Case Hardening Questions

[Long John]

I'm fixing to case harden a lock for a rifle and I have a couple of questions for those of you who are more knowledgeable about this than I am.

1.)  I figured that I could use a 3" diameter schedule 40 black iron pipe nipple 8 " long with a threaded iron cap for the bottom and a flat plate for the top as my crucible.  Is that enough volume for a single lock plate, cock, top jaw screw and top jaw?  How much charcoal does one need surrounding the steel parts to be hardened?

2.)  When case hardening every one seems to has dump the hot parts into a water quench, but the folks who wrote the instructions for the Chambers locks recommend a light oil quench for the frizzen, lest it crack.  Do you guys who case harden the lock include the frizzen?  Do you quench in light oil?  How do you ensure the frizzen doesn't crack if you just use water?

3.) Brownell's sells both wood charcoal and bone charcoal.  Which does one use?  Or do I use some of each?  If, so, in what proportions?  Brownell's gets a pretty fair chunk of change for their charcoal.  Pure carbon (carbon black) is made on the industrial scale by pyrolyzing sugar.  (I've been in the plants that make it for work.)  Has anyone tried that for gun-making?

4.) I don't have a heat-treating furnace and no place to put one if I did.  I plan to make an impromptu charcoal furnace with loose fire brick in the back yard.  How long does one keep the crucible at temperature (red-hot) to achieve a suitable case hardening?

Thanks for your insights into this subject.

Best Regards,

John Cholin

[doug]

relative to the quench; you can also float about 3/8 to 1/2 inch of oil on top of the water.  The oil will take some of the temperature shock off before the parts reach the water.  Something you may have to worry about is the long flat lock plate warping if it is dumped into the water.  An alternative would be to lower the plate into the water on edge ie with the long axis parallel to the surface of the quench

cheers Doug

[Mark Elliott]

John,

You need to be able to control the temperature to control the colors.   Search on previous color case hardening threads for answers to your questions.   Jerry Huddleston has provided a lot of good information on this.  The bottom line is that I don't think you can do a good color case without a temperature controlled furnace.  

I get what I think are good results using just plain hardwood charcoal from Lowes.    I wouldn't pay for the expensive bone charcoal from Brownells.

As to the frizzen,  I wouldn't try to get a color case on a tool steel frizzen.   If I wanted some color,  I might treat it separately for a blue/black finish. 

I think your crucible should work if you could heat it correctly.

[L. Akers]

r.  Something you may have to worry about is the long flat lock plate warping if it is dumped into the water.  An alternative would be to lower the plate into the water on edge ie with the long axis parallel to the surface of the quench

The quench must be direct from the crucible into the quench with, ideally, no contact with the air.  The entire contents of the crucible, including the charcoal, are dumped at once so there is no way to "lower the plate" into the quench the way you would a knife blade.

Items to be cased must be held at temperature for 2-3 hours or longer depending on how deep you want the case.  The quench should have a substantial column of small air bubbles rising thru the quench (causes more colors).

I don't have the equipment to do casehardening either so I send mine out to Classic Guns in Crete, Il.  I don't case  frizzens but will blacken them instead.

[smart dog]

Hi John,
I cannot help you with how to use a fire or charcoal to keep up the heat.  I have an oven with controller so I don't worry about the heat source.  You will need some way to add fuel and introduce air to keep the heat up for an hour or more.  I believe most modern locks use steels with sufficient carbon to be through hardened without having to add carbon so casing is not necessary.  You could simply heat the parts to glowing red and quench immediately in oil.  Then heat them again to a tempering temperature.  The advantages of case hardening is that it replaces any carbon burned of during heating, it can produce nice colors if desired, and if you pour the pack without the parts being exposed to air, you will get no scaling.  That brings me to your pipe crucible. Your proposed container is sufficiently large for the lock plate but may not fit other parts  all together.  You may have to do your parts in several batches.  I generally like at least 1/2" of bone and wood charcoal to surround each part and parts should not touch.  The problem with the pipe is that the screw cap will take time to unscrew, a process that will be difficult to do quickly when glowing red hot.  You'll have to just have one thread or so engaged so it will come off quickly.  The other problem with the pipe is that it is very hard to pour the contents as a solid unit into the quench. The pack tends to come out in a stream and the parts get exposed to air before hitting the water.  I use a rectangular metal box with a lid. When I pour the lid and contents fall into the water as a solid brick, which produces good results particularly if colors are desired.  Don't worry about just using room temperature water for quench if case hardening.  You will risk cracking if you simply heat the part in the open and quench in water rather than oil.  When case hardening, unless the lock plate is very thick, I usually attach it to a flat bar of 1/4" steel using the lock bolt holes and threaded holes in the bar.  I thread screws into both plates leaving 1/2" space between that will be filled with charcoal in the pack. The heavy bar blocks the plate and prevents warping during quench.  I use Brownell's charcoal (bone and wood) and have no experience with other packing material.

dave

[JPK]

Long John, I do a fair amount of case color hardening with good results so to your topic.
1. Your crucible of pipe idea is sound. Heat the pipe to burn off any oil or paint before using it. Use a large enough pipe or pipes to enclose the parts with a least 1/2" of charcoal on all sides, I prefer more on top and bottom. Tap the pipe to settle pack but don't compress it. It must be full.
2. The frizzen should be done just as the maker instructs as it is an alloy steel made to be oil quenched. The lock plate, pan, hammer and bridle can all be cased with water quench. Dry them and reheat in your kitchen oven at 375 degrees for one hour. The oil for the frizzen quench should be pre heated to 150 F and be at least a gallon to insure no cracks.
3. Brownells charcoal works great and I mix it 1 bone to 4 wood most times. You can use lump charcoal that you would BBQ with broken to about 1/4" instead of buying it from Brownells but the bone is best bought. I have never tried carbon black. I have used the old Kasenite with wood charcoal and got fair results.
4. A good large fire that makes the crucible glow light orange all over does work just be careful not to knock your work over in it. At least an hour at temperature will give a good case. When you pull the crucible from the fire allow it to go to red before quench. I like rain water but tap water works fine. And agitate the water just before quench.

[smart dog]

Hi JPK,
I respectfully disagree with your tempering suggestions for the flintcock and bridle.  Today's cast steel lock parts are not the wrought iron of yesteryear and a flintcock tempered at 375 risks breaking during use.  That has happened to me as I learned the process, which I do on every rifle I make. I recommend 490 for the plate and flintcock and at least 550 for all the internal parts.  The frizzen can be tempered at 390-410 with good results and no breaking at the toe.

dave 

[T*O*F]

I'm fixing to case harden a lock for a rifle

John,
Your opening statement says nothing about "color case hardening" yet everyone assumes that right off the bat.  If you want to just harden the lock plate 99% of their instructions probably don't apply. 

So, instead of everyone assuming something that might not be true, are you just trying to case harden the plate or color case harden it?

[Acer Saccharum]

John, that is about the size of my crucible.

I just use the wood charcoal. You can get colors with wood, if that's what you want to do.

Build a deep fire, with a lot of charcoal UNDER the crucible so the fire can burn down with plenty of fuel under the pot, and charcoal around the crucible to get the sides of the pot to red. You'll need a blower to get the fire cranking. The bottom end of the pot will get hotter than the top, unless you can also force some air in from the sides.

[smart dog]

I'm fixing to case harden a lock for a rifle

John,
Your opening statement says nothing about "color case hardening" yet everyone assumes that right off the bat.  If you want to just harden the lock plate 99% of their instructions probably don't apply. 

So, instead of everyone assuming something that might not be true, are you just trying to case harden the plate or color case harden it?

Hi Dave,
No, not everyone assumes he wants colors, which is why I wrote that case hardening can produce colors IF DESIRED.  My comments apply whether you want colors or not.

dave