Is Passivation or Black Oxide Finish better for Stainless Steel?
A discussion started in 2007 and continuing through 2017 . . .(2007)
Q. I am trying to evaluate two supplied metal threaded studs. Both are manufactured using 'CRES' (Corrosion Resistant Steel?). The stated finish on one is 'passivated' the other is 'black oxide'
My questions are:
What are relative advantages or disadvantages of using one finish over the other?
Is there a non-destructive test to confirm passivation has been performed? (Is visual sufficient?)
Consumer - Knoxville, Tennessee
A. The passivated one will be more corrosion resistant, unless the black oxide is oiled or waxed.
- Navarre, Florida
A. No definite answer. Depends upon the particular CRES alloy, supplemental treatment given the black oxide, usage and corrosive environment.
- Goleta, California
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October 24, 2016
Q. If one of these two processes were to be used in an interior of a vehicle on a very small piece of SS (430L or 434L) what would the best process be? This small piece is made to blend with other black items in the interior of a vehicle.
- Janesville, Wisconsin USA
October 25, 2016
A. The main thing I try to point out in these situations is, if you want a coating anyway (black oxide, paint, powder coat, etc.), why use stainless steel in the first place? You may as well save on material costs and use mild steel.
The main point of stainless steel is the surface is more corrosion resistant as the bare metal (usually with passivation, of course).
If you must, then stainless can be painted or powder coated without too much trouble, but processes like black oxide and electroplating typically require stainless to be activated using a very harsh acid mix.
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