Carbon equivalent (CE) is a measure of the weldability of a material, particularly in relation to the heat affected zone (HAZ) during welding. It is a calculation that takes into account the carbon content, as well as other alloying elements that can affect the behavior of the material during welding, such as manganese, silicon, and sometimes other elements like chromium, molybdenum, nickel, and vanadium.
The carbon equivalent is typically calculated using the formula CE = C + (Mn/6) + (Cr+Mo+V)/5 + (Ni+Cu)/15, where C, Mn, Cr, Mo, V, Ni, and Cu represent the percentage of each element in the material. The resulting value is then compared to a threshold value that depends on the welding process and the material being welded.
A high carbon equivalent indicates that the material is more prone to hardening and cracking in the HAZ during welding, which can lead to reduced weld quality and potential failure. This is because higher carbon content and other alloying elements can promote the formation of hard, brittle microstructures in the HAZ that are more susceptible to cracking under the high stresses and thermal gradients of welding.
To maintain good weldability, it is important to select materials with a carbon equivalent that is appropriate for the welding process and conditions, and to use proper welding techniques that minimize heat input and avoid excessive cooling rates that can lead to HAZ cracking. In some cases, preheating or post-weld heat treatment may be necessary to reduce the risk of cracking and ensure good weld quality.