Equivalent carbon content

The carbon equivalent is a measure for assessing the weldability of steels in materials science.

Definition

The carbon equivalent is a measure for assessing the weldability of unalloyed and low-alloy steels in materials science. The carbon content, and a variety of other alloying elements in the steel for its behavior. To assess the weldability is therefore in the carbon equivalent of the carbon content and the weighted proportion of the elements which are similar affect the weldability of the steel, as would be expected from carbon, combined into a numerical value. Here, a value of the carbon equivalent less than 0.45% implies a good weldability. Higher values ​​require - depending on the processing thickness - pre-heating of the material. From a value greater than 0.65, the workpiece is suitable for welding only with increased effort, as there may be martensite to cold or hardening cracks.

Calculating the carbon equivalent

To calculate the carbon equivalent, there is no universal method.

Commonly used are:

  • Carbon content is more than 0.18 %: CEV = C Mn / 6 ( Cu Ni ) / 15 ( Cr Mo V) / 5
  • For short cooling times and to assess the cold cracking: CET = C (Mn Mo ) / 10 ( Cr Cu) / 20 Ni/40
  • For short cooling times and root welds: PCM = C Si/30 ( Mn Cu Cr ) / 20 Ni/60 Mo/15 V/10 5 B

The alloy components are to be used in percent. In general, the carbon equivalent is specified in the material certificate, so that the user this calculation does not have to make yourself. Under certain circumstances, however, the usability of the specified there CEV for the specific application questionable.

Effects of high carbon equivalents

With increasing carbon equivalent of a variety of problems during the welding of the workpiece are to be expected, including:

  • Hardening and embrittlement of the workpiece in the heat affected zone

And caused by the fact

  • Different types of cracks in the structure

Measures to increase the weldability

  • Preheat
  • Selection of a suitable weld geometry
  • Using appropriate electrodes

Welding of cast

The carbon equivalent is also important for the execution of repair and construction welding of castings, because by this value, the preheating temperature can be determined during welding. For example, leichtlegierte steel castings shall be preheated in a CE value of 0.6 % at 250 ° C in order to weld them without errors. As with the existing steel wall thickness of the welded areas is an important factor even when cast.

Criticism

The carbon equivalent is an auxiliary variable for the weldability dar. However, since this depends on a variety of factors, their exact definition of the material and the type of weld is subject. Thus, the carbon equivalent is not to be regarded as universally valid value, but must be matched to the respective application. For carbon contents of less than 0.18 %, the application of the PCM, it is recommended, for example, in many sources.

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