Carbon Equivalent for steel, low alloy, C-Mn steel and cast iron


What is Carbon equivalent in welding?

The Carbon Equivalent or C.E. concept is used on ferrous materials, mainly steel (Carbon steel, Low alloy steel, C-Mn steel) and cast iron, to determine different properties of the alloy when more than just carbon is used as an alloying elements. 

In welding, equivalent carbon content (C.E) is used to define the weldability of steel and to know how the different alloying elements influences the hardness of the steel that has to be welded. This is then directly related to hydrogen-induced cold cracking or cold cracking, which is the most common weld defect for steel, thus it is most commonly used to determine weldability. Higher concentrations of carbon and other alloying elements such as manganese, chromium, silicon, molybdenum, vanadium, copper, and nickel tend to increase hardness and decrease weldability. Each of these elements tends to influence the hardness and weldability of the steel to different magnitudes, however, making a method of comparison necessary to judge the difference in hardness between two alloys made of different alloying elements.

There are two commonly used formulas for calculating the equivalent carbon content. One is from the American Welding Society (AWS) and recommended for structural steels and the other is the formula based on the International Institute of Welding (IIW).

The AWS states that for an equivalent carbon content above 0.40% there is a potential for cracking in the heat-affected zone (HAZ) on flame cut edges and welds. However, structural engineering standards rarely use CE, but rather limit the maximum percentage of certain alloying elements. This practice started before the CE concept existed, so just continues to be used. This has led to issues because certain high strength steels are now being used that have a CE higher than 0.50% that have brittle failures.

CE formula

Pcm formula for carbon Equivalent

The Japanese Welding Engineering Society adopted the critical metal parameter (Pcm) for weld cracking, known as Pcm formula.

Pcm formula

CET formula for Carbon Equivalent

The CET formula is based on similar elements to the CEIIW formula with the exception of Vanadium, although carbon is considered to have more significance than the other elements.

CET formula

Relationship between Carbon Equivalent and Weldability of Steel

Carbon equivalent directly affects the weldability of the materials. As the C.E. values increases, the weldability of the materials decreases. Materials with low carbon equivalent offers excellent weldability with minimum precautions. This precautions such as additional preheat, use of low hydrogen electrodes, post heating, etc. increases as the value of C.E. increase.

Below table shows the relationship between C.E. value and material weldability.

Relationship between Carbon Equivalent and Weldability of Steel

To calculate easily and accurately carbon equivalent based on IIW, AWS, Pcm and CET, in one step instantly use our online calculator. Click on the below link.

Online carbon equivalent calculator, CET & CEV calculator (materialwelding.com)

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