Answer
Passivation is a chemical treatment (usually with nitric or citric acid) that removes free iron from the surface of stainless steel rings and enhances the formation of a protective chromium-oxide layer. During the coiling and handling process, microscopic particles of carbon steel from the tooling can become embedded in the surface. If not removed, these particles will rust, leading to localized pitting corrosion even in stainless steel. The process is typically governed by ASTM A967 or AMS 2700. For medical or food-grade applications, passivation is mandatory to ensure biocompatibility and prevent contamination. Without passivation, the 'stainless' property is compromised at the microscopic level, which can lead to premature failure in corrosive environments.
