Magnetic Permeability of stressed SS
Magnetic Permeability of stressed SS
(OP)
I am designing a deep drawn SS can to be a shield for a magnetic sensor. We need the relative permeability of the shield to be as close to 1 as possible so as to not interfere with the sensor. Annealed 304 or 316 SS should be on the order of 1.0 to 1.02. What can I expect the permeability value to be for stressed 304 and 316?





RE: Magnetic Permeability of stressed SS
Tradionally for the situation you describe, 305 is used. It has been used for deeply drawn TV components which must have very low permeability. Get at least 12% nickel. Sometimes it is sold with as little as 10.5%.
In extreme cases 21-6-9, a nitronic alloy, can be used.
RE: Magnetic Permeability of stressed SS
How much are you going to draw?
I'll try to get you some strain vs perm data.
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Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Magnetic Permeability of stressed SS
A Rel. Perm of 10 would be unexceptable. I was hoping to avoid post-draw heat treating because of the extra cost and possibility of added distortion.
The Can is a Cylinder closed at one end with an O.D. at .750" and about 1.25" depth. Wall is approx. .02".
We need about 50k pieces annually. Finding a vendor to fabricate this and who also has knowledge of magnetic property inspection has been a problem.
I'll look into 305 and 21-6-9. Also any charts on perm vs strain would be helpful.
Ron
RE: Magnetic Permeability of stressed SS
Just for kicks I measured some tensile samples. I still don't see numbers over 1.02 at the fracture surface.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Magnetic Permeability of stressed SS
305 and 316 has a Ni range of 10 to 13 or 14%. Is it reasonable to specify 305 or 316 with Ni content greater than 12%? If cost/availability is a problem, what are my alternatives?
Ron
RE: Magnetic Permeability of stressed SS
I belive that most of the magnetic transfromation that you see on drawn parts is due to the high amount of work on the surfaces.
I see more magnetism in tubing that has been ground than I do in cold drawn product.
You might have better luck (and lower cost) finding some 8.5% or 9% min Ni 304.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
Very few people in the industry realize that 201 is equivalent to 305 in drawability and magnetic properties. How could anyone sell 305 if this were known? That's one of the reasons we're writing the book.
RE: Magnetic Permeability of stressed SS
From the lack of information and often misinformation that I have found, I think this subject would be a valuable addition to your book- especially for the instrumentation/sensor community that needs very low perm. components.
Specifically need practical advice for non-metallurgist on how to select/specify SS material and fabrication processes to minimize the formation of martensite and obtain low perm. parts.
Ron
RE: Magnetic Permeability of stressed SS
You'll have it. Can you describe for me a longer list of end uses and technical reasons for wanting low permeability?
I'll have to have an applications chapter on choice of stainless for magnetic properties.
Anyone else is welcome to offer suggestions. By the way, ASM has formally agreed to publish the book.
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
The short answer is that the customer requested SS.
The primary function of the shield is protection from the environment, although it does drain static charge and attenuate EMI.
SS does have some advantages over brass or aluminum - other common deep draw candidates. One of the main advantages is lower eddy current.
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
Found this reference with a MAGNETIC PERMEABILITY vs PERCENT COLD WORK chart for 302, 304, 304L and 305- http://www.stal.com.cn/pdffile/302304304l305.pdf
It confirms what you all said - 305, with as much Nickel as I can find, seems the way to go. As a plus it is more readily available and lower cost than some other choices. We will prototype our parts and check the results.
QUESTION -- WHAT SHOULD I SPECIFY ABOUT THE DEEP DRAW PROCESS THAT WOULD REDUCE THE POSSIBILITY OF MARTINSITE?
Draw reduction of 20 -35% was previously mentioned. Anything else?
RE: Magnetic Permeability of stressed SS
The highest nickel 305 commonly available is 12% from Ulbrich. Tell them I sent you. I developed it for them about ten years ago.
RE: Magnetic Permeability of stressed SS
To answer your questions on a list of applications for low perm. SS:
Basically any application that requires the properties of steel plus a need to be magnetically transparent.
This list would include magnet sensors to include inductive, hall-effect, GMR technology; Compass direction finders etc. Low perm SS is specified for oil drilling equipments (to not disturb sensitive magnetometers.) Low perm SS is used on various military systems to reduce the magnet signature (example: ship hulls in being evaluated ,etc.) Also low perm SS is specified for components near large magnet fields where it is important not to be attracted to the magnet such as industrial electric welders, superconducting coils in scientific, nuclear and medical (MRI) equipment.
Ron
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
http://as
http://www.nidi.org/nickel/0999/5-0999n.shtml
Ron
RE: Magnetic Permeability of stressed SS
Resists corrosion
very non-magnetic
strong
high ductility = high damage tolerance
But not at todays prices.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Magnetic Permeability of stressed SS
The Calypso was a ex wooden mine sweeper.
As posted above its an ongoing thing of who is the better at hiding, finding, or blowing up the other, with this work being carried out not far from me. They don't kill as many fish as they use to as electronics have taken over.
RE: Magnetic Permeability of stressed SS
RE: Magnetic Permeability of stressed SS
This topic is worth a separate thread. It of course depends upon which grade of stainless, but so are actually anti-ferromagnetic near 0 K.
As far as AL6XN for naval vessels, I understand they are getting some major attention because of their superior resistance to explosions ( as distinct from projectile penetration ) and their better acoustic signature than other non-magnetic materials. This alloy beats titanium and HSS armor plate materials.
RE: Magnetic Permeability of stressed SS
I found this reference on the magnetic effects of Stainless. It is a good summary with Cold Work vs. Permeability chart. It is written for the non-metallurgist.
http://
Ron
RE: Magnetic Permeability of stressed SS
We ran sample parts out of our deep draw tool of both 316 SS and 305 SS. The 305 was selected for Ni content of 12% or greater.
The 316 parts had a measured permeability of 1.15 right out of the tool and 1.0003 after solution anneal.
The 305 parts measured 1.003 right out of the tool.
Our specification required 1.05 MAX. So, if 316 were used, we would require a post draw anneal.
Thanks again for everyones help with this.
RE: Magnetic Permeability of stressed SS