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

CZ....Yup, 100 + years ago it was "black magic" and nobody talked about it, all hush-hush.............voodoo is a good word.......


Tony....tell us about crapping your pants when you dropped the parts in the quench....!......

In big casting operations, sand casted parts go through shakers on mesh belts. Sand wears stuff out. The parts also run through annealing furnaces on long time controlled belts. A furnace can be 100 feet long or longer. All about time, temp, and flow.
We were changing the shafts and pillow blocks on a shaker. The shakers are adjacent to the furnace lines for minimum handling of parts. Normal maintenance. Standard 4" GM spec shafts and bearings. Every GM plant uses the same shaft size and bearing set.
Well, suddenly I saw a flash, felt a wave lift me in the air, and then the world was all orange, and then black as the deepest mine shaft. I could not breath. I was engulfed in fire, but it was not very hot.
Then, I was sitting on my arse in the blackness. Then Orange embers began to fall like a firey snow storm. A whirlwind of orange sparkly embers in the pitch black. Then, like stars on a cloudy, moonless night, the sodium vapor lamps 50 feet above, began to show through the blackness. Their glow increasing with each heartbeat, and the settling of the ash.
I stuck my face into my shirt to try and catch a breath in the dust and fire. The firey soot settling all around me.
Light finally returned enough to move. You can't run when you can't see.
I looked for my partner Dave. He was in the shaker at the blast.
Dave's a very sober guy. Smooth as Hubel's glass. He was looking at me.
He say's to me, "You alright kid?" I check myself for damage, just a few dents. I shake my head yes. "Go on and take alook for any meat around by the control office, them's the kind that kills people." I stumbled across the pile of pump castings and cinder blocks over to the control booth. There was no one inside. No....meat to be found at the blast site. Just mangled chainlink, refractory cement, and cinder blocks.
I looked across the aisle to the furnace. The gas fueled annealing furnace had had a gas build up of un burned fuel, and had blown a 30 foot section of the tunnel out. Directly across the aisle from the control booth, which disintegrated and rained parts and block at Dave and I. Well, mostly I.

The operator came running down the aisle to find Dave and I. We were OK. He'd been on break. Or he'd have been the meat.
His office was destroyed. A direct hit, that saved my life.
The fire was the carbon rich gas burning in the atmosphere. The cinders, the accumulated soot and ash that was blasted off the ceilings, beams, and machinery during the blast. It was ready for paint after the soot fell.
Within an hour, division level GM managers were in the plant interviewing us.

Sometimes it's better to be lucky than good.

Well I thought this was an open discussion of case hardening. I thought in fact I "Asked" more questions than made Statements. One or two did provide some answers, which certainly sounded reasonable.

I am not trying to "Throw Water" on anyones endeavor. I do think anyone who wants to attempt case hardening though needs to fully understand it is not as casual a feat as for instance Rust Bluing & should definitely be interested in learning all they can about the process.

I suppose if someone asks a question, to which you have no idea as to the answer, just "Attack" the questioner is a viable tactic. Well for my part you just totally lost all my respect. As this thread started I was actually thinking you were a good source of some things I wanted to further learn on the subject. Missed That One BIG time.

PS; I have seen a case hardened part so full of cracks one had absolutely no need for a microscope, or even a magnifier for that matter to see them. It was a non gun related part & newly made, not an irreplacable antique.

PPS; Yes I am quite familar with Magna-Fluxing. This part didn't need it though to show up the cracks.

An old Mule trader once took some Black Polish & shined up an old decreptid mule. He then sold it to an unsuspecting Green Horn. Next day Green horn comes around & tells him, You know that mule you sold me Yesterday, He died last night. Old Mule trader says "Well, He Ain't Never did Nuten like Dat Afore.

OK, well it goes like this Doug...I was standing there and....

Actually...better not..:)

Miller:

Well, for my part, you lost all my respect about one and one half years ago, maybe one year ago on a similar thread regarding CCH......you came in with your same machine shop scenario and began an essay on critical temperature.......everybody else was wrong, but you were right.......that is the way it read......

I think you belong to a group that believes: --"if I have not experienced it, then it probably has not happened"........?.......Could be wrong, but your posts sure read this way.........

Sorry, but I think the information you seek is available at most libraries, electronic or otherwise and then you can complete your book or whatever the use is for the information you are gathering.....

Best,

We don't progress if we don't study and learn.
Disagreements should be settled as possible by facts. By evidence.
I'll ask Smith tomorrow about double heat treated parts and carbon migration. He's only heat treated a few Billion dollars worth of parts.
My guess at this time would be that for thicker parts, GM doesn't care. Samples are tested, accepted, rejected, or accepted and sent out for rework.
But I will definately find out.

A better discussion would be how to control colour pattern.

I'm glad for any feedback personally. I'm quite new here so suck it all up. I'd also be interested to hear about how to change pattern at some point.

Right now, I'm happy with my results. It looks like if I find guns to restore myself that any pattern changes are good! And as long as I find things that haven't already been re-coloured I'm in with a good set of tolerances ready for re-colouring.

Of course thing's could go wrong but I'll have to take that as it comes!

T

Doug;
I guess I just don't "Treat" the "Heat Treatment" of structural parts of a gun quite as casually as many do. I certainly have not "Claimed" to have all the answers. I personally do not consider "Myself" qualified enough to attempt to re-color harden a gun frame of my own. Questions I have raised are simply things I would like to know answers to prior to allowing anyone to do one of mine. I thought perhaps You had some of these answers, definitely appears I was Wrong Big Time on that.
Machinery's Handbook recommends a higher temp for for hardening than many today are using for color hardening, so again I ask;
What affect does this have on the hardening of the case?? I assume you do understand that when the part is carburized via heating in the carbon atmosphere to a temp above its critical temp, the deeper into the metal you go the lower the % of carbon added is. Charts are readily available, Done by Metalurgists which state the critical temp for carbon steels of varying carbon content, this is nothing I did or imagined. So I ask again "IF" you have carburized a part to a total depth of .010" & you subsequently heat & quench from a temp that has only reached the critical temp of the first .002" of that carburized depth, what portion of it will be hardened? Also what affect does this have on the integrity of the part.
My own personal knowledge is simply not enough to answer all this, So I "ASK" & then all I get for my troubles is a Personal Attack for asking. I guess essentially that tells me what I need to know, "You Don't Have a Clue" or you would have answered rather than attack the asker.

Miller-

I would guess you read ALL the previous posts, not sure......?...

If a metal lab inspects my parts and says the hardness depth averages 1.2 to 1.5 mm, then I believe their findings to be correct and valid, their x-ray and micron microscopes are quite accurate I think, since they inspect for hidden voids, blisters, structural integrity and the like, not only surface variation and hardness......and since all the parts pass mil spec S 6090A at the temperatures that I am using there is no further information that I require...... all the parts are approved for return to service, guns included, as per the lab......I don't know of any gunsmiths that use a lab for CCH, do you....?....I use it because it is owned by a close friend......

Since you appear interested in some more data, I suggest you take two Flues receivers that you mentioned, case one and run destructive tests on both receivers. You would need to crush both receivers in a press with meters and gauges attached. This would give you the 'structural' comparison testing you seek........A against B.....both from the same manufacturer, same alloy, same size etc......Or you could load both weapons to extremes with gradual increases until they explode and measure the results....Or you could just saw them in half and study the loop.......

Since you have NO clue what temperatures I am using, you therefore have no way to reference this information against your machine shop handbook and your charts and graphs........and since you have "never cased" one single part yourself, I don't think you understand what is involved....maybe as an observer....?.....Maybe your machine shop did not have a high tech aircraft metal lab.....?......Maybe you should read some books on aircraft inspection parameters first, then read your machine shop book.....?.........

Everyone has a different risk tolerance.
Investments to old guns, we are all different.

This is from the horses mouth. I trust him with my life.

Carbon is a solute in the steel solvent. It migrates above a certain temperature along a concentration gradient. If the temp is too low it doesn't migrate from the carbon rich pack through the carbon poor steel. As temp is raised, it migrates along a curve that looks like a hockey stick. Relatively fast for the first .025 and then ever more slowly across the cross section.
At 1650 degrees F, (his most common carburizing temp) he said we are talking hours and hours of soak time to allow, not push the carbon atom to migrate only a little further into the steel. Thousandths, not inches.
When asked about the effect of multiple annealings and carburizings, he said " The carbon equalizes above temp with the surrounding environment. So, if packed in a carbon poor environment for annealing, carbon atoms migrate toward the areas of lowest concentration from highest. Both a little deeper (as soak time permits) but mostly outward toward the low concentration packing chips."..."This leaves residual carbon atoms in the case, but they cannot be driven deeper until critical temp is reached in a carbon rich environment. There is not enough carbon in the surface to create the gradient necessary to allow the migration deeper. They will go "out" just as likely as "in" in this case. Leaving a piece of steel with a very low concentration of carbon in it. (Soft)

But wait, there's more.

The time gradient is different for thick or thin parts.
Here is the common ground for the bickerers.
Small parts can much more easily be hardened through with successive heat treatings. Leaving them brittle. They are easier to allow carbon to migrate through, and the distances are smaller. So, less time to equilibrate.
How small parts are packed and processed, he believes, should be different that the larger forgings.

Well, what about an action that was repeatedly heat treated?
In the annealing, the equilibration lowers carbon content to a low level. The next heating in a carbon rich environment slowly raises the carbon content from the outside in, and starts the gradient migration all over. It would take hours and hours to add a slight increase in depth from the prior state.
So, first the annealed part has to reattain where it was before, and then follow the time gradient to let carbon migrate a tiny bit deeper. Up until that moment, carbon atoms are as likely to migrate outward, as inward. The gradient favors outward until the previous percentage is attained.

Now here is where I blend in what Dr. Gaddy told me.
"Color hardening is very very thin."
"Microns thin."
That suggests to me a thin case on the part, and a much shorter time of soak than what Smith has been talking about.
Achieving a color case for decorative purposes does not allow carbon atoms to migrate very deeply into an action. Even if done multiple times. The times at temp are either too short, or temps too low.
Again, deeper for thin parts.

So, as a guy that doesn't have a kiln, I am guessing that most colorers bring a part up to a temp pretty quickly, soak it a relatively short time, and then quench it. Leaving a micron thick film of oxides, which is more decorative, than strengthening. A wear surface. Not strengthening.
The implied conditions followed don't allow for very deep penetrations. But, for all I know, you guys are soaking these actions for days and days, just in case. It doesn't seem to be necessary in order to create a decorative skin.

So, what do you think? Am I full of it?

You can always cut up an old action and look at it under a loop to determine case depth necessary. But I suspect that information is already out there.