Dear Sir, I'm trying to passivate 2

[Santosh Ingale]

Dear Sir,
I'm trying to passivate GRADE.SS303 with dilution of 10% Nitric Acid and Water 90%.But, not getting proper surface result.Observed surface looks some whitish colour marks looking for help.Please have a look at photo for understanding.please suggest me a way,Thanks a lot

 

[isoca]

You can start by taking a look at the recommendations given by ASTM A380 and A967.

 

[EdStainless]

Buy a copy of A967 and read it.
10% nitric at RT isn't going to passivate (clean) properly.
303 can be problematic since it has such low corrosion resistance due to the deliberate inclusions.
If the white isn't visible to start with you can be assured that your solution has nothing to do with it other than making it obvious.
The variation in surface finish must be pre-existing.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Santosh Ingale]

Hello isoca & Edstainless,
Thanks, For sharing your knowledgefull views.Actually, I have followed standard practice ASTM A380 only.Further i will take a look to A967 too as suggested by you.But, the thing is white marks (what's it exactly) is it frosting And I'm sure this white marks not present before Passivation. It's formed after passivation process.Is there any way to get this marks cleanout.
Note : Before Passivation there is machine oil present on the surface can it will be cause for thus marks & also are this marks are acceptable or it will cause any rejection.Please help me out.Thanks again

 

[EdStainless]

You should degrease (hot alkaline maybe) before passivation.
A straight nitric will not etch the surface, the condition must be pre-existing.
The passivation could be making it more visible but it wouldn't cause it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[WKTaylor]

NOTE1. 303 SStl in any form is generally prohibited for use in MIL Acft due to cracking issues. I only know of 1-or-2 exceptions for parts... and there have been service bulletins for recurring inspections 'just-in-case'.

Per AMS2700... Method 1 passivation [conventional acid] treatments for all 303 CREs have somewhat unique passivation chemistry requirements... and the chemistries aren't even close to Your description.

Of course Method 2, citric acid chemistry seems to apply to most CR steels universally... but has it's own unique issues.

OH YES in every instance 'bath chemistry' must be strictly monitored/controlled, per ARP4992, Periodic Test Plan for Process Solutions. Where I work, there is a 'push' to method 2... simply because of general environmental, toxicity and disposal issues... but there is 'learning curve'.

Other info, 'good-to-know'.

AMS-STD-753 Corrosion-Resistant Steel Parts: Sampling, Inspection and Testing for Surface Passivation

When bath passivation is not possible... such as for field units [remote sites]... and passivation of 3xx SStl parts is required... then I have a 'field-fallback' I've used for years with moderate success... training and adhering to tech procedures per per USAF T.O. 1-1-691 is/are required for [A] and . When is done/removed to expose clean bare-SStl the surface develops a natural/thin passivation film.

A. Apply PPG-Semco Pasa-Jell 101 to chemically 'clean/scrubbed [scotchbrite] surfaces and deburred edges'. This develops a thin passivation film 'good-enough' for epoxy primer adhesion in structural repairs. This is 'jelled-form' of phosphoric acid that is easier to control on small surfaces. [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1680273436/tips/PPG_Semco_Pasa-Jell_Gnrl_PDS_l7csh1.pdf[/url]

B. Another option is phosphoric acid cleaner per MIL-C-10578 Type III.

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