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?
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Magnetic Permeability of stressed SS 4
- Thread starter Ron07663
- Start date
Austenite that has been deformed can have permeability up to 10 or 20. It depends on amount of deformation, temperature at which the deformation occurs, and alloy composition, the higher the total alloying, the less transformation.
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.
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.
EdStainless
Materials
You can buy 304 with various min Ni also. The trick is availability.
How much are you going to draw?
I'll try to get you some strain vs perm data.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
How much are you going to draw?
I'll try to get you some strain vs perm data.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
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4
- Thread starter
- #4
Thank you for the rapid response.
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
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
EdStainless
Materials
When we draw 304L, 316L or 21-6-9 we see no measurable increase in perm. We are tlaking about standard chemistries. Our draw reductions are in the range of 20-35% (area reduction). We still get perms that are not over 1.02.
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.
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.
- Thread starter
- #6
I have had experience in the past with 304 becoming magnetic after a deep draw. From your comments, it looks like if the Ni content is on the low end of the range (Ni in 304 is 8 to 10%), the material is more susceptible to becoming magnetic.
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
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
EdStainless
Materials
316 is a killer today. The surcharges on Mo are huge. You will end up paying about 30-35% more for 316 than for 304. Usually the gap is closer to 15%.
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.
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.
If you want the best value for making this part use 201 with 5% Ni and 7% Mn. Allegheny probably makes it. What counts in surpressing martensite formation is total alloy, not just nickel. Anything you put in except cobalt helps. 201 is the cheapest. I just saw on Allegheny's website that they are promoting it because of nickel's high cost.
Yes. Plus, you would lose dimensional tolerances.
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.
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.
- Thread starter
- #11
mcguire:
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
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
Ron07663
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.
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.
- Thread starter
- #15
sreid:
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.
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.
I don't have any references on hand but getting the vibration out of the windmill I recall that the Navy uses a lot of 321 SS down the road at one of their labs that deal with things that need to be non-magnetic. All my info is for annealed material no mention of cold work.
- Thread starter
- #17
FYI:
Found this reference with a MAGNETIC PERMEABILITY vs PERCENT COLD WORK chart for 302, 304, 304L and 305- 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?
Found this reference with a MAGNETIC PERMEABILITY vs PERCENT COLD WORK chart for 302, 304, 304L and 305- 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?
If you have a means of drawing it at slightly elevated temperatures, you can prevent the martensite formation. 20F increase in deformation temerature gives the same effect as 1% nickel...pretty good cost trade-off.
The highest nickel 305 commonly available is 12% from Ulbrich. Tell them I sent you. I developed it for them about ten years ago.
The highest nickel 305 commonly available is 12% from Ulbrich. Tell them I sent you. I developed it for them about ten years ago.
- Thread starter
- #19
mcguire:
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
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
"Low perm SS for military systems --".Mcguire this is an important area of application,RON has done well to identify this use. Infact I wanted to discuss with you about this application. The defence of the nation is at stake based on this singular property. However, the work horse alloys are 304 and 304L grades for under water mine applications. I cannot discuss more on this application and magnetic signature on ship's hull.
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