Passivation is a best practice after manufacturing for newly machined stainless steel parts and components. Its benefits include:
1. Creating a chemical film barrier against rust.
2. Extending the product’s lifespan.
3. Removing contamination from the product’s surface.
4. Reducing the need for maintenance.
How does passivation work?
Stainless steel is an iron-based alloy composed of iron, nickel, and chromium. Its corrosion resistance comes from the chromium content. When exposed to oxygen in the air, chromium forms a thin film of chromium oxide that covers the stainless steel surface and protects the underlying iron from rusting. Passivation aims to enhance and optimize the formation of this chromium oxide layer.
During passivation, stainless steel is immersed in an acid bath, which dissolves the free iron from the surface while leaving the chromium intact. The acid removes the free iron chemically, resulting in a uniform surface with a higher proportion of chromium.
After the acid bath, when the stainless steel is exposed to oxygen in the air, it forms the chromic oxide layer over the next 24 to 48 hours. The higher proportion of chromium at the surface allows for the formation of a thicker and more protective chromium oxide layer. By removing free iron from the surface, passivation eliminates opportunities for corrosion to initiate.
The resulting passive layer provides a chemically non-reactive surface that protects against rust.
When is passivation of stainless steel required?
Passivation is necessary as a post-fabrication process after grinding, welding, cutting, and other machining operations involving stainless steel. Although stainless steel naturally resists corrosion under ideal conditions, passivation is still recommended to ensure optimal performance.