Did I anneal or case harden my axles shafts?

D

D.sebens

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So I have some automotive axle shafts I threw into my burn pile last night to anneal. I’ve used the wood stove before for smaller sections and it worked great.

The burn pile will probably be going for a few days and they are buried. Do you think they will come out annealed or do you think they will come out case hardened from being buried in a co rich environment?

I think they will be annealed but maybe the carbon content on the surface will be higher?
 
They will come out annealed. In the environment you describe, the carbon will readily convert to CO2 and not infuse into the steel. To case harden, you need both the steel and the carbon to be in an oxygen free environment for quite a while (together) so that the carbon will infuse into the surface of the steel. The longer the two are together at red heat, the deeper the carbon penetration.
 
That makes sense. I was thinking that now as they are buried in the ashes and trapped in the fire I wondered how much co is in there? The fire has cooled a lot at this point though and I suspect they would be dull red in a pitch black room at best.
 
As with anything when you take a technical process and turn it into an uncontrolled and improvised substitute procedure, the outcome can be quite "variable". But if you get the fire hot enough, odds are they come out annealed. How annealed? Probably plenty well enough to work with.

if you're ever doing that in a burn pile again, aim for the center of the pile, higher up. That's where it gets HOT. Metal will find it's way to the bottom of it's own accord, and when you find it again, it'll be down deep in the coals.
 
SLK001 said:
They will come out annealed. In the environment you describe, the carbon will readily convert to CO2 and not infuse into the steel. To case harden, you need both the steel and the carbon to be in an oxygen free environment for quite a while (together) so that the carbon will infuse into the surface of the steel. The longer the two are together at red heat, the deeper the carbon penetration.
Click to expand...
This.

If anything you removed carbon from the surface of the steel.

Do you intend to re harden these after making something?
 
They were at the top. They worked themselves down. I don’t have any plans. Just wanted some metal on hand for what ever projects I might do.
 
I found some white cast iron slugs cleaning up a place and threw them into the trash fire to see if I could get them hot enough to transform into malleable cast iron. I got the fire cranking and threw the slugs in. The fire burned well into the night and the next day was still burning coals about 2 feet deep. The next day I dug into the still hot pile with a pitch fork and retrieved one of the slugs. It was still red hot in sunlight so I dropped it back in. 5 days after the fire was started I dug out another slug with the pitch fork, it was no longer glowing but was still hot enough to cause water to boil. I let it all set over the weekend and dug them out and they were still warm to the touch. I haven't tested to see if they are machinable yet as I really don't have a project for them yet. I have used the trash fire to anneal some railroad bolts, 1-1/4" diameter and they come out dead soft and they will reharden with a quench in oil. Not knife grade or anything but hard enough to not cut with a file.
 
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