Need to passivate (430 or 430F/430FR???)

[Vsid]

Let me start off by saying I’m not a metallurgist, I’m a chemical engineer. I have a metallurgist problem though! I bought a stainless steel stock pot, which has some small rust spots/streaks on the bottom after an hours-long soak in tap water. I understand I need to re-passivate it. The manufacturer of the pot told me it’s 18/0 steel, which I think means it’s the same as 430. I have the chemicals (nitric acid and NaOH) needed to passivate it, but I don’t know if its 430 or 430F/FR. There are different passivation methods for the two, correct?

How can I tell? Will it hurt to be safe and follow the NaOH regimen with 430, even though it doesn’t need it?

Thanks in advance for your help!

 

[kenvlach]

Pots are usually manufactured by deep drawing or spinning, so likely 430. 430F is worse for cold forming but better for cutting, so usually available as bar stock. But, can't be sure. A quick dip of a free-machining SS in acid (e.g., 35 vol% nitric) will give a positive ID from the H₂S smell.

For passivation process, see HOW TO PASSIVATE STAINLESS STEEL PARTS from Carpenter Techn.:

http://crswnew.cartech.com/wnew/techarticles/TA00042.html

This article shows a hex. chrome passivation for 430 (same as well as for 430F), Type II per QQ-P-35C, but QQ-P-35C Types VII or VIII can be used as well. Some people use the Type VIII solution (hot nitric) for 430F although not per spec.
QQ-P-35C

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=50793

It won't hurt 430 to be passivated per the procedure for 430F involving the extra alkaline steps.

For optimal corrosion resistance, the smoother the surface the better. Prior to the passivation process, remove the stains & buff the surface using SimiChrome or similar. It leaves a film, so degrease before further processing.