The authoritative public forum
  for Metal Finishing since 1989
-----

Testing after the passivation process

I work for a company that manufactures specialtly razor blades (medical, food processing, industrial). I am in the process of developing a passivation system. I am using a citric acid wash on 400 series stainless steels with less than 16% chromium content. I have passivated parts but now want to certify the passivation process per ASTM A967 -01. According to the standard there are 6 tests available. I have ruled out the copper sulphate ⇦this on eBay or Amazon [affil links] and nitric acid tests due to my chromium content being too low (Am I correct for doing this?) I have also ruled out the water immersion and high humidity test due to the time involved unless I have no other options. The free iron test I do not believe applies since most of my parts are small (size of a nickel up to 5 inches long). I am looking at doing the salt spray test. I have some questions regarding paragraph 16.2 in the standard. "in accordance with Practice ASTM B117 for a minimum of 2 h using a 5% salt solution". I am confused with this and need some clarification. Is the spray continuous? Is there a salt specification for the solution? I am assuming I need to spray my parts with the salt solution and then place them in a controlled atmoshpere for temperature and humidity for 2 hours. Any help would be greatly appreciated.

Thanks

Cory R. Mason
- Fremont, Ohio, U.S.A.
2005

---

Hello Cory-

Almost anytime you see reference to 'salt spray' in corrosion tests it means Condensing Salt Fog and, yes, the fogging in ASTM B117 is continuous. That method contains a specification for salt. Your samples would be placed in a purpose-built cabinet where they would be in the path of condensing salt fog as it responds to gravity. For your minimum needs you might consider a lab corrosion testing service.

Harold D. Hilton
- Chicago, Illinois, USA
2005