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Carbon Equivalent Calculator
Enter steel chemistry to get the IIW carbon equivalent and a plain-language read on weldability and hydrogen-cracking risk — the concept behind preheat requirements on the CWI exam.
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. This is a screening estimate of hardenability and hydrogen-cracking risk — not a substitute for the WPS or governing code, which set the actual preheat requirements.
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How Carbon Equivalent Predicts Weldability
Steel that hardens readily in the heat-affected zone is more prone to hydrogen (cold) cracking, and carbon plus the alloying elements drive that hardenability. The IIW carbon equivalent collapses the chemistry into one number — CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 — so an inspector can gauge risk quickly. A higher CE means a harder, more crack-sensitive microstructure and a stronger case for preheat and low-hydrogen practice.
Treat the result as a screening indicator, not a preheat value. The governing code or the WPS sets the actual preheat and interpass temperatures, factoring in thickness, diffusible hydrogen, and joint restraint that a single number cannot capture. CE tells you why preheat is called for; the code tells you how much.
Frequently Asked Questions
What is the carbon equivalent (CE) formula?
The most common formula is the IIW (International Institute of Welding) equation: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, with all elements in weight percent. It rolls the alloying elements into a single number that estimates hardenability and hydrogen-cracking susceptibility relative to plain carbon steel.
What CE value needs preheat?
As a rough screening guide, a CE at or below about 0.40 is generally readily weldable, 0.40–0.60 shows increasing risk where preheat and low-hydrogen consumables are commonly needed, and above 0.60 indicates high cracking susceptibility that typically requires preheat and strict hydrogen control. These bands are guidance only — the WPS and governing code set the actual preheat.
Does carbon equivalent set the exact preheat temperature?
No. CE is a screening indicator of risk, not a preheat value. Actual preheat comes from the code (for example AWS D1.1's prequalified tables or Annex methods) or the WPS, which also account for thickness, hydrogen level, and restraint. Use CE to understand why preheat is required, then read the required temperature from the code or procedure.
Why do the alloying elements have different divisors?
Each element contributes differently to hardenability, so the formula weights them: manganese is divided by 6, the chromium/molybdenum/vanadium group by 5, and the nickel/copper group by 15. Carbon enters at full weight because it is the strongest driver of hardness and cracking risk.
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