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Does Welding increase permeability of 316L Stainless Steel?

January 20, 2010

Hi, my name is Peter and I work for a company that makes electron guns.

We have been experiencing magnetism problems in one of our products made out of 316L Stainless Steel. I know 316L is mostly non-magnetic in the annealed condition and that work hardening the material makes it magnetic. My theory is that the welding operation of the part increases the permeability of the 316L material sufficiently enough that when it is exposed to a high magnetic field, it develops magnetic properties. The part is located in the lens of the gun, which is where the magnetic field is focused so not exposing it to a high magnetic field isn't an option. We attempted de-gaussing the part, but when re-exposing it to the magnetic field, it regained its magnetism.

Can anyone verify my welding theory or point me in the right direction?

Thanks,

Peter Bertozzi
Employee - Wilton, NH, USA

You are on the right track. When welding austenitic stainless steels like Type 304 or 316, the molten metal will actually solidify with some amount of ferrite in it, usually less than 10%. It is this ferrite that is magnetic. I suggest you talk to your welding supplier and your stainless steel supplier about this issue. A Google search with terms like "316 stainless welding ferrite" will also give you some additional information.

Toby Padfield
Automotive components supplier - MI, USA
January 22, 2010