Pit Initiation at Single Sulfide Inclusions in Stainless Steel

Webb, Eric G.; Alkire, Richard C.

doi:10.1149/1.1474432

Cited by 66 publications

(47 citation statements)

References 17 publications

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“…21,22 The development of this technique led to advances in the past twenty years regarding the understanding of pitting corrosion at non-metallic inclusions in stainless steels. [23][24][25][26][27][28] Chiba et al developed a micro-electrochemical system for in situ high-resolution optical microscopy, which can be used for the morphological analysis of pitting during the very beginning of the initiation process. [29][30][31] In this study, we used this technique to investigate the initiation site of pitting of AISI 1045 ferrite-pearlite steel.…”

Section: 10mentioning

confidence: 99%

Real-Time Microelectrochemical Observations of Very Early Stage Pitting on Ferrite-Pearlite Steel in Chloride Solutions

Kadowaki

Muto

Sugawara

et al. 2017

J. Electrochem. Soc.

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The initiation site and morphology during the early stage of pitting on AISI 1045 carbon steel that has a microstructure of primary ferrite and pearlite were investigated in boric-borate buffer solutions with and without NaCl at pH 8.0. The pits initiated by micro-scale polarization were in the pearlite only and not in primary ferrite. In situ real-time observations during the micro-scale polarization of pearlite in a boric-borate buffer solution with 100 mM NaCl indicated that the pits were polygonal or rod-like in shape. In addition, it was found that the pit growth direction was the same as that of the pearlite lamellae that consisted of ferrite and cementite. Field-emission electron probe micro analysis detected segregated points of sulfur in the ferrite lamellae. On the basis of their etching behavior in 3% nital, the corrosion resistance of the cementite was estimated to be higher than that of the ferrite lamellar structure. Thus, pits readily initiated in the ferrite lamellae and proceeded along the ferrite lamellae. Ferrite-pearlite steel is widely used in the production of bars, plates, steel wires, etc.1-3 because of its high strength, ductility, toughness, wear resistance, and low cost.3-5 Pearlite has a lamellar structure that consists of ferrite and cementite (Fe 3 C) phases. A fine pearlite structure improves the mechanical properties of steels in terms of strength and ductility.6-8 While ferrite-pearlite steels exhibit excellent mechanical properties, their pitting corrosion resistance is relatively low. It is widely believed that the boundaries between the different phases act as initiation sites for localized corrosion in chloride environments. 9,10When ferrite-pearlite steel that does not undergo any surface treatment is exposed to chloride environments, the steel readily suffers from pitting corrosion. Although the steel is successfully protected from corrosion by coating and/or painting, to prolong their service life and improve their reliability, it is necessary to elucidate the initiation mechanism of pitting on ferrite-pearlite steel.The pitting corrosion process involves two stages: initiation and propagation.11 In chloride environments, pitting is initiated by a breakdown of the passive film on steel during a local active dissolution process that exposes the bare steel surface to the environment. This film-free dissolution involves the hydrolysis reaction of metal cations and results in acidification. Chloride ions migrate into the pit to maintain electrical neutrality, and the simultaneous accumulation of chloride ions combined with the high level of acidification accelerates the active dissolution inside the pit. There have been many reports about the propagation stage of pitting corrosion in ferrite-pearlite steels. A comparison of the active dissolution rates and the electrochemical properties of ferrite and cementite have been widely discussed. It is commonly believed that cementite has a lower dissolution rate than ferrite. Yumoto et al. synthesized stoichiometric Fe 3 C films with...

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Section: 10mentioning

confidence: 99%

Real-Time Microelectrochemical Observations of Very Early Stage Pitting on Ferrite-Pearlite Steel in Chloride Solutions

Kadowaki

Muto

Sugawara

et al. 2017

J. Electrochem. Soc.

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“…In this study, parameter sensitivity analysis was applied to the pit initiation model developed by Webb and Alkire. 13 The perturbation effects of thirteen parameters on 21 output variables were investigated. The output variables considered were the potential and concentrations of 20 species at the bottom of a microcrevice which is believed to be the most probable location for pit initiation.…”

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confidence: 99%

Parameter Sensitivity Analysis of Pit Initiation at Single Sulfide Inclusions in Stainless Steel

Kamrunnahar¹,

Braatz²,

Alkire³

2004

J. Electrochem. Soc.

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Sensitivity analysis methods were used in conjunction with a mathematical model for corrosion pit initiation in the vicinity of MnS inclusions in stainless steel to investigate the relationship between physicochemical parameters and the potential and concentration distributions. The finite difference method with central differences was used to calculate sensitivities. The mathematical model of pit initiation included 20 species plus the potential and 13 physicochemical parameters including rate constants for chemical and electrochemical surface reactions and equilibrium constants for homogeneous reactions. It was found that the potential and concentration profiles are most sensitive to the Tafel slope of the rate of electrochemical dissolution of sulfur-containing inclusions and least sensitive to changes in the equilibrium coefficients of the homogeneous reactions. The rate constant for the electrochemical reaction for dissolution of sulfide inclusions was also found to be significant. The procedure provides a first step toward selecting the most important parameters, designing critical experiments, and selecting the hypothesis that best fits experimental data.

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“…[9][10][11]13) It has been well reported that localized corrosion initiates in stainless steels at inclusions, in particular, MnS inclusions. 9,10,12,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Many mechanisms of pit initiation at Mn(Fe,Cr)S inclusions have been proposed, but the basic mechanism is that either the inclusion begins to dissolve or the matrix around the inclusion dissolves, leading to the acid pitting mechanism. The low pH causes preferential dissolution of Mn(Fe,Cr)S inclusions, releasing sulfur species that are known to cause damage to oxide films by suppressing repassivation, as well as by initiating further Mn(Fe,Cr)S inclusion dissolution.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Pitting Corrosion Resistance of Type 430 Stainless Steel by Electrochemical Treatments in a Concentrated Nitric Acid

et al. 2014

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Electrochemical surface treatments have been attempted in 5 kmol/m 3 HNO3 solution to improve pitting corrosion resistance of Type 430 stainless steel. Three different surface treatments were carried out for the same time period (2.9 h) under conditions of immersion, potentiostatic polarization at 0.9 V vs. Ag/ AgCl/sat.KCl reference electrode (E=+0.222 V vs. SHE) and potential cycling between 0.6 and 0.9 V. The pitting corrosion resistance was evaluated by an ordinary pitting potential measurement and droplet tests which simulates atmospheric corrosion in marine environments. It was found that the potential cycling treatment is most effective among them to improve pitting corrosion resistance. The surface analysis by EPMA and XPS indicated that the potential cycling most successfully removes MnS inclusions and increases Cr content in the passive film.

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Pit Initiation at Single Sulfide Inclusions in Stainless Steel

Cited by 66 publications

References 17 publications

Real-Time Microelectrochemical Observations of Very Early Stage Pitting on Ferrite-Pearlite Steel in Chloride Solutions

Real-Time Microelectrochemical Observations of Very Early Stage Pitting on Ferrite-Pearlite Steel in Chloride Solutions

Parameter Sensitivity Analysis of Pit Initiation at Single Sulfide Inclusions in Stainless Steel

Improvement of Pitting Corrosion Resistance of Type 430 Stainless Steel by Electrochemical Treatments in a Concentrated Nitric Acid

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