UK Steel Chemical Composition — BS EN 10025-2 Limits for S275 and S355

Chemical composition limits for UK structural steel grades S275 and S355 per BS EN 10025-2:2019, including carbon equivalent value (CEV) requirements for weldability and UK National Annex modifications. Essential reference for material specification, welding procedure qualification, and procurement verification for steelwork fabricated to EN 1993-1-1 with UK NA.

Quick access: UK Steel Grades | UK Steel Properties | UK Beam Sizes | UK Bolt Capacity | All UK References

BS EN 10025-2 Chemical Composition Limits

The chemical composition of UK structural steel sections (Universal Beams, Universal Columns, channels, angles) supplied by British Steel to BS EN 10025-2 must comply with the following maximum limits for ladle analysis:

Element S275JR S275J2 S355JR S355J2 S355K2
C (t ≤ 16 mm) 0.21 0.18 0.22 0.20 0.20
C (t > 16 mm) 0.21 0.18 0.20 0.18 0.18
Si (max) 0.40 0.40 0.55 0.55 0.55
Mn (max) 1.50 1.50 1.60 1.60 1.60
P (max) 0.035 0.030 0.035 0.030 0.030
S (max) 0.035 0.030 0.035 0.030 0.030
N (max) 0.014 — 0.014 — —
Cu (max) 0.55 0.55 0.55 0.55 0.55
CEV (t ≤ 40 mm) 0.40 0.40 0.45 0.45 0.45
CEV (40 < t ≤ 63 mm) 0.40 0.40 0.47 0.47 0.47
CEV (63 < t ≤ 100 mm) 0.42 0.42 0.49 0.49 0.49

Values are maximum permitted percentages from ladle analysis per Table 2 of BS EN 10025-2:2019. CEV is calculated per the IIW formula: CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15.

UK National Annex Requirements

The UK NA to BS EN 1993-1-1 (NA.2.4) requires that all structural steel supplied to UK projects comply with the BS EN 10025 series. For UK-rolled sections (British Steel, Scunthorpe), chemical composition certificates must be verified against the specified grade and subgrade.

Key UK-specific points:

CEV Impact on Welding Procedure

The CEV determines the preheat temperature required per EN 1011-2. For UK fabrication shops:

For UK projects specifying S355J2, the CEV of 0.45 % is at the threshold where moderate preheat becomes necessary for thicker sections. Always verify the actual CEV from the mill certificate before finalising the welding procedure specification (WPS).

Through-Thickness Properties for Z-Grade Steel

For connections where significant through-thickness strain is expected (e.g., welded joints to loaded flanges of heavy UC sections), EN 10164 Z-quality steel may be required. The UK NA to EN 1993-1-1 recommends Z-quality assessment per EN 1993-1-10 where lamellar tearing risk exists.

Z-Quality Max S (%) Min Reduction of Area (z-direction)
Z15 0.010 15%
Z25 0.007 25%
Z35 0.005 35%

The sulphur content is the primary control on through-thickness ductility. Z25 is typically specified for UK moment connections where welding is applied to tension-loaded flanges.

Worked Example — CEV Calculation for S355J2 Column Section

Given: Mill certificate for 254×254 UC 89: C=0.14%, Mn=1.45%, Cr=0.04%, Mo=0.01%, Ni=0.03%, Cu=0.02%, V=0.002%

CEV calculation: CEV = 0.14 + 1.45/6 + (0.04+0.01+0.002)/5 + (0.03+0.02)/15 CEV = 0.14 + 0.242 + 0.010 + 0.003 = 0.395%

At CEV = 0.395%, this S355J2 UC section is readily weldable without preheat for thicknesses up to 20mm. For the 17.3 mm flange, no preheat is required per EN 1011-2. For the thicker end plate (> 25 mm), a minimum preheat of 50°C would be recommended.

Design Resources

Frequently Asked Questions

What is the maximum carbon equivalent (CEV) for S355J2 steel per BS EN 10025-2?

The maximum CEV for S355J2 depends on thickness: 0.45 % for t ≤ 40 mm, 0.47 % for 40 < t ≤ 63 mm, and 0.49 % for 63 < t ≤ 100 mm. These limits ensure adequate weldability under EN 1011-2 welding procedure standards. For thicknesses above 100 mm, the CEV should be agreed between purchaser and manufacturer.

Does the UK National Annex modify chemical composition requirements for EN 1993-1-1?

The UK NA to BS EN 1993-1-1 does not directly modify chemical composition limits but requires compliance with BS EN 10025-2. UK practice typically specifies S355J2 for primary structural sections with CEV verification against EN 1011-2. The UK NA also requires steel grade selection per BS EN 1993-1-10 for fracture toughness, which indirectly imposes composition controls through the required Charpy subgrade.

What is the sulphur and phosphorus limit for UK structural steel?

For BS EN 10025-2 grades, the maximum sulphur and phosphorus content is 0.035 % each for standard JR grades, and 0.030 % each for J2 and K2 grades. These limits ensure adequate ductility and through-thickness properties. For Z-quality steel (EN 10164), the sulphur limit reduces to 0.010 % max for Z35 quality to prevent lamellar tearing.

How do I verify chemical composition for UK steel sections from British Steel?

British Steel provides mill certificates with each delivery showing ladle analysis results including C, Si, Mn, P, S, N, Cu, and calculated CEV. The certificate should be cross-checked against BS EN 10025-2 limits for the specified grade. If CEV exceeds the limit, EN 1011-2 welding procedure requirements apply including minimum preheat temperature calculation.

Related Pages

Educational reference only. All design values are per BS EN 1993-1-1:2005 + UK National Annex and BS EN 10025-2:2019. Verify all values against the current editions of the standards and the applicable National Annex for your project jurisdiction. Designs must be independently verified by a Chartered Structural Engineer registered with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.