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Carbon equivalent calculator

Enter a steel composition and get CE(IIW) — the same quantity EN 1011-2 calls CEV — alongside the Pcm cracking parameter, the weldability band and what it implies for preheat. Runs in your browser. No sign-up, no email.

Composition

Weight percent. Leave an element blank if it is not present or not reported.

Load a typical composition

CE(IIW)

Also written CEV in EN 1011-2

0.00
—
Pcm (Ito–Bessyo)0.000
Governing index—

Take this composition further. The same chemistry, with your route, heat treatment and section thickness, gives yield, tensile, hardness, elongation and fatigue life — each with its uncertainty, and a plain statement of where the model is weak. Open it in METALLAI with this composition →

How it is calculated

Both formulas below are the ones METALLAI uses inside its own weldability screening, written out in full so you can check the arithmetic rather than trust the box above.

CE(IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 Pcm = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B

CE(IIW) is the International Institute of Welding formula, identical to the CEV used in EN 1011-2. It was derived for carbon-manganese and low-alloy steels and weights the alloying additions heavily. Pcm is the Ito–Bessyo cracking parameter, which weights carbon much more strongly and was developed for modern low-carbon and HSLA steels, where CE(IIW) tends to overstate the risk.

Which one governs

The convention this calculator follows — and the one used in METALLAI's classifier — is CE(IIW) above 0.15 % carbon, Pcm below it. Both are always shown, because on a borderline steel the disagreement between them is itself information.

Weldability bands

CE(IIW)ReadingUsual practice
≤ 0.40Good weldabilityNormally weldable without preheat
0.40 – 0.50ModerateLow-hydrogen consumables; preheat 50–100 °C often advisable
> 0.50Poor weldabilityPreheat above 150 °C normally required; consider PWHT

Separately, Pcm above 0.35 indicates high susceptibility to hydrogen-assisted cold cracking regardless of what CE(IIW) says.

This is a screening index, not a welding procedure. Carbon equivalent indexes only how readily the heat-affected zone forms hard martensite — one of the three conditions for cold cracking, alongside diffusible hydrogen and restraint stress. Combined thickness, consumable hydrogen scale, heat input and joint restraint all move the real preheat requirement. Use the band to decide whether preheat is a question at all, then size it with EN 1011-2 Annex C or AWS D1.1 Annex H, and qualify the procedure.

Worked example — AISI 4340

Taking a typical mid-range 4340 at 0.40 C, 0.70 Mn, 0.80 Cr, 0.25 Mo, 1.80 Ni:

CE = 0.40 + 0.70/6 + (0.80 + 0.25 + 0)/5 + (1.80 + 0)/15 = 0.40 + 0.1167 + 0.2100 + 0.1200 = 0.847

That sits well inside the poor-weldability band. In practice 4340 is welded only with substantial preheat — in the region of 250 °C — strictly controlled low-hydrogen consumables, and a post-weld heat treatment. It is a good illustration of why a high-strength quenched-and-tempered steel that is excellent in every other respect can be the wrong choice the moment a weld enters the design.

Composition ranges differ between standards and between heats. Always compute from your own heat certificate; the presets on this page are nominal mid-range values for orientation only.

Questions

What is a good carbon equivalent for welding?
Below about 0.40 CE(IIW), a carbon or low-alloy steel is generally weldable without preheat under normal conditions. Between 0.40 and 0.50, low-hydrogen consumables and a preheat of roughly 50–100 °C are usually advisable. Above 0.50 the steel is considered to have poor weldability and preheat above 150 °C is normally required. These are screening bands: section thickness, hydrogen level, restraint and heat input all shift the real requirement.
What is the difference between CE(IIW) and Pcm?
CE(IIW) weights manganese and the alloying elements heavily and was derived for carbon-manganese and low-alloy steels above roughly 0.15 % carbon. Pcm weights carbon far more strongly relative to the alloying elements and was developed for modern low-carbon and HSLA steels, where CE(IIW) overstates the cracking risk. Use CE(IIW) above 0.15 % C and Pcm below it — this calculator returns both and tells you which one governs.
Does carbon equivalent tell me the preheat temperature?
Not on its own. It indexes how readily the HAZ forms hard martensite, which is one of three conditions for hydrogen-assisted cold cracking. The actual preheat also depends on combined thickness, consumable hydrogen scale, restraint and heat input. Use the band to decide whether preheat is a question, then size it with EN 1011-2 Annex C or AWS D1.1 Annex H.
Does carbon equivalent apply to stainless steel?
No. CE(IIW) and Pcm were derived for carbon, carbon-manganese and low-alloy steels. Austenitic stainless steels do not harden by martensite formation in the same way; their weldability is governed by ferrite number, sensitisation and hot cracking, assessed with a Schaeffler or WRC-1992 diagram. Putting a 304 into a carbon-equivalent formula produces a number that does not mean anything.
What is the carbon equivalent of AISI 4340?
About 0.85 for a typical mid-range composition — see the worked example above. That is firmly in the poor-weldability band, and 4340 is normally welded only with preheat around 250 °C, low-hydrogen consumables and a post-weld heat treatment.

Carbon equivalent is one term of the answer

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