Last updated: Jun 05, 2024

Carbon Equivalent Calculator

Q: At what carbon equivalent value does preheating of steel before welding become necessary?

Preheating steel before welding may be necessary if the carbon equivalent is between 0.4-0.6 . Preheating is compulsory if the carbon equivalent is above 0.6 .

Created by Krishna Nelaturu

Krishna Nelaturu

Krishna holds a Master's degree in Applied Mechanics and never shies away from asking questions and digging deeper. He has two years of experience in steel castings and a particular fascination for vehicle dynamics. For his thesis, Krishna developed a new optimization method to reduce squeak and rattle in premium cars. He is passionate about mathematics and physics and constantly wonders about our place in the Universe. He also loves stories and storytelling and hopes to write a book someday. See full profile

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Table of contents

Carbon equivalent formulae for steel Example CE calculation How to use this carbon equivalent calculator FAQs

Our carbon equivalent calculator is here to help you determine the equivalent carbon content in alloy steel based on the composition of different alloying elements. Carbon equivalency makes understanding the behavior of an alloy easier because we understand iron-carbon phases better than other iron-alloy phases.

There is more than one formula for calculating carbon equivalent (CE). In the following article, we shall learn how to calculate the carbon equivalent of steel using the different carbon equivalent formulae.

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Carbon equivalent formulae for steel

As mentioned before, converting the presence of different alloying elements in steel to carbon equivalency makes predicting the behavior of steel easier because the iron-carbon phases are better understood than other iron-alloy phases.

The most common use of carbon equivalent (CE) is to predict the weldability of steel. Hydrogen-induced cold cracking is the most common weld defect in steel, which depends on its hardenability. In higher concentrations, alloying elements such as carbon, manganese, chromium, silicon, molybdenum, vanadium, copper, and nickel increase the hardness of steel and decrease its weldability.

The American Welding Society (AWS) recommends the following carbon equivalent formula:

\footnotesize \begin{split} \rm CE = C &+\rm \frac{Mn + Si}{6} + \frac{Cr + Mo+ V}{5}\\[1em] &+\rm \frac{Cu + Ni}{15} \end{split}

where:

$\rm CE$ — Carbon equivalent of the steel as a weight percentage according to the AWS recommended CE calculation;
$\rm{C}$ — Weight percentage of carbon in the steel;
$\rm{Mn}$ — Weight percentage of manganese in the steel;
$\rm{Si}$ — Weight percentage of silicon in the steel;
$\rm{Cr}$ — Weight percentage of chromium in the steel;
$\rm{Mo}$ — Weight percentage of molybdenum in the steel;
$\rm{V}$ — Weight percentage of vanadium in the steel;
$\rm{Cu}$ — Weight percentage of copper in the steel; and
$\rm{Ni}$ — Weight percentage of nickel in the steel.

According to AWS, steel with CE higher than 0.4% has a potential for cold-cracking in the heat-affected zone (HAZ).

The International Institute of Welding (IIW) has adopted the formula proposed by Dearden and O'Neill and is widely used nowadays. It is similar to the AWS formula except for the exclusion of silicon from its CE calculation:

\footnotesize \begin{split} \rm CE = C &+\rm \frac{Mn}{6} + \frac{Cr + Mo+ V}{5}\\[1em] &+\rm \frac{Cu + Ni}{15} \end{split}

The weldability rating for this CE calculation method depends on the steel producer. One such weldability rating is shown in the table below:

Weldability of steel as a function CE.
CE(IIW)	Weldability
Up to 0.35	Excellent
0.36-0.40	Very good
0.41-0.45	Good
0.46-0.50	Fair
Over 0.50	Poor

The Japan Welding Engineering Society (JWES) recommends a critical metal parameter $\rm (Pcm)$ to indicate the potential for weld cracking, given by:

\footnotesize \begin{split} \rm Pcm = C &+\rm \frac{Si}{30} + \frac{Mn + Cu + Cr}{20}\\[1em] &+\rm \frac{Ni}{60} + \frac{Mo}{15} + \frac{V}{10} + 5B \end{split}

where:

$\rm Pcm$ — Critical metal parameter of the steel as a weight percentage; and
$\rm{B}$ — Weight percentage of boron in the steel.

The JWES also has another method for calculating carbon equivalent, given by the formula:

\footnotesize \begin{split} \rm CE = C &+\rm \frac{Si}{24} + \frac{Mn}{6} + \frac{Ni}{40} + \frac{Cr}{5}\\[1em] &+\rm \frac{Mo}{4} + \frac{V}{14} \end{split}

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Example CE calculation

Let us learn how to calculate the carbon equivalent in steel with an example. Consider a steel with the following composition:

Alloying element	Composition (wt %)
Carbon	0.15
Silicon	0.25
Manganese	1.2
Copper	0.01
Boron	0.0001

Substituting these values in the formula recommended by AWS, we get:

\!\footnotesize \begin{split} \rm CE &=\rm C + \frac{Mn + Si}{6} + \frac{Cr + Mo+ V}{5}\\[1em] &\qquad +\rm \frac{Cu + Ni}{15}\\[1.2em] &= \rm 0.15 + \frac{1.2 + 0.25}{6} + \frac{0}{5}\\[1em] &\qquad + \frac{0.01 + 0}{15}\\[1em] &=\rm{0.15 + 0.2416667 + 0.0006667}\\[1em] \rm CE &\approx 0.3923 \end{split}

Similar substitution in the other formulae will yield the results as tabulated below:

CE formula	Calculated CE (wt %)
CE (AWS)	0.3923
CE (IIW)	0.3507
CE (JWES)	0.3604
Pcm	0.2193

How to use this carbon equivalent calculator

Our carbon equivalent calculator is simple to use:

Enter the weight percentage composition of each alloying element in their respective fields.
Ensure you don't leave blanks — if any element is absent in your alloy, enter 0 in its field.
The calculator will automatically determine the carbon equivalent in the following manner:
- Carbon equivalent calculated using the AWS formula is labeled CE (AWS);
- Carbon equivalent calculated using the IIW formula will be shown as CE (IIW);
- Critical metal parameter calculated using the JWES formula is labeled Pcm; and
- Carbon equivalent calculated using the JWES formula is labeled CE (JWES).

FAQs

What is the carbon equivalent of AISI 1018 steel?

According to the IIW recommended formula, the carbon equivalent of AISI 1018 steel is 0.35%. To calculate this value, follow these steps:

Collect data on the maximum allowed composition of alloying elements in AISI 1018 steel: C: 0.20%, Mn: 0.90%, P: 0.04%, S: 0.05%.
Use the values in the IIW formula for carbon equivalent:

CE = C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5 = 0.20 + 0.90/6 + 0 = 0.35
Visit our carbon equivalent calculator to calculate the CE value using other formulae.

What is the weldability of steel with carbon equivalent of 0.40%?

Steel with a carbon equivalent of 0.40% has very good weldability. It can be welded without pre-heating and has meager chances of developing cold cracking.

At what carbon equivalent value does preheating of steel before welding become necessary?

Preheating steel before welding may be necessary if the carbon equivalent is between 0.4-0.6. Preheating is compulsory if the carbon equivalent is above 0.6.

What is the relationship between the hardenability and weldability of steel?

Hardenability is inversely proportional to a steel's weldability. A steel alloy with higher hardenability will have lower weldability and vice versa.

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