430 Stainless Steel Corrosion at punched holes?

[CostDown]

I have a roll formed profile in 430 stainless steel, that sporatically develops rust at the punched holes. Some do, some don't, when tested under ASTM B117 Salt Spray Testing for 500hrs. What causes the rust to form around the holes, and not eleswhere on the part? Is there a treatment I can do to the part to eliminate? Passivation, use SS punches, age the part, chemical cleaning? or is it the burr causing corrosion initiation sites?

 

[EdStainless]

My hunch is that the punched hole either has a burr, or some metal has been smeared and folded forming crevices. Either way you have sites for easy corrosion initiation.
How do you de-burr?
A quick deburr with a falp wheel and then a passivation to remove any Fe residue would be my suggestion.
How important is the looks? Maybe a light pickle may be easier.

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[CostDown]

Currently we do not deburr. We are using a pre-brushed coil for the rollform and from there it goes straight into final assembly. Looks are quite important as it is a visible trim piece. We are looking into a passivation step. Thanks for the input EdStainless.

 

[stanweld]

Why some holes corrode and others do not may be due to punch wear. Do you notice an increase in corrosion with time and do you see a reduction in corrosion after punch change out?

 

[griffengm]

Were the holes punched with tools used on carbon steel prior to punching the SS?

Griffy