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Equivalent Carbon Content (CE / Pcm)

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The IIW carbon equivalent and Ito-Bessyo Pcm quantify the risk of hydrogen-induced cold cracking (HICC) in the heat-affected zone during welding and directed energy deposition. Both metrics combine alloy composition into a single number that drives preheat requirements.

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IIW Carbon Equivalent

CE_IIW = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
C
Carbon[wt%]
Mn
Manganese[wt%]
Cr
Chromium[wt%]
Mo
Molybdenum[wt%]
V
Vanadium[wt%]
Ni
Nickel[wt%]
Cu
Copper[wt%]

IIW formula per ISO/TR 17671-2. Valid for carbon and low-alloy steels with C > 0.18%. For lower-carbon steels use Pcm.

Ito-Bessyo Pcm

Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B
C
Carbon[wt%]
Si
Silicon[wt%]
Mn
Manganese[wt%]
Cu
Copper[wt%]
Cr
Chromium[wt%]
Ni
Nickel[wt%]
Mo
Molybdenum[wt%]
V
Vanadium[wt%]
B
Boron[wt%]

Preferred for C < 0.18%. Developed by Ito & Bessyo (1968) for low-carbon high-strength structural steels.

Preheat estimate

T_preheat ≈ 350 × √(CE_IIW − 0.25) [°C, when CE > 0.25] T_preheat = 0 [when CE ≤ 0.25]
T_preheat
Minimum preheat temperature[°C]
CE_IIW
IIW carbon equivalent[—]

Seferian empirical formula. Conservative estimate — actual preheat may be lower with hydrogen-controlled processes (low-H electrodes, dry shielding gas). Per EN ISO 13916.

Interpretation notes

AM contextIn LPBF, rapid solidification and the powder-bed preheating effect partially mitigate HICC, but high-CE alloys (CE > 0.6, e.g. H13) still require platform preheating to 150–200°C to prevent delamination and micro-cracking.
DED & WAAMMulti-pass DED builds accumulate heat; monitor interpass temperature to stay above preheat but below overtemper limits. H13 must not exceed 250°C interpass or secondary carbides coarsen.
Applicability limitsCE_IIW was developed for ferritic/martensitic steels. For austenitic stainless steels (316L), the dominant failure mode is hot cracking (Schaeffler diagram, Creq/Nieq), not HICC. For 17-4PH, martensite hardening is the concern.

Sources