The third frame I ever made was for me. Talking about a whole frame from start to finish, not counting the hundred or so tandems I had worked on, as the apprentice at Santana in the '70s. It was a lugless touring frame made with "regular" 531 DB, not superlight but not Tourist gauge either. As in .9 DT and ST, .8 TT, decently light for back then. The first two frames were lugged racing bikes and I was ready to try something different

Instead of doing as I'd been taught (where's the fun in that?), I looked at the filler rod catalog and just ordered the strongest stuff, Allstate #11, which is nickel-silver. Let's call it NS for short. I just used the normal paste flux for brass, whatever we used back then. The fillets were a bear to file smooth because the stuff is very tough to file. I did some multi-day tours, up to a week with full camping gear, often enough on dirt roads, a decent strength test. Then a few years later I sold it to a guy who was going to ride it around the world. I never heard from that guy again, so maybe he died when the frame threw him in a ditch? But I did tell him I'd fix it if it broke, so I hope he'd have told me. I like to think that frame is still out there, being ridden. I can dream can't I?

I've done a bit of brazing with NS since then, and in all that time, I've never heard of cracking while cooling (or at other times).

Paul Brodie, in his Youtube channel, has showed us how he made lugless MTBs BITD, and unless he only recently started using NS, it sounds like that's how he did all of them. What's that, hundreds, or is it thousands? I dunno how prolific he was. But he didn't make the fillet with NS, he only brazed the tubes with NS (some call it "tinning") and then followed that by fillet-brazing with brass. (He calls it bronze, same thing.) Same flux, and I don't think it's NS-specific flux he's using. Obviously he wasn't using SS tubing, so brass was an option. Why then wouldn't he just do the whole joint in brass? Why 2 different fillers on each joint? You'd have to ask him. But I doubt he saw any cracking after the NS brazing step, or he wouldn't have kept doing it.

Yes this is long-winded and somewhat irrelevant since Duane's problem was with thick-wall SS, not thinwall Cr-Mo or 531. I just wanted to point out that NS has been successfully used to make bike frames, and they didn't crack while cooling. So Duane's experience must have more to do with the SS, or maybe the thick wall, or both.