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Passivation and laser cutting/stamping of stainless steel [UK] 

October 14, 2009

We have a requirement to get some small stainless parts fabricated and passivated from a 300 series stainless steel. They are 0.012" thick and about 6" x 1".
I know that standard theory tells me to passivate last but since these are virtually sacrificial plates to protect the underlying structure I am not too worried about the passivation as much of it will get damaged in service. However it has to be done as we only have limited freedom in the design. The important question is would these pass the copper sulphate test from AMS2700 after being laser cut or stamped from a sheet if it were passivated first.
We are just trying to save on racking time and cost.
Thanks for any help.

Ciaron Murphy
Chemist - South Wales, UK

The answer is very simple, since stamping after passivation leaves you with not passivated surfaces, meaning free iron, your piece will probably not pass the copper sulfate test, and you wil se a nice copper edge on you piece.

Bo Kønig
- Odense Denmark

Oftentimes 300 series parts will pass copper sulfate even prior to passivation unless there is some iron surface contamination happening during the manufacturing process. Stamping is the kind of thing that can cause this contamination, but neither is it a certainty. The heat affected zone from laser cutting will be more susceptible than the rest of the part until and unless it is passivated, but it depends on the grade and the laser settings as to just how bad that will be, i.e. if it might still pass copper sulfate.

I think you can't really know without doing some sample pieces and actually performing the copper sulfate test.

I should say that I can't endorse the sort of "cheating" you are thinking of doing, but you did already admit to knowing better. Unless these pieces are in service in a harsh corrosive environment it may not really matter anyway.

Ray Kremer Stellar Solutions, Inc. McHenry, Illinois