View Full Version : Accidental Heat Treat.....

January 04, 2009, 11:34
Long story short: Can exposure of a FAL receiver and locking-lug to approximately 600 Deg. F for about 20 minutes hurt it's strength properties any? My vague knowledge of metalurgy says "no", because I seem to recall parts needing to get up to 800 to start annealing, but I don't trust my memory...... I also know that silver soldering (often done on fine guns, and post-ban muzzle-brakes) requires a temp of ~900F

Now for the background, I was baking on a Gun Kote finish onto a FAL I'm building, and I was using my incredibly precise :tongue: Outdoor gas grill (w/hood, to enclose the parts, like an oven). I've done this numerous times before, but usually in the summer. Because of the frigid temperatures outside, I put another burner on low. Anyhow, when I cam back about 15 minutes later, I noticed that the temperature was nearly 600, as opposed to the usual ~400. I immediately backed off, and thought nothing of it, since I know machine guns can easily get to that temperature around the chamber during sustained fire. However, when I took the rifle out, I noticed that the locking lug had a fringe tint of purple (red wine) on it. What is interesting is that only the barrel was over heating elements. The whole receiver was off to the side, and never received any direct heat. In fact, the GunKote finish on the receiver stayed the same color, where as the front of the barrel (nearer an element turned darker)

Any thoughts from those educated in heat-treatment? Is the whole receiver junk (It's steel, not an aluminum one)? Has the locking lug lost it's heat-treatment?


L Haney
January 04, 2009, 12:31

I think you're OK with 600 deg F.


January 04, 2009, 13:53
I think that as long as you let it cool down normally and did not quench it, you'll be okay. Quenching could set up some stresses that could affect it.

January 04, 2009, 14:13
Thanks guys. And a phase-state chart to boot! I haven't had to look at one of those in years! What I could find on the web is that most Gas grills cant get much above 700 Deg F, which is 371 C, which isn't even on that chart, so I think I'm good to go!


January 12, 2009, 17:01
The process of drawing temper is done after hardening. A reduction in the hardness decreases the brittleness and increases the toughness to prevent cracking or breaking. Hence the need for surface hardening of some parts which are not only subjected to surface wear, but shock as well (M14/M1A bolt lugs). Drawing or baking is done at a much lower temperature - as low as 400F - however the duration of exposure is measured in hours so per your description, you could not have done anything significant to the hardness.