Okay, another stupid question

Ian

Notorious member
I tried handling them after a minute or two laying on the towel after the brief base quench. I could pick them up with my bare fingers but can assure you it didn't take long to examine them! They were still pretty hot on both ends, so I wouldn't be surprised if these don't reach maximum hardness on the base and may be harder on the noses than otherwise. I'll test them again tonight and see what's happening. So far the noses of the big HP bullets are harder than the air-cooled control bullet tested, but the other bullet noses of the long, skinny .30 cal. ones hadn't quite reached the air-cooled hardness after 23 hours.
 

popper

Well-Known Member
Thermal conduction is directly related to length so the 30 cal gives a length (radii) of 0.150, keep about 1/4" from nose and body should harden. Probably 5-6 sec for 1" long 30 cal. Steam is an insulator so you need some extra time after the sizzle.
 
A

AMTom

Guest
the key to heat treating and quenching a lead alloy is the quench.
it is the fast cooling that makes them hard.

This is why the core of heat treated bullets will NOT be the same hardness throughout after heat treating, as Ian has observed. The same is true of steel. It's impossible to cool the inside as quickly as you cool the outside.
 

Rick

Moderator
Staff member
Logic would say so huh? The metals industry disagrees with you though. Think I'll stick with what the PhD's have to say on the subject.

Lead and steel are two different metals and do not have the same characteristics. Steel is surfaced hardened, lead is not.
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Brad

Benevolent Overlord and site owner
Staff member
I don't have any proof but I can see where a large diameter bullet could have a slightly softer core. A 45-50 cal bullet will have a core that does cool a little slower than a 30 cal bullet.
How much difference it makes I don't know. I also have no idea how to test it as I would worry that any method I know of to get to the center would lead to work softening.
Maybe we could get Bill, our resident ME, to do some heat transfer numbers?
 
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AMTom

Guest
So, since the metal's distance from the coolant is irrelevant, and all of the metal will achieve the exact same hardness, then we have the answer!
Heat treating could never make a bullet with varied hardness!
Thanks to those doctors, there is no need to test what really happens!
 

Brad

Benevolent Overlord and site owner
Staff member
Steel is not an element like iron or lead.
Ah, but steel is largely iron with a few other elements added in. An awful lot like our largely lead bullet with a few other elements added in.

I don't think we get a thin skin per se but a gradient of hardness in larger bullets. The real question is how steep a gradient and how relevant is it?
 

Brad

Benevolent Overlord and site owner
Staff member
There are obvious differences of opinion on the matter of hardening bullets thru quenching. We may just need to agree to disagree.

This isn't directed at any one person but rather all who post on the forum. Let's not go down the road other forums have and allow specific differences of opinion to create factions and discontent.
 

fiver

Well-Known Member
it's hard to wrap your head around.
what makes sense to me and many others just seems wrong from how I know it should be.

but then again they say you can't go faster than the speed of light either.
 

358156 hp

At large, whereabouts unknown.
Long ago it was said that mortal man could never survive the brutal forces of traveling 100 MPH.
 

Hawk

North Central Texas
When I was younger, I wasn't mortal.
Now, I seem to be getting more mortal every day!
 

Rick

Moderator
Staff member
When I was younger, I wasn't mortal.
Now, I seem to be getting more mortal every day!

No kiddin huh? I was well above mere mortals and bullet proof, these days it would be nice to get back up to mere mortal. :confused:
.
 

popper

Well-Known Member
Lead hardening is done by 2 methods, precipitation and solution hardening. Both involve adding a different material. Precipitation involves the liquid/solid transition where solution hardening is a super saturated mixture that gets frozen in place. Pouring can be both, H.T. is the second. You pour a 700F melt into a 400F mould, wait 4-5 sec for hardening. 2F/0.001 distance, ~ the same delta T for quenching (heat flow is linear and the thermal resistance of lead is quite low). The steam from a water quench lasts about 1/2 sec and IS an insulator, also expands and pushes cold water away from the boolit. Quenching a boolit is just like discharging a capacitor through a resistance - Ohms law. exponential decay.
 
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358156 hp

At large, whereabouts unknown.
Lead hardening is done by 2 methods, precipitation and solution hardening. Both involve adding a different material. Precipitation involves the liquid/solid transition where solution hardening is a super saturated mixture that gets frozen in place. Pouring can be both, H.T. is the second. You pour a 700F melt into a 400F mould, wait 4-5 sec for hardening. 2F/0.001 distance, ~ the same delta T for quenching (heat flow is linear and the thermal resistance of lead is quite low). The steam from a water quench lasts about 1/2 sec and IS an insulator, also expands and pushes cold water away from the boolit. Quenching a boolit is just like discharging a capacitor through a resistance - Ohms law. exponential decay.

Got a version for those of us who only speak english?
 

popper

Well-Known Member
Ok,English version.
1) you can't harden pure with heat - it's lead. 2) you can't measure the hardness of the inside cause anything you do to get to the inside softens it. OK? Some thermal conductivity - basically speed of cooling - Pb=20, steel=30 ,Cu=220, Sb=10, Al=120, H2O= 0.3, steam=0.09. 3) lead alloy doesn't freeze at the solidus temp, it bounces back and forth between liquid/solid and makes 'layers of different %s of lead/impurities called Precipitation hardening. The % is called the saturation amount. Sn & Sb tend to 'glob' or pool in these areas. Haven't found any reliable source but IMHO, As is primarily a grain refiner for Sb. Impurities (Cu/As/Cd, etc.) at or below the saturation level tend not to pool. Above the saturation %, they can be frozen into place with rapid cooling. Sb & Sn tend to accumulate in dendrites (like icicles) in the solid alloy, hence the brittleness of high Sb alloy - big chunks that break easily. Cu solubility at room temp is 0.3% but by RAPID quenching, it can be up to 6% (at. wt.) without pooling.
That help?