life span of charcoal

[holzwurm]

I've been playing around with anealing a friz by packing it in charcoal and heating it in a crucible. Does charcoal have a life span or can I continue to ues it?

[Acer Saccharum]

As long as it's black, it's charcoal. When it burns, it combines with oxygen and what's left is white ashes. You can sort out, screen out, your charcoal and use it until it's all used up.

But, If using it for pack hardening, I would use fresh charcoal every time. What you are doing in the crucible is creating a carbon rich atmosphere. If your charcoal is almost spent, then you may not get the depth of case that you want.

So, yes, you can screen it, dry it out, heat with it, but its value is certainly depleted.

Maybe cook your burgers with it.

T

[keweenaw]

It's fun to disagree with Acer.  He's right that if it's black it's charcoal.  The issue of whether it's spent or not is another matter.  Wood charcoal by itself doesn't give much color - at least that's my experience - but it will give whatever depth of case on wants if it's hot enough and in the pack long enough.  Some percentage of bone or leather charcoal seems to aid greatly in getting good color.  Clearly there is something going on here besides generating the CO that is entering the pores in the hot steel.  I would guess that it is the compounds liberated from the animal charcoal that generate most of the color and it's these compounds that would be depleted with multiple heats.  If all one wants to do is to harden the steel, I think you could use your charcoal as many times as you want.  Since some is lost each pass you're always adding a percentage of new for each heat anyway.  I've reused the charcoal from a mixed wood and bone pack and gotten better colors the second time around than the first.  Just make sure to give the stuff a long time to get thoroughly dry.

Tom

[holzwurm]

  color case hardening is a whole other learning curve for me Gentlemen. At the moment all I'm doing it anealing a friz - I know I'll have to harden it after I'm finished but we'll cross that bridge when we come to it

Just make sure to give the stuff a long time to get thoroughly dry.

Dry! how did it get wet? Are you referring to when the crucible is pulled out of the oven and the whole content, lock parts and charcoal, is dumped into a bucket of cold water. Is that the wet you are refering to?

[flintriflesmith]

I've been playing around with anealing a friz by packing it in charcoal and heating it in a crucible. Does charcoal have a life span or can I continue to ues it?

You don't need any charcoal at all to anneal a frizzen. Just heat it to a red and allow it to cool slowly. Some steels like to be cooled VERY slowly and for those you may need to place the red hot part in ash or lime so it will be insulated.

Heating in a charcoal filled crucible is for re-hardening (case hardening) a steel thatdoesn't already have enough carbon in it.
Gary

[holzwurm]

AHA! another wrong turn - well, thanks for the info. I thought I was doing it right but guess not. Amazing what you find when you ask a question.

[Acer Saccharum]

Oh, sorry, Jerry, here's how charcoal gets wet:


Dry it out and use it until it's used up. In your case, you won't be wetting your charcoal, you will just let it cool slowly, it its crucible. This will keep oxygen off your frizzen, and adding carbon to the steel all the while. You won't get a bit of scale on it or lose any steel to oxidation, important to consider when you have parts that are already fitted.

Gary is right that you don't need the crucible and charcoal to soften a frizzen.

Tom

[Acer Saccharum]

It's fun to disagree with Acer. ..... Clearly there is something going on here besides generating the CO that is entering the pores in the hot steel......

Tom

Tom, through disagreement we might learn something new. I like to have disagreement, too. I hate it when I'm always right!

I didn't know about better colors second time around.

FYI:
I spoke with my professional heat treater on how they caseharden their parts in big batches. I was curious about holes in parts getting casehardened if they didn't have charcoal packed in them.

He said, first of all, they don't use charcoal to caseharden. They use an electric furnace filled with methane gas. So, yes, any gaps or holes will get hardened. This is a carbon rich ATMOSPHERE, not hardening by contact with charcoal, bone, etc.

I assume a closed crucible filled with carbon rich material, with heat applied, will make a carbon rich atmosphere. All oxygen is consumed by the carbon during the early stages of heating. Heat the steel, surround it with carbon gas, and the carbon soaks into the steel.

The treater said if you don't want a threaded hole to get casehardened, pack it tightly with steel wool. The wool absorbs the carbon, leaving the threads soft.

[keweenaw]

Commercial carburizing of carbonitriding is done in an closed furnace with an atmosphere or carbon monoxide or CO and Ammonia gas.  These gases enter the "pores" in the steel as it is held at temperature.  These processes rarely develop any color on the parts.  One might get a bit of a straw type color or some really faint  blues when carburizing.  Carbonitriding gives a nice steel gray color.  In the pack hardening that we do, the oxygen in the crucible is consumed quickly as Acer says, and the pack then liberates carbon monoxide which enters the steel. 

For annealing I bury parts I don't want to scale in a crucible that's packed with cast iron chips for heating to critical temperature.  Common cast irons are full of carbon and when lathe turned or milled give short chips.  The carbon in the cast iron is sacrificed to absorb the oxygen and hence no scale.  As Gary says how slow you need to cool will depend on the steel.  I keep a pail of fine wood ash in my shop to bury stuff in for slow cooling.  I also use the cast iron chip cover for heat treating carbon steel pieces to reduce scale and surface carbon loss.

Tom

[Acer Saccharum]

Tom S, if I want to anneal, may I pack in charcoal and let cool? Is there ant harm in that? Especially if I'd like to keep the carbon level up in the steel.

I like your method of packing in cast iron chips, I have lots of those!

[keweenaw]

Should be no problem in annealing in a carbon pack although I've never cooled anything in the pack.   It won't add any amount of carbon to the material even at critical temperature unless you keep it there for an hour or more which you won't be doing for annealing.  As long as it's not scaling you won't be losing any carbon and I find it easy to use the cast iron.  Steel chips wouldn't serve the same purpose as the iron as they aren't high enough in carbon to take up the oxygen.  I like the cast iron chips for doing knife blades that I want to finish bright.  I can get the blade almost final sharp before heat treating, heat in the iron chips pull out and immediately oil quench.  No real scale on the blade, just the burned on carbon from the oil that will wipe off.  After tempering, just do a final sharpening with no heavy stoning necessary.

Tom

[Acer Saccharum]

Tom S, thanks for that tip on heat treating blades. Soon I am going to make a bunch of small chisels, and the iron chips will be just the ticket to keep the blades clean.

May I add your input to the case hardening/heat treating thread in Tutorials?

Thanks, Tom C

[keweenaw]

Fine by me to add this information to the tutorial.