Stable Pitting Research Articles

Statistical Distribution of Critical Pitting Temperature of Stainless Steels

The range of Critical Pitting Temperature (CPT) for five different stainless steels is measured to determine whether it is wide or narrow. The impact of bulk solution composition and surface passivation on CPT was also measured in order to evaluate the relative importance of pit initiation and pit propagation on CPT. The results of the study revealed that CPT can be measured within a narrow range (±1.3 °C) regardless of the alloy and bulk solution composition. It is also shown that experimental error caused by crevice corrosion can lead to a wider range of CPT values. These results are explained using the Salinas-Bravo and Newman CPT model. It is shown that, for the conditions studied herein, CPT is not dependent on pit initiation, but rather, it is a transition phenomenon, i.e., CPT is determined by the transition from metastable to stable pit growth.

Localized corrosion and repassivation behaviors of additively manufactured titanium alloys in simulated biomedical solutions

The localized corrosion behavior of additively manufactured (AM) titanium alloys is studied based on the relation between pitting potentials, the flux of oxygen vacancies in a passive film, and the repassivation rate using potentiodynamic polarization, Mott–Schottky, and an abrading electrode techniques. The relationship between the localized corrosion resistance and the repassivation behaviors of AM titanium alloys was explained by the survival probability constant based upon the point defect model which describe the generated oxygen vacancies and accumulated cation vacancies affect the occurrence of the localized corrosion. Localized corrosion can be initiated by survival pits under sufficient conditions of the breakdown passive films. Survival probability is constant means a quantitative probability value of the transition from metastable pit to stable pit to occur localized corrosion. The higher the survival probability constant of AM titanium alloys, the more difficult repassivation and the easier occurrence of localized corrosion.

Revealing the Corrosion Resistance of 316 L Stainless Steel by an In Situ Grown Nano Oxide Film.

It is widely accepted that the corrosion resistance of stainless steel originates from a compact Cr2O3 layer in the native passive film that serves as a barrier to aggressive ions. However, this suggestion has been questioned by some researchers. They believe that protectiveness might be related to the film recovery. Herein, the pitting development of bare 316 L stainless steel was compared with a corrosion-resistance enhanced steel obtained by tuning the native passive film of the alloy. Statistical software was employed for tracing the size and number of pits on the alloy surface. The statistical results for 12 weeks in 1 M sodium chloride solution (80 °C) revealed that there was a crossover in the growing rates of stable pits (diameter > 9 µm) between the bare alloy and the film-enhanced one. Stable pits on bare 316 L occurred early but showed a comparatively slow increase in the following weeks, demonstrating that self-repairability of metastable pits rather than impermeability of the native passive film plays the key role in the early stage of pitting corrosion.

Dependence of Pit Growth Rate on Applied Potential and Chloride Concentration under Conditions with and without Fluid Flow

Pitting corrosion on stainless steel is one of the most serious problems caused by seawater intrusion into power plants because it possibly perforates boundary structures, such as piping or containers, and leads to solution leakage. Although the evaluation of the pit growth rate in accordance with the corrosion condition is required to secure the plant’s safety, the dependence of the pit growth rate on various corrosion conditions is not fully understood. In this study, the effects of applied potential and chloride concentration on the pit growth rate on Type 304L stainless steel were assessed with and without fluid flow by performing the pit penetration test with in situ observations of pit initiation and penetration. An artificial one-dimensional pit experiment was performed to obtain a fundamental understanding of pit growth with and without fluid flow. In addition, three-dimensional pit growth behavior was further analyzed by measuring a dissolution current of a single three-dimensional pit. In the pit penetration test, the effects of applied potential and chloride concentration on the pit growth rate differed depending on the fluid flow condition; the pit growth rate is almost independent of the applied potential and chloride concentration without fluid flow, whereas the growth rate was decreased by decreasing the potential and chloride concentration with fluid flow. For the results of the artificial one-dimensional pit experiment, regardless of the fluid flow condition, stable pit growth in the depth direction was suggested to be diffusion-controlled. Measuring the time variation of the dissolution current of a single three-dimensional pit indicated that the three-dimensional pit growth involves temporary passivation and reactivation, which depend on the fluid flow condition and applied potential. This suggested pit growth in the pit penetration test proceeded discontinuously depending on the corrosion conditions, resulting in a dependence of the pit growth rate on the corrosion conditions.

Pitting Performance of Cold- and Hot-Rolled Nickel-Saving High-Strength Metastable Austenitic Stainless Steel

Nowadays, nickel-saving metastable austenitic stainless steel (MASS) has become the right solution to meeting the growing requirement of higher strength, better corrosion resistance and more cost saving for the automobile industry. Better understanding of the pitting mechanism of the MASS after either cold- or hot-rolled can offer guidance for the producing of high-performance automobile steel. In the current work, for uncovering the pitting mechanism of the cold- and hot-rolled MASS, the microstructural evolution and pitting performance of nickel-saving metastable austenitic stainless (MASS) steel after cold- (CR) and hot-rolling (HR) were researched via electron microscopy technique and electrochemical methods. Austenite composites the main phase of the MASS. Small amounts of martensite film were proven to form in the MASS. The precipitation of Cr-rich M23C6 carbides was observed in the CR-MASS, while no carbides existed in the HR-MASS. The pitting resistance of the HR-MASS was better than the CR-MASS, which could be attributed to the fact that the stable pits in CR-MASS were initiated near the carbides, whereas the MnS inclusion would serve as the initiation sites for stable pits in HR-MASS. Findings in this work will provide a guidance for developing new generation MASS for automobile industry.

Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting.

Materials produced by additive manufacturing (AM) often have different microstructures from those obtained using conventional metallurgy (CM), which can have significant impacts on the materials’ durability, and in particular, resistance to corrosion. In this study, we were concerned with the susceptibility to pitting and environmentally assisted cracking (EAC) of 17-4PH martensitic stainless steel (MSS). We focused on the evolution from pitting to EAC, and the behaviour of MSS produced by AM was compared with that of its CM counterpart. Potentiodynamic polarisation tests were combined with chronoamperometry measurements performed without and with mechanical loading to study both stable and metastable pitting and the influence of stress on these processes. EAC tests were carried out and combined with observations of fracture surfaces. MSS produced by AM was more resistant to pit initiation due to fewer and finer NbC particles. However, the propagation kinetics of stable pits were higher for this MSS due to a higher amount of reversed austenite. The stress was found to stabilise the metastable pits and to accelerate the propagation of stable pits, which resulted in an increased susceptibility to EAC of the MSS produced by AM. These results clearly highlighted the fact that the reversed austenite amount has to be perfectly controlled in AM processes.

On the Nature of Critical Potentials for Aluminum Repassivation

Repassivation (Erp) and pitting transition potential (Eptp)1,2 are considered critical parameters in aluminum pitting, because they have been associated with repassivation phenomena3,4. The physical meaning of Erp has long been well-established in the literature as the threshold between stable pitting and complete repassivation of the material5–7. The nature of Eptp, however, has not been thoroughly explained in the current literature apart from the primary assumption that it represents the commencement of repassivation4. Moreover, experimental investigation and evidence to expand this argument as well as to explore the relationship between these two potentials has been scarce4.The present work aims to address these open questions with cyclic potentiodynamic polarization (CPP) and potentiostatic experiments conducted on high purity Al in NaCl. Repassivation trends at and below Eptp were explained based on the assumption of actively corroding fractions which were dependent on the applied potential. Morphological transformation was also observed during polarization as evidenced by electron microscopy and X-ray microtomography after the electrochemical tests. The observation of a distinct Erp separate from the Eptp during slow CPP scans was related to the charge passed and was hypothesized to be the net effect of the gradually decreasing actively corroding area at potentials below Eptp, which resulted in morphology that restricted mass transport out of the pits, which delayed complete repassivation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. References K. Nisancioglu and H. Holtan, Corrosion Science, 18, 1011–1023 (1978).K. L. Moore, J. M. Sykes, and P. S. Grant, Corrosion Science, 50, 3233–3240 (2008).S. T. Pride, J. R. Scully, and J. L. Hudson, J. Electrochem. Soc., 141, 3028 (1994).M. Yasuda, F. Weinberg, and D. Tromans, J. Electrochem. Soc., 137, 3708 (1990).A. Broli and H. Holtan, Corrosion Science, 13, 237–246 (1973).G. S. Frankel, J. R. Scully, and C. V. Jahnes, J. Electrochem. Soc., 143, 1834 (1996).G. S. Frankel, J. Electrochem. Soc., 145, 2186 (1998).

(Digital Presentation) Comparison of Electrochemical Measurements to Atmospheric Corrosion Experiments on Additively Manufactured 316L

As interest in the commercial implementation of additively manufactured (AM) metal components increases, so does the need to understand the corrosion behavior of these materials. AM metals deviate in microstructure and surface quality from traditionally processed metals which impacts their corrosion properties. Currently there are no studies investigating the variation in corrosion behavior for AM components printed on different machines. This work compares the breakdown potential, an indication of stable pit growth and the loss of passivity, from 316L stainless steel samples printed on several machines. A correlation between breakdown potential and the surface microstructure, unique to parts printed on different machines, will be discussed. Additionally, the electrochemical measurements are correlated with salt fog experiments. Finally, pit morphology from accelerated atmospheric corrosion exposures (salt fog and constant humidity/contamination lab exposures) are compared to a real-world exposure (coastal environment) of AM 316L. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-4063 A

Study on Key Parameters for Jet Impacting Pulverized Coal Deposited in Coal-Bed Methane Wells

Cleaning out the pulverized coal deposited at the bottom of a coalbed methane (CBM) well is key to achieving continuous CBM drainage and prolonging the workover period. In this study, Fluent is used in conjunction with the standard k-ε model and the Eulerian-Eulerian model to simulate and analyse jet erosion of deposited pulverized coal particles. The depth and width of the stable erosion pit that is formed by jet-impacting deposited pulverized coal under different conditions are determined and provide a theoretical basis for the cleanout of pulverized coal in the bottom of a CBM well. In this paper, the three parameters of the jet target distance, nozzle diameter and nozzle outlet flow velocity are selected to perform an orthogonal simulation. The change trends in the depth and width of the scouring pit with time are determined. The results show that jet impacting of deposited pulverized coal can be categorised into four stages, periods of rapid growth, stability, jet swing and dynamic stability. A sensitivity analysis shows that the nozzle outlet flow velocity has the strongest influence on the depth of the scouring pit among the selected parameters. The depth of the jet impact pit can reach the maximum depth at t = 3 s, while the width of the impact pit can reach the maximum after t = 7 s. This can provide key design parameters for CBM well pulverized coal impacting operation. It is of great significance for capacity damage control during CBM well workover operation.

Critical Pitting Temperature of Stainless Steel: Deterministic Vs. Probabilistic Behavior

The concept of the critical pitting temperature (CPT), which is described as the temperature below which stable pits are not formed regardless of applied potential and exposure time, has received considerable attention in the literature. Over the past few decades, many attempts have been made to assess the CPT of stainless steel as a function of alloy composition, alloy microstructure, bulk solution composition, and surface roughness. In contrast to the pitting potential, which is known to be probabilistic in nature, CPT is believed by most to be a deterministic phenomenon that can be measured within a few degrees Celsius [1]. This notion has been validated by many authors who have observed a narrow range of CPT for several alloy/environment combinations [2,3]. Some authors have recently challenged this idea by reporting scattered CPT values [4]. This work seeks to determine whether the CPT falls within a narrow or wide temperature range (i.e., is CPT a deterministic or probabilistic phenomenon?).To answer this question, potentiostatic CPT measurements were performed using 1 cm² 904L stainless steel electrodes and an applied potential of 750 mV (Ag/AgCl). Temperature was increased at a rate of 1 °C/min, and the CPT was determined using the temperature at which current density rapidly increased. The CPT of 904L stainless steel was measured in four different conditions to evaluate the effect of bulk Cl⁻ concentration (0.05 and 1.0 M NaCl), passivation in 20 vol.% HNO3, and the presence of a corrosion inhibitor (0.02 M NaNO3).Figure 1 shows a cumulative graph of the CPT values of 904L obtained using the four different conditions. In this graph, n is the number of the n th pitted sample and N is the total number of experiments (i.e., 10). For all test conditions, the CPT was measured within ± 1.8 °C, which is in agreement with the reproducible CPT values reported by others [3]. Figure 1 shows that the CPT of 904L is independent of passivation in HNO₃. Further, decreasing bulk solution aggressiveness from 1.0 M NaCl to 0.05 M NaCl does not result in scattered CPT values. However, some authors have reported a considerably broader range (i.e., ± 10 °C) for the CPT of stainless steel (AISI 316L and 2205), as discussed previously. One possible explanation for their larger reported CPT range is the occurrence of crevice corrosion at the interface of the alloy/inert support (e.g., epoxy mount), which results in an inaccurate CPT measurement. To evaluate this hypothesis, the current density vs. temperature curves for two conditions were compared (see Figure 2). The blue and red curves show potentiostatic polarization results for pure pitting corrosion (i.e., crevice-free CPT measurement) and pitting + crevice corrosion, respectively. The gradual increase of the current density with temperature for the red curve suggests the presence of a crevice at the alloy/epoxy interface, which was confirmed using SEM to characterize the electrode post-polarization. On the other hand, when no crevice corrosion occurs, the current density shows a sudden increase at the CPT.The results of this study reveal that the CPT of 904L can be measured to within ± 1.8 °C, regardless of bulk solution aggressiveness (e.g., 1.0 M NaCl and 0.05 M NaCl solution) or passive state before polarization. This finding is in contrast to what some authors have suggested recently. The scattered CPT values reported in the literature are most likely due to contributions from both pitting + crevice corrosion rather than pitting corrosion alone. Acknowledgments Financial support provided by Natural Sciences and Engineering Research Council of Canada (NSERC) is gratefully acknowledged.

Investigation of acidity on corrosion behavior and surface properties of SS304 in simulated PEMFC cathode environments

This study presents the influence of acidity on the corrosion performance and surface properties of AISI 304 stainless steel (SS304) in the simulated cathode condition of proton exchange membrane fuel cells (PEMFC) with various concentrations of H2SO4. The electrochemical tests indicate that the corrosion resistance of SS304 samples decreases gradually with the solution acidity ascending, but the stable current densities (0.043–0.547 μA cm−2) in the simulated solutions after polarization (0.6 V, 5 h) are all lower than that of the relevant DOE 2025 target (icorr < 1 μA cm−2). Obvious pitting corrosion occur in the solutions with H2SO4 concentration higher than 10−3 M. The surface wettability and interfacial contact resistance (ICR) of the potentiostatically polarized SS304 show an upward trend with the solution acidity increasing, and whether the SS304 samples are polarized or not, their ICR (0.274–1.232 Ω cm2) is far higher than the latest DOE 2025 technical target (<0.01 Ω cm2). The results reveal that surface modification is indispensable for SS304 as bipolar plates, and more attention should be paid to possessing high and stable pitting resistance, hydrophobicity, and interfacial conductivity in an acid environment.

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

Stainless steels (SSs) easily suffer localized corrosion damage, such as pitting corrosion, in mixed solutions of acetic acid and sodium chloride. Currently, few works have been focused on the early stages of the pitting corrosion (metastable pitting corrosion) process of SSs in a chloride-HAc mixture solution. In this work, the effects of acetic acid (HAc) and its concentration on metastable pitting corrosion and the uniform corrosion of 304 SS in 0.6 mol/L NaCl solution were investigated by a slow-scanning potentiodynamic polarization test, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that the uniform corrosion rate of 304 SS increases after HAc addition but, with an increase in HAc concentration, the corrosion rate decreases. In the presence of HAc, the metastable pitting potential (Em) and stable pitting potential (Eb) move negatively, but the number of metastable pits notably decreases. HAc has a promoting action on the growth rate of the metastable pits and facilitates the transition from metastable pits to stable pits. The influence of HAc is related to a decrease in solution pH and the chemical adsorption of HAc.

Revealing significant effect of nitrogen on prolonging pitting corrosion lifetime of martensitic stainless steel by modelling approach

The prediction models of pitting corrosion lifetime for martensitic stainless steels (MSSs) with different N contents were developed by statistical approach. The modelling and experimental results show that after N-alloying, the metastable pit initiation time was dramatically improved, and the transformation from metastable into stable pitting was retrained, which resulted in the increase of overall stable pit initiation time from 0 to 419.05 and 459.84 days with 0.15 and 0.41 wt% N addition, respectively. Afterwards, N significantly restrained the growth of stable pits. The present models reveal the mechanism of how N influences each stage of pitting corrosion.

Effect of hydrostatic pressure on the pitting corrosion of 17-4PH martensitic stainless steel

The effects of hydrostatic pressure on the performance of passive film and the pitting growth process of 17-4PH martensitic stainless steel (17-4PH SS) were investigated by electrochemical measurements and stochastic theory. The results revealed that the growth rate and compactness of the passive film were changed by hydrostatic pressure, which inhibited the diffusion of point defects in the passive film and enhanced the protection performance of the passive film. The change of the performance of the passive film affects the pitting nucleation, metastable pitting process and reduces the transition probability from the metastable pitting to the stable pitting, which eventually leads to the decrease of pitting sensitivity of 17-4PH martensitic stainless steel.

Promotion of pitting corrosion at hydrogen-enriched α/γ phase boundaries in austenitic stainless steel weld joints

Weld joints can experience numerous defects, which may become enriched in hydrogen and form pits after an attack. However, few in situ studies have been conducted on the relationship between hydrogen enrichment and pitting initiation sites. Moreover, the mechanism by which hydrogen enrichment promotes the initiation and propagation of pitting is unknown. In this study, the pitting susceptibility of austenitic stainless steel weld joints that had been used for 6 years in a hydrocracking unit was investigated. Scanning Kelvin probe force microscopy (SKPFM) was performed to characterize the Volta potential before and after hydrogen removal. The α/γ phase boundaries of the as-received samples were mostly enriched in hydrogen. Furthermore, the α/γ phase boundaries were the preferential locations for the initiation and propagation of pits, which were located at sites of hydrogen enrichment. The results of focused ion beam analysis revealed that the pits deepened along the α/γ phase boundaries and achieved stability. Hydrogen enrichment promotes the transformation of metastable pits to stable pits, which may be the mechanism underlying the promotion of pitting propagation by hydrogen enrichment.

Role of gradient nano-structured surface in collapsed pitting corrosion on AISI 316L stainless steel during tribocorrosion

Stable corrosion pits with collapsed characteristic were found on 316L stainless steel far below pitting potential during tribocorrosion in NaCl solution. The gradient nano-structured surface (GNSS) formed by surface deformation played a decisive role in inducing the collapsed pits. High density crystalline defects and dilution of Cr in topmost region of the GNSS resulted in normal pitting corrosion. Cracking was induced by local stress concentration at the bottom of the pit. The propagation of crack crossing the grain boundaries in the GNSS by anodic dissolution stress corrosion cracking (SCC) and dissolution of crack interior led to collapse of the surface.

The effect of applied stress on the crevice corrosion of 304 stainless steel in 3.5 wt% NaCl solution

The effect of applied stress on the crevice corrosion of 304 stainless steel in 3.5 wt% solution is investigated. The delayed and immediate crevice corrosion of 304 stainless steel could occur under various applied stresses and different polarized potential. Both these two types of crevice corrosion are developed from the evolution of metastable pits. The lifetime of metastable pits is prolonged with the increased stress and the secondary metastable pit is observed under 400 MPa applied stress. This contributes to increased probability of metastable pits transiting to stable pits and then promotes crevice corrosion development with the increased stress.

Mathematical modeling of selective dissolution of AISI 304 steel in circulating chloride-containing waters during operation of heat exchangers

Purpose. Investigation of the effect of chloride-containing medium, chemical composition and structural heterogeneity of AiSi304 steel on selective dissolution of metals ΔCr, ΔNi and ΔFe from stable pits.&#x0D; Research methods. X-ray structural analysis, optical microscopy, energy dispersive microanalysis, analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits.&#x0D; Results. Based on the analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits, it was found that ΔFe from pits on the surface of AISI 304 steel in model circulating water with pH = 4...8 and chloride concentration of 300 and 600 mg / l decrease with an increase in it. the amount of oxides (1.98...3.95 microns), the average diameter of the austenite grain and increase when the average distance between the oxides and the volume of b- ferite in steel increases. It is proved that ΔNi from pits decreases with an increase in the amount of oxides in steel (1.98...3.95 μm), the volume of b- ferite and a decrease in the average diameter of austenite grain.&#x0D; It was determined that ΔCr of steel from pits mainly depends on the concentration of chlorides in the model circulating water, the amount of oxides (1.98 ... 3.95 μm), the average diameter of the austetin grain and the volume of b-ferite. It is hypothesized that this is due to the intensity of adsorption of chlorine ions on imperfections in the structure of AISI304 steel near these oxides at the intersection with the grain boundaries of austenite, where pits nucleate and grow.&#x0D; Scientific novelty. It was established for the first time that the coefficient of selective dissolution of Cr from pits on the surface of AISI 304 (ZCr ) steel in the circulating waters of the river decreases with an increase in the volume of b-ferite in the steel, the average diameter of austenite grain and a decrease in the amount of oxides. This can facilitate the transition of metastable pits to stable ones. Moreover, this process is autocatalytic; therefore, it does not depend on the parameters of the model circulating water.&#x0D; Statement of tasks. Based on the established features of selective dissolution of ΔCr, ΔNi and ΔFe from pits on the surface of AISI304 steel, to study the effect of its plastic defermation on pitting resistance in chloride-containing model circulating waters.&#x0D; Practical value. The developed mathematical models are used to assess the pitting resistance of AISI304 steel in model circulating waters, depending on its parameters and the environment where heat exchangers made of this steel operate.

Effect of Molybdate on the Stability of Pit Growth in Duplex Stainless Steel 2205

In the present study, the criteria of pit stabilization and salt formation have been investigated for DSS 2205 using the lead-in-pencil electrode in order to explore the contribution of molybdate in stable pit growth. Results show that the E pit shifts to positive values with increasing molybdate concentration. It is found that the increase in E pit could not be explained by the changes in DC crit and DC sat, since these values are slightly reduced by adding molybdate to the solution. In contrast, the active dissolution rate of the metal assessed by i diss,max is hindered in the presence of molybdate ions. Therefore, it is proposed that the mechanism for the inhibitory influence of molybdate can be attributed to an increment in the intersection point of i diss,max/i diff,crit (which reflects E crit), and i diss,max/i lim (which reflects E sat). Therefore, increasing the E crit and E sat at the pit growth process is responsible for the observed raising of the E pit in presence of molybdate.

Beneficial Effects of Cerium Addition to Sulfide Inclusions on Pitting Corrosion Resistance of Stainless Steels

The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. The chemical composition of the inclusions affects the pitting corrosion resistance of stainless steels. It is known that the inclusion solubility in aqueous solutions affects pitting corrosion resistance. The dissolution of sulfide inclusions produces S species and exposes the bare surface of the steel matrix, resulting in high pitting susceptibility near the inclusions.1 Cerium is expected to be an additive element for insolubilizing water-soluble inclusions because Ce tends to form sulfides and Ce-sulfides exhibit low solubility in aqueous solutions. Additionally, Ce ions have been shown to be effective in the corrosion inhibition of stainless steel. In this study, a microelectrochemical technique was applied to analyze the effect of Ce addition to sulfide inclusions on the pitting corrosion resistance of stainless steels.2,3 To analyze the effect of Ce addition on water solubility of CaS inclusions, spark plasma sintering was used in the facile fabrication of stainless steel specimens containing artificial Ce-added and Ce-free inclusions.3,4,5 The pit initiation resistance at the Ce-added CaS inclusions was higher than that at the Ce-free CaS inclusions. The surface of the Ce-free CaS inclusions largely dissolved during immersion in 0.1 M NaCl, while a large part of the Ce-added CaS inclusions remained undissolved. Thermodynamic calculation showed that CeS is less soluble than CaS.To analyze the effect of Ce ions on pitting at sulfide inclusions, a type 304 stainless steel (Fe-18Cr-8Ni-1.5Mn-0.02S) was prepared by vacuum induction melting. Manganese sulfide inclusions existed in the specimens. Polarization curves were measured in 3 M NaCl and 2.97 M NaCl-0.01 M CeCl3. Pitting occurred at the MnS inclusions in the Ce3+-free solution, whereas no stable pit was generated in the Ce3+-containing solution even when metastable pitting events were observed.It was found that Ce addition inhibits the dissolution of water-soluble inclusions and improved pitting corrosion resistance. Moreover, the Ce3+ ions are expected to inhibit the pitting even after the dissolution of Ce-added inclusions.