Case hardening and case coloring

[flatsguide]

Dave, thanks much for the info. I have seen a few youtube videos were the volume of water was aerated with a healthy stream of bubbles. Is that necessary? Looking at Paragon furnaces and trying to figure out what chamber size would be best.
Regards, Richard

[James Rogers]

James . That is great information. What fascinates me about those iron gun mounts is they almost look like they were cast.
 Do you see any evidence of that? Your information made me recall a iron side plate I saw on an English gun from the late 1700's.  It looked like it was cast also. What made me suspicious was it had some of the same flaws in the same places I saw on other identical side plates.

Jerry,
 From what I can tell from the tool evidence underneath the plates, they were formed. Probably in a form designed just for the platte. You can also see the planishing tracks where they were refined. This is my best guess off of memory from a couple of years ago. ; )

[David Rase]

Richard,
I do not aerate my quench.  I use a 32 gallon plastic garbage can filled with well water.  I do not wrap or block my parts, but I do take great pains to ensure my parts are packed correctly to hit the quench to prevent warping.  My favorite crucible is made from a 3" piece of square tubing.

Here are 2 photos from a color case hardening demonstration I did at one of our Washington Gunmakers Guild bi-monthly meetings last year.





Here is a picture of a lock I did in June of 2014.  Temperature was 1500 with a 2/3 wood to 1/3 bone mixture of Brownell's charcoal cooked for 1 hour after reaching temperature.  I can show you photo after photo of tangs, actions and locks with basically the same colors and patterns with this combination.

[smart dog]

Hi Richard,
I have a Neycraft oven with a Paragon computer controller.  The cavity in the oven is 9" x 9".  I would buy the largest chamber size you can afford.  The computer control is a real plus if you are going to do much heat treating (it really helps when making springs).  Dave R's example is very good but I believe 1500 degrees is on the high end for reliable colors.  The key is to make sure no air hits the parts before they are in the quench.  If the parts are exposed to air you will see ugly grey splotches mixed with the colors.  If I am not concerned with colors, I typically bring the parts to 1575-1600 degrees.  The photos below show results from the method I use and described.

dave
 
 

[flatsguide]

Dave R and Dave, Thank you both for taking the time and effort to post the pictures and replying. I would be happy to get results like that shown in either photo. Great file work on both locks! I'm taking away the idea of not letting any air hitting the parts while dumping is imperative. Since the lock plate is relatively thin, do you make any sort of fixture to hold it to prevent warping. I can see were a vertical tube would let the lock plate slide straight into the water where both sides would cool at relatively the same rate so the plate may not need a fixture...would you all agre with that? DaveR, you mentioned you used well water? Although I live in the country I am not on well water. I am sure there is chlorine in the tap water we use. Is that a problem?
Thanks for the numbers...I see a furnace in my future.
Much appreciated, Richard

[David Rase]

Dave,
Nice colors on the Harpers Ferry lock. 

Richard,
I use well water because that is what I have.  Don't know if chlorine is good, bad or indifferent.  Maybe someone else knows the answer.  You picked right up on the design of my crucible and a vertical approach to the quench. 

When I held down a full time job, I, like most of us had limited time to divide up on all the different aspects of building a longrifle.  So when I came upon a process that gave me results that met my standards, I stuck with that process.  Now that I have retired I hope to do more research and experimenting and fine tune a few things.

David

[smart dog]

Hi Richard,
Dave R shows a really nice crucible for the pack.  The large rectangle must allow his pack to drop like a solid brick, and the vertical orientation absolutely will reduce risk of warping.  I began by using a chunk of 3" steel pipe capped on one end and with a loose lid on the other.  The pipe did not release the pack as a solid and it poured out.  That is when I found a steel rectangular pan with lid that worked very well.  I don't know if chlorine will affect the colors.  Oxygen and nitrogen do but I cannot say about chlorine.  I learned my method using rainwater.  I lived in Ketchikan, Alaska, and we captured rain water off our roof and stored it in a 7000 gal cistern for our water supply.  Now in Vermont, I have a well.  My water contains a lot of iron which may be the reason I am getting wonderful results on wood with ferric nitrate crystals.  You can prevent warping of thin lock plates by simply attaching it to a 1/4" thick flat bar of steel using the lock bolt holes and machine screws.  It is really very easy.  I don't worry about other parts like frizzens, ramrod thimbles, etc.  Richard, based on my experiments, temperature had the following effects (all heat soak times were 90 minutes):
1375-1425 degrees   -   colors dominated by blues and purple, amber color subdued
1425-1475 degrees   -   nice mix of blues with purple and amber
1475-1525 degrees   -   purple mostly gone, blues present, amber becoming dominant
1525-1575 degrees   -   amber dominant blues subdued, no purple at all
1575-1600 degrees   -   mix of amber and grayish tones

dave

[jerrywh]

 Smart dog and Dave Race are both very good at what they do. Anybody would do well to follow their advise. Race and I have been good friends for many years. In my opinion he is one of the best traditional gun makers in the country today.  
 I like smart dog's color chart. My experiments pretty much coincide with his on the colors. I have found that a temperature above 1650 or 1700 pretty much destroys all colors. I think that the higher temp. creates so much steam around the part that it makes the outcome uniformly gray.

[flatsguide]

Dave,DaveR and Jerry,
I agree Jerry...All three of you in fact.
Thanks so much for your detailed advice and sharing your hard won knowledge. It is much appreciated and I hope to do it justice. Just a few days ago my wife said she was interested in making Dichroic glass jewelry..guess what, one needs an oven for that work. So popping for a furnace is a win win.
DaveR, how long is your crucible ?

I came across the info below it is from the 1924 machinery handbook. It may be of interest...

Casehardening for Colors. -- For hardening and at the same time coloring such parts as wrenches, etc., the following mixture may be used: Mix 10 parts of charred bone, 6 parts of wood charcoal, 4 parts of charred leather and 1 part of powdered cyanide. The leather should be black, crisp and well pulverized, and the four ingredients well mixed. The object in charring the bone and leather is to remove all grease. The parts to be colored must be well polished and should not be handled with greasy hands. To obtain satisfactory work, these rules must be observed. If the colors obtained are too gaudy, the cyanide may be omitted, and if there is still too much color, leave out the charcoal. The parts to be colored and hardened should be packed in a piece of common gas pipe having a closed end. Pipe is preferable because the pieces can be dumped into the cooling water with little or no exposure to the air. The open end of the pipe can be places close to the surface of the water before the parts are removed, but with a box there would be more or less exposure. This class of work should be heated to a dark cherry-red and kept at that temperature for about four or five hours. If the temperature is too high, no colors will appear. The tank should be arranged with a compressed air pipe connecting with the water pipe at the bottom in such a way that a jet of air is forced upward, thus filling the tank with bubbles. There should also be a sieve or basket in the tank for receiving the work. After quenching, place the parts in boiling water for five minutes and then bury them in dry sawdust for half an hour. Another mixture recommended for coloring consists of 10 parts granulated bone, 2 parts bone black and 1 part granulated charred leather.

[smart dog]

James Rogers,
Is the lock plate from a gun made by Joseph Heylin?  He is one of my favorite British makers.

dave

[jerrywh]

flatsguide.
  4 or 5 hours is way to long for gun parts. The penetration rate of the carbon into the metal is approximately .010 pr. hour at 1550° F. Remember this happens on all exposed surfaces therefore a lock plate that is .125 thick will be infused to a depth of .040 or .050 from each side with carbon. In effect this transforms the whole plate into high carbon steel throughout.
 This is not necessary. By the way parts shrink when case hardened to some extent. They also shrink when hardened and tempered. Enough so that a spring may not fit the original holes it did if fitted before heat treating. An hour at the proper temp if sufficient. Heat penetrates steel at approximately .125 in 20 minutes. When you heat a piece of steel to red heat visually it is not immediately that hot on the inside. Try to think of heat treating as though you were cooking a biscuit. Just heating a biscuit to 350 does not get it done. It may take 15 minutes to get it done on the inside. Steel is like that.

[flatsguide]

Thanks Jerry, got it, good to know. I noticed Smart dog soaked his parts for 90 minutes.
Thanks Jerry

[James Rogers]

James Rogers,
Is the lock plate from a gun made by Joseph Heylin?  He is one of my favorite British makers.

dave

Dave,
Yes sir, it is on a Joseph Heylin fowling gun with John King sterling furniture dated 1767 and a Eudal Pous of Barcelona barrel. I admire his work for that period also.  

[David Rase]

DaveR, how long is your crucible ?

flatsguide,
The overall length of my crucible is 7 1/2".  The OD of the square tubing is 3".  The welded flange on the end is 4" square as is the lid.  I made the lid and flange larger than the flask so when it is laying in my oven air is allowed to circulate around all 6 sides.  I can pack a lock plate and pan, frizzen, cock and top jaw and all the screws and lock bolts in the crucible.   
David

[flatsguide]

Thanks Dave, The reason I asked was to get some idea of the oven chamber size . Did I understand that after packing and putting the 4 inch lid on you lay the crucible on its side?  If so how do you fasten the lid so it does not come off. In the photos you sent of the dumping process what was the purpose of the other fellow assisting with the hooked rod. I hope you don't mind this nooby asking the basic questions.
BTW what is the size of your ovens chamber.
Thanks much, Richard

[smart dog]

Hi Flatsguide,
My oven is only 9" high and you need some clearance from the insulating baffles.  That is why I use a flatter rectangular pan and cover and also why I do not orient lock plates vertically for the pour.  I would do as Dave does if I could but I think his crucible would be too large for my oven. Instead, my pack drops into the quench horizontally and I have to block thin lock plates to prevent warping. It is what it is and I adapt.  Blocking is not hard to do and I suffer no ill effects from my set up compared with Dave's.

dave

[David Rase]

Thanks Dave, The reason I asked was to get some idea of the oven chamber size . Did I understand that after packing and putting the 4 inch lid on you lay the crucible on its side?  If so how do you fasten the lid so it does not come off. In the photos you sent of the dumping process what was the purpose of the other fellow assisting with the hooked rod. I hope you don't mind this nooby asking the basic questions.
BTW what is the size of your ovens chamber.
Thanks much, Richard

Richard,
Here is a picture of my crucible which should help answer a few of your questions.  As you can see in the photo, my lid has 2 tabs that get pinned to the crucible. 



The gentleman assisting is using a hook to pull the pin.  After I remove the crucible from my oven, I set the crucible on a piece of wood spanning the quench tank.  I place a piece of sheet metal over the wood to keep the wood from burning when I set the crucible on it.  Prior to sliding the crucible off of the plank an assistant uses a hook and pulls the pin.  This frees the lid up so when I slide the crucible off the plank the lid along with the charcoal and the parts dump directly into the quench.
I think my furnace is 9" x 9" x 6 1/2".  The kiln is 220 VAC.  If I was to do it over again I would buy a furnace with about a 10" x 13 1/2" x 6 1/2" capacity.  I hope this information helps.
David

[smart dog]

Dave,
That is a really nice crucible.  I think I am going to weld up a copy.  My only problem is I work alone so I'll have to figure out a single man procedure.

dave

[flatsguide]

Thanks Dave that answers the question just fine. I guess if one is doing this solo he could put a large nail in the board set the loop over the nail and just pull the crucible off the board.
Back to looking at ovens.
Thanks, Richard

[flatsguide]

This furnace is on the top of my list...

http://www.paragonweb.com/HT14D.cfm

[jerrywh]

 I made my own furnaces. I have made  7 furnaces. Directions and supplies can be found on the net. A good place to look is ceramic shops. For electric furnaces I use the controls off of old electric stoves. Pyrometers can be bought from E bay or ceramic shops. Look up kiln supplies. When I first started I made a propane furnace out of a 5 gallon bucket lined with castable refractory cement. Lot of places sell that. You can use a hand held type K pyrometer with a   stainless steel probe to check the temp. Acer has some real good cheap ideas for heating the pack of crucible. Maybe he will chime in. He has shown this on the forum several times before.

[flatsguide]

Thanks Jerry, I will look into going that route.

Regards, Richard

[JCKelly]

Smart Dog
 You say your case-hardened frizzens spark better than a store-bought & hardened one

Makes sense to me.

The as-cast frizzen has some carbon burnt out of the surface, just exactly the opposite of case hardening.
By case hardening it yourself, you are restoring some of this lost carbon.

I missed whether you case harden a new, soft frizzen or one that has already been hardened once.

The other defect of investment cast steel parts is that the grains are amazingly coarse. This makes the steel, at whatever hardness, less ductile, less likely for the flint to remove a nice curly chip (frizzle) of steel. By almost any heat treatment, annealing, heating red hot and air cooling, or by casehardening it the grain size of the steel gets refined.

Fine grained steel is tougher, better than coarse grained, always.

The neat thing about steel is that if you have coarse grained metal, you can refine the grains by heat treatment.

For parts that you do not want to break it would be really cool to know the carbon content of the original casting.

Where strength is concerned there is more to color case hardening than just the pretty colors.

A two-part series on color case hardening, by Oscar L. Gaddy, was published in Double Gun Journal, Winter 1996 and Spring 1997.

As far as cast "steel" side-plates in the 18th century, they would be Malleable Iron. That is a cast iron with some ductility. Frames of Allen pepperboxes were malleable iron, as were frames of that French pinfire revolver used in the late Unpleasantness Between the States. London Colts with "steel" mounts actually had malleable iron backstraps & triggerguards.

Jim Kelly, P.I.T.A. metallurgist since 50+ years

[Joe S.]

How you folks handling the thinnest of parts like patch boxes ect?Yes these treatments will make the metal brittle but looking to keep your iron parts matching in color.Baking in the oven to take some of the brittleness out of parts seems to be the answer but keeping them from warping would be the bigger concern,your thoughts?

[jerrywh]

I don't recommend case hardening anything as thin as a patch box and I do not shine the bottom of my shoes.
 Thin stuff like that might come out looking like a potato chip.