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luober
05-30-2008, 09:12 PM
I know that the annealing of ferrous metals is quite different from non-ferrous metals and here is my question. When hot freshly cast lead bullets are dropped from the mold into water they become harder, but if heated brass case necks are plunged into cold water they become soft? Both lead and brass are non-ferrous metals and they should react the same way, shouldn't they? If not, then how would you anneal a lead bullet? I have been casting and handloading since 1969 and this thought had never ocoured to me until today. Go figure. Please be specific with your reply if you know the answer to this question. Thanks

grumpy one
05-30-2008, 10:25 PM
Copper-based metals, such as brass, are annealed by undoing the work-hardening that has occurred, which only requires making them temporarily soft enough so that internal stresses relieve themselves. After that you could cool them either quickly or slowly, it doesn't matter in terms of stress-relief. In practice you quench them just so that you won't have additional grain-growth or oxidation due to being held at an elevated temperature for more time.

Lead alloys do not work-harden, but some of them do precipitation-harden (mainly, those that contain antimony or arsenic). Precipitation hardening happens during and after cooling, as a result of crystals of other metals forming in the lead matrix. You minimise precipitation hardening by cooling the alloy slowly, thus allowing the matrix to stretch and stress-relieve itself. Thus, unlike copper-based alloys, lead alloys' hardness is sensitive to cooling rate.

You can anneal lead alloys by holding them at an elevated temperature for long enough for existing precipitates to go back into solution, then cooling them slowly. For bullet casting purposes, usually an hour is long enough to hold them at the high temperature, but they need to cool over several hours. If you are using a kitchen oven, just switch it off and allow the bullets and oven both to cool naturally, which usually means overnight.

Firebird
05-31-2008, 03:03 PM
louber

You are a little off in your use of the term annealing.
Heat-treating is using heat (and sometimes also cold) to effect the grain structure (and therefore strength, ductility and hardness) of a metal object.
Annealing is a specific kind of heat-treatment. It is the process that heats, then slowly cools a metal object in order to soften and restore ductility to the object. Annealing never makes a metal harder, it only softens metals.

MtGun44
05-31-2008, 07:39 PM
What the grumpy one said.

Bill

luober
06-01-2008, 11:10 AM
Thank you all who answered this question for me. I had never thought about this before yesterday. It is reassuring and satisfying to be connected to such a wealth of info. Thanks,

luober