Carbon Equivalent Value (CEV) Formula

Per EN 1011-2, the carbon equivalent value for structural steels is:

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

For EN 10025-2 non-alloy structural steels, the simplified form applies since Cr, Mo, V, Ni, and Cu are typically at trace levels:

CEV ≈ C + Mn/6

The CEV is the primary indicator of weldability. Steels with CEV ≤ 0.45 generally require no preheat for thicknesses up to 30 mm under normal shop conditions per EN 1011-2.

Chemical Composition Limits by Grade

S235JR — EN 10025-2

Element t ≤ 16 mm 16 < t ≤ 40 mm 40 < t ≤ 100 mm 100 < t ≤ 150 mm
C max 0.17% 0.17% 0.20% 0.20%
Si max — — — —
Mn max 1.40% 1.40% 1.40% 1.40%
P max 0.025% 0.025% 0.025% 0.025%
S max 0.025% 0.025% 0.025% 0.025%
N max 0.012% 0.012% 0.012% 0.012%
CEV max 0.35% 0.35% 0.38% 0.38%

Note: S235JR has the lowest carbon content of the structural grades, giving excellent weldability. The CEV is typically 0.30-0.35 for standard rolling. No preheat is required for any thickness under normal conditions.

S275JR — EN 10025-2

Element t ≤ 16 mm 16 < t ≤ 40 mm 40 < t ≤ 100 mm 100 < t ≤ 150 mm
C max 0.18% 0.18% 0.20% 0.22%
Si max — — — —
Mn max 1.50% 1.50% 1.50% 1.50%
P max 0.025% 0.025% 0.025% 0.025%
S max 0.025% 0.025% 0.025% 0.025%
N max 0.012% 0.012% 0.012% 0.012%
CEV max 0.40% 0.40% 0.40% 0.42%

S275JR has slightly higher carbon and manganese than S235JR, giving increased strength while maintaining good weldability. CEV of 0.40 allows welding without preheat for thicknesses up to 40 mm.

S355JR — EN 10025-2

Element t ≤ 16 mm 16 < t ≤ 40 mm 40 < t ≤ 100 mm 100 < t ≤ 150 mm
C max 0.20% 0.20% 0.22% 0.24%
Si max 0.55% 0.55% 0.55% 0.55%
Mn max 1.60% 1.60% 1.60% 1.70%
P max 0.025% 0.025% 0.025% 0.025%
S max 0.025% 0.025% 0.025% 0.025%
N max 0.012% 0.012% 0.012% 0.012%
CEV max 0.42% 0.42% 0.43% 0.45%

S355JR has the highest carbon and manganese content of the standard structural grades. The CEV of 0.42-0.45 indicates that preheat may be necessary for thicknesses exceeding 40 mm, particularly in highly restrained joints.

S355J0, S355J2, and S355K2 — Impact Tested Variants

The J0, J2, and K2 suffixes indicate Charpy impact testing requirements (per EN 10025-2) but do not change the chemical composition. S355J0, S355J2, and S355K2 have identical chemical limits to S355JR at the same thickness range. The differences are:

Suffix Charpy Test Temp Min CVN Energy Application
JR 20°C 27 J Interior, low-temperature risk
J0 0°C 27 J Exterior temperate climate
J2 -20°C 27 J Cold climate, fracture-critical
K2 -20°C 40 J Higher toughness, offshore/wind

Weldability Guidelines per EN 1011-2

Grade CEV Range Preheat Required Electrode Type
S235JR 0.30-0.35 None (any thickness) EN ISO 2560-A 42
S275JR 0.35-0.40 None (t ≤ 40 mm), 50°C (t > 40 mm) EN ISO 2560-A 42
S355JR 0.40-0.45 50°C (t > 30 mm), 100°C (t > 60 mm) EN ISO 2560-A 46
S355J2 0.41-0.45 Same as S355JR EN ISO 2560-A 46
S355K2 0.42-0.47 75°C (t > 25 mm), 125°C (t > 50 mm) EN ISO 2560-A 46/50

Preheat recommendations assume ambient temperature ≥ 5°C, low-hydrogen welding process (MAG/MIG or basic electrodes), and hydrogen levels HD ≤ 5 mL/100g. Increase preheat by 25-50°C for cellulosic electrodes or high-moisture conditions.

EN 10025-2 Sulphur and Phosphorus Limits

All structural grades per EN 10025-2 have a maximum of 0.025% phosphorus and 0.025% sulphur. For improved formability or lamellar tearing resistance, specify:

These fine-grain grades offer lower P and S limits (typically 0.020% max) and improved CEV control.

Worked Example — CEV and Preheat Determination for Welded Connection

Problem: A fabricator is welding a moment-resisting end-plate connection using S355JR plates: flange plate 32 mm thick, end plate 25 mm thick. The shop ambient temperature is 8°C. Determine preheat requirements per EN 1011-2 and verify CEV compliance.

Step 1 — CEV Calculation per EN 1011-2: Mill certificate reports: C = 0.16%, Mn = 1.42%, Si = 0.38%, Cr = 0.08%, Ni = 0.06%, Mo = 0.02%, V = 0.04%, Cu = 0.14%.

CEV = 0.16 + 1.42/6 + (0.08+0.02+0.04)/5 + (0.06+0.14)/15 = 0.16 + 0.237 + 0.028 + 0.013 = 0.438. Per EN 10025-2 Table 7, S355JR limit at t ≤ 40 mm = 0.42. CEV = 0.438 exceeds limit.

Step 2 — Resolution per EN 10025-2: Option A: Upgrade to S355J2 (CEV limit 0.45 for t ≤ 40 mm). CEV 0.438 < 0.45 — acceptable. Option B: Special agreement with mill for CEV ≤ 0.44 on S355JR. Option C: Use S355N (EN 10025-3, normalized fine-grain) with CEV limit 0.43 for t ≤ 40 mm. 0.438 > 0.43 — still exceeds.

Step 3 — Preheat Determination per EN 1011-2 Annex C: With S355J2, CEV 0.438, t = 32 mm: Minimum preheat 50°C (hydrogen scale D, HD ≤ 5 mL/100g per EN ISO 2560-A). For highly restrained end-plate moment connection, increase by 25°C → preheat to 75°C. Interpass temperature maintained 150-250°C per EN 1090-2 Table 16.

Step 4 — Electrode Selection per EN ISO 2560-A: For S355J2, use G 46 5 M21 (MAG, 1.2 mm wire, Charpy 47 J at -50°C) or E 46 5 B 42 (SMAW basic electrode). The "5" designator confirms -50°C Charpy — provides ample margin for -20°C service.

Step 5 — Heat Input Control per EN 1011-2: Target heat input: Q = 0.8 × U × I / (v × 1000) = 0.8 × 27 × 260 / (6.25 × 1000) = 0.90 kJ/mm. Within recommended 0.8-2.5 kJ/mm for S355 per EN 1011-2 Table C.1.

Result: Upgrade to S355J2 (CEV 0.438 < 0.45 limit). Preheat 75°C (50°C base + 25°C for high restraint). G 46 5 M21 electrode. Procedure qualified per EN ISO 15614-1 for EXC2.

Frequently Asked Questions

What is the carbon equivalent value for S355JR steel?

S355JR has a CEV of 0.42-0.45 depending on thickness, calculated per EN 1011-2 as CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. For thicknesses up to 40 mm, CEV max is 0.42. For 40-100 mm, CEV max is 0.43. For 100-150 mm, CEV max is 0.45.

Does S235JR require preheat before welding?

S235JR does not typically require preheat before welding at any thickness under normal shop conditions. The CEV of 0.30-0.35 is well below the 0.45 threshold where preheat becomes necessary per EN 1011-2. In cold weather (below 5°C) or highly restrained joints, a minimal 50°C preheat may still be advisable as good practice.

What is the difference between S355JR and S355J2 chemical composition?

S355JR and S355J2 have identical chemical composition limits per EN 10025-2 for the same thickness range. The difference is in Charpy impact testing: JR requires 27 J at 20°C, while J2 requires 27 J at -20°C. The actual measured chemistry may vary slightly between heats to achieve the lower-temperature toughness, but the guaranteed maximum limits per the standard are the same.

Related Pages

Educational reference only. Chemical composition limits per EN 10025-2:2019. CEV per EN 1011-2:2001. Verify actual chemical composition against mill certificates and EN 10204 Type 3.1 inspection documents before welding. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

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