Heat Treating and Re-softening

[454PB]

I did some experimenting over the last few years to determine how long heat treating takes, and how long it lasts.

This sample was cast from clip on WW alloy, cast in a Lyman 452424 mould, and dropped into water right out of the mould. The same boolit allowed to air cool tested 11.8 BHN using my Lee hardness tester. After 3 weeks, the water quenched boolits tested 29.9 BHN, that was on 04/05/2013.

Test 2 on 04/28/2016 the test sample was at 24.8 BHN.

Test 3 (today) 06/04/2020 the test sample was 13.0 BHN.

When I heat treat in this manner, I always size the boolits as quickly as possible, usually within hours, and always the same day. I do that for two reasons, first because they are really tough to size after they have begun to harden, and second because sizing supposedly removes some or all of the hardening. I have not tested that theory yet, but I will at some point.

One theory I have tested is that the hardening is only on the surface. I filed one heat treated boolit off to a depth of over 1/3 of the diameter and found the hardness goes at least that deep.

So, if you have heat treated boolits laying around that are seven years old, they are nearly back to the original alloy hardness.

[rking22]

Very interesting long term test, thanks for the data. Not what I expected, but my primary experience is with steel and aluminum. Wonder what hardness the air cooled would be today??

[sureYnot]

Thank you.

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[PJEagle]

Thank You.

Very helpful information.

[Zingger]

I want to echo the thanks for posting your findings. These are very interesting and informative.

[Shuz]

Here's my findings--Lee 44-200RNFP cast and air cooled on 10/31/14 was Saeco 6. On that day I quench cast a few, and today they measure Saeco 10. The air cooled that were cast that day measured Saeco 8 today(6/5/20). Perhaps the composition of the alloy determines how long the heat treatment lasts? These lee 200 .44's were cast from "dental film backers".

[454PB]

Heat treating requires antimony. The dental X-ray backers have none, only a small amount of tin and pure lead.

[StuBach]

Thanks for the info, very cool to have such long scope data

[JonB_in_Glencoe]

Thanks for this info, good to know.

I did a test in 2015 with Oven heat treating.
I only went two years out. I should see if I still have some of those boolits laying around.