Originally Posted by
dsaul
Bromptons are made from chromoly steel. They are brazed because that's just how Brompton has chosen to join them. Chromoly, 4130, 531, 631, 853 and all of the other supersteel alloys used in bicycle frame building can be TIG welded with no heat treating afterward. There are a few BMX companies that heat treat their production frames after welding, but none of the custom framebuilders I know heat treat their steel frames. It's just not necessary to produce a frame whose strength far exceeds the loads placed on it.
Agree, but if the point is to get the excellent tensile, yield, and fatigue strength of 4130 (or whichever is used) post-weld heat treat gets that for you. Is brazing used because it's stronger than a non heat-treated weld? I'd suspect that welding would be stronger. The joints are fillet-brazed, correct?