dgeesaman
Gold $$ Contributor
I don't know the answer to that but I've often thought that given the imprecise temperature control with flame annealing, empirically (and with a little science sprinkled in) over time it may have just worked out to be a safe Tempilaq indicator temp that yields some softening without the risk of going overboard. Realistically, even using Tempilaq, with flame annealing I'd bet the true case temps well over shoot 750 because of how quickly temps are rising and instantaneous temp reading isn't really how Tempilaq is designed to be used. When I use it inside the case neck it pretty much seems to go immediately from nothing to charred which tells me it's likely well over 750.
Basically, this begs someone to perform flame annealing with proper hardness and microstructure measurements just as AMP did for induction and salt bath annealing. I don't think AMP owes a study of flame-annealing to anyone - they already tested salt bath annealing, which had a reputation for being a highly controllable at-home process.
Has anyone in the flame annealing sphere done the metallography to back up their product/process? (I ask, openly because I'm not seeing any sources that go back to hardness in the cross-section)
David