Calculator
Carbon equivalent calculator (CE IIW and Pcm).
Enter the heat or product chemistry in weight percent to get the IIW carbon equivalent and the Ito-Bessyo Pcm side by side, with a note on which index usually suits the carbon level.
What carbon equivalent tells you
Carbon equivalent (CE) turns a steel’s full chemistry into one number that behaves like carbon content alone. Carbon is the main driver of hardenability, so a weld’s heat-affected zone in a higher-CE steel is more likely to form hard, crack-prone microstructure as it cools. Alloying elements push the same way, but less strongly per percent, so each one is divided by a factor before it is added to carbon. Designers, buyers and welding engineers use CE to compare heats, to check a mill certificate against a purchase specification, and as one input to the welding procedure; a steel plant digital twin with heat traceability such as Steel Twin keeps that chemistry joined to the heat’s grade and order. Two formulas cover most searches: the IIW formula and Pcm.
How it is calculated
| Index | Formula (all elements in wt%) | Typical use |
|---|---|---|
| CE(IIW) | C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 | Carbon and carbon-manganese steels with carbon above about 0.12%; quoted on many structural steel certificates |
| Pcm (Ito-Bessyo) | C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B | Low-carbon, microalloyed steels with carbon at or below about 0.12%, such as many pipeline and modern plate grades |
Pcm gives boron a large weight (5 × B) because a few parts per million of boron can raise hardenability sharply. CE(IIW) leaves silicon and boron out. The calculator uses a single split at about 0.12% carbon, as some line-pipe specifications do; near that boundary, use whichever index your product standard or purchase specification names. A missing element is entered as 0, which understates the result if the element is really present, so use the full analysis where you have it.
A worked example (illustrative)
These numbers are illustrative only and are not from any plant or grade. Say a heat analyses 0.16% C, 1.40% Mn, 0.35% Si, 0.10% Cr, 0.02% Mo, 0.03% V, 0.05% Ni, 0.10% Cu and 0.0005% B (the calculator’s defaults).
- CE(IIW) = 0.16 + 1.40/6 + (0.10 + 0.02 + 0.03)/5 + (0.05 + 0.10)/15 = 0.16 + 0.2333 + 0.0300 + 0.0100 = 0.433
- Pcm = 0.16 + 0.35/30 + (1.40 + 0.10 + 0.10)/20 + 0.05/60 + 0.02/15 + 0.03/10 + 5 × 0.0005 = 0.16 + 0.0117 + 0.0800 + 0.0008 + 0.0013 + 0.0030 + 0.0025 = 0.259
Note that manganese contributes more to CE(IIW) here than carbon does, and that Pcm sits well below CE(IIW) for the same heat. The two indices are on different scales, so a CE limit can never be checked against a Pcm value.
Limits, preheat and the standard you work to
This tool does not recommend a preheat or say whether a steel is weldable. Maximum CE values are set by the product standard, grade, thickness and edition named on your order, and preheat depends on thickness, joint restraint, heat input and hydrogen level as well as chemistry. Follow the applicable welding standard and your qualified welding procedure specification (WPS). These formulas are illustrative; confirm the index, the limit and the method with the official standard or your welding engineer.
Where Steel Twin fits
A hand calculation checks one certificate. Steel Twin keeps each heat’s lab chemistry joined to its grade, sales order, slabs and coils, so a chemistry index can be checked against the order as soon as the lab reports and any hold carries the heat’s full history. Read how that chain works in heat genealogy from charge to coil, and what to do when a heat misses its grade in quality holds: re-treat, regrade or divert.
Questions
How do you calculate the carbon equivalent of steel?
Use the IIW formula: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, with every element in weight percent from the heat or product analysis. For 0.16% C and 1.40% Mn with small residuals, CE is about 0.43.
What is the difference between CE(IIW) and Pcm?
Both turn chemistry into one hardenability index. CE(IIW) suits carbon and carbon-manganese steels above about 0.12% C; Pcm, from Ito and Bessyo, suits low-carbon microalloyed steels at or below about 0.12% C and adds silicon and boron. They are on different scales and cannot be compared directly.
What is a good carbon equivalent for welding?
There is no single number that suits every steel. The maximum CE is set by the product standard, grade, thickness and edition named on your order, and preheat also depends on thickness, joint restraint, heat input and hydrogen level. Follow the applicable welding standard and your qualified WPS, and confirm with your welding engineer.
Why does boron count five times in Pcm?
Because very small boron additions, a few parts per million, raise hardenability strongly in low-carbon steels. Pcm weights it as 5 × B so that effect shows up in the index; CE(IIW) leaves boron out. Enter boron in wt%, so 5 ppm is 0.0005, or the Pcm result will be badly overstated.
See it on your own data. Steel Twin — Every heat, traced to the coil. Book a 30-minute working session with an engineer.