Hi Jon

As a relatively high C Cr-Mo steel, this material will tend to harden when welded. In thin sections this will be less pronounced than in large sections. I am not sure what thickness your roll cages are, but if they are thin enough, you may get away with no PWHT. I know that this type of material is often used in air frames without performing PWHT.

Typically a higher heat input would be more beneficial in ensuring that the material does not harden too severely. As such, GTAW welding will probably give a better result. This will however depend a lot on your welding parameters. I would suggest a relatively high pre-heat. (Around 250°C)

Hope this helps.

Regards
Niekie Jooste
Fabristruct Solutions

From many years of welding 4130 roll cages for Walker Evans,Ivan Stuart,etc,we used mainly tig and most used a rod called super missile rod,but thats expensive and hard to find,you can use tig or mig and dont stress relieve,its best to have an experienced welder weld it,where are you located?

There is a good article at
www.tigdepot.com
and on the Lincoln site

Seems to me that it would be specified if it is for a roll cage, as in racing series has a specific filler. I personally have only tig welded on thin stuff, .035 walled 4130 tubing, and I use just a "mild" steel filler, an ER70-S2 I believe. Reason being, elongation was what the engineer was after, not high strength from a 4130 type filler.

You have to specify your requirements and dimensions. Thickwalled with high yield strength requirements for off-shore or thinwalled without strength requirements for racing frames will give a differrent procedure.
ER 70S-3 or 6 is ok for low strength.
TIG-welding can lead to high dilution% which will have negative influence on thoughness.
Preheating necessary about 200-250 degrees C to avoid cracking and slowly cooling.
Do not use higher heat-inputs because it will soften your HAZ and weld metal (coarse grains).