Passivate after hardstamping stainless steel

[PermanentCharpy]

I have received a number of parts that I need to stamp heat numbers to for traceability. The stamps are made of an unknown material, but do not seem to be corroded in any way, so perhaps they're stainless too, but I doubt it.

Should I passivate the stamped area of the parts after I have hand stamped them - they are made of UNS 32750. I have on hand Nitric Acid to perform the passivation. Service will be submerged in sea water.

Thanks all.

 

[TugboatEng]

Sorry for the terse answer but...

Why not?

If you have the capability and the cost is minimal, passivation is always better.

 

[PermanentCharpy]

We're working in a dock, so any passivation will be require specific waste disposal. It's not impossible, but if we don't strictly need to, I'd like to avoid it. We have the chemicals here as we did some stainless steel welding where pickling was definitely needed.

If there isn't risk that this stuff corrodes badly due to the stamping, I will leave it. A little bit of surface rust is fine, but these parts are being replaced due to their legacy parts suffering from crevice corrosion on the threaded elements, hence my concern. The stamping I am applying is to an external surface with no risk of confined spaces for crevice corrosion to initiate, so I doubt it's a problem, but if anyone on this forum has direct experience with something like this it would be appreciated.

Don't have a problem doing it, but would rather avoid if it's not necessary.

 

[TugboatEng]

I don't have any experience with duplex stainless but I do have a bit of experience with marine environments. I do believe duplex is still subject to crevice corrosion. Do you need the high strengths of duplex? Copper alloys aren't subject to sensitization and would never require passivation.I apologize that this is not related to your question.

Docks are one of the most challenging environments. They combine salt spray with evaporation to create extremely high chloride concentrations. There is no rinsing to remove contaminants from surfaces. Stainless steel will always rust so a little bit of extra ferrite on the surface probably isn't going to have any noticable impact when weighed against all of the other problems.

 

[EdStainless]

Yes, passivate.
It isn't so much the stamps as what surface debris could be imbedded.
Or if the stamps have ever been used on steel you would imbed that material.
You have altered the surface condition, passivate.

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

Can one interpose a stainless foil as a sacrificial material to avoid contamination?

 

[PermanentCharpy]

All, thank you for the input - the way forward is clear.

 

[WKTaylor]

Is steel stamping really essential?... there are other ways to permanently mark high strength SStl alloys without serious surface effects... assuming You pre-clean [solvent or detergent or 'pickle' or etc?] the material surface in question... such as...

Dot-peen parking [small dot impressions, shallow or deep].

Acid-Etch marking

Laser-etch marking

As far as passivation is concerned... if You really see the need... AMS2700 Has method I and Method 2...
Method 1 - Passivation in Nitric Acid, types 1-to-8
Method 2 - Passivation in Citric Acid

Method 2 is NOW preferred by USAF, where practical, because it works for most SStl and is environmentally 'friendlier'.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[EdStainless]

But for Citric passivation to really work it needs to be hot.
Whereas room temp 40% Nitric always works.
When we needed to spot passivate we used the disposable diapers and cut a piece a bit larger than our area and then soaked it with acid and applied it. Let it stand 15-30min, remove and place in disposal bag, and then rinse the area.
Very little waste.

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P.E. Metallurgy, consulting work welcomed