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Carbon Equivalent (CE IIW, Pcm) and Preheat Estimator

Carbon equivalent is the fastest check of how likely a steel is to cold crack when welded. This calculator computes the IIW formula and Pcm from the mill certificate and gives a rough preheat for planning.

Your numbers

wt %
wt %
wt %
wt %
wt %
wt %
wt %
wt %
wt %
mm

Your results

Carbon equivalent (IIW)
0.45
IIW formula: C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15.
Indicative preheat temperature
150
Degrees C. Confirm with your code method and a procedure qualification.
Pcm (Ito-Bessyo)
0.289
Used for lower carbon steels, C at or below about 0.12 percent.
Indicative preheat by CE band
125
Degrees C. Rough guide only.
Thickness adjustment
25
Degrees C added for thicker sections.

Indicative guide only. Real preheat depends on hydrogen level, restraint, heat input and the method in your code (for example EN 1011-2 or AWS D1.1 Annex). Qualify the procedure by test.

Save results:

Indicative preheat vs carbon (other elements fixed)

Sweeps Carbon (C) from 0.05 to 0.4, holding your other inputs fixed.

Mill certificates inside your ERP

Optional: explore capturing chemistry per heat and linking it to weld jobs.

Optional. The tool and every export work without this. No spam.

How to use it

Take the heat analysis from the mill test certificate and enter C, Mn, Si, Cr, Mo, V, Ni, Cu and B. Add the combined thickness of the joint. The tool returns CE IIW, Pcm and an indicative preheat. Use CE for carbon above about 0.12 percent and Pcm for the low carbon steels.

  • Use heat analysis, not product analysis, if you have a choice
  • Combined thickness is the sum of plates meeting at the joint
  • Boron matters in Pcm for HSLA steels
  • Treat the preheat as a start for a procedure test

The formulas

The IIW carbon equivalent is C plus Mn over 6 plus the sum of Cr, Mo and V over 5 plus the sum of Ni and Cu over 15. Pcm is C plus Si over 30 plus Mn, Cu and Cr over 20 plus Ni over 60 plus Mo over 15 plus V over 10 plus five times B. Higher values mean greater hardenability and a higher risk of hard, crack-prone heat affected zones.

Reading the result

As a rule of thumb, a CE under about 0.35 is readily weldable without preheat in thin sections. From 0.35 to 0.45 caution is needed, especially in thick or restrained joints. Above 0.45 preheat and low hydrogen practice are commonly required. This tool turns that into a rough temperature, which is a planning figure rather than a specification.

Common mistakes

People apply a CE preheat to every joint, ignoring hydrogen level, heat input, restraint and thickness. They also mix the Pcm limit for low carbon steels with high carbon steels, or take chemistry from the wrong heat.

  • Ignoring hydrogen control
  • Wrong heat number used
  • Single plate thickness instead of combined
  • Treating the result as code compliance

Frequently Asked Questions

Which formula should I use, CE IIW or Pcm?

CE IIW is the common choice for carbon and carbon-manganese steels, often with carbon above about 0.12 percent. Pcm was developed for low carbon, high strength steels with carbon at or below about 0.12 percent. Use the one your standard names.

Is the preheat temperature a code value?

No. It is a banded estimate for planning. Codes such as EN 1011-2 and AWS D1.1 give their own methods that include hydrogen level, heat input and restraint. Always confirm by following the code and qualifying the procedure.

Why does thickness raise preheat?

Thicker sections remove heat faster, so the heat affected zone cools more quickly and hardens more. More preheat slows the cooling. Combined thickness counts, so a tee joint of two plates is thicker for this purpose than either plate.

Does it work for stainless or aluminum?

No. Carbon equivalent applies to carbon and low alloy steels. Austenitic stainless and aluminum have different weldability concerns and no carbon equivalent preheat approach.

If material certificates and chemistry live in your ERP or quality system, Netray can help pull them into calculations like this and attach the result to the work order.

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