Home Annealing of Hardened Drill Rod?

[Alan Carruth]

Now, if you'd put that in a charcoal fire, you'd have case hardened it, at about .0005" thickness of case per hour.

Alan Carruth / Luthier

[Andy Birko]

Actually, that was a charcoal fire. It was lump charcoal though, not briquettes. For the type of grill i have, briquettes leave too much ash so you pretty much have to use lump charcoal (which tastes better too!) If there was any case hardening I certainly didn't notice it.

When I tried a file against the un-treated hammer, it didn't leave a scratch. After the annealing, it instantly felt like mild steel. It cut and machined just fine.

Thanks to my employer giving me the summer off ( and the rest of eternity for that matter) I should have the project finished soon and I'll post a pic.

[Alan Carruth]

The traditional ingredients for case hardening are iron, red heat, and carbon monoxide. The CO adsorbs on the iron surface, and two molecules of CO combine to form CO2 and liberate one atom of carbon, which then diffuses into the iron. In your case there was probably enough air circulating to limit the amount of CO present, and you might have only gotten a little bit of case in some spots. Meanwhile, red heat plus oxygen reverses the reaction, drawing carbon out of the surface and softening the steel. Steel can be tricky stuff...

Alan Carruth / Luthier

[David King]

Kasenit or Cherry Red hardening compounds are reliable ways to add some surface hardness to low and medium carbon steels. It looks like Kasenit might be off the market.

[Andy Birko]

Steel can be tricky stuff...

Indeed. It's almost magic what can be done.

I looked around a bit and I don't think that the traditional method of case hardening works on tool steel as it's already a very high carbon steel, unlike plain old iron. Apparently case hardening doesn't work with over .5% carbon content.

Finally even if some additional carbon was introduced in the fire, the cool down period was so slow that we still ended up with all pearlite , even if this happens to be an air hardening tool steel. My grill is about made from some sort of 3/4" ceramic and takes a long time to cool down!

I actually did very well in my materials classes 20 years ago and this little project has brought back a lot of info I thought was gone for good! Still, I couldn't have done it without everyone's help - that's why I asked.

[Andy Barnhart]

I know the OP resolved this another way, but I just happened on this thread and figured I should offer info on how I do it. I bought a small piece of ceramic wool insulation. Mine is about 2' x 1' as I just needed it for knife/chisel/gouge blades. Lay it out flat in a safe location (like in your fireplace with no fire going or on the hearth or stove is okay if you don't have animals or kids to worry about). Lay the piece of steel on one half of the insulation, not too close to any edge. Use a torch (propane works okay, but MAPP is quicker and easier) to heat the metal to red. Carefully fold the insulation over it and set a flat stone on top to keep it folded. You want one that won't roll off and doesn't weigh enough to compress it much but keeps it folded. Let it cool; it should take hours.

[Andy Birko]

Just a quick follow up on this project - it failed miserably! The gears (probably plastic) of the planetary tuner I used obviously couldn't handle the torque of a tuning peg and stripped out in the blink of an eye.

I think the idea is sound but I'm not sure I want to seek out a tougher gear set....sounds expensive.

[David King]

Would a banjo planetary gear head be all metal? Otherwise a battery operated screwdriver is equipped with two planetary gear heads stacked one on the other.

[Andy Birko]

A banjo gear head tuner is exactly what I used but it was a $15 one so perhaps some are steel and some are nylon. I haven't taken this one apart to see what's inside yet.

The cordless drill/screwdriver thing is a good idea though - ones with obsolete & dead batteries are all over the place so I can almost certainly find one for free.

[Romeo Suave]

First of all forget about the color of heat, that info has no value for you.
The charcoal grill is a good idea for a forge. You want to get the drill steel up to critical temp, that is the temp that it loses magnetism no matter what the color is.
So, test with a magnet, when you have reached critical temp, just plunge it into a bucket of sand and let it cool naturally and it will be annealed when cool.