Do red hot steel temps kill magnets?

misque

misque

Joined
Jul 9, 1999
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I seem to be killing magnets rather handily these days. After a couple of dozen or so checks on red hot heated steel the magnet loses it's magnetic properties.:confused:
So, my question is, what's going on here?:(


All the best,
Mike U.
 
get a bigger magnet and use the edge of the blade rather than the flats I use an old magnet off a car subwoofer, don't even need to touch it just get close and it pulls.
 
YEA. magnets lose their magnetic field eventually anyway. but things always happen faster with the introdution of heat. since your steel is red hot, the molecules in the magnet start moving faster and anything which will ever happen to it will happen right then and there, in this case, since it'll lost the "magnetness" anyway, and you're heating it up, it just happens faster.
 
OOPS. i got that mixed up with chemical reaction. i believe that the magnet thing is when it cools down while NOT pointing to magnetic north and then the (magnetic) "patterns/forces/fields" start overlapping. can anybody elaborate on that?
 
To the first part, yes. High heat kills even neodymium magnets fast. I quench mine after checking, especially if it wasn't critical yet and the magnet stuck.
As for why, I was under the impression that magnetics were pretty dependent on crystalline structural alignment, and taking a ferrous metal to higher temps skews that, but I'm not positive. It's just a general impression.
 
I believe the order of most easily demagnatized to least easily is:

Alnico (Usually the red painted or blue painted ones for the hardware store)

Ferrites - (often speaker magnets)

samarium cobalt / neodnyium - rare earth

If you're using Alnico, ferrites are very inexpensive from radio shack or the home store.
 
Yes as the others have said heat kills magnets. However you dont need to keep the magnet on ther hot steel long either it is atracted or not just a quick touch is all you need don't leave it on sliding it up the full length of the blade. just a quick touch here and there.

A mate has a mechanics pick up magnet it is on an expandable handle a bit like a car aerial. it bends at right angles at the end.

We just ran 2, 3 day courses 33 blades tested. Thomas has had the magnet for 8 courses and his own work at home. It may just be the type of magnet or the time you take.

The other thing is if you remember high school science you can re magnetise by wrapping many turns of fine insulated wire around the
core of metal. and passing a dc current through it. As long as the metal is not soft iron it will magnetise. (Price verses effort)

Good luck, also good to see you are actually checking the temperature not relying on guess work with the heat treat.
 
Thank you gents! Just what I needed to know and even more and it's all useful info.:cool:

Thanks again!


All the best,
Mike U.
 
Reg,

I don't believe you can re-magnetize modern magnets by using a coil and a dc source.

One idea might be if your had one of those instituional magnetic door holders which are just electromagnets, if you have the power nearby the forge they might prove more durable in regards to heat. You could put a floor switch on it and just hit the switch when you need to check.
 
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