Carbon Equivalent Calculator
This carbon equivalent calculator works out the carbon equivalent value, or CEV, of a steel from its alloy composition, which fabricators use to judge how easily the steel can be welded and whether preheat is needed. It uses the International Institute of Welding formula, the most widely quoted one, which adds the carbon to weighted fractions of the manganese, chromium, molybdenum, vanadium, nickel and copper. You read those percentages straight off the mill certificate or material data sheet, type them in, and the calculator returns a single number along with the contribution from each group so you can see what is driving the result. The idea is that alloying elements behave a little like extra carbon when it comes to hardening the steel as a weld cools, so a higher carbon equivalent means a greater risk of a hard, brittle heat affected zone and hydrogen cracking. As a rough screen, a value under 0.40 is usually readily weldable, 0.40 to 0.60 tends to need preheat and low-hydrogen consumables, and above 0.60 needs preheat, interpass control and often post-weld heat treatment. Treat the number as a guide only: the real preheat requirement also depends on plate thickness, joint restraint, hydrogen level and the welding process, so always follow a qualified welding procedure for structural or pressure work.
A carbon equivalent of 0.335 is below 0.40, so this steel is generally considered readily weldable with little or no preheat. Confirm against the material specification and welding procedure.
Figures are weight percentages from the mill certificate. Actual preheat also depends on thickness, restraint, hydrogen level and process. Estimate only; follow a qualified welding procedure.
How it works
The International Institute of Welding formula is CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, with every element entered as its weight percent. Carbon counts in full because it has the strongest effect on hardening. Manganese is divided by 6, the chromium, molybdenum and vanadium group by 5, and the nickel and copper group by 15, reflecting how much each contributes to hardenability relative to carbon. The three split figures above show those grouped contributions so you can see where a high number comes from. Add them to the carbon term to get the total carbon equivalent.
Worked example
A typical low-carbon structural steel reads C 0.18, Mn 0.80, Cr 0.05, Mo 0.01, V 0.00, Ni 0.05 and Cu 0.10. The carbon term is 0.180. The manganese term is 0.80 / 6, which is 0.133. The chromium group is (0.05 + 0.01 + 0.00) / 5, which is 0.012, and the nickel group is (0.05 + 0.10) / 15, which is 0.010, so the alloying additions total 0.022. Adding these gives a carbon equivalent of about 0.335. Because that sits below 0.40, the steel is generally readily weldable with little or no preheat, though thick sections or high restraint may still call for care.
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