Carbon equivalent calculator

Input the percentages of elements from the mill certificate. The primary output is the IIW carbon equivalent, CE, which is the figure quoted in Australian structural welding practice. The Ito-Bessyo cracking parameter Pcm is calculated alongside it, because on a modern low carbon microalloyed steel the IIW formula on its own overstates the problem.

Nothing you type leaves your browser. This runs in the page, in JavaScript. A mill certificate composition describes a specific heat of steel on a specific job, and none of it is transmitted, stored or logged. Why that matters.

The calculator

Carbon is the only entry that is required. Every other element counts as zero when left blank, which matches a mill certificate that does not report it. Enter weight per cent, so 1.40 per cent manganese is entered as 1.40.

Composition, weight per cent

Carbon (C)
Required, used by both formulas

Manganese (Mn)

Chromium (Cr)

Molybdenum (Mo)

Vanadium (V)

Nickel (Ni)

Copper (Cu)

Additional elements, used by Pcm only

Silicon (Si)
Not used by the IIW formula

Boron (B)
As a percentage: 20 ppm is 0.0020

Result

Updates as you type

Carbon equivalent, IIW (primary): –
Enter a carbon content to see a result.
Pcm, Ito-Bessyo (supplementary): –
The low carbon steel weld cracking parameter. Use it in place of CE when the carbon content is low, typically at or below 0.16 per cent, which covers most modern microalloyed and thermomechanically controlled plate. It is supplementary here: CE is the primary output.

Formula and assumptions

IIW carbon equivalent

CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
The International Institute of Welding formula, and the one the previous AWI calculator used. All values in weight per cent.

Ito-Bessyo Pcm

Pcm = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B
The weld cracking parameter for low carbon steels. Boron enters as a raw percentage multiplied by five, so it dominates quickly: 30 ppm of boron, entered as 0.0030, adds 0.015 to Pcm on its own.

Which one to use

The two formulas answer different questions and they are not interchangeable.

CE, IIW. Derived from hardenability behaviour on the carbon manganese steels of the period. It weights manganese heavily. On a modern low carbon high manganese plate it reads high, and it can call for preheat that the steel does not need.
Pcm. Derived from weld metal and heat affected zone cracking tests on low carbon steels. Weights carbon far more heavily relative to the alloying elements. It is the better indicator below about 0.16 per cent carbon.

Both are indicators of the same underlying risk: a hard, hydrogen sensitive microstructure in the heat affected zone. Neither is a preheat temperature.

Indicative bands for CE

Read these as orientation before you open the standard, and nothing more.

Indicative CE bands, IIW carbon equivalent
CE	Indication
Below 0.40	Generally low hardenability. Preheat rarely required on thin section.
0.40 to 0.45	Caution. Assess section thickness, restraint, hydrogen level and ambient temperature before concluding that preheat is unnecessary.
0.45 to 0.60	Preheat normally required.
Above 0.60	Preheat and controlled hydrogen practice required.

These bands are indicative only. They take no account of combined thickness, joint restraint, the hydrogen scale of the consumable, arc energy, or the ambient temperature at the time of welding, and every one of those changes the answer. Preheat has to be determined from the applicable standard, not from a calculator.

Assumptions

Weight per cent, from the mill certificate. Not ppm, and not the specification maximum. A carbon equivalent calculated from the maximum permitted composition of a grade is a worst case for purchasing, not the number for the plate in front of you.
Carbon is required. Blank elements count as zero, which matches an unreported element. Non numeric or negative entries produce a dash rather than a number.
Product analysis, not ladle analysis, where you have the choice. Segregation means product analysis can sit above the ladle figure, and the heat affected zone responds to what is actually in the plate.
One plate at a time. Welding two grades together means running the calculation on both and working to the more onerous result.

Worked example

A carbon manganese plate with C 0.18, Mn 1.40, Cr 0.10, Mo 0.03, V 0.02, Ni 0.15, Cu 0.20, Si 0.30, B nil.

CE = 0.18 + 1.40/6 + (0.10 + 0.03 + 0.02)/5 + (0.15 + 0.20)/15
= 0.18 + 0.233333 + 0.030000 + 0.023333
= 0.467
band: 0.45 to 0.60, preheat normally required

Pcm = 0.18 + 0.30/30 + 1.40/20 + 0.20/20 + 0.15/60
+ 0.10/20 + 0.03/15 + 0.02/10 + 5 x 0
= 0.18 + 0.010 + 0.070 + 0.010 + 0.0025
+ 0.005 + 0.002 + 0.002
= 0.282

The gap between the two is the point of showing both. CE 0.467 puts this plate in the preheat band. Pcm 0.282 is a modest figure. At 0.18 per cent carbon the IIW formula is the one to work from, and the high manganese is doing most of the work in it, which is worth knowing before anyone argues about the preheat.

How preheat is actually determined

A carbon equivalent is an input to that decision, not the decision.

Structural steelwork. AS/NZS 1554.1 Section 5 sets preheat from combined thickness and the steel type, together with the process and consumable hydrogen level. Work from the table in the current edition of the standard.
Pressure equipment. Preheat and post weld heat treatment come through AS 1210 for pressure vessels and AS 4041 for pressure piping, with the procedure qualified under ISO 15614. Preheat is an essential variable, so changing it is not a site decision.
Recording it. AS/NZS ISO 3834 is the quality system requirement to specify preheat on the welding procedure, control it during welding, and keep the record. A correct preheat that nobody recorded is an audit finding.

If the calculator and the standard disagree, the standard wins.

Disclaimer

AWI provides this calculator as a free resource to the welding industry. Validate the accuracy of any result before relying on it. AWI accepts no responsibility for consequent losses from the use of these resources.