Annealing - What the..!

[303Guy]

I oven annealed a few boolits of unknown pedigree. (My excellent record keeping is such that I have no idea what went into any of them!)[smilie=1: Why would some darken and some not? Some boolits seem have actually gotten harder! Of one lot, some darkened, some didn't but the hardness seems the same. I need these things to get softer.

http://i388.photobucket.com/albums/oo327/303Guy/OvenAnnealedBoolits.jpg

[Mk42gunner]

Different alloys?

Different levels of oxidation?

The ones that seem to have gotten harder really doesn't make sense, to me.

As to the record keeping, I have a small pile of harder than WW,an equally small pile of softer than WW, then there is the rest. One of these days I need to actually get busy and mark them; I even have the metal stamps to make a durable mark...


Robert

[lwknight]

I think the unknown answer is in the unknown question.

[303Guy]

Well, I wasn't sure what question to ask. Anyone able to explain? Why would oven heating to near slump point - three samples actually had some slump - then cooling by simply switching off the oven and waiting?
One of the previously fairly soft boolits that had some slump has actually hardened considerably. It also darkened.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-733F.jpg

[sagacious]

...
One of the previously fairly soft boolits that had some slump has actually hardened considerably. It also darkened.
Any substance on the lead--such as traces of swage lube-- may darken as the lead is heated.

What were the actual hardness measurements? First you state that some seem harder, and some seem the same, then you state that one has actually hardened. It sounds as though no measurements were taken. Are you guessing as to what the hardness is/was/should be? That makes it very difficult to quantify the changes, and leads to all sorts of mysterious analyses. Good luck.

[303Guy]

I do have a simple hardness measuring system. It involves placing the boolit between the sharp edges of a digital vernier, setting it to zero then giving it a squeeze between finger an thumb. It does give a fairly consistant result but I havent attempted to relate it to BHN or anything. It's not a very linear measurement but helps me compare and assess the hardness. For example, 50-50 Lino-lead gives me a zero reading and the softest I've tested gives me a reading of -0.35mm (-.0138"). Not at all scientific but it's all I've got for now. Normally (or previously) I've been able to soften boolits from -0.15 to -0.25mm. At -0.25mm they work quite well in the test tube and in the field. On this system, the boolit that showed some slump gave me a reading of zero! It started out at about -0.15mm. It had been swaged.

My first thoughts were that surface contaminants were responsible for the colour change but now I'm not sure. I'll do a re-test.

I have no idea which is which and only a vague idea of what's in them. They can't be all bad.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-574F.jpg Load development - fired into sand. Same batch.

[lwknight]

I don't know much regarding your question but, those inside out boolits are awesome!

[sagacious]

It had been swaged.
303Guy,
I reckon you've got the answer to your second question right there.

Lead work-softens with cold working. Thus, the hardness of swaged lead alloy does not give an accurate reflection of the hardness of it's chemical composition as measured in the as-cast condition. It has been mechanically softened.

When it's heated to the recrystallization temp, lead alloy will harden or soften to the extent that it's chemical composition and cooling rate allow. In your example, slow cooling gives full anneal of that specific alloy, but it cannot soften more than that. Annealing means the alloy returns to the un-worked condition specific to that alloy, which may be softer or harder than the metal before annealing-- because some metals work harden, and some work soften.

So, soft(ish) swaged lead bullets become hard(er) after heating. This is the same mechanism that causes roofing lead, sheet lead, pipe lead, any rolled or extruded lead product etc, to display increased hardness after melting and pouring into ingots-- the material returns to it's as-cast hardness.

Good luck, and good shooting. :drinks:

[JonB_in_Glencoe]

sagacious,
thanks for the info...very helpful to me in my understanding of annealing and working metal.
although I have my feet wet, I'm still quite new to all this bullet casting and swaging.
Jon

[lwknight]

Some stuff that could be in mystery alloy could just be harder than lead and will never get as soft as lead. actually not many metals can get soft like lead but many metals can harden up a lead alloy. Worked or not worked. It could go either way.

[sagacious]

Some stuff that could be in mystery alloy could just be harder than lead and will never get as soft as lead. actually not many metals can get soft like lead but many metals can harden up a lead alloy. Worked or not worked. It could go either way.

Please allow me to offer a slight clarification and correction. All primary binary alloys of lead are harder than pure lead. Any metal alloyed with pure lead will increase it's hardness-- there is nothing one can add to make lead softer than it's pure form.

To the best of my knowledge, hardness change upon annealing cannot go either way without prior cold working. If the alloy was not cold-worked, protracted annealing offers no control over crystal grain size, and thus no strengthening can occur. No precipitation hardening can occur, because lead and it's alloys age-soften. Cast quenched lead alloy will get softer upon protracted annealing. So, non-cold-worked lead alloy cannot get harder upon annealing.

Regards, and good shooting. :drinks:

[303Guy]

Yes! That all makes sense now. Thanks sagacious. Those as cast boolit appeared to harden on 'annealing' would likely have have not been in their natural state due to casting effects in the mold. I only found out about age softening from this forum. I had some fairly hard boolits I had case two and a half decades ago that were quite soft when I pulled out of storage - that had me baffled at first! (Thought I was losing my memory!):mrgreen:

[sagacious]

303Guy,
Glad I could help. Thanks for sharing your observations with us. This was an interesting exercise is practical metallurgy! :)

[lwknight]

Sagacious , you say that stuff pretty good.
Sorry , I don't always say things trhe way that I'm thinking them.
And I don't understand everything that I know on some things.

[sagacious]

LWKnight,
No worries at all, I wasn't trying to take you to task or anything. I know you are on top of it, I just wanted to clarify if possible.

Sometimes too much explanation is no good either. It's hard to balance it and get it just right, and I certainly cannot claim to get it right anywhere close to every time.

Regards as always, and good shooting! :drinks:

[Marlin Junky]

303,

I kinda breezed through this... did you mention your annealing temp. I've found that higher Pb content alloys will develop a color cast when "baked" at over 450F.

MJ

[303Guy]

Marlin Junky

I had the oven set to max of 270 Celcius (518 F). There were three boolits with some slumping and one that bent without any surface melting.