Weld Carbon Equivalent Calculator
Calculate carbon equivalent (CE) and minimum preheat temperature for welding steel.
Uses the IIW formula with C, Mn, Cr, Mo, V, Ni, Cu to assess crack risk.
Carbon equivalent (CE) is a single number that combines a steel’s alloying elements into an estimate of its hardenability and susceptibility to hydrogen-induced cracking (cold cracking) during welding.
The IIW (International Institute of Welding) formula:
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
All values are weight percentages. Carbon is the most potent hardenability element, followed by manganese, chromium, molybdenum, and vanadium in the second group, and the less-effective nickel and copper in the third.
Interpreting CE:
- CE < 0.40: Good weldability, no preheat normally needed
- CE 0.40-0.45: Marginal; preheat may be needed depending on heat input and plate thickness
- CE 0.45-0.60: Preheat required
- CE > 0.60: Very high preheat needed; special procedures required
Minimum preheat temperature. One common empirical formula:
T_preheat = 112 x sqrt(CE - 0.25) degrees C (for CE > 0.25)
The purpose of preheat is to slow the cooling rate after welding, giving dissolved hydrogen time to diffuse out before the heat-affected zone (HAZ) becomes fully martensitic. Cold cracking typically occurs hours or days after welding, not during it.
Other formulas. The Pcm (Japanese) formula weights carbon more heavily and is better suited for low-carbon, high-strength steels:
Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B
This calculator uses the IIW formula, which is standard for structural and pressure vessel steels.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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