A rush job came in the shop the other day. It was a part made from 4130 chromoly and it was 1-1/4" thick. while thin wall 4130 tubing can be tig welded without a preheat or post heat treatment, ...Thick 4130 requires a preheat in order to avoid hard and brittle areas. Preheating slows the cooling rate and drives off moisture and is needed for high strength low allow steels like 4130 and 4140 in order to avoid cracking and hard brittle zones. | Welding Tips & Tricks