The Customer specified the following requirement: Purchased Material: Stainless Steel Magnetic Permiability <1.5. We machine this part for the customer. Will we be able to maintain this value after machining.
We would re-quote the job for a post machining anneal heat treat. The main point of my inquire would handling and being in contact with other metals i.e., bare or galvanized steel racks re-induce magnetism?
Cold working is the only way to change the magnetic properties. As stated above the only way to remove any properties induced by cold working is to heat the 303 above the Curie Point.
I think as long as you avoid significant cold work (forging and forming operations) you will have no problem with typical screw machine operations. Keep your cutting rates on the low side to be sure. You will have to have tests performed to be sure and they can only be done on standard test pieces, not finished parts. I would ask your customer how they intend to check it.
There is a difference between magnetic (ferromangetic) and magnetised.
It is possible that due to the materials thermomechanical history it is slightly ferromangetic. This could be due to retained delta ferrite or some strain induced matrensite. If this is the case then you may be magnetising the material by the way that you handle it.
We manufacture cold finihsed tubing all of the time that has magnetic permiablity above 5, but it must be demagnetised to a specified residual field level.
It is also possible that you have material that is very lean on Ni (to save money) and therefore not real stable. It could be that your machining is working the surface layer enough to make it profoundly magnetic. I doubt this, 303 machines well enough that you shouldn't impart much work.
If the bar is non-ferromagnetic to start with you sould be able to manufacture non-ferromagnetic parts.
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