Effects of Sensitization on the Metastable Pitting Corrosion of 304 Stainless Steel

Abstract

The effects of sensitization on the metastable pitting behaviour of 304 stainless steel in 3.5 wt.% NaCl solution were investigated via electrochemical measurements and microscopic observations. Results showed that sensitization decreased pitting potential and slightly affected metastable pitting potential. Sensitization treatment increased the nucleation frequency of metastable pitting, promoted its propagation and changed the shape of current transients. The results of scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that metastable pitting was initiated at MnS inclusions for the solution-treated and sensitized samples. The combined effects of the passive film and inclusions were considered to play a vital role on the metastable pitting behaviour.

Corrosion Behavior of Sensitized AISI 304 Stainless Steel in Acid Chloride Solution

“…Microstructure of as received AISI 304 SS ( Figure 1 ) observed by OM is polyhedral, austenitic with numerous twins that could be related to annealing or rolling. According to the chemical composition of SS, visible inclusions could contain Mn [ 14 , 20 , 21 ].…”

“…Currently, the relation between sensitization and the pitting corrosion susceptibility of austenitic SSs is the subject of numerous studies [ 13 , 14 , 19 , 20 , 21 , 22 , 23 ]. In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs.…”

“…Currently, the relation between sensitization and the pitting corrosion susceptibility of austenitic SSs is the subject of numerous studies [ 13 , 14 , 19 , 20 , 21 , 22 , 23 ]. In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs. According to the available references, most electrochemical PP tests were carried out on the ground surface in pH neutral chloride solutions at room temperature [ 14 , 19 , 20 , 21 ].…”

“…In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs. According to the available references, most electrochemical PP tests were carried out on the ground surface in pH neutral chloride solutions at room temperature [ 14 , 19 , 20 , 21 ]. The authors of [ 22 ] compared the effect of various mechanical surface treatments on the pitting corrosion resistance of sensitized AISI 304 SS in 3.5 wt % solution at 23 and 50 °C.…”

Effect of cerium on the initiation of pitting corrosion of 444-type heat-resistant ferritic stainless steel

“…However, most nucleates, which are defined as metastable pits, could be repassivated, whereas only a few nucleates could grow continuously to stable pits. When a pit nucleation occurs, the current increases sharply over the background level and suddenly drops to the background current again [29]. This current transient is caused by the dissolution of active sites; therefore, the number of current spikes directly reflects the distribution of pit nucleation on steel surfaces.…”