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RyanMark

Annealing Bronze

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Does bronze (specifically tin bronze) need to be quenched after annealing (to soften it)? I've read many times that it does, but this seems to contradict that copper and bronze can only be hardened by cold working. Would heating and letting air-cool leave the bronze workable, just as with quenching? From what I understand, it's the heat that's relieving the stress, so I'm wondering what effect quenching has on the microstructure. Thanks!

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Having done mostly cold forging of brass, bronze(both tin and silicon based), Sterling silver, copper and other silver/copper alloys I have found that if you do a water quench after you get a nice low red color you will end up with a more malleable metal that by just doing an air quench. Nonferrous metals are made softer by annealing and made harder by working. The more you work the metal the bigger the grains grow, when you anneal the heat breaks down these large grains into smaller grains. Must be magic in the water verses the air :blink:

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Work hardening does not grow grains but piles up the dislocations in the crystals.

OTOH annealing can cause re-nucleation of grains if the dislocations are prevalent enough and so can decrease the grain size.

Since elevated temps grow grains cutting the time spent *hot* by quenching helps.

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Thanks Thomas,
I want larger grains so that the material is softer, so I suppose I need to keep it dull red for at least a few minutes. I know that "recovery" happens all at once if there is enough energy stored in the dislocations. Today, I hammered a bronze plate (~17% tin), with a med-light force, and them annealed it, and re-hammered it. I made noticeable dents and bends in the plate, and a very slight reduction in thickness, but no cracks so far. Good sign!

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