What is/are the hardening mechanisms for lead and it's alloys?

[stephen m weiss]

After reading hundreds to thousands of posts, guides and charts on the topic, when my 17yr old son asked how Antimony and Tin allowed hardening and why quenching improved hardness, I still had to wing it. Of course I told him I was speculating, but I have never heard the slightest metallurgical explanation of how and why this stuff works, just what works and how much it works. I just checked my two old materials books, one just on metallurgy, and not the slightest mention of lead hardening. It's as if it was a military secret.

Based on my edjuamacation and years of heat treating steels, cres, copper, brass, and platinum, as well as doing section microphotography of metal grains, I postulated:

Water dropping stops grain formation by rapidly cooling first by boiling-surfact convection, then rapid convection, propably before the bullet hits the bottom of the water. It also induces substantial residual stress due to the outside cooling hardening first then getting sucked in to the middle as it cools. So the outside is at considerable compressive residual stress while the middle is at even larger residual tensile stress. The middle will be at yield strength, and the outside will be at about half yield strength. Over the next few weeks, the pure lead areas of the grains creep and relieve the residual stresses, much like a tempering operation in quenched steel. Tempering lead at an elevated temperature but not near solution anneal temperature should produce the same result, only much faster. (One reader claims to use 200F for 2 hours to achieve what 4 weeks at room temp will do.) I explained that lead creeps readily at room temperature, meaning that it flows like a fluid, continuously at continuous stress, even low stress. The flow rate should be proportional to stress and exponential to the absolute temperature, or inversely proportional to the difference between lead temperature and melt temperature. I expect that the alloying elements simply provide dispersion strenghthening, thus their linear hardening curves, and simply act as dislocation blockers in the metal matrix. In slow cooling the lead grains tend to push the alloying elements, impurities, to the grain boundaries which is the lowest energy condition. Impurities at the grain boundaries still provide dislocation blocking, but not so well as well dispersed impurities. The residual stresses cause compresive hardness tests to give low values. If a material is already halfway to compressive failure, adding compressive stress just finishes it off, at half the added stress.

Now, you may be thinking, I asked a question but then answered it myself, are you just a braggart or what? Nope, but I always have a pocket of hypothesis I am attempting to disprove about anything I can measure and care about. If someone has a better hypothesis, and I can get them to state it.. it will be my opinion as soon as I can cross test it thoroughly!

So, has anyone got a different hypothesis, or even know of research that has been done?

I am curious that nobody talks about using some of the age hardening techniques that work so great in steel, copper, titanium and platinum, producing yield strengths of 30x the pure metal stength, so about 100ksi for lead. No body talks about different close packing phases, like face centered tetrahedrons or body centered tetrahedrons. Perhaps they exist at too low a temperature to be useful.

[longbow]

This is about the best I have found so far:

http://www.lasc.us/HeatTreat.htm

I have a publication "Lead and Lead Alloys" by The Consolidated Mining and Smelting Company of Canada Limited that provides information, largely for uses of lead, but references both:

- "Lead in Modern Industry" by Lead Industries Association

http://www.amazon.com/Lead-In-Modern-Industry-Author/dp/B000JC9DSO
http://books.google.ca/books/about/Lead_in_modern_industry.html?id=vdPQAAAAMAAJ&redir_esc=y

and

- "Metals Handbook" by The American Society for Metals:

http://www.ebay.ca/itm/Metals-Handbook-Desk-Edition-1985-/281470068927?pt=US_Texbook_Education&hash=item4188ec68bf
https://www.scribd.com/doc/50889588/Metals-Handbook

I do not have either.

My take on quenching antimonial lead is simply that fine grains structure is formed in a eutectic alloy. The faster the quench the finer the grain... to a point. The finer the grain, the harder the alloy.

For interest:

A table from "Lead In Modern Industry" shows hardness of cast lead/antimony alloy increasing in hardness to 15.3 BHN at 145 antimony (as cast air cooled).

A table from "Metals Handbook" shows an 8% antimony/lead alloy will reach 26.3 BHN when heated to 456 degrees F then quenched and aged 1 day. Tensile strength is listed at 12,500 PSI which appears to be the strongest lead/antimony alloy... at least listed.

Both tables are published in "Lead and Lead Alloys"

That's about all I've got.

Longbow

[stephen m weiss]

OMGosh, you just reminded me, I have a Metals Handbook, Vol 1, 1961, that was being tossed out when some big, corrupt, East Coast corporation took over my mom and pop high tech firm that was 2 miles from my surf break.. still sore about that one...

Anyway.. I will check that out. It's memory was stored in a diff section of my brain from the core metallurgy stuff. It was in the "Stuff tossed out by the evil empire" section lol. I havent done real heat treating stuff since, just been doing automation engineering.

[stephen m weiss]

Interesting: The metals handbook lists no quenched values for 1% and 6% Sb but does for 4% and 8%. While the unquenched values are pretty linear with alloy content..the quenched values go to about 12ksi and not much higher, 11.67ksi for 4% and 12.5ksi for 8% Sb. This argues that it is much more than dispersion hardening.

[Cowboy_Dan]

"Now, you may be thinking, I asked a question but then answered it myself, are you just a braggart or what? Nope, but I always have a pocket of hypothesis I am attempting to disprove about anything I can measure and care about. If someone has a better hypothesis, and I can get them to state it.. it will be my opinion as soon as I can cross test it thoroughly!"

Now, that is what science is all about. A process of conjecture and refutation. I don't have any novel hypotheses to offer, but as a philosopher of science I can say your method of discovery is sound. Next step is to try to empirically falsify your hypothesis. It is only a good as your attempts to prove it wrong.

[stephen m weiss]

Haha.. yes of course I am trying that... If I were correct, then I should be able to quench from 455F to boiling water, let the pot of water air cool in several hours, and have already age hardened characteristics. I am just trying to figure out which cooking pot gets sacrificed as the quench pot.. my home depot bucket wont work! I will put crumpled alum foil on the bottom of the boil pot to catch the bullets softly and turn the pot off and allow boiling to cease so the metal pot bottom is no more than 212F.

It would please me to not have to wait days or weeks to test my bullets. I am having real issues getting flaw free 223 casts and dont know what flaw size will cause what inaccuracy at what hardness and pressure curve.

[BattleRife]

I don't think it has anything to do with any military secrets, it's just that in the vast majority of applications the softness of lead is considered a virtue or an irrelevance, and the users have little reason to pursue hardening the material. I don't recall the metallurgy of lead being mentioned even once in my four years of education as a metallurgical engineer. Digging through the most comprehensive of the textbooks I have in the room with me now (Physical Metallurgy Principles, 3rd Ed., Reed-Hill & Abbaschian 1992) the index shows only one mention of lead, and that is to illustrate an unusual mechanism of solidification segregation*. Since hardening of lead was of interest in only a couple of industries I would think the most probable source of literature on the topic would come from old research papers catering to battery and type printing industries. Unless the lead makers themselves put out some reference information to help spur development work.


*- For those interested, it seems there is a form of gravitational macrosegregation that occurs in some alloys, best illustrated by the hypereutectic lead-antimony system. As the melt drops below the liquidus temperature, alpha-antimony crystals begin to form and deplete the liquid of antimony until the remaining liquid has a eutectic composition, at which point the melt begins to freeze. But the antimony crytals have a much lower density than the eutectic liquid and float to the top of the melt, so that if cooling is sufficiently slow the resultant ingot exhibits a heterogeneous mix of dispersed antimony crystals in a eutectic lead-antimony matrix at the top, and a near homogeneous eutectic composition at lower depths.

[BattleRife]

As to actual mechanisms, I believe any sort of strain hardening can be discounted because lead anneals at room temperature. I had always assumed that precipitation hardening was regularly used industrially because bullets made from wheel weights can be hardened by heating and quenching (to form a solid solution, I figured) then allowing to sit around for several days (giving time for fine microprecipitates to form in the crystals that impede dislocation motion and strain the crystal lattice). What little benefit tin provides can probably be attributed to solid solution strengthening.

But these are all just guesses. Maybe I'll take a few minutes to cast about the interweb and see if I can come up with anything.

[C. Latch]

http://i78.photobucket.com/albums/j85/clatch/Mobile%20Uploads/80A652CE-2C90-45AE-A8B7-3A49DE318BB6_zpsipz0pfnm.jpg (http://s78.photobucket.com/user/clatch/media/Mobile%20Uploads/80A652CE-2C90-45AE-A8B7-3A49DE318BB6_zpsipz0pfnm.jpg.html)

[C. Latch]

Lyman cast bullet handbook 4th edition

[BattleRife]

Here is what we are looking for.

Taken from http://www.keytometals.com/Article88.htm on Nov. 11, 2014. Highlighting in orange added by me.

Heat Treating of Lead and Lead Alloys

Abstract:
Lead is normally considered to be unresponsive to heat treatment. Yet, some means of strengthening lead and lead alloys may be required for certain applications. Lead alloys for battery components, for example, can benefit from improved creep resistance in order to retain dimensional tolerances for the full service life. Battery grids also require improved hardness to withstand industrial handling.

Lead is normally considered to be unresponsive to heat treatment. Yet, some means of strengthening lead and lead alloys may be required for certain applications. Lead alloys for battery components, for example, can benefit from improved creep resistance in order to retain dimensional tolerances for the full service life. Battery grids also require improved hardness to withstand industrial handling.
The absolute melting point of lead is 327.4°C (621.3°F). Therefore, in applications in which lead is used, recovery and recrystallization processes and creep properties have great significance. Attempts to strengthen the metal by reducing the grain size or by cold working (strain hardening) have proved unsuccessful. Lead-tin alloys, for example, may recrystailize immediately and completely at room temperature. Lead-silver alloys respond in the same manner within two weeks.
Transformations that are induced in steel by heat treatment do not occur in lead alloys, and strengthening by ordering phenomena, such as in the formation of lattice superstructures, has no practical significance.
Despite these obstacles, however, attempts to strengthen lead have had some success.

Solid-Solution Hardening

In solid-solution hardening of lead alloys, the rate of increase in hardness generally improves as the difference between the atomic radius of the solute and the atomic radius of lead increases. Specifically, in one study of possible binary lead alloys it was found that the following elements, in the order listed, provided successively greater amounts of solid-solution hardening: thallium, bismuth, tin, cadmium, antimony, lithium, arsenic, calcium, zinc, copper, and barium.
Unfortunately, these elements have successively decreasing solid-solution solubilities, and therefore the most potent solutes have the most limited solid-solution hardening effects. Within the midrange of this series, however, are elements that, when alloyed with lead, produce useful strengthening.
A useful level of strengthening normally requires solute additions in excess of the room-temperature solubility limit. In most lead alloys, homogenization and rapid cooling result in a breakdown of the supersaturated solution during storage. Although this breakdown produces coarse structures in certain alloys (lead-tin alloys, for example), it produces fine structures in others (such as lead-antimony alloys). In alloys of the lead-tin system, the initial hardening produced by alloying is quickly followed by softening as the coarse structure is formed.
At suitable solute concentrations in lead-antimony alloys, the structure may remain single phase with hardening by Guinier-Preston (GP) zones formed during aging. At higher concentrations, and in certain other systems, aging may produce precipitation hardening as discrete second-phase particles are formed.
Alloys that exhibit precipitation hardening typically are less susceptible to over aging and therefore are more stable with time than alloys hardened by GP zones. Lead-calcium and lead-strontium alloys have been observed to age harden through discontinuous precipitation of a second phase Pb-Ca and Pb-Sr in lead-strontium alloys as grain boundaries move through the structure.

Solution Treating and Aging

Adding sufficient quantities of antimony to produce hypoeutectic lead-antimony alloys can attain useful strengthening of lead. Small amounts of arsenic have particularly strong effects on the age-hardening response of such alloys, and solution treating and rapid quenching prior to aging enhance these effects. Hardness Stability. For most of the two-year period, the solution-treated specimens were harder than the quench-east specimens. Other investigations have also shown that alloys cooled slowly after casting are always softer than quenched alloys. The alloys with 2 and 4% Sb harden comparatively slowly, and the alloy containing 6% Sb appears to undergo optimum hardening.
Application. Because of the detrimental effect of antimony on charge retention, the effort to reduce antimony contents of the positive plates in lead-acid storage batteries has led to the trend of replacing eutectic alloys with a Pb-6Sb-0.15As alloy. Battery grids made of this arsenical alloy will age harden slowly after casting and air-cooling. However, storing grids for several days constitutes unproductive use of floor space and results in undesirable interruptions in manufacturing sequences.
Although large-scale solution treatment of battery grids might be difficult to justify economically or to achieve without some distortion, quenching of grids cast from arsenical lead-antimony alloys offers an attractive alternative method of effecting improvements in strength. The suitability of quenched grids can be assessed by comparing with the hardness level that battery grids require in order to withstand industrial handling (about 18 HV, the hardness of the eutectic alloy). The alloy containing 2% Sb clearly does not respond sufficiently to be considered as a possible alternative. The 4% Sb alloy, however, attains a hardness of 18 HV after 30 min, and the alloys that contain 6, 8, and 10% Sb could be handled almost immediately.

Dispersion Hardening

Another mechanism for strengthening of lead alloys involves elements that have low solubilities in solid lead, such as copper and nickel. Alloys that contain these elements can be processed so that no homogenization results; most of the strengthening that occurs is developed through dispersion hardening, with some solid-solution hardening taking place as a secondary effect. The resulting structure is more stable than those developed by other hardening processes. Dispersion strengthening also has been achieved through powder metallurgy methods in which lead oxide, alumina, or similar materials are dispersed in pure lead.

[BattleRife]

Lyman cast bullet handbook 4th edition

Definitely appears to be more comprehensive than the trifle of information they printed in my Third edition. Sections 1-4 appear to be primers on materials science so that people can understand sections 5 and 6, which are the meaningful ones. How extensive are those sections?

[cbrick]

This should answer your questions.

Quoted from Dr. Glen E. Fryxell, From Ingot To Target - Chapter 3: Alloy selection and Metallurgy

http://www.lasc.us/Fryxell_Book_textonly2.pdf

Metallurgy of the Cast Bullet

Lead-tin (Pb-Sn)
Which metals do we add to lead to make better bullet metal and why? The first and most obvious need here is to make the alloy harder, but there are other factors that play into this answer as well. Historically, tin was used because it was readily available in pure form, mixed easily with molten lead and contributed desirable properties to both the molten and solidified alloy (castability and hardness, respectively). Tin also increases the hardness of the alloy but does not interfere with the malleability of lead (a key point that we‘ll return to). Tin lowers the viscosity and surface tension of the molten alloy, allowing it to fill out the mould more effectively, resulting in a higher quality bullet. Tin is limited in its ability to harden lead, achieving a maximum hardness of about 16 BHN at 40% tin. These binary lead-tin alloys undergo slight to moderate age softening upon storage (1-2 BHN units), with the harder alloys undergoing more of a change than the softer alloys. The hardness of a binary lead-tin alloy generally stabilizes after about 2-3 weeks. Heat treating binary lead-tin alloys does not provide any change in hardness. At typical lead pot temperatures, lead and tin are infinitely miscible with one another, at the eutectic temperature (361o F) tin is still soluble to the tune of 19%, but at room temperature tin is still soluble in lead at the 2% level, meaning that as the bullet cools down there is significant precipitation of a tin-rich solid solution in the form of granules and needles in a matrix of lead-rich solid solution. It is important to recognize that tin is well mixed in the matrix and it hardens lead by making the matrix itself harder.

Lead-antimony (Pb-Sb)
Antimony on the other hand hardens lead alloys much more efficiently, with only 1% antimony producing a BHN of 10 while it takes 5% tin to do the same, and it takes only 8% antimony to achieve a BHN of 16, as compared to 40% tin. The name "antimonial lead" refers to binary lead alloys with 1-6% antimony, with the higher antimony alloys (i.e. those with >1% antimony) commonly being called "hard lead" in industry. While antimony increases the hardness of lead, it does so by impairing its malleability. At typical lead-pot temperatures (ca. 700o F), antimony is only moderately soluble in lead alloys, and as the temperature drops, the solubility of antimony is markedly lower than that of tin. At the eutectic temperature for a binary lead-antimony alloy (484o F), only 3.5% antimony is soluble (note that this is 123o F hotter than of the tin eutectic temperature, but the antimony solubility is less than 1/5 that of tin). At room temperature the equilibrium solubility of antimony in lead is only 0.44%. The precipitated antimony appears as small rods, at the grain boundaries and within the grains themselves. Electron micrographs of lead-antimony alloys clearly show discrete particles of antimony surrounded by a matrix of lead-rich solid solution. In contrast to lead-tin alloys, lead-antimony alloys age harden, sometimes as much as 50% or more. When these alloys are air-cooled, some antimony is retained in the lead-rich matrix and as a result these alloys age-harden as this antimony continues to slowly precipitate. This usually takes 10-20 days to achieve full effect.

It is important to recognize the antimony hardens lead alloys by a fundamentally different mechanism than does tin. Antimony hardens the alloy by precipitation of a separate crystalline antimony phase, which reinforces the squishy plastic lead phase that’s in between the hard antimony crystals. These alloys tend to be brittle because the plastic (squishy) lead phase gets its hardness from the reinforcing hard antimony rods. As the matrix gets deformed the brittle antimony rods shear off and the soft metal fails. In the case of the lead-tin alloys, the tin is more uniformly distributed through out the matrix, making the matrix itself harder, so plastic deformation of the alloy is more uniform and progressive, not the slip/shear of lead-antimony alloys.

The following paragraphs f chapter 3 discuss multi-component alloys (Pb/Sb/Sn) and how they work together.

Rick


The quoted article from Key to Non-ferrous Metals is what the article Heat Treating Lead/Antimony/Arsenic Alloys (www.http://lasc.us/HeatTreat.htm) was based on.

[C. Latch]

Definitely appears to be more comprehensive than the trifle of information they printed in my Third edition. Sections 1-4 appear to be primers on materials science so that people can understand sections 5 and 6, which are the meaningful ones. How extensive are those sections?


I found them to have all the information I could ever want on the subject, though, to be honest, some folks might want more than I did.

[oldlincoln]

Maybe my question has been answered and I am too dull to find it, but I want to know how lead / antimony alloys respond to accelerated age hardening. Aluminum alloys are routinely age hardened after solution heat treating in industry. Do lead alloys behave similarly? I would like a stable known hardness right away rather waiting for days or months, if possible. What say ye metallurgists?

[cbrick]

Maybe my question has been answered and I am too dull to find it, but I want to know how lead / antimony alloys respond to accelerated age hardening. Aluminum alloys are routinely age hardened after solution heat treating in industry. Do lead alloys behave similarly? I would like a stable known hardness right away rather waiting for days or months, if possible. What say ye metallurgists?

The age hardening time curve of Pb/Sb alloys is controlled by the percentage of Sb. The lower the Sb the longer for full age hardening. That's why in the Key to Metals paper they state that 2% isn't suitable for industrial use, in the paper they are referring to wet cell battery plates. They state that 6% is suitable.

Lead does not respond the same as aluminum or steel for that matter. That's why those that state that you can case harden lead are wrong. Heat treat steel and you have a surface hardness, heat treat lead and it's the same all the way through. No case hardening of lead is possible.

Rick

[oldlincoln]

Understood. There was mention of a caster that held solution treated bullets at 200° for a few hours and had an increase in hardness. I know that Al7075 will fully age after 24 hours at 375°F. The alloys I am interested in are like 6%Sb ,2%Sn, trace As and the balance Pb.

[cbrick]

I don't know how that could speed up the aging time curve, it's still the same percentage of Sb. By rights that should anneal the alloy, I don't know by how much at 200 degrees but that is how a heat treated Pb/Sb alloy is annealed, heat it up and then let it cool slowly. I can't say it won't work because I've never tried it but I sure don't understand how it could. Perhaps someone with the right equipment would like to try it and report the results.

Rick

[stephen m weiss]

I can sure understand that the antimony rods create hardness, but if there was enough mobility at room temperature to allow the Sb find other Sb and create rods, wouldnt there be massive creep and dimensional instability as well? I find it much easier to believe that room temperature creep behavior simply relieved the large stresses caused as these structures formed while cooling in the still soft and mobile lead matrix. Also, since lead and antimony have very different coefficients of thermal expansion, wouldnt there be large plastic strain zones around these rods immediately following rapid quenching?

cbrick, you do agree that if the lead were large enough to have a conductive time constant that interfered with quenching, then the surface which cooled faster would have increased hardness over the interior? Also, you do agree that pure lead, brought close to its melt point while retaining solidity and in close proximity to a highly soluable atomic particle, such as tin, might allow the diffusion of tin into the lead matrix and then be harder at teh surface after cooling, yes? Also, shouldnt the top of my ingots which are speckled with teh floating antimony crystals have increased hardness compared with teh bottom? I can test this once my pencils get here hehe. I am sure my pocket knife will work fine for comparison though.

By the way, thanks tons for the help and info.. now I gotta review solution versus dispersion hardening.. they sorta became one in my old brain..

[cbrick]

cbrick, you do agree that if the lead were large enough to have a conductive time constant that interfered with quenching, then the surface which cooled faster would have increased hardness over the interior?

Not according to all the papers I've read from the metals industry I read while writing the articles. Partly agreeing with you that it may take a day or so for the middle to catch up (speculation on my part) it will end up the same hardness through and through.

As into this as you seem to be why not invest in a BHN tester? For ease of use and direct BHN read-out I recommend the LBT. Cannot do ingots on it though. A lot of folks measure ingots but I believe that because of the difference in cooling time that an ingot will not give the same result as a bullet cast from that ingot.

Rick

[stephen m weiss]

I might buy a hardness tester. I used a very expensive one for several years, it was a great random number generator. It could create +/-10% readings on metals which were +/-.5% in properties. I believed that friction was the issue, though the paper claimed that variations in surface hardness were to blame. Scratch tests didnt seem to show such variations in surface hardness at the scale of the indentors. I have avoided measurement techniques dominated by stiction through the years. But, noisy numbers are better than no numbers.

I kind of want a dogbone mold so I can do pull tests and get all the cool information that provides. A section of .1 dia would be easy to pull by hand watching my 200 lb spring gage. Or I could hook it up in my drill press and NOT get a workout... hehe Each time I cast with a new alloy I could just make a few dogbones and get the Yield, Ultimate, and %Elongation. It would make it REAL obvious if I had brittle bullets.

[C. Latch]

What exactly are you doing with all this info, anyway?

Are you making bullets or science projects? Either is fine, I'm just curious.

[popper]

my 17yr old son asked how Antimony and Tin allowed hardening and why quenching improved hardness, Unless or until he understands atomic/molecular structures & forces, the answer is tin doesn't much, Sb is better and quenching just freezes the atoms in place. You basically have an amalgam of hard & soft stuff. Then explain atomic mobility in a solid for the age hardening part. If you are looking for the answer, study 'super cooling' at the solidus line - battlerifle's last paragraph. Hardening high %Pb complex alloys involve a process using heat & pressure as well as quenching, > BHN 30 achieved. Don't bother trying the process at home. As for your testing, I've found rotational shear testing to be the best method. You will see the outside/inside strength patterns. Boolit shooting is all shear strength related, not compressive - still a relatively 'plastic' material.

[stephen m weiss]

Heh, well, making bullets but in my way of doing things. I try to establish and maintain 'design control' of such things which means connecting and correlating it with all the theory I have every heard of or learned. Never met a law of nature I didnt like! (Can't say that of laws of man.) My boy is inbetween chem and AP chem in high school and in AP Physics currently, so he can sorta pick up my hand waving explanations. He has been hearing about metal matrix (and silicon matrix) behaviors his whole life, so its not new to him. He has seen all the cup and cone, beach marks, proud grains in compressive failure etc typical of failure analysis.

Casting at high pressure? Sounds great; that is exactly what I have been wanting with full automatic control so I can just program the thing, maintain the calibrations and clean it! :) Near perfect densities and controlled quench curves. Drool!

Rotational shear? like sticking each end in a collet and twisting it to failure?

[stephen m weiss]

I tested some heat treats: ]

After heating at 450F for about 45 min to 55 min, and ice water quenching, took an H pencil to scratch (~19BHN)

then soaked at 200F for 2 hours took a 2H pencil to scratch (~21BHN)

or soaked at 234F for 1hr, took an HB to scratch. (~14BHN)

So, the quick hardening technique works. But dont go much over 200F, the seem to soften up.

I also tried quenching to boiling water. These came out very soft. So that didnt work.

[popper]

Did you test the same boolit? Need to run the tests on separate AC boolits. Try 450 for 2 hrs. One treatment for each. IIRC, Felix stated that 200F stable temp annealed all alloys to ACd. I'm experimenting with twice HTd, seems to bring up the BHN.

Rotational shear? like sticking each end in a collet and twisting it to failure? Yup, but I used vise grips on RD170 gr standard LG rifle boolits. I was interested in fracture pattern, toughness. Learned some interesting things about alloy, as you have noted, once the plastic strength is exceeded, strength drops dramatically. Rotational shear was a sudden failure, didn't have a way of measuring force required. Definitely was a difference in AC, WD, HT - ascending order. Failure always occurred at the same LG base edge. Odd.

[stephen m weiss]

I was only testing bullets from the same small batch. I didnt test the same one exactly. Once I did the 200F treat, I assumed I would have to do at least another full 455 F anneal before believing anything about it. As I was using pencil testing, its not like there was any scatter to results. 4 big ranges for hardness pretty much iron out any scatter.

I repeated the 200 F hardening test like 5 times. It always works. Sometimes it was 186F for 2 hours, that worked. Sometimes it was 198F for 45 min, that worked too. I didnt nail it down as to exactly what temp/time curve would work, but 238 F for 45 minutes brought it 25% below AC, so I suspect the safest temp for my +/-25F convection oven is like 175F. It seems to vary depending on what other appliances are running on the circuit, and also the air temp in the garage, and changes sometimes when i turn it back on.

What's LG?

I am gonna work on my hardness testing methodology. At this point, I plan to use a conical indentor (pilot punch) mounted in 2x2" stock with a 55 lb dumbell for load. The 2x2" will have 3 feet, 2 remote for stability and the punch. The weight will be mounted as directly over the punch as possible. I can use a bathroom scale and/or my 200 lb spring scale to measure the indentor load. This should vertually take out friction. Only the levelness of the floor I place it on and stability of the structure can change, and probably not more than the 1% spring scale readout.

I will try the rotational shear test, with the 200 lb spring scale to measure peak force. I have a 50 lb scale as well, hmm.. Shear stress =Tc/J Now whats poissons for lead alloys? haha

[blackthorn]

LG= Lube Grove

[popper]

I used the 9mm sizer die in the press with a digital 'spring' scale. You want to measure the force to just indent/break surface the Pb. Force drops way off after that. I used a 9mm case in the die as a stop, fishing line around the decapper pin. Watched the scale till I just got tension on the line, ~ 0.010" indention. Even with my crummy lever it appeared very accurate. Didn't try to correlate to BHN but used the lever rule to calc. actual force on the Pb. Learned a lot but just use the results on target to set my alloy now. I may resurrect that kludge next year for some testing. Deforming Pb is always in shear, even when you squish it. Movement is lateral to applied force. Bending is different.

[MtGun44]

The specific mechanism of age hardening in both aluminum and lead alloys that form
Guinier-Preston zones (6000 [Al-Si] and 7000 [Al-Zn] series aluminum alloys and Pb-Sb
alloys) is that they form this extremely small zones of inhomogeneity that actually
mechanically obstruct the motion of dislocations, thereby hardening the alloy.

Perfectly stacked single crystal metals have extremely low energy required to move
dislocations through the part, so they are extremely malleable, VERY easily deformed.
Anything that interferes with dislocation motion causes hardening.

Bill

[stephen m weiss]

Guinier-Preston zones, gonna have to look that up. That would explain the apparent saturation with Sb that occurs past 4% Sb. Increased creep resistance is reported at even higher Sb, so hopefully reading up on Guinier-Preston zones will shed some light on that behavior. (my homework pile is getting taller)

Interesting note on just breaking the surface. My instinct said the opposite. I am interested in predicting the behavior of a .06 wide driving band as it is crushed crossways with a .03 wide land. The deformation can be as low as .309/.308 or .312/308. The sizing alone clearly exposes the entire zone to massive yield, below the surface. There are 3 distinct phases of loading: sizing the bullet, initial insertion into the lands, and accelerating down the lands toward the muzzle.

During sizing, the tangent of the die lead in angle times the coefficient of friction will tell you the ratio of shear to compressive force, with Mohrs circle and one of the strain energy models, von mises predicting yield best. That strain zone with it's residual stresses will then begin creeping to relive teh highest stress zones.

During insertion to the rifle grooves, a very fast and explosive event, it is much like the die lead in situation as far as types of stress. A significant difference is that the compression-shear occurs so fast that there is little time to conduct away yield induced heat energy.

Zipping down the barrel is an interesting affair. The bullet could quickly begin riding on a layer of lube-melt and have about .03-.05 for a coefficient of friction. There could be a few tight spots that create additional yield. There could be rough spots that cause a sawing-broaching removal of bullet material. All of the friction energy, about 20 foot lbs, will be dumped into the land/driving band just been squished yield zone at a nearly constant rate. If there is direct contact with hot bullet gases, those will donate some more heat. The fairly cool lands will be trying to conduct away heat buildup, much harder if there is much lube layer. Lube will be melting, the phase change sucking up heat energy. Our experience with these types of event tells us that the EXACT behavior of the lube nearly dominates the whole thing, with bullet fit to lands being just as critical.

haah, ok I guess I had a moment on my first cup of coffee before kids got up and got all geeky on this! :)

Oh, I got my indenter working. With 90 deg included cone indentor and a 40 lb dumbell, I get .05 inch dia dents in my 22 BHN bullet bases. Straight force/area would indicate 17,000 psi, while correcting for sine of the half angle and neglecting fricion would give 12,000 psi. That looks pretty believable. I have several improvements to make. The indentor surface is really rough, the stability feet need to be wider, its a balancing act, and I need to actually measure the load, not just look at the side of the dumbell.

[MtGun44]

Are you familiar with dislocation motion and dislocation tangling as the atomic level mechanism for
malleability and work hardening?

Also, lead alloys will tend to anneal away work hardening at room temperature and binary Pb-Sn solders
will not sustain any significant locked in stresses over time, they creep away down to a few hundred
psi or so. In soldered joints in electronics, this saves a lot of assemblies from damage, something I
have explained to electrical designers many times working in stress analysis of microelectronic
assemblies.

Another interesting effect which is seen in precipitation hardened Pb alloy parts is that they will
exhibit work softening, which I have not seen a specific explanation for on the atomic level, but
I interpret as the G-P zones being disrupted mechanically and tangled dislocations being
mechanically forcefuly reordered to permit easy dislocation movement again. Complex stuff and
does not always behave like other alloys.

Bill

[popper]

Guinier-Preston zones Fancy name for atomic mobility/attraction/repulsion in a solid.

ratio of shear to compressive force Makes NO difference, all lead movement is due to shear forces. Stress from compression causes shear strain. Lead is not a structural metal so generally not covered in materials literature. Bending of a steel beam does give compression & tensile strain. Lead is like modelling clay, it just slumps - shear.
Some of the newer electronic leadless 'solders' have pretty unusual characteristics increasing the stress problem, some of the newer lead (not Pb) plating won't even solder well.

[stephen m weiss]

I guess I could believe that shattering the antimony rods could cause permanent strain softening. I have been wondering about strain softening.

Lead doesnt instantly creep or instantly anneal at room tempertaure, and antimony grades are markedly better at resisting creep. I will get around to looking up rates, but a buddy engineer ran a high temp solder creep test for weeks and weeks at pretty high stress at room temp. LOL it was like 6 foot of .06 dia solder with a couple of pounds hanging on it. It sure wasnt moving fast, like a quarter inch per week. I wish I remembed the details better.

I still cant understand your point on shear strain popper. Sure all compressive strain can be resolved to shear strain at 45 degrees, that's true for any material. I sure bend lead slag, seems to behave like other ductile metals. All ductile materials have ductility due to shear dislocation motion. How is lead any different?

[andrew375]

The technical name for the process is Precipitation hardening (http://en.wikipedia.org/wiki/Precipitation_hardening) . The process is time/ temperature dependent.

[popper]

I sure bend lead But not your boolits, I hope.