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What metal can be permanently magnetized and remain stainless and workable as small washers

August 19, 2009

I would like to know what metal can I use, which must remain stainless and absolutely not rust and which at the same time can be permanently magnetized.
I need to manufacture small washers with diameter 2.0 mm, thickness 0.5 mm and laser drill small holes on them, which are in diameter of 0.02 mm to 0.10 mm. Then I need to permanently magnetize them. The metal to be used must remain stainless and as such that the humidity, rust and water does not block the small 0.02-0.10 mm holes while they must remain open.

I would be very thankful, if someone could help me in this question and give some information as well how to magnetize the washers with the strongest possible magnetic power and permanent result.

[last name deleted for privacy by Editor]
medical instruments - United Kingdom

First of four simultaneous responses -- August 22, 2009

I do not think that there is any metal that will reach the Utopian status that you are seeking.
First, these are very small, so they will not have a large magnetic force. Actually, it will be rather small.
The 400 series SS can be magnetized, but I would not call it permanent, by my definition, and it will rust in many cases.
I would try AlNiCo which is a common magnet. True some are used in super electromagnets, but it might be worth a try.

James Watts
- Navarre, Florida

Second of four simultaneous responses -- August 22, 2009

All metals are subject to oxidation when exposed to humidity. Even stainless steel. I think alternatives would be better.

You could use a magnetizable ceramic. For example, you could make a slurry with magnetite and binders, and bake these washers.

Another option would be to use a ferromagnetic metal, and coat it or passivate it with a corrosion-resistant material with a good permeability. This is usually what's done with rare earth metals.

Robert H Kinner
- Toledo, Ohio

Third of four simultaneous responses -- August 22, 2009

I have spent quite a long time reading about magnets as they massively affect the sound of any musical pickups that rely on them or speakers that use them in the drive coils. I was also interested in them due to their use in magnetic suspension in things like turbo molecular pumps. But I can't profess to know everything possible with them.

I can't think of any strongly magnetic materials that are also stainless. One of the definitions of stainless is that it's not magnetic.

That brings me to a suggestion that you use something like neo-dym magnetics (super magnets) and coat them. There are a bunch of places selling them online and I've seen some washer like versions. Whether or not they'll be as thin as you want them I'm not sure.

Also, a lot of magnetic materials don't like being magnetised along their short dimension, e.g. the thickness of a washer.

In terms of coatings, there a whole lot of them at your disposal. For medical use, a good thick coat of chrome would be a starting point.

From there, I'd go for more exotic coatings like one of the platinum group; platinum or rhodium maybe.

Other ideas could be an epoxy powder coat finish or some form of teflon. DuPont do a liquid teflon that can be applied and then dried onto the surface. PTFE is of coarse a big player in medical instruments since it'll go through an autoclave and is all but 100% inert.

John Heritage
- UK

Fourth of four simultaneous responses -- August 23, 2009

Firstly, no stainless steel is totally corrosion resistant, so there must be a compromise between materials and its operating environment. Secondly, only 200 and 400 series stainless steels are magnetic, although 300 series will become slightly magnetic under some circumstances. You may find the 200 series offers you the best option (201, 202 perhaps).
Other metals, such as nickel and cobalt will exhibit a degree of magnetism and corrosion resistance, but the level of reistance is dependent on the environment. You could also perhaps use a high nickel - chrome alloy that will have a degree of magnetism, but not as much as a stainless steel - this will be more corrosion resilient than stainless steel, but again, nothing can be certain for your environment.
You could also talk to the University of Birmingham Materials Science or Metallurgy departments - they may be able to help you out; they are based in Edgbaston.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

September 14, 2009

dear sir.

you can go in for ss grade 316 and coating of titanium nitrate coating by PVD process on the metal completely finish your operations before send ing for coating it may be 5 microns to 8 microns. the matl should be completely magnetised before sending for tin coating also alternatively you can try ceramic coatings to 5 microns which will prevent 100% corrosive.

with warm regards.

B. Manickavelu
- Bangalore, India

September 24, 2009

Hi Sir

We could really do with some more information here. Stainless against what environment - in vivo? in vitro? What orientation for the magnetic field?

I would speak to magnet manufacturers first. What you need may be available off the shelf! What you describe sounds very like the ferrite cores once used for computer memories.

If you are thinking of implants, gold plating may be the best option.

One more thought. Consider any coating process before magnetising. These tiny magnets will coalesce into an unmanageable mass unless kept separate so barrel plating would be a problem

geoff smith
Geoff Smith
Hampshire, England

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