You would be better googling carpenter technology they make the raw materials for Reynolds, we buy ours from a company that believe it or not is the same stuff they make arrester hooks out of and its double the strength of their air hardening
All of em go by the HSLA monicker which is the modern way of saying alloy steel it seems
531 was manganese moly ,a bit like T45 the newer stuff is supposedly better for tig though in all honesty most materials will survive the test regime which is pretty flawed, we have tons of test data now on different frames using different test methods
Its a lot of hype for publicity and a nice sticker, to us engineering types its filed elsewher under a different title
Maybe, but its called marketing and market prescence, ask any cyclist or motorcyclist to name a frame tube material and he is likely to say "Reynolds". Thousands of bums have done thousands of miles on bicycles and motorbikes with frames of Reynolds tube.
If you ask a VTwin bike enthusiast to name an aftermarket engine-he is likely to say S&S, cams-ditto or Crane.
You can have a superior product but if folks don't know about it and /or it has not got a history in the market, they will choose the well known name unless its been shown to have lost its edge I suppose.