Developments In Citric Acid Passivation Of Stainless Steel

摘要

Stainless steel passivation is a mysterious process to many, but one that is important in the metal finishing industry to get the full benefit from corrosion resistant steel alloys. The principles of passivation are explained. Traditional nitric acid based passivation methods are compared to more recent citric acid based methods, including differences in safety, disposal issues, ease of use, and resulting corrosion protection. Grades of stainless steel that require special methods are pointed out, such as the need for alkaline precleaning of high sulfur grades and the benefits of higher pH citric acid solutions for the martensitic and precipitation hardening grades. The difficulties of passivating stainless steel castings and laser marks on stainless steel are discussed. Passivation testing methods and industry specifications for stainless steel passivation are discussed.