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Letter 2108
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Tom Pullizzi |
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I have a couple old Remington rolling block actions that need color case hardening. I saw a 3year old post regarding this and have a question. When you say plunge it into water do you mean the container or its contents?
Thanks,
James Arnold
aspiring gunsmith - Syracuse, New York
Case Hardening
The following is a composite of two excellent posts on case hardening
by subscribers Bruce Conner and Ward French.
It can be found at:
http://members.aol.com/illinewek/faqs/case.htm
For readers wishing to pursue colour case hardening further, I
strongly recommend a series of two articles by Mr. Oscar Gaddy on the
subject, found in the winter 1996 and spring 1997 issues of the
Double Gun Journal.
Bruce begins:
Case hardening involves putting carbon (or a combination of carbon
and nitrogen) into the surface of the steel to make it a high-carbon
steel which can be hardened by heat treatment, just as if it were
tool steel or any other high carbon steel. Only the outer skin gets
hard this way, the center is still tough and malleable. This makes
for a strong part with a tough surface.
Ward continues:
Low carbon steel, i.e. steel with about 20 points or less of carbon,
cannot be made to harden by heating and quenching, as higher carbon
steels can. Low carbon steels are tough, soft and flexible. They wear
quickly and batter easily.
Many parts, including gun actions in days gone by, were made with low
carbon steel. It was cheap, strong and easy to machine. Unfortunately
it would not stand up to the battering of use in the field. Case
hardening added carbon to the surface skin of the steel part and left
it in a state which could be hardened by quenching.
To case harden a part (the process is also known as pack hardening)
the finished low carbon steel part is placed in a sealed container,
packed with a high carbon compound. In the old days this was simply
animal hide or bone. The container filled with parts and carbon
bearing material was brought to a red heat and held at that
temperature for a time determined by the size of the part. The time
might be from a half hour up to several hours. As the bone or hide
became carbon in the container, and a carbon rich gas formed, some of
the carbon would infuse into the surface of the steel. Over time this
would penetrate several thousandths of an inch, producing a high
carbon surface on the low carbon steel part.
At the proper time the container is removed from the furnace and the
contents dumped into a quenching bath, usually water with perhaps a
surface coat of oil to lessen the shock of the quench. The high
carbon surface skin becomes glass hard, but the low carbon body of
the piece remains soft and very ductile and able to resist shock.
Properly done it made a simple and very durable system for treating
metal action parts.
Colors are produced when the steel surface is cooled unevenly,
capturing the natural blues, oranges and yellows of cooling steel.
Several methods are employed to do this. Stevens moved the parts into
the quench in a jerky fashion, producing a barred effect of color.
Perazzi did the same. In the London trade the quench bath, usually a
barrel with soft water and a skim of oil, was agitated by stirring,
or with bubbles of air, producing a mottled effect on the
steel.
Bruce adds:
Color case hardening is done much the same way except that generally
only leather and bone are used as the carbon source. I don't know why
this works better than charcoal, but it does. You get more brilliant
colors with them. The other thing you do is modify the quenching
bath. You need a source of bubbles. LOTS of bubbles to really rile up
the quench bath. Adding a bit of potassium nitrate to the water
increases the brilliance of the colors as well, but isn't a
requirement. You have to watch the temperature more closely with
color case hardening or the colors won't come out well. Don't go over
1350 F.
Kasenit and similar compounds are a lot easier to use and you can
just use a torch. You heat the part up red, dunk it into the Kasenit
compound and get a good coating of it sticking to the steel in the
places you want hardened. Then reheat it up to a good red and quench
it in water. This can be repeated to increase the depth of the case
hardening. It works very well and is quite fast, but leaves a kind of
dull grey color to the surface. For parts that are internal it works
great and if you make the hardening deep enough, you can polish the
metal and still have a hard surface.
Ward continues:
The colors have nothing to do with the effectiveness of the case
hardening. Many, if not most, parts are hardened without colors. The
surface takes on a dull gray look. The London makers usually polish
this surface bright. It is glass hard, but without the decorative
affect of the colors.
Anyone who has a case colored part should be aware that colors will
fade on exposure to direct sunlight over an extended time period.
Parts must be protected. Clear fingernail polish or a similar lacquer
will protect the surface and a gun case or cabinet will do the rest.
Case hardening was widely used on all lock parts except springs, and
the process could be carried out even on the frontier with a minimum
of equipment and knowledge.
Good shooting,
Ward and Bruce
Walter Taber
- Houston, Texas
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September 3, 2008 The leather and bone composition is correct. I have tried this myself to case harden frizzens for flintlock pistols and rifles. It produced a hardness sufficient to resist a file. I tried several lenghts of exposure to heat and got results from just the surface hardened to hardening to a depth where the part shattered when dropped like it was glass. There are many old world recipes using various components (sea salt, chamber lye (urine), calcium, etc.) but all of them included leather or bone or a combination of both (animal carbons). Hardening was usually "in the white" leaving a grayish or white metalic, frosty, look. I found an old English recipe "MOXON's Method" that I use to this day. It uses a tin with lid in which you fill with powdered bone, leather dust, charcoal powder and a small amount of calcium carbonate. The ratios can be adjusted for different effects but typically 3 of bone, two of leather, 1 of charcoal and one half carbonate. You place the item to be hardened into the mixture, add a little vinegar (it will eubilesse). Let finish and stand so the mixture completly covers the part when done bubbling. Drill a small hole in the lid so you can observe the color of the mass. Cover & Heat til mass is blood red, hold for half an hour after reaching temp. Quickly remove lid and quench part in cool water with tongs, keeping it moving. For color, try an oil and water mix (make sure it is well agitated so the oil is in thorough suspension) instead of just cool water. This causes uneven cooling and renders different surface appearances. Remember, this can be dangerous and should be done outside where spills, splashes cannot damage or harm. Always wear a full face shield [link is to product info at Amazon], insulated protective gloves [link is to product info at Amazon] and apron [link is to product info at Amazon]. Have a charged hose ready to wet you down if hot fluid spashes on you. Have fun, experiment but survive to enjoy it! Mike Zacharko
I am an artist/hobbyist and hold a PHD and TRI, I have been making guns for many years.Recently I have been wanting to try Colorcase Hardening Recievers. My question for all you vetrans out there is... what do you use for packing the parts? Earl Niganobe
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