doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Color Case Hardening - 2

Doug (PA24)

Thanks for the complements Sir,

Looks like you’ve been doing this for far longer that I, always willing to exchange ideas.

When I first started doing CCH, I built all kinds of fixtures out of stainless steel to tame warpage, one of the thing I found though, is that it’s probably not necessary; here’s my thoughts:

When you quench the part, you’ve got over 1000 deg temp change in a split second. The metal will move. Too many times I’ve removed a block/fixture only to watch the part “spring” once the fixture is removed. I also think that HEAVY blocking may actually increase warpage due to retained heat.

One of the great properties of true case hardening is that the core is still soft, meaning that the part is still quite “tweakable” , and is easily bent.

I stopped using blocking for the most part (still block receiver rails & the barrel holes in receivers). Blocking now is mostly to enhance colors.

If Color Case hardening is done correctly: reasonable temps, clean water with no additives (Salt) warpage should be minimal and easily fixed if it does occur.

Thoughts?

Mike

Nitro Express:

Incorrect......."the depth of hardening is ultimately limited by the inability of carbon to diffuse deeply into solid steel".....check with any metal laboratory or metallurgist.....

That is why for over 150 years it was called the "hardened skin"......


Mike:

Yes, I agree with your comments and observations.....I still block most parts, but do not use stainless....but low carbon steel blocking.....and as you stated......as long as CCH is done properly....i.e. temps etc......I totally agree.....

Best,

Mike, agree. Actually I didnt block the action. It's fine. Tightly packed in the carbon. For the sides I'll use carbon steel as Doug suggests.
T

Doug

Is there a reason that you don't use stainless? Reason I'm asking is that I talked with anothe gentleman who swears by cast iron for his crucibles & blocking. But he also has a local foundry that will cast for him.

I like stainless because it will last, after a couple of dozen quenches or so with carbon steel, the steel bloks are toast.

I know some folks don't like SS because it harder to machine, but since I mostly use carbide here in the shop, that's not an issue for me.

My SS crucibles & blocking have lasted a long time... some since day one.


V/R

Mike

My Canister is also carbon steel...but I let it cool naturally in the hope that it won't deform too quickly. I read mr Gaddys piece in the journal and he also used SS.

T

Mike--

The carbon steels have more carbon than stainless and I think enhance the colors......they do wear out and 'peel' as you go along, all the old timers that showed me specified carbon steels....so I just kept it up.....I know the old factories here and in Europe used carbon steel for their crucibles obviously....

Like you, I make all my own stuff, so it's no big deal to replace whatever wears out......stainless is probably better, I've not tried it...and I would have to compare and see if there is any color difference....?.......I'm not sure the extra carbon helps, but I was led to believe that it does...who knows.....we'd have to run tests 'side by side'....

Most of the folks use carbon steel I think.....probably cost...?...

Agreed. Much easier to get and form carbon steel for me. I also made the canister and it is easy to replace at the cost of about £20/$30

T

Not a metallurgist, But, only partially correct I believe. The penetration of the carbon does indeed slow the deeper it penetrates & for practical purposes there is indeed a limit of depth to be reached. However, I do believe that on a thin structural part, as for instance the side walls of a Light-weight Flues frame it would be entirely possible to achieve "Too Deep" a case leaving a part subject to cracking from its brittleness.

I have one question which I can't recall ever seeing addressed. When the part was originally Carburized it was brought up to heat in a carbon rich atmosphere & held at heat until the desired depth of penetration was achieved. Annealing the part removes only the hardening effect of the subsequent quench, it doesn't remove the carbon. Now upon subjecting the part to Re-Carburization does it immediately begin to obtain deeper penetration.

From my limited knowledge of the subject as I understand it the critical temp of a piece of carbon steel varies according to the % of the carbon, the higher the temp the lower the C'temp. It would thus seem to me a high enough temp would need to be maintained prior to the quench to harden the entire depth of the case. It would thus seem quite plausible that at some of the very low heats from which some quench to help in the prevention of warpage they might thus be achieving a very Superficial hard case with the major depth to which a declining % of carbon has attained might well remain unhardened. While this might seem desirable to minimize wrpage, it would also seem to be less than desirable for the purpose of hardening.

While true I am not a metallurgist, I did spend 35 years in machine shops where heat-treating of various types (including case-hardening, just not for color) was carried out. My experience was that any time a piece of steel was heated to above its critical tamp & quenched there was a modicum of RISK involved & that Every Time it was subsequently Re-Done, that risk grew slightly.

Miller; all makes sense to me.
T

PA24, you are incorrect..... see 2-piper's reply reference thin cross sections of the receiver, trigger mounting plate, opening lever and small parts. If you look at enough re/cased receivers and parts you'll start seeing cracks. And may I ask where you took your degree in metallurgy??