I have welded chro moly with just the normal set up 75% 25% argon, C02, er70s6 wire. Welding some bike forks to some 1" sch. 40 mild steel tube. To make myself a deer cart. There is a lot of opinions of the use of Mig on chro moly. I've heard that some race teams weld this way. But not sure if that is true or not. Probably shy away from it for critical applications
