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R'Man;
A most excellent & informative post. You have brought up a point which needs to be understood by all contemplating having this done. This is the fact that a carburizing cycle "Changes" the composition of the outer layer (The Case) of the steel. Indeed the depth of the case is controlled by how long a part stays at temp in the carbon mixture. Every time it goes back in the furnace for further heating a little more carbon is added to the case. Thus every time a part goes back in the furnace it will be slightly "Changed" from what it was previously in actual composition. Even alloy steel can experience a slight compositional change in heat treatment from certain alloying elements "Cooking Out" of them, from oxidation. These steels are often heated in a molten salt to minimize this.
The problem with the color case hardening is we cannot simply heat enough for "Just" the color without destroying the hardness of the case, & we cannot process in such a way as to preserve its hardness with out going up into the range where more carbon will be absorbed & the part then be quenched from above its critical temp, which is almost certain to result in "Some Amount" of dimensional change.
To me the Risks are simply not worth it for a little Vanity for the colors. The proper original hardness of the case itself has not been lost, only the color.


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Rocketman and Miller,

Those are the two best posts I've ever read on this matter. Thanks for taking the time.

Stan


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2p, thanks for the reply. Here are some comments.
You have brought up a point which needs to be understood by all contemplating having this done. This is the fact that a carburizing cycle "Changes" the composition of the outer layer (The Case) of the steel. Indeed the depth of the case is controlled by how long a part stays at temp in the carbon mixture. Every time it goes back in the furnace for further heating a little more carbon is added to the case. Thus every time a part goes back in the furnace it will be slightly "Changed" from what it was previously in actual composition. A craftsman who understood the "change" issue could make a rehardening cycle very short and without a carbon rich environment and still have a hard case. Thus, you would restore the hardness to the case with a minimum of change in case carbon content or depth. Even alloy steel can experience a slight compositional change in heat treatment from certain alloying elements "Cooking Out" of them, from oxidation. These steels are often heated in a molten salt to minimize this. I agree that cooking out and cooking in (usually carbon) alloying elements are issues. Anyone can do a simple case hardening of a simple piece of mild steel. Gun actions are not simple pieces, not at all. Therefore, I will always suggest that gun actions that are to be recased are done only by craftsmen.

The problem with the color case hardening is we cannot simply heat enough for "Just" the color without destroying the hardness of the case, & we cannot process in such a way as to preserve its hardness with out going up into the range where more carbon will be absorbed & the part then be quenched from above its critical temp, which is almost certain to result in "Some Amount" of dimensional change. Certainly recoloring without tempering out the hardness of the case is an issue. Dr. Gaddy thought it paractical. But, I can't yet cite the metalurgy to do it. A careful study of hardness vs temper temperature would need to be made (the higher the temper temperature, the lower the hardness and brittleness). If rehardening, there is no need to soak the piece above critical temperature - reheat and immediately quench will produce full hardness (core temperature is not an issue as it will not heat treat under any circumstances, only surface temperature). Nor is there any need to expose the piece to additional carbon. So, we can see a method to minimize ally changes. There remains the issue of minimizing dimensional changes due to the heating and cooling.
To me the Risks are simply not worth it for a little Vanity for the colors. The proper original hardness of the case itself has not been lost, only the color. [/quote]

In my opinion, and it is only an opinion, most guns can be refurbished to a very acceptable level without recoloring. However, when one is to be fully restored, made as near new as possible, then recoloring is in order. My caution is that recoloring, including rehardening, is not a step to be undertake lightly. A recolored action on a refurbished gun looks out of place. However, a "silver" action on a restored gun also looks wrong. One needs to understand the difference in work and cost between a refurbishment and a restoration.

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R'Man;
Several good points there. Yes I think it is true that a total soak of the action would not necessarily be required as long as the surface was heated to aboive the critical temp for the depth of the case. This would be somewhat akin to the process used on some machine tool ways referred to as "Flame Hardened" though a slightly diferent process. Since case hardening itself does not necessarily produce color, I simply don't have the experience here to say whether the colors could be restored with out the addition of "New" animal carbon being added.
Of all the things I ever read from Oscar this was the one place I disagreed with him. I had some correspondance with him via PM, but didn't really get to carry them to their conclusion from his untimely death. His contention was that it was totally unnecessary to quench from above the critical temp & that only the hardness in the case resulting from the higher carbon content was needed. In fact he thought perhaps this was the way the factories processed them. I Disagree. Done this way the only reason for a quench at all would be to produce the colors. It is of course true that even unhardened a high carbon steel is harder than a low carbon one by some amount. I am though firmly convinced that the original method was not just "Color Cased" but "Color Case Hardened".
It is true I believe that the action if totally unhardened would be capable of carrying the load of firing due to an adequate amount of steel, but that wear resistant surface would be lost.


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Case hardening can't increase the tensile strength of the action as the modulus of the case is very near to that of the core. Therefore the core will fail from plastic deformation at the same force with or without the case layer. However, the case layer will be harder and will be more wear resistant; can that be called strength? Also, the higher carbon content will make the case layer more corrosion resistant.

I'm quite sure that the hard layer came before the colors were recognized as "pretty" and desirable. Rub the color layer off and you still have a hard, silver colored, corrosion resistant layer.

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Rocketman --- John Gillete of Classic Guns inc. does post quench after the CCH.



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Lot's of chatter from lots of people who 'never have'....and 'never will' color case harden any guns......but just read books...and pass out mis-information...

I've only done a hundred or so over the years but have learned:

a...The Manufacturers intentionally serial numbered each part of a gun for a reason...not just because they had nothing better to do.....

b...The guns were in an assembled state, minus the springs, hammers and other parts not cased.....and are the same now by good smiths....screws in place, floor plate or lock plates or both in place ...a tight, secure unit....

c...Then put in a crucible then the furnace....

d...The critical temperature was never surpassed back then and is not now days by experienced smiths...

e...Once all these serial numbered hand fitted parts are cased together, and quenched the proper way...they all become a beautiful matching set of parts.

f...Uberti...Turkish firms...Beretta...Pedersoli, just to name a few are doing quite well with CCH....and even take return guns for re-case....as Colt does...or did...

g...If you've had parts move around, someone screwed up...period


If you like torches and pickle juice or someone elses wear and tear on your gun and you have convinced yourself that it looks good....the 'ol run hard and put away wet look that some call ageing....then leave it like it is and smile from ear to ear.....just throw 'er behind the seat of your pick up.....


Doug



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I've never understood how a lockplate could be cased without producing a potato chip but reading all whatever it is that I've read and haven't done led me to believe the bits and pieces were packed in there in a disassembled state. I saw a critique of recoloring on a gun which was alleged to have been torched that suggested that the colors (read heat eyes) were bogus because they were continuous across mating seams (say trigger plate and bar or lockplate and bar in the case of a LCS) and that that wouldn't occur if parts were heated separately, as,according to the unstated assumption, they would if the guns were cased by bone charcoal and heat in the time-honored and legitimate process. . . mumble, jumbo, jumble mumbo. Personally, I didn't think that indirect evidence of torching was necessary with that gun but it does make clear that some folks think that in the legitimate process(es) parts were packed in an unmarried state so to speak and might take exception to b. above. Course some folks are wrong some and a lot a lot and a few just a little bit so undoubtedly it might take a team of historians (and a book) to prove or disprove that the one true process has always been followed by everybody (without a clock and a pyrometer) now and forever, world without end, Amen.

Stamping parts with a serial instead of a generic part no. is understandable when and where parts are hand-fitted and one part fits but one gun but I don't see it as more necessary to a procedure for which parts that go together are together than it would be for many procedures (including repair) where they wouldn't. But I admire your confidence that you've seen it all.

jack

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Originally Posted By: "PA24"
d...The critical temperature was never surpassed back then and is not now days by experienced smiths...


On one of your above statements you were absolutely correct, I have "Never" cased a shotgun action. I did serve a certified 4yr machinist apprentiship which included a course in heat treatment of metals. I worked another 31 yrs in machine shops & was in on a lot of heat treatment, just not gun parts.
I can "ABSOLUTELY ASSURE YOU" if the "CRITICAL TEMPERATURE" is not reached the part has not been "CASE HARDENED", only colored. I can equally assure you the gunmakers of old did not go to all that work, expense & time doing all that fancy packing of the parts in charcoal which you have mentioned "JUST FOR THE COLOR", No they Case Hardened Them. They knew there was a high possibility of dimensional changes & did all in their power to minimize it. "If" you didn't go to the critical temp most of that would be totally unnecessary.
If you anneal parts, then heat them "BELOW" the critical temp of the skin then you have Destroyed all the hardness of that original case & insofar as I am concerned have "RUINED" that gun. As Lily Tomlin used to say in the big rocking chair "THAT"S THE TRUTH".
Of course "I DON"T HAVE ANYTHING TO SELL".
PS; Ask any metallurgist what it takes to "Harden" a piece of steel. Hardness is not produced by quenching unless the part is over its critical temp. Just because a piece of 1020 steel happened to be forged into the shape of a dbl shotgun action it doesn't harden any different than a part for anything else. This is a basic metallurgical fact & I was a metal worker.

Last edited by 2-piper; 12/04/09 12:01 AM.

Miller/TN
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