View Full Version : Pack carburizing media

03-09-2009, 10:50 PM
I would like to compare notes on pack caburizing methods and see what others are using for media.

I have heard of common wood charcoal,stuff made from beans,coffee grounds and sawdust.Also what size mesh media works best and the list goes on.

So if you have done any what has worked best for you?

03-09-2009, 11:06 PM
For just general pack hardening, plain wood charcoal is probably as good as anything. Mesh size should be fine enough for intimate contact of all surfaces. Older issues of Machinery's Handbook have a pretty good section on pack hardening that covers the basics. I don't know if it is still included.

If you intend to do color case hardening, it becomes much more involved. Not only will the selection of materials be more critical, the quenching also plays a very major part in developing the colors.

Here is a very long write up on one person's travels in duplicating the colors of Marlin rifles. He did finally get beautiful results;


Mike Hunter
03-10-2009, 11:08 AM
I do quite a bit of pack hardening (Color Case hardening) here in the shop. Biggest question is; are you wanting to do this strictly for hardening purposes of are you also looking for aesthetics? Basic pack hardening is easy, getting good colors a bit more difficult.

For basic hardening all you really need is some carbon material that readily releases its carbon when heated, bone meal, leather etc. Coffee beans, peach pits etc I haven’t tried.

The material is readily available, Ebonex sells the bone char, or I’ve got used stuff here in the shop, I could be talked into sending you some if you just want to “play”.

Mike Hunter
Hunter Restorations

03-10-2009, 11:28 AM
I have used Kasenit to pack harden small parts with great success. It would be a bit pricey for large parts though I'd say. Don't know if it will give much color.

03-10-2009, 12:39 PM
As I recall, there is quite a bit on this in one of the Machinists Bedside Reader. He talks about coloring and how to make the compound from charcoal, fruit pits, stuff like that. If I recall, it was done in his fireplace.


03-10-2009, 12:45 PM
Lautard did write quite a bit on CCH, but made it a bit more of a mystery than it is. His articles are interesting, but one would do well to look elsewhere for better information before plunging in, especially if the part is of any value.

03-10-2009, 01:24 PM
JC,that's about the conclusion I have come to as well,plain ole wood charcoal.I am going to try making some with soybeans though since reducing the size would be easier.

Mike,I am after working hardness,color case looks to be something that would require a lot of trial and error which sadly I don't have time for right now.

I work a lot of 8620 alloy and most times just do a water quench which ends up around a 32-35Rc,good for pins,die blocks etc.But pack carburizing if done right can produce a part with a proper case and a soft core with less effort and $$$ than induction treating.

I have pulled some nice looking colors though and I did write down the process so maybe I can repeat the "accident" later:)

Craig and Gunsmither,ya Kasenite,I've used it before,never tried it as pack hardening though.

Peach pits has me wondering what effect if any the arsenic in them has on the end result?

03-10-2009, 01:36 PM
The carbon in the charcoal is the active ingredient in any of the materials used. Hardwood and bone seem to be the most commonly used, probably simply because of availability. The use of other materials is primarily to create the additional colors, I don't know how much is science at that point, but the various formulas were a closely guarded secret of the makers.

8620 is a good material for case hardening, soak time will determine the depth and hardness of the case. It will take beautiful colors if processed properly.

Mike Hunter would certainly qualify as resident expert, any advice he can give will be to the point. Take a look at some of the examples on his site.

Mike Hunter
03-10-2009, 02:18 PM
8620 case hardens beautifully.

I probably have over twenty reference books on pack / case hardening, most from around 1900 when the process was in common use. Lots of good info in them, how long to soak at what temp to give desired depth of case.

You really need to have bone / leather char in your pack, wood/vegetable charcoal alone doesn’t readily give up its carbon, the animal char gives up the carbon (in the form of carbon monoxide/dioxide) readily, it also seems to act as an activator.

Earlier I made an offer to send you some used bone /wood charcoal, its been used once, I don’t reuse it because once its quenched I don’t know the percentage of wood to bone (the ratio needs to be a bit more specific for expensive firearms) but its perfectly acceptable for hardening.

If you want some simple recipies… drop me an e-mail.

Your Old Dog
03-10-2009, 05:36 PM
The CCH process from Colt firearms was to put multiple guns on a circular rack/oven with burning leather and bone. The guns circulated around and around and that's how the honest randomness of the coloring. I've see pictures of the oven and it looked pretty crude, it was not round but rather oval in shape.