Many applications, primarily those that involve welding, have a “carbon equivalent” requirement. The carbon equivalent, or CE, is a number generated from an equation that relates alloying elements to a percentage of carbon.
In steelmaking, the properties of the steel are determined by many inputs. Cooling rate, carbon percentage, alloying elements, and many other variables affect the steel’s characteristics. Metallurgical research allows us to predict the microstructure given the carbon content and temperature, but adding alloying elements can greatly alter the results.
This is a problem for applications that require rapid heating and cooling, such as welding. If the steel is too hard, it is likely to crack after it’s been welded. The steel can be heat treated before and after welding to prevent cracking, but how do you decide which steels needs to be heat treated if they are heavily alloyed and you cannot predict their characteristics?
Because we know how plain carbon steels are likely to react to welding, we needed a method to relate alloyed steel to plain carbon steel.
Enter the CE:
The CE equation allows us predict the hardness of an alloyed steel based on its plain carbon steel equivalent. If the CE is 0.35% or below, the risk of cracking after welding is low. Above 0.35%, and especially above 0.40%, heat treating may be necessary.
More CE formulas exist, and many with increasingly detailed equations. As the range of steel products expands and our research continues, more specific equations are needed to better predict weldability.