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.
[3] 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.
The following carbon equivalent formula is used to determine if a spot weld will fail in high-strength low-alloy steel due to excessive hardenability:[2] Where UTS is the ultimate tensile strength in ksi and h is the strip thickness in inches.
[2] A special carbon equivalent was developed by Yurioka,[7] which could determine the critical time in seconds Δt8-5 for the formation of martensitic in the Heat Affected Zone (HAZ) in low-carbon alloy steels.