{"id":14744,"date":"2025-04-23T01:34:55","date_gmt":"2025-04-23T09:34:55","guid":{"rendered":"https:\/\/qd-evergreen.com\/?p=14744"},"modified":"2025-04-23T01:53:16","modified_gmt":"2025-04-23T09:53:16","slug":"stainless-steel-passivation","status":"publish","type":"post","link":"https:\/\/qd-evergreen.com\/en\/stainless-steel-passivation\/","title":{"rendered":"Stainless Steel Passivation: Definition, Process, Standards"},"content":{"rendered":"\n

What is Stainless Steel Passivation?<\/h2>\n\n\n\n

First of all, we need to know that stainless steel is naturally resistant to corrosion; the key lies in the surface layer of chromium oxide film (Cr\u2082O\u2083) with a thickness of only 3-5 nanometers.<\/p>\n\n\n\n

Passivation treatment is like doing “deep skin care” for stainless steel: dissolving free iron particles on the surface through an acidic solution (commonly used nitric or citric acid), while stimulating the reaction between chromium and oxygen to re-generate a dense and homogeneous passivation film. This process does not change the thickness of the material, but can make the corrosion resistance increased by more than 10 times.<\/p>\n\n\n\n

An example<\/strong>: a food factory mixing tanks used three months after the weld corrosion, which is due to the welding will lead to the “chromium depletion zone”, this area of chromium content of only 8.2%, while the standard requirement of at least 10.5%.<\/p>\n\n\n

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\"Stainless<\/figure><\/div>\n\n\n

Passivation vs. Electroplating<\/h3>\n\n\n\n

Plating is a “coat” for the metal, while passivation is a “self-healing” stimulus for the metal. The plating layer will peel off over time, while the quality passivation film is metallurgically bonded to the substrate.<\/p>\n\n\n\n

A single 30-minute nitric acid passivation can extend the salt spray test time of stainless steel from 24 hours to 200 hours.<\/p>\n\n\n\n

Cognitive misunderstanding: passivation \u2260 no corrosion<\/h3>\n\n\n\n

Passivation films are stable in a PH range of 2\u201311, but may rust when exposed to strong acids (such as hydrochloric acid) or chlorine ions (such as seawater). Remember: Passivation improves corrosion resistance, but it is not a permanent corrosion prevention measure!<\/p>\n\n\n\n

Why Does Stainless Steel Need Passivation?<\/h2>\n\n\n\n

“316L stainless steel is said to never rust. Why do medical devices<\/a> need to be passivated?”
 The truth is that the “stainless” properties of stainless steel need to be supported by ideal conditions. Unpassivated devices can rust at any time when the following conditions are encountered:<\/p>\n\n\n\n