Different magnets for different critical points? Just wondering.

J

Johnbeck180

Joined
May 16, 2011
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I was thinking about this the other day and was wondering about it, thought maybe some of you could answer this for me. When heat treating lets say 10 series steel you need to bring it to no magnetic (critical point) witch I have done before. I use a magnet from the bottom of one of those 6 inch steel catch pans, I'm a mechanic and I had an extra one laying around. It has the magnet on bottom so you don't loose your nuts and bolts. My question is will a stronger magnet move the critical point of the steel to a higher temp? And will a Weaker magnet do the opposite. Some magnets loose their magnetism when heated. Does this factor in in any way to how the steel will react to the magnet. Or is it when steel gets to critical point it doesn't matter what kind of magnet you use it's going to be non magnetic no matter what? I hope this makes sense.

Thanks, John Beck.
 
Once a steel reaches curie temperature, it loses its magnetic property, so strength of magnet won't matter. I have found that the closer you get to curie temperature, as parts of the steel start to transition to non-magnetic, the magnetic attraction weakens, but once the entire blade is to temperature, it will be non-magnetic no matter the strength of the magnet.

--nathan
 
Curie point is not the critical temp needed for hardening. Please read the stickies about heat treating

-Page
 
I have wondered the same about the magnets used during the return from non-magnetic. My thoughts are that the magnetic field would allow the moliques(sp) to realign magnetically, possibly more compactly and may allow better for better strengthening?
 
Steel does not have a molecular structure - it has a crystalline lattice structure. The density is constant, meaning that it cannot be compacted or compressed any further.

I'm not sure about using magnets in this way to modify the physical properties of the steel - I don't think it would really do anything.
 
John Beck,

Page knows what he is talking about - loss of magnetism and heat treat temp are only similar for certain steels.
 
The steel and its atoms form their structural arrangement in the biggest magnet around - The earths magnetic field. Not much a small magnet is going to do to affect that.

The curie point is set by physics, and you can't alter it. You could say that the ferromagnetic to paramagnetic conversion is locked by the universe and the rules that drive it.
As far as changing the orientation and compaction of the lattice for steel....the above sentence also covers that subject.

What you can do to affect your steel is to use the best HT parameters possible. Close temperature control, oxygen exclusion, proper pre-conditioning for grain and structure ( cycling), and proper tempering will do far more than any other attempt.....why, because these are based on the laws of physics. Follow the rules and physics will get you to the finished line every time.

From time to time you will read of people who claim to "compact" the steel by cold forging or some other technique like forging with the blade aligned with true north. While these people may be great smiths, they are poor physicists. The regularly resurrected myth of edge packing to increase the density and hardness of the blade is one of these. I have attached a photo of what happens when someone actually succeeds in an attempt to rearrange the shape of an atom.
 

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A few guys here have said the phrase "currie point", which may mean nothing to you.
And they want you to read the stickies.
It's a good idea.
But in the meantime:
To put this simply, it's the iron in the steel that is going non-magnetic. And the iron is the same from one steel type to another.
For the most part, regardless of the particular alloy, nearly all of the steels we work with go non-magnetic at right about the same temp.
I've see numerous specifications at this temp, but nearly all of our steels will go non-magnetic between 1414-1418 degrees.
After that, "critical" temp is determined by the combination of the other alloys included in your particular steel's recipe.
Having a magnet around is a good idea.
It won't tell you everything, but it WILL tell you that you are approaching that level of temperature where you need to start paying attention. ;)
 
Awesome info guys!!! Thanks a lot. I'm doing a lot of stock removal now since its really to cold outside to forge. Can't wait till it warms up a bit, here in Indiana it that time of year where the weather teases you, one day it will be 50-55 degrees then the next two weeks its 20 degrees. Just warm up already. Thanks for the info guys. :0)
 
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