The Carbon Equivalent Value (CEV) is a calculated parameter used to assess the hardenability and, by extension, the weldability of steel. It expresses the combined effect of all alloying elements on the microstructure as if they were an equivalent amount of carbon.
Common Formula (IIW/IEC formula):
CEV (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
The concentrations of the elements (C, Mn, Cr, Mo, V, Ni, Cu) are inserted in weight percent (%).
Calculation Example for S275JR:
Assume a typical composition: C=0.17%, Mn=1.20%, Si=0.30%, P=0.025%, S=0.020%, Cu=0.20%. (Assume other elements are negligible residuals).
CEV = 0.17 + (1.20/6) + (0/5) + (0.20/15)
= 0.17 + 0.20 + 0 + 0.013
= 0.383 (or 0.38%)
Importance for S275JR:
Predicts Weldability: A lower CEV (<0.40%) indicates excellent weldability. It means that the heat-affected zone (HAZ) adjacent to a weld is less likely to form hard, brittle martensite upon rapid cooling, thereby minimizing the risk of hydrogen-induced cold cracking (HICC). This allows for less restrictive welding procedures (lower or no preheat).
Specification Requirement: While not always explicitly stated in EN 10025-2 for JR grades, many mill internal standards or project specifications for S275JR set a maximum CEV, commonly CEV ≤ 0.40% or 0.44%. This provides an additional guarantee of good weldability.
Procedure Qualification: Welding procedure specifications (WPS) often reference the CEV of the base metal to determine necessary preheat temperatures and interpass temperatures.
Therefore, the CEV is a crucial engineering number that bridges the gap between the steel's chemistry and its practical fabrication performance, especially for welding.