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Q & A: Magnetizing T304 stainless steel

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Most recent answer: 10/14/2011
Q:
T304 stainless tubes unannield , 1.625 x .020 wall. Checking for magnetic presence by using a large magnet. Could this be magnatizing the tubes in doing so?
- Stan Ostaszewski (age 64)
Worcester,ma USA
A:
According to the sources I could find, annealed T304 SS is non-magnetic having a magnetic permeability of close to 1.  However cold working of this steel can induce a permeability of up to 2.  To set the scale, the permeability of soft iron can be in hundreds or even in the thousands.  But what I think you want is the amount of induced permanent magnetism, or coercive force, that remains in the SS after you have removed the external magnetic field.  I couldn't find  any data on this.
 So the answer is, you can't tell without trying it out.    The way to do it is to see if the SS is a bit magnetized before and after your inspection by sprinkling a few soft iron filings on the tube and seeing whether they stick or not. 
The stainless shim-stock I have in my lab is only very weakly magnetic and I saw no evidence of it retaining magnetism when I applied a fairly strong external fields to it.

LeeH

(published on 10/14/2011)

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