Materials
How to weld 4130 chromoly
Quick answer
To weld 4130 chromoly: use TIG with ER80S-D2 filler, filler matched to the parent metal (ER80S-D2, or ER70S-2 for less critical tube work), and prepare properly — acetone wipe, clean tungsten, tight fit-up. The key adjustment vs mild steel: similar to mild steel; control heat input to protect the HAZ.
Process and filler
Process: TIG with ER80S-D2 filler. Filler: ER80S-D2, or ER70S-2 for less critical tube work. Roll-cage and motorsport tube in Australia: preheat 150–200°C on thick sections and follow the rulebook for post-weld conditioning
Preparation
Acetone wipe, clean tungsten, tight fit-up. Fit-up matters more than most beginners expect: a gap you can see daylight through is a gap the filler has to fill, at the cost of heat control.
Amps and approach
Set current by thickness as you would for steel, then apply the adjustment: similar to mild steel; control heat input to protect the haz. Run test coupons first — every 4130 chromoly joint tells you loudly when the parameters are wrong.