Queendom Tools

Carbon Equivalent Calculator

For metallurgists and welding engineers who must report a carbon equivalent from a mill certificate, this page gives the two formulas that matter — IIW CEV for general structural steels and the Ito-Bessyo Pcm that low-carbon steels actually need — from one set of composition numbers.

This tool computes the IIW Carbon Equivalent (CEV) and Ito-Bessyo Pcm values based on the percentages of alloying elements. These calculations are critical for assessing the weldability of steel, with the Ito-Bessyo Pcm being particularly suited for low-carbon steels. The dual-formula weldability check uses IIW CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 and Ito-Bessyo Pcm = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B.

Carbon Equivalent Tool

CEV (IIW)

0.000
C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Pcm (Ito-Bessyo)

0.000
C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B
Note: Pcm is generally suited for low-carbon steels (C below about 0.11%). Preheat determination also depends on factors like thickness, hydrogen level, and restraint (as per AWS D1.1 Annex H, EN 1011-2). Therefore, this tool does not provide weldability classes or preheat recommendations.

How to Use This Calculator

  1. Copy each element's percentage from the mill certificate into its own field (C, Mn, Cr, Mo, V, Ni, Cu, Si, B).
  2. Leave any element not reported on the certificate blank — it is read as 0 wt %.
  3. Watch the CEV (IIW) readout and its substituted terms update as you type.
  4. Read the Pcm (Ito-Bessyo) readout alongside it, using it where carbon is below about 0.11%.
  5. Note that neither number on its own fixes a preheat — thickness, hydrogen level and restraint still have to be considered.

FAQ

Q: What is the difference between CEV and Pcm?
A: CEV (IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 and is the general structural-steel formula; Pcm (Ito-Bessyo) = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B and suits low-carbon steels, i.e. carbon below about 0.11%.
Q: Why does this carbon equivalent calculator not give me a preheat temperature?
A: Because preheat depends on thickness, hydrogen level and restraint as well as composition (AWS D1.1 Annex H, EN 1011-2); the tool reports CEV and Pcm and deliberately assigns no weldability class.
Q: How is boron handled in the carbon equivalent formula?
A: Only the Ito-Bessyo Pcm includes boron, as the term 5B — with B entered in wt %, a boron level of 0.005 wt % contributes 0.025 to Pcm. The IIW CEV has no boron term.
Q: What if my certificate does not report every element?
A: Enter only the elements the certificate lists; a blank field is treated as 0 wt % in both formulas, so CEV and Pcm still compute from the reported composition.