Effect of pitting nucleation on critical pitting temperature of 316L stainless steel by nitric acid passivation

• Critical pitting temperature (CPT) increases markedly by nitric acid passivation.
• Inclusions dissolution and Cr2O3 enrichment are main reasons for increase of CPT.
• Effect of thickness of passive film on CPT is less influential.
• The micro-mechanism model of CPT has been developed.

The effect of pitting nucleation on critical pitting temperature (CPT) of 316L stainless steel is investigated by electrochemical measurements, morphology observation and XPS analysis. CPT increases dramatically after being passivated by nitric acid, which is mainly attributed to inclusions dissolution and Cr2O3 enrichment in passive film. However, the thickness of passive film is less influential. Pitting nucleation is suppressed through passivation, which leads to the increase of pitting nucleation temperature. Consequently, critical current density (icrit) shifts to higher temperatures, indicating the enhancement of CPT. In other words, CPT is influenced by both pitting growth chemistry and pitting nucleation.