Not disagreeing with you but when brazing, the melted brass fuses the base metal parts together and the brass filler rod that melted is still brass. I’ve never taken it so hot to boil the brass but I’ve liquified the steel and it still bonded together and held. The brass that the OP has shown in the picture never melted. My annealing process takes the coloring down the body past the body shoulder junction just like many factory cases. I do this intentionally because the die sizing moves all this and I want it to loose hardness also.
The problem is more when oxygen is allowed to come into contact with the metal without any form of protection
Steel itself will actually do the same thing I am talking about, boil, bubble, become porous,
spit pop and sputter etc. ......if there is no shielding to protect the surface layer.
You ever see someone's welds.... who THINKS they know how to weld
yet it looks like a porous bubbly mess, even though the 2 base metals are fused together?
You can weld and melt steel, stainless, brass Alum. etc... just fine (if there is some form of shielding)
When brazing, you need some sort of flux right?
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And for what it's worth here, you CAN anneal with an oxy/acetylene torch
if you know what you're doing, since the bottles will likely last for years and it is a good somewhat inexpensive manner of doing so since it only takes maybe 3 seconds to get the brass dull red
I just don't recommend it to most people unless they are a Journeyman welder who has years of experience with a Victor and knows how to set and adjust their regulators and most importantly knowing to never adjust the Acetylene past 15 psi since that amount of compression alone can cause combustion.
Much like diesel will self ignite with the right amount of compression/PSI
Acetylene only needs 15 PSI
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Hence why I have said if a person sticks to propane they should not have any problems