Magnetic Properties

[sreid]

Iron, cobalt and nickel are known as the Iron Triad and all have high magnetic properties (high permeability). But if nickel (and chrome) are added to iron one gets, say, 316 stainless steel that has low permeability. There is probably a simple atomic level explanation for this but I have never seen it.

 

[MagMike]

The nickel helps produce an austenitic microstructure which has a face centered cubic crystal structure. Iron is not magnetic in the fcc phase, so that contributor to magnetic output is eliminated.

Then Cr is antiferromagnetic and it tends to overcome the magnetic moment that would have been produced by the nickel.

If 316 is plastically deformed, the energy from the deformation can sometimes change the crystal structure to body centered cubic, allowing the iron to become ferromagnetic.

Iron-Nickel alloys (without Chromium) are highly magnetic.

 

[EdStainless]

and don't forget Co.
It is a matter of electron spins, and crystal structure.
It also matters if you are talking about hard or soft materials.
In soft materials you also need to account for the dissruptive effect of various impurities.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

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