DustyMojave wrote:


Figured this deserved a separate thread.

IMHO, 4130 Chromoly really needs to be welded Tig. I know of one person that I would trust to Mig 4130. And that is only because of exactly how we welds. I cannot duplicate his methods, SUPER hot and quick! One of the things that makes Chromoy an issue is the heat affected zone associated with welding. The nice thing about Tig is that that tha HAZ can be minimized.

Mig would be awesome, if you normalized the tubing after the welding process...

I was thinking it should be another thread Mace as I answered Dave's post in the other thread. I was thinking in BodyTech, but OK.
Since I don't see any means to cross reference an individual post in this forum, here are Dave and my answers from there:





I agree with you also MACE in that technique used for MIG welding 4130 is important to the end result. More true than for other welding situations.

Found this tech article on welding Chrome Moly.

Welding Race Cars

Welding 4130 Chrome Moly Steel for Race Cars
During the WW II era 4130 high strength steel was used for some aircraft components. At that time oxy-acetylene was the welding process of choice for many of these items. The preheat and slow cooling inherent with that process made welding the nominal 0.30 carbon steel relatively straight forward (assuming one could oxyacetylene weld!). However with more modern welding process like TIG and MIG, the cooling rates can be much faster and care must be taken to avoid forming high hardness and brittle Martensite on cooling transformation. On heavier sections preheat and post weld heat treatment should be used. With the proper post weld heat treatment strengths of 200,000 psi can be achieved with reasonable toughness by tempering the Martensite that forms in the heat treating process. However when welding race car tubing, preheat is not often used nor are the parts post weld heat treated.

Most of the tubing used for race car construction is referred to as normalized. This refers to the heat treatment and cooling rate the tubing was subjected to in manufacture. Most normalized tubing will range in tensile strength from 100,000 to 115,000 psi. This can be welded with the proper filler metals to achieve similar strengths. Although there are more weldable grades of steel (those with lower carbon content from 0.06 to 0.15) in the 100,000 to 115,000 psi tensile strength range readily available for plate and sheet, 4130 remains a commonly used grade for tubing. Just be sure to take the precautions noted when welding.

The following is extracted from an article I wrote for the American Welding Societies technical journal called "The Welding Journal". It has additional information to that presented in the publication.

Also stated that most inportant is to use feed wire that is proper for Chrome Moly or weld strenght would be in the 70,000 psi range, probably still fine for an 11 car.
www.netwelding.com/Welding%204130.htm
Jeff