Quench casting caveat

[Shuz]

Many folks know that lead alloys can be hardened by quench casting. The purpose of this post is to alert some to the fact that the hardness level achieved may not be consistent. For example, last Friday (9/7/12) I used a 6 cavity Lee mould 44-225 RNFP to quench cast a few boolits to see if they performed better in a finicky Marlin 1894 .44 mag rifle. First I got the mould up to temperature by casting and air cooling a couple a hunnert boolits. The alloy I used was a mixture of wheelweights, dental film backers and a little tin added(1to 2%). This alloy has air cooled tested to Saeco 7 on many occassions. It did so also on Friday. However my quench cast boolits varied from Saeco 8 to Saeco 10, and various boolits continue to test from 8 to 10 today.(9/12/12). I attribute this to the fact that not all boolits came out of the mould at the same time before they hit the water. To reach a more consistent hardness I am now gonna size these inconsistent quench cast boolits and then heat treat them in a toaster oven. Naturally I'll have to lube them before I shoot them. It seems a shame to have to go to all this extra work, but I wanna be as consistent as I can in trying to get this Marlin to shoot better .432 boolits.

[smokey496]

Works for me.

[btroj]

Heat treating will generally give a more consistent result.
I water drop because it is quick and easy. I don think the hardness difference matters in most applications so I ignore it.

I am a firm believer in doing things as simple as possible to get a desired result.

[tomme boy]

Let them sit for a month or two. Then see where the hardness is at.

[sqlbullet]

A couple years ago I helped my son with a science fair project about heat treating metal. Since I cast bullets we worked with lead. I handled all the toxic part, and he captured data and then tallied results, did research and of course the final write up.

We cast 180 bullets at three temperatures: 650°, 700° and 750°. We used a Lee 6 cavity TL401-175 SWC. The sprue cool time was timed, and the cadence was timed. Half of each group was water quenched from the mold by dropping every other cast in the water. The lead was isotope lead from 31.5 lb cores.

Thirty air-cooled and 30 quenched bullets were selected at random from each temperature range. This gave us 18 series of ten bullets each. These were placed in plastic bags.

Series 1-6 were from the 650° cast, series 7-12 were from the 700° cast and series 13-18 were from the 750° cast.

Series 1,7,13 were air cooled only.
Series 2,8,14 were water dropped from the mold.
Series 3,9,15 were air-cooled, then heated to 350°X1 hour without quenching
Series 4,10,16 were air-cooled, then heat treated to 450°X1 hour and quenched
Series 5,11,17 were water dropped, then heat treated 350°X1 hour without quenching
Series 6,12,18 were water dropped, then heat treated to 450°X1 hour and quenched

Hardness was tested using a Lee Hardness Tester.

Series 2 average: 25.88, std. dev: 1.05
Series 4 average: 16.44, std. dev: 1.45
Series 6 average: 17.38, std. dev: 0.94

Series 8 average: 29.50, std. dev: 1.15
Series 10 average: 20.46, std. dev: 1.24
Series 12 average: 21.83, std. dev: 1.14

Series 14 average: 32.41, std. dev: 1.67
Series 16 average: 24.87, std. dev: 1.29
Series 18 average: 25.33, std. dev: 1.54

This data seems to dispel two of the predominantly held opinions. First, in every case a higher hardness was achieved dropping from the mold. Second, there is not a statistically significant difference in the uniformity of hardness among the water dropped versus oven treated lots of bullets.

I attribute this to a couple of things.

First, the sprues were cut early. No smears were encountered, but the cadence was fast the the bullets were very hot from the mold. Probably hotter than could be achieved in an oven without the possibility of some slump. Air cooled bullets were lightly frosted.

Second, the cadence was extremely uniform, and that mold has been lee-mented well and releases very uniformly.

I don't doubt the OP got different results. There are many factors at play that impact the uniformity and total hardness. My point is that if your casting cadence is uniform you can achieve the uniformity and hardness of oven heat treating by water quenching from the mold.

One other item of note. These samples were preserved and tested again 24 months later. The air-cooled boolits had increased in hardness by about 50%, from an average of 11.5 to an average of 17. The quenched boolits had softened, the amount depending on how hard they were, some by as much as 24%, 32.41 to 24.64. And, the boolits that were in the range of 21-23 changed only an average of 4.5% It appears this lead wants to be about a 22 bhn and will time harden or soften towards that number.

[Shuz]

" I attribute this to the fact that not all boolits came out of the mould at the same time before they hit the water."

Interestingly, I heat treated the same boolits for 1/2 hour at 475 deg and quickly quenched the whole batch. 36 hours later I'm getting some boolits to read Saeco 9 and others read Saeco 10!

Perhaps something has gone wrong with my Saeco testor? I've been using this tool for over 20 years now and I have always been impressed with it's "repeatability" within samples of the same batch of boolits.

Over the years, boolits heat treated will usually test Saeco 10 as soon as an hour after quenching. In my experience, air cooled boolits sometimes take several days to stabilize.

Anybody else experience similar results with a Saeco hardness testor?

[runfiverun]

it takes about 10-12 days for air cooled boolits to stabilize.
but they are affected by quicker cooling too casting in 30-f temps versus 70-f temps will affect thier hardness.
water quenched will harden quicker initially but takes about 14 days minimum for the whole batch to be close in hardness.
now here again temperature will affect your bhn 25-f difference in mold temp,or a second sooner/later opening the mold or even the water heating up through a session will affect you bhn for a period of time.
letting them age will bring them closer in consistency and they maintain that hardness for quite some time [10 years ish]
i generally stay well ahead in my water quenched casting and generally don't shoot them for 6 [or more] months.

[popper]

Sounds right for electrotype or 50/50 Pb/#2. WD just speeds up the hardening process. The trend is toward a particular hardness, determined by the alloy. Now add a grain refiner or go to a 6:1 Sb/Sn and you get a different story.