Weld Carbon Equivalent Calculator
Calculate carbon equivalent (CE) and minimum preheat temperature for welding steels.
Uses the IIW formula with C, Mn, Cr, Mo, V, Ni, and Cu content to assess weld cracking 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.