Passivation is the removal of free iron and other contamination resulting from handling, fabrication, or exposure to contaminated atmosphere. This is performed by immersing the steel in an oxidant-like nitric acid.
- Grades with at least 16% chromium (except free machining grade such as 303): 20-45 volume % nitric acid, at 21oC to 32oC for 30 to 60 minutes.
- Thorough water rinsing must follow all passivating treatment
- Passivating solution, paste and gel are available commercially.
- Contact time should be in accordance with Supplier’s recommendation
- All stainless steel (except free machining grades): 8-11 volume % of sulfuric at 65 to 80oC for 5 to 45 minutes
- Grades with at least 16% chromium (except free machining grades): 15-25 volumne of nitric acid + 1-8 volume % hyrdofluoric at 20-60oC for 5 to 30 minutes
- Thorough rinsing must follow pickling treatments;
- Free machining grades such as 303, 410 and 416: 10-15 volume % nitric acid + .5-1.5% hydrofluoric acid, at 20-260oC for 5 to 30 minutes;