doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Who is doing quality color case hardening?

Think it would be good to have a Gunsmithing Forum on this site; lots of serious talent here.

Alex, PA24 and others have given some very good advice on keeping the temps low.

As an example of this: recently got a Winchester 1886 in; customer called me saying that he had it CCH by another company, and his gunsmith had broken the buttplate trying to assemble the gun.

He asked that I weld up & CCH the BP, and assemble his 86. Gun came in and I could tell immediately that the CCH parts were quenched at too high a temperature (Colors were way too dark). Then when trying to assemble the gun, found that the frame was warped enough that the bolt would not fit in the frame, hammer wouldn’t fit in the lower tang (that bad).

Called the customer up, gave him the bad news, and told him that the frame was repairable but; I wasn’t about to fix the frame without annealing it first.

So annealed the frame, about 5 hours straightening the frame and then re CCH. That inexpensive CCH job cost him some serious $$$.

In my guesstimation here is what the first …Expletive.. did wrong:

Did not anneal frame before CCH
To hot & too long soak at hardening temp
Did not properly block the parts
Quenched at too high a temperature.
Quenched in a weak Brine solution (which cools much faster that straight water)


FYI: For those of you that may not know, Ebonex is the only manufacturer of Bone Charcoal in the country… So no matter who supplies the Bone Charcoal ie.. Brownells, Midway etc. Ebonex manufactured it. You can call them directly and order straight, generally at a better price if you buy in quantity & open an account. Might be good for commercial & institutional consumers.

I just got a 50 lb bag in from them today @ $2.10 p/lb,...has almost doubled in price since my last order

CJ

Iam in total agreement with you Mr. Mike ! In case our gracious host Mr. Dave reads this, a gunsmithing forum would certainly benefit all the readers of the other forums. Most all of us have a need from time to time for some sort of smithing advice or contacts. Well, I feel this type of forum would certainly attract the attention of our current membership as well as show the growth of this bbs to others & attract new members & sponcers. FWIW

MH - excellent discussion. Thanks.

Sticking with your example above, is the frame mild steel or does it have enough carbon to do some through hardening? When you anneal the frame, are you actually annealing only the case "skin," or do you actually soften the frame some? Do you have a process more compicated than passing the frame through critical temperature and then cooling slowly? In theory, it would seem that the "skin" would anneal as soon as it reaches critical and that the pre-annealing would not be necessary; any ideas as to why the first annealing step is necessary? Since the frame already has a case "skin" of high carbon steel from the factory case process, why do you soak it again? Does warpage come from unequal "skin" stress early in the heat or from unequal "skin" stress coming out of heat, like in quench? Or, does it come from within the base metal? Thanks, if you care to answer these.

Rocketman

Geesh; hard Questions… Hope you bear with me while I try and answer this off the top of my head w/o aid of my metrology and heat treating books.

These old frames were made out of low carbon steel, what we would call SAE 1018 – 1020 today, 0.1 -0.2 % Carbon. Steels with less than 0.25% carbon are generally classified as mild or non hardening steel.

Medium Carbon Steels have 0.25% - 0.5% carbon (SAE 4140)
High Carbon Steels 0.5% and higher carbon content, (SAE 1095)
Generally the last two digits of steel’s SAE number will tell the carbon content.

Case hardening is used on mild steels.
Thru hardening process is used on medium and high carbon steels.

Hardening occurs during heat treating when the steel (containing sufficient carbon) is cooled rapidly (quenched) from above its critical temperature. Mild steel heated and quenched from above its critical temperature will show no increase in hardness. In order to harden mild steel, its carbon content must be increased. To do this, the steel is placed in a carbon rich environment (Bone & Wood Charcoal) at a high temperature (above critical point). As bone & wood charcoal (almost pure carbon) is heated; it starts to produce Carbon Monoxide and a small amount of Carbon Dioxide gas, which is readily absorbed by the steel at higher temps. The longer the steel is held in this environment the deeper the penetration of carbon or “Case”.

When I anneal a frame, I generally heat it above its critical temp in a low oxygen environment (prevent scaling) and let it cool gradually, generally 12-14 hours. Annealing will remove the hard outer (case) hardening, and normalize the steel, relieving internal stresses, the frame in total is normalized.

Your Question : “it would seem that the "skin" would anneal as soon as it reaches critical” is interesting, and yes I wondered that myself, “wouldn’t the steel self anneal when heated above critical temps”. The simple answer is no. Annealing takes time and slow cooling, think of an ice cube melting at 36 degrees, it will melt but it takes time. Also since the bone/wood mixture starts producing Carbon Monoxide far below the steel's critical temp, and the steel will start to absorb this carbon below its critical temp, you are actually adding to the carbon already in the outer layer.

Does warpage come from unequal "skin" stress early in the heat or from unequal "skin" stress coming out of heat, like in quench? Or, does it come from within the base metal? Yes.. The majority of warpage comes from uneven cooling of the metal during quench, the more mass (thicker the material), obviously the more retained heat and the longer it takes to cool, this can be from milliseconds to seconds. I’m always concerned with thin areas attached to a larger mass. The temperature of quench and the ability of the quench to absorb/transfer heat away from the part have a significant impact. Quenching parts in boiling water will greatly reduce the shock of quenching, but will also reduce the amount and depth of hardening. Another example: SAE 1095 is an oil quench steel. Oil’s reduced ability to transfer and absorb heat buffers the shock of quenching this high carbon steel. If 1095 were quenched in water (greater heat transfer) you would have significant issue with warpage, cracking and uneven hardening.

So did I pass?

Mike, you get an A+ on my report card...

You may want to explain to them how NOT blocking-supporting parts (large open areas, which heat and cool at different speeds and temps) will cause them to warp as well....i.e., the rifle receiver you mentioned was probably cased without the bolt or a dummy bolt in place.......and possibly without the trigger block in place ?

The warping is minute, but nonetheless it must be fixed....this CAN ALL BE AVOIDED IF DONE PROPERLY...AS MENTIONED ABOVE....

Most gun metals and tool steels case to a depth of about .005..not much more.....

The greatest harm to any case color is U.V. light...leave your gun in the sun for long periods, or in a glass doored gun cabinet, exposed to sunlight and the case colors will rapidly go bye-bye.......that's why the old guns just have the "mottled" look, still very hard...but the colors are gone.....and there are some you will see at the shows 100+ years old that look like new...they have been "kept in the dark"..!!!!

I use dummy screws etc. to secure actions etc., in the crucible...as I am sure you do as well.....

Best Regards,

I don't know anything about metalurgy or heat treating either one, and about all I know about doubleguns, I learned here from listening to our experts. So, not to dispute the quote above, but I thought that Dr. Gaddy had always advised that UV would NOT harm or fade case colors, and that only wear would remove them.

Did I have that wrong???...Geo

George, in a private showroom at the Colt factory the lighting was flouresent & was left on 24 hours a day. About once a year + the SAA were removed due to fading on the display side to be redone. I agree, UV seems to wash out colors. In fairness, I have heard others say the same as the good Dr. Also, I have left a coupon that is CCH in my shop window for the past three years that hasn't faded one bit. I donno, looks like a toss up. FWIW

Hi George:

I've run some tests over the years.....casing two identical pieces of steel....put one out in the sun...leave one in a drawer.....ultimately, the one outside will lose it's color quite fast....like 6 mos....the one in the drawer will stay brilliant..?? Of course, that was the Arizona-Utah sun, which is the real deal as far as sun goes.............when I say lose, I mean a fade, not complete loss.....obviously the longer you leave it out, the more it fades....

That has been my experience...so I would have to stand by it ...other fellows have confirmed this as well...

Best Regards,

Thanks for the additional information...as Muderlak would say "Investigation continues"...Geo