## Carbon Equivalence Formula

## Carbon Equivalence Formula

(OP)

I am trying to get some information on the formula used to determine the Carbon Equivalence that is related to preheat requirements for structural steel welding.

ASTM A6 has a formula that includes terms for the following elements: C, Mn, Ni, Cr, Cu, Mo & V

The AWS code D1.1 & D1.5 has a formula identical to the ASTM A6 formula except it includes a term for Silicon, Si.

Can anyone explain the reason ASTM would not want to include the term for Si in their formula? The AWS formula is slightly more restrictive because of this extra term. However, I am inclined to go with the AWS version since AWS is strictly a welding and fabrication code and not a general materials specification. If you know anything about the ASTM formula or carbon equivalence in general I'd appreciate the information. Thanks

ASTM A6 has a formula that includes terms for the following elements: C, Mn, Ni, Cr, Cu, Mo & V

The AWS code D1.1 & D1.5 has a formula identical to the ASTM A6 formula except it includes a term for Silicon, Si.

Can anyone explain the reason ASTM would not want to include the term for Si in their formula? The AWS formula is slightly more restrictive because of this extra term. However, I am inclined to go with the AWS version since AWS is strictly a welding and fabrication code and not a general materials specification. If you know anything about the ASTM formula or carbon equivalence in general I'd appreciate the information. Thanks

## RE: Carbon Equivalence Formula

There are several versions of carbon equivalent formula's that were developed specific to the families of steel – low carbon low alloy, C-Mn, C-Mn-Si, etc. For example, the CE formula applicable to low carbon steel does contain the Si term, although this contribution has a very small effect on the total CE and subsequent preheat requirements because of the size of the denominator.

For C-Mn low alloy steels, the CE (IIW) formula is generally accepted. The ASTM committee felt that this formula being more readily accepted should be endorsed in A-6.

AWS is responsible for their standard and decides on their use of a CE formula. Since I deal with ASME B&PV code steels, in QW-403.26 Section IX, the CE formula accepted by ASTM A-6 is used.

## RE: Carbon Equivalence Formula

If you could point me to a reference enumerating the steels acceptable to the ASTM A6 formula, that would be a big help. Thanks for everything.

## RE: Carbon Equivalence Formula

## RE: Carbon Equivalence Formula

C + Mn/6 + Cu/40 + Ni/20 + Cr/10 + Mo/50 + V/10

I've never seen Si included in there.

I believe the intent is just to account for trace ammounts of effective carbon present as result of the additional alloying elements. This is important to determine if a steel has high propensity for cracking after welding. The CE threshold may vary for different applications. I typically see maximum allowable value of 0.40 in specifications I work with.

another note worth mentioning, don't use nominal specification values when calculating CE. I typically run this formula using actual values reported on mill certification for the heat of steel that we are welding.

## RE: Carbon Equivalence Formula

C.E. = C% + Mn%/6 + (Cr%+Mo%+V%)/5 + (Ni%+Cu%)/15

## RE: Carbon Equivalence Formula

CE =C+Mn/6 + (Cr+Mo+V)/5 + (Si+Ni+Cu)/15

in section 10.9 and talks to the reason why it's important,

Cheers

Rob