in welding, equivalent carbon content (c.e) is used to understand how the different alloying elements affect hardness of the steel being welded. this is then directly related to hydrogen-induced 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).