Heat treating fun...

[hoffman]

I got the little furnace just above 1800 deg and didn't push it because that's about as hot as I need it. I brought a chunk of a2 about 1" x 1/4" up to 1400 deg and crept it up to 1800 and let it dwell for about 20 min. I could see the "shadows" swimming over the surface at 1800 deg and it was pretty neat! I'm not sure about the magnet test because I don't have any suitable magnets around. Do you pull the part out and check it?

I'll have to do some more reading on the subject and give it a go again.

I've just noticed a couple of HSM's have posted about getting small furnaces and may be interested in some of my tinkering...

[Ian B]

Magnet test - if you have some cheap ones, I suppose you could stick one to the side of the metal before it goes in the oven - when you hear the clunk of the magnet dropping off, it's passed the test :-)

Ian

[darryl]

Hoffman, just about any magnet will work for the test. Mount one on the end of a steel rod and poke it at the heated piece in the furness. Don't remove the hot piece from the furnace.
Just don't use such a strong magnet that it will move the piece around in the furness.

You might attach the magnet to the rod by wrapping some brass wire around it. That way the magnet has less attractive force to the steel, because the wire prevents contact between the magnet and the steel. The other advantage to binding it to the rod with brass wire (or monel or stainless) is that you won't have an adhesive that could let go with the heat of the furness.

My guess is that a craft magnet would be the best for this. They are cheap, everywhere, and don't have so much strength that you would have a sticking problem, even with small parts in the furnace. They are also tolerant of higher tempuratures than the newer nib magnets.

Looking forward to the results of your first 'file test' of a hardened piece. You're re-stimulating my interest in heat treating, and fabrication of a suitable oven. I've wanted to do that for years.

[Your Old Dog]

Whats the deal with the magnets? I heat treated all my S5 chisels and never needed a magnet. I just followed the Machinery Handbook wherein it said how many minutes to soak the steel per 1" per cross sectional area. When heat soak was finished I dunked them into 10W parafin base motor oil and DID NOT swirl so that it was self annealing and they worked perfect.

I was always kind of intimidated by the red hot steel and don't think I'd care to do the magnet thing unless I had to for some compelling reason.

[Jpfalt]

The magnet test just makes sure that the steel is to austenetizing temperature. Once that is achieved the steel can be quenched. The test goes back to the good old days when temperature controllers were not available and temperature control came from a manual gas valve or a forge bellows. I agree that Machineries Handbook or the heat treating handbooks work OK if you're into all those new fangled electronic controllers and pyrometers and such, but it just isn't the way grandpa used to do it.

[Dave Opincarne]

It's used to ascertain wether or not the correct temp and change in crystaline structure has occured. Visual indicators are not reliable since ambient light can change the apparent color of the workpiece.

[precisionworks]

The magnet is easiest to use when a rosebud head is the heat source. Just heat, test, heat, test. As soon as the magnet does not stick immediately quench.

If the pyrometer on the oven is accurate you shouldn't need to test with the magnet.

------------------
Barry Milton

[hoffman]

It didn't get hard but it got REALLY HOT! It had a thick scale on it that chipped off reminded me of welding slag but it was even all over.

I drug a file across it and it didn't seem to be any harder...

Like I said, I was really just fooling with it but it'd been neat if it had came out hard as chinese arithmetic...

I still need to figure out the sequence. Do I bring the furnace up to temp and then put the part in? When does the time start? I didn't quench the part because I thought a2 was "air quench"... Then there's annealing and all.

All the info is on the net I just haven't invested the time to study because I wasn't sure if I'd get the furnace up to speed.

------------------
Hoffman in Warner Robins Ga

[cliff69]

I don't think it will get hard unless you quench it, JMO

[hoffman]

I im thinking about getting one of these:
http://www.northerntool.com/webapp/w...33801&R=333801
for my parts washer and using it in a tub for quenching parts. Maybe build a second oven for annealing because the temps don't need to be as high.

Just something to think about...