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Steel Composition: Carbon Equivalent & Pcm

Compare four stated composition-index formulas from entered elemental weight percentages.

Formula & worked example
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How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

With 0.10% carbon, 1.20% manganese and 0.24% silicon, and the remaining listed elements set to zero, the IIW index is 0.30%, the silicon-inclusive index is 0.34%, the WES/JIS-form index is 0.31% and Pcm is 0.168%.

CE IIW = C + Mn/6 + (Cr + Mo + V)/5 + (Cu + Ni)/15; silicon-inclusive CE = CE IIW + Si/6; WES/JIS-form CE = C + Si/24 + Mn/6 + Ni/40 + Cr/5 + Mo/4 + V/14; Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B

Worked example

Enter these known values and leave the other values blank.

Carbon (C): 0.1 %
Manganese (Mn): 1.2 %
Silicon (Si): 0.24 %

Carbon equivalent including Si/6: 0.34 %
IIW carbon equivalent: 0.3 %
WES/JIS-form carbon equivalent: 0.31 %
Pcm composition index: 0.168 %

Assumptions and limitations

Enter weight percent as the percentage number: enter 0.10 for 0.10% carbon, not 0.001. A boron content of 10 ppm is 0.001 wt%. Defaults of zero mean an assumed absence, not an unknown assay result.
These are different empirical composition indices. Select the formula required by the applicable material specification or procedure; the indices are not interchangeable.
The retained input ceilings are C 2%, Mn 14%, Si 0.6%, Cr 27%, Mo 1%, V 0.6%, Cu 2%, Ni 10% and B 0.003%. They are calculator input bounds, not validated application ranges for every formula or steel grade.
The outputs alone do not establish weldability, a safe preheat temperature, heat input, hydrogen control or a qualified welding procedure. Material and procedure requirements need their own assessment.

Common questions

Why do the carbon-equivalent values differ?

Each formula assigns different weights to alloying elements and was developed for particular purposes and materials. For example, the silicon-inclusive expression adds Si/6 to the IIW expression.

Can this replace a welding procedure or material specification?

No. It evaluates the displayed formulas from composition numbers. It does not assess the joint, welding process, restraint, heat input, hydrogen level or required procedure qualification.

References

Bookify replaces rounded-down output ceilings with the exact formula sums at the captured composition limits, so the allowed endpoint does not falsely fail validation.

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