The invention relates to a ternary gaseous mixture formed from argon, helium and oxygen, characterized in that it is formed from between 19.5 and 20.5% of helium, between 2.7 and 3.3% of Oi, and argon for the remainder (volume %), and to the use thereof as gaseous protection in a method of electric arc welding of at least one steel part to carbon, using a fusible filler wire. Preferably, the welded parts overlap or cover each other and the rotary arc welding takes place where the parts overlap.