Metastable pitting behaviour of austenite stainless steel under compressive residual stress

Abstract

Metastable pitting behaviour of austenite stainless steel after compressive deformation in an acidic NaCl solution was investigated. The results show that the pit initiation rate increases while both metastable pit lifetime and growth rate decrease after compressive deformation. Meanwhile, the ratio of the surface oxide fraction of Cr to Fe increases whereas the average size of stable pits is smaller and shallow disk‐shaped under compressive residual stress. The results reveal that with the aid of enrichment of Cr oxides and compressive residual stress, which helps break the remnants of the undermined passive film, pit repassivation can be accelerated.

Effect of HAc on the Metastable Pitting Corrosion of 304 SS in NaCl Solution

“…The polarization curve in the basic solution (0.6 mol/L NaCl solution, pH 7.2) presented a broad passive region with a very low passive current density (0.35 μA/cm 2 ). As the potential increased, many current fluctuations were observed in the passive region, which indicated the occurrences of metastable pitting corrosion before stable pitting occurred [ 3 , 24 ]. After HAc was added, the corrosion potential of 304 SS moved in a positive direction, the broadness of the passive region was reduced, the passive current density visibly increased and the number of current fluctuations was reduced significantly.…”

“…The nucleation rate of metastable pits can be reflected by the number of current fluctuations in the polarization curves [ 3 , 24 ]. Figure 2 b shows the average values of the accumulative quantity of current fluctuations in five parallel testing curves for 304 SS in each solution.…”

“…The potential when the first apparent current fluctuation occurred, with a maximum peak higher than 0.02 μA, was denoted as the metastable pitting potential ( E m ), and the potential when the current increased continually was denoted as the stable pitting potential ( E b ). The rate of metastable pit initiation was obtained by the accumulative quantity of the current fluctuations [ 3 , 24 ]. Each current peak displays the typical characteristic of a slow rise followed by a quick drop.…”

“…During the pitting corrosion process of stainless steels, before the occurrence of stable pits, some micro-sized metastable pits may occur, reflected by the transient fluctuations of the current in electrochemical monitoring signals, which correspond to the process of nucleation, growth and repassivation of the metastable pits [ 3 , 4 ]. If the metastable pits grow continuously and do not repassivate, they will develop into stable pits.…”

Influence of inhibitors on the corrosion behavior of the X5CrNi18 10 stainless steel‐welded joint

“…Frankel [ 4 ] suggested that the repassivation of metastable pits is associated with the breakdown of the cover passive film and dilution of the environment inside the pit. Guan et al [ 5 ] found that the formation of metastable pits is noticeably heavier in NaCl solution under compressive surface stress in AISI 304L stainless steel. Also, the formation of stable pits from metastable pits occurs at a much more positive pitting potential E pit .…”