"Now, I was unaware that anyone welding 4130 in the aerospace industry used anything but VIM melted 4130 filler. The aerostructures companies my employer works with would kick you out of the office if you suggested anything else."

yeah, aerospace is a different category. Aircraft spruce sells the mild rod, EAA teaches it, and it's been done for 100 000s of airframes. Actually it's interesting to hear aerospace is still making airframes out of 4130 tube. That may explain all the secrecy around the F-35.

"One of the biggest misconceptions, and I've said it here before, is the difference between hardness and hardening. A 0.3% carbon steel will harden, and to an appreciable degree with just 0.20% molybdenum in it. ... i assure you that 4130 tube for bike frames doesn't require a 'superquench' at all. I... What it won't have is high hardness. But that's not a problem, indeed, it's beneficial."


When you put it that way, I can see the confusion. Unless the harden-ability allows material levels of hardness who cares whether you heat treat it. It's all good. If your hammers don't cost 300 dollars, and you don't FEA every minor design change (or anything in the whole industry), then as a boatbuilding giant once said to me about epoxy admixtures, "I just don't think you need to take it that far".

I am certainly not suggesting anyone superquench, or anything-quench, a bicycle frame.

"And please, stop with the 'points of carbon'? For my sanity, pretty please? It's just a darned percentage, after all... :-)"

100 points equals 1 percentage point, though possibly not in engineerese. My recollection is that there was a 100% failure rate of engineering students at my University, 10 000 points to you, as far as passing the entry English exam is concerned.