MarkT wroteCheck out this tiny video on http://www.verlicchi.it/ then chose English and then chose factory. Frame looks familiar.
I always heard from "experts" that the factory Works frames were tig welded and the replacement corse frames were Mig welded. Looking at the welds on both- they both look Mig welded- and I think Mig welding could OK with 4130
If I remember correctly (way back 40 years or so) you can Normalize (no pre- or post heat treat) Mig OR Tig 4130 and use ER70S-2 (or ER 80D-2) filler metal. In some ways the thick rope-like Mig welds I see on most of the frames make sense if the frames are 4130--because the shallow concave fillets that I often see on many Tig welds have a higher percentage of carbon (dilution with the 4130) and they cool down pretty fast and thus increase the chance of developing brittleness and small cracking . The slower cooling rate of the thick Mig welds could be less prone to brittleness and micro cracking-- but you have to have a good jig.
But---Tony just finished weld training so I bow to his more recent data.
Yes, I am a bonafide EXPERT after eight, three hour sessions!
I asked my welding instructor who also does fabrication for one of our V8 Supercar teams (like NASCAR, but they turn right as well) and he tells me that TIG on mild steel is a harmless pastime (like the bevel frame previously posted) but on 4130 he would NEVER MIG anything requiring a goodly amount of strength. My brother-in-law confirms this, and the cars he makes put out three thousand horsepower (but not for more than about 5 seconds at a time!) Those chassis are all TIG'd 4130 tube and they impact the fence with much regularity and don't bend much.
Neither, however, are clever enough to know the chemistry of why one is better than the other, just experience I guess.
I perused a few close-ups of Corsa bikes. ALL look to be MIG'd. Please show me a photo of one that isn't!!
