The carbon equivalent number for carbon steels indicates the weldability of the steel, in particular, the carbon equivalent is an indicator of the requirement for preheat to achieve ideal weld properties. Carbon equivalent numbers less than 0.40 should not require preheat.
NOTE: This formula is for carbon steels only.
CE = (C + Mn / 6.0 + (Cr + Mo + V) / 5.0 + (Ni + Cu) / 15.0)
CE: Carbon Equivalent, C: Carbon, Mn: Manganese, Cr: Chromium, Mo: Molybdenum, V: Vanadium, Ni: Nickel, Cu: Copper