1.20 minimum for A992. While the two grades are broadly equivalent, S355 offers slightly higher yield strength in thinner sections and a higher fu/fy ratio, which provides better strain-hardening capacity and improved resistance to net section fracture in tension connections.

Why does steel yield strength decrease with plate thickness? Thicker steel plates cool more slowly after hot rolling, resulting in a coarser ferrite grain microstructure with lower yield strength. This thickness-dependent strength reduction is codified in EN 1993-1-1 Table 3.1, which provides Fy values for each thickness bracket. This is not unique to European steel — ASTM A6 and AS/NZS 3679.1 also specify thickness-dependent Fy reductions, though the bracket boundaries and reduction magnitudes differ between standards.

When should I specify Z-quality (Z25 or Z35) steel? Z-quality (through-thickness ductility per EN 10164) should be specified when welded connections subject the steel to through-thickness tensile stress. Common scenarios include: full-penetration welded moment connections (end plates, column stiffeners), thick column base plates with full-strength fillet welds, and any joint where the steel is loaded perpendicular to the rolling plane. Z25 (25% min reduction of area) is adequate for most structural connections. Z35 (35%) is reserved for very thick plates (>40 mm) with high restraint.

Related Pages

• EN 1993-1-1 Beam Design Guide — Section classification, Mc,Rd, LTB
• EN 1993-1-8 Connection Design Guide — Bolts, welds, joint classification
• EN 1993 Column Buckling Guide — Curves a0-d, Nb,Rd
• European Bolt Grades EN 1993-1-8 — Bolt classes 4.6 to 10.9
• European Weld Electrode Selection — EN ISO 2560/14341 matching
• Beam Capacity Calculator
• Column Capacity Calculator
• Section Properties Lookup

Educational reference only. All steel grade values are nominal (characteristic) values per EN 10025 and EN 1993-1-1. Verify all properties against the current edition of the applicable EN standard and the relevant National Annex for your project jurisdiction. Material certification to EN 10204 Type 3.1 is standard for structural steel — request Type 3.2 for critical applications. All design values are PRELIMINARY — NOT FOR CONSTRUCTION. Results must be independently verified by a licensed Professional Engineer or Chartered Structural Engineer.