Carbon equivalent calculator
One number that says how the steel will behave when it cools: whether the heat-affected zone hardens, and whether preheat is needed before the first run.
Chemical composition, % by mass
Welding conditions — used for the preheat figure
Two formulae, two uses
CE (IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. This is the classic index quoted on certificates and in steel standards; it works well for carbon-manganese steels above about 0.18 % C.
CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40. This is the one EN 1011-2 method B uses for the preheat calculation, and it fits modern low-carbon fine-grained steels better.
| CE (IIW) | Weldability | What to do |
|---|---|---|
| up to 0.40 | Good | No preheat needed, ordinary electrodes |
| 0.40–0.60 | Limited | Preheat 100–200 °C, low-hydrogen electrodes, baked |
| above 0.60 | Poor | Preheat 200–350 °C, keep it warm while welding, stress relief afterwards |
Reading the result
Below 0.40 % CE, ordinary structural steel welds without preheat. From 0.40 to 0.60 the risk of a hard heat-affected zone is real and preheat depends on thickness, hydrogen and restraint — feed the CET into the preheat calculator. Above 0.60 preheat and controlled cooling are not optional, and post-weld heat treatment usually enters the procedure.
The composition has to come from the mill certificate for that heat, not from the grade designation. Two plates both stamped S355J2 can differ by 0.05 % C and 0.3 % Mn and still be within specification — which is enough to move CE across a decision boundary.
Common grades
| Grade | C, % | Mn, % | CE ≈ |
|---|---|---|---|
| S235JR | 0.17 | 1.40 | 0.40 |
| S355J2 | 0.20 | 1.60 | 0.47 |
| C22 | 0.20 | 0.50 | 0.28 |
| C45 | 0.45 | 0.65 | 0.56 |
| 30ChGSA | 0.30 | 1.00 | 0.67 |
The CE column is worked out with the IIW formula from the same composition rather than copied, so the table and the calculator cannot drift apart.
Frequently asked questions
CE or CET — which do I use?
CET when the question is preheat to EN 1011-2: that is the figure method B works with. CE to IIW is the older, more widely quoted number for a first view of weldability. The calculator gives both, because both turn up in documents.
Where do I get the analysis?
From the 3.1 inspection certificate to EN 10204 that comes with the material. Without one there is no CE — the grade name will not do, because the standard allows a range and heats spread across it.
What does a CE above 0.40 mean?
That the hardenability is enough to form a hard structure on fast cooling, and with it cold cracks. From 0.40 the preheat is calculated rather than guessed; from 0.60 post-weld heat treatment belongs in the procedure as well.
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