Dependence of the Critical Pitting Temperature on surface roughness

Abstract It has been known for many years that highly alloyed stainless steels display a critical pitting temperature (CPT), which is the lowest temperature at which the growth of stable pits is possible. In the work reported here, the effect of varying surface roughness was investigated using potentiostatic and potentiodynamic CPT measurements on 904L stainless steel in 1 M NaCl. The results demonstrated that increasing the smoothness of the sample surface causes an increase in the CPT, even though the CPT exhibits a markedly more deterministic character than does the pitting potential. Using a potentiostatic technique, the highest measured CPT was 56 °C for a surface polished to a 3 μm finish, whilst the lowest measured CPT was 46 °C for a surface ground to a 60 grit finish. These results are consistent with an explanation of the CPT proposed by Salinas-Bravo and Newman [Corros. Sci. 36 (1994) 67].