Water dropping ingots?

[TexasJeff]

Probably a dumb question, but . . .

I'm curious about lead hardness as it relates to air-cooling, water-dropping (and maybe even dirt-dropping--we'll see how Lloyd's dirt-dropped boolits shoot :-D).

Guessing that the hardness scale/factor occurs after the lead has regained a solid form and cooled--and that would be depend on whether the boolits/ingots were air-cooled or water-dropped, heat-treated, etc.

So, is there anything in the molecular composition of lead that would make the lead increase in hardness each time it is melted and cast?

In other words, if you water-dropped your ingots, the hardness scale would increase. But when you re-melt the lead (in ingot form), does the lead then resume it's original "hardness" once it cools again? Or if you water-cooled your ingots, melted them and then water cooled them again, would it increase the BHN?

My gut-feeling says it wouldn't, but I was also never a very good student way back in high school and college when it came to physics and chemistry.

Jeff

[cohutt]

starts over each time, not cumulative from successive melt/water drops.

[Blammer]

if it were cumulative they'd be building buildings with it! It'd probably be the hardest substance known to man!

that would be a hoot!

plus it'd suck for casting bullets as it'd probably be a one or two time use before it got too hard to be usable.

[billyb]

waste of time, might be a little dangerous with water around the smelt. Bill

[grumpy one]

In theory the antimony-induced hardness of ternary lead-tin-antimony alloys comes from two causes. First, the presence of antimony crystals in the lead matrix disrupts the slip planes in the lead, restricting slippage, or creep (pure lead is more a viscous material than a solid one: over a twenty year period its ultimate stress is in the hundreds of psi). Thus adding antimony to the alloy increases its hardness, even if air-cooled or annealed. The second cause of antimony-induced hardness is precipitation hardening. The solubility of antimony in lead is temperature-dependent. At 484*F it is 3.5%, but at room temperature it is only 0.44%, so during solidification and cooling antimony is being precipitated. When it precipitates below the solidification temperature it has to force its way into the lead crystal lattice after the latter is formed, and this stresses the lattice. The amount it stresses the lattice depends both on the amount of antimony crystals which have already formed (thus disrupting the slippage planes) and how quickly the precipitation happens relative to the slippage capacity of the matrix.

So, antimony precipitates in the lead matrix due to cooling after solidification, but if it cools very slowly the matrix slips (creeps) simultaneously and relieves the resulting stress so not much precipitation hardening occurs. Also, the precipitation process proceeds slowly at room temperature, so the precipitation hardening continues for a year or more, but at an exponentially slowing rate.

If the alloy is quenched from just under 484*F, the slippage of the matrix that can occur while it is still hot and malleable, is minimized and maximum stress in the lead matrix (and therefore hardness) occurs. If at any subsequent time the alloy is heated, the matrix will soften, promoting slippage, and also permitting antimony crystals to be re-dissolved in the lead matrix. If subsequent cooling is slow, there will be slippage during the re-precipitation of those dissolved crystals, so precipitation hardening will be minimal.

Short answer: annealed lead-antimony is harder than pure lead. Quenched lead-antimony is harder still. Quenched lead-antimony can be converted to annealed lead-antimony by heating then cooling slowly. Annealed lead-antimony can be converted to quenched lead-antimony by heating then cooling quickly. Provided time is permitted for full dissolution of the precipitated antimony before re-cooling, you can do this repeatedly.

[theperfessor]

Every time you fully melt the alloy the former crystalline state is irrelevant, the hardening/annealing/heat treating process starts over again upon solidification. As a liquid the atoms/molecules are (under equilibrium conditions) randomly distributed and take up no definite position relative to other molecules; in the solid phase the relative positions of the atoms/molecules in a crystalline form determines the properties of the resulting material. The various heat treating processes described by grumpy one are what allow you to control those properties by controlling the crystalline form during the solid state.

But every time you fully melt it, you start over....:-D

[TexasJeff]

Thanks y'all.

Figured as much, but it was a lazy Saturday afternoon and I got to wondering about it while I waited on the WW to melt in the smelting pot.

Jeff