There is some dispute over whether the corrosion resistance of stainless steel can be enhanced by the process of passivation. Essentially, passivation is the removal of free iron from the surface of the steel. This is performed by immersing the steel in an oxidant, such as nitric acid or citric acid solution. Since the top layer of iron is removed, passivation diminishes surface discoloration. While passivation does not affect the thickness or effectiveness of the passive layer, it is useful in producing a clean surface for a further treatment, such as plating or painting. On the other hand, if the oxidant is incompletely removed from the steel, as sometimes happens in pieces with tight joints or corners, then crevice corrosion may result. Most research indicates that diminishing surface particle corrosion does not reduce susceptibility to pitting corrosion.
Additional Reading
- Citric Acid Passivation of Stainless Steel - Lee V. Kremer's article discusses the use of citric acid passivation as an alternative to nitric acid passivation of stainless steel.
- Passivation of Stainless Steel - Dan Englebert's article defines passivation and describes how it is performed and verified.
- Phase Diagram Glossary - These are definitions of several relevant terms, including 'ferritic steel', 'microstructure', and 'plain carbon steel'.
- Sheffield Shows Its Metal - The British Canadian Chamber of Trade and Commerce provides this article on Sheffield that includes some history of stainless steel.
- Stainless Steel Property Database - The Hendrix Group provides this database of material properties, including compositions, corrosion properties, cost data, specifications, and categories of steel.
- The Stainless Steel Information Center - The Specialty Steel Industry of North America sponsors this resource, which includes general information about stainless steel, industry news, publications, workshops and training, and information for students.
- What Are Martensites? - This site offers a description and pictures of the martensitic crystal transformation in steels.
