Discontinuity of the passivating film at nonmetallic inclusions in stainless steels

“…49 The surface oxide films which form on the sulfide inclusions are known to act as a barrier against the dissolution of the inclusion. 25,29,50,51 Lillard et al proposed that MnS inclusions are passivated by Cu deposition. 21 They analyzed the surface of the MnS inclusion using atomic force microscopy and scanning Kelvin probe force microscopy, and found that Cu deposition on the MnS inclusion causes the MnS ennoblement and passivation during pit propagation.…”

Section: Resultsmentioning

confidence: 99%

Micro-Electrochemical Properties of CeS Inclusions in Stainless Steel and Inhibiting Effects of Ce³⁺Ions on Pitting

Nishimoto

Muto

Sugawara

et al. 2017

J. Electrochem. Soc.

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Micro-scale polarization data from small surface areas of stainless steels with either CeS or MnS inclusions was measured in NaCl and Na 2 SO 4 solutions to elucidate the dissolution and pit initiation behavior of both types of inclusions. Stable pitting was initiated at the CeS inclusion at potentials which exceeded the dissolution potential region of the CeS inclusion, whereas a stable pit at the MnS inclusion was initiated in the dissolution potential range of the MnS inclusion. Thermodynamic calculations indicated that the Ce 3+ ions are likely to be produced by the dissolution of the CeS inclusion. In the micro-scale polarization of a small area with a MnS inclusion, stable pitting at the MnS inclusion was inhibited in NaCl solutions containing Ce 3+ . The formation of a shallow trench was observed at the MnS inclusion/steel matrix boundary in the Ce 3+ -containing solution, whereas a deep trench was formed in the Ce 3+ -free solution. It is suggested that the Ce 3+ ions inhibit trench formation at the MnS/steel matrix boundary, resulting in improved pitting corrosion resistance at sulfide inclusions. While stainless steels are successfully used in corrosive environments, they sometimes suffer from pitting. Improving the pitting corrosion resistance of stainless steels is of the utmost importance because of the vital role these steels play in infrastructure, transportation, energy, in bridges, and buildings in general. The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS in Cl − -containing environments, 1-10 and hence considerable research has been carried out to clarify the mechanism of the pitting at MnS inclusions. It has been proposed that the initial step of the pit initiation process at MnS inclusions is the anodic dissolution of the inclusions and that the complete dissolution of the inclusions is not required for pit initiation.11-21 The release of S-containing species during MnS dissolution increases pitting susceptibility at and around the inclusions. Webb and Alkire demonstrated that the dissolution of the inclusions produces S 2 O 3 2− ions and leads to weak acidification near the inclusions.14 Chiba et al. proposed that the synergistic effect of chloride ions and dissolution products from MnS causes trench formation at the boundary of the inclusion/steel matrix, and pitting occurs at MnS inclusions as a local transition from the passive to the active state of the steel matrix inside the trench. 19 The effect of minor elements on the pitting at MnS inclusions has been investigated. Lillard et al. proposed that Cu ions are released from the steel matrix inside the trench and MnS inclusions are ennobled by Cu deposition. 21They suggested that the ennobled MnS inclusions accelerate pit propagation inside the trench. It is therefore reasonable to assume that the inhibition of the dissolution of the inclusion will directly suppress the formation of trenches, resulting in an improvement in the pitting corrosion resistance of stainless steels....

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“…It is believed that the interface between the oxide inclusion and steel matrix possesses an electrochemical activity that is different from the steel in the environment, affecting the local pitting corrosion. It was found that some oxide inclusions do not adhere tightly to the steel, and crevices can be formed at the interface, resulting in discontinuity of the passive film, if formed, at the inclusion/steel interface. It was also detected that some oxide inclusions can result in the generation of a poor Cr region at the inclusion/matrix interface, increasing the local corrosion activity.…”

Section: Introductionmentioning

confidence: 99%

Investigation of micro‐electrochemical activities of oxide inclusions and microphases in duplex stainless steel and the implication on pitting corrosion

Zhang

Dai

et al. 2019

Materials & Corrosion

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In this study, the oxide inclusions contained in the 2205 duplex stainless steel were characterized, and the pitting corrosion initiated at the inclusions was statistically analyzed. The micro-electrochemical behavior was measured by a home-designed capillary microelectrode technique. Results show that three types of oxide inclusions are contained in the steel, namely, Al-Mg-O (inclusion A), Al-Si-Ca-O (inclusion B), and Al-Mg-Si-Ca-O (inclusion C) inclusions. Inclusion A possesses higher electrochemical stability than the steel substrate, and there is no corrosion pit initiated on the inclusion. Inclusions B

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Discontinuity of the passivating film at nonmetallic inclusions in stainless steels

Cited by 57 publications

References 11 publications

Effect of grain size on pitting corrosion of 304L austenitic stainless steel

Effect of grain size on pitting corrosion of 304L austenitic stainless steel

Micro-Electrochemical Properties of CeS Inclusions in Stainless Steel and Inhibiting Effects of Ce³⁺Ions on Pitting

Investigation of micro‐electrochemical activities of oxide inclusions and microphases in duplex stainless steel and the implication on pitting corrosion

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Discontinuity of the passivating film at nonmetallic inclusions in stainless steels

Cited by 57 publications

References 11 publications

Effect of grain size on pitting corrosion of 304L austenitic stainless steel

Effect of grain size on pitting corrosion of 304L austenitic stainless steel

Micro-Electrochemical Properties of CeS Inclusions in Stainless Steel and Inhibiting Effects of Ce3+Ions on Pitting

Investigation of micro‐electrochemical activities of oxide inclusions and microphases in duplex stainless steel and the implication on pitting corrosion

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Micro-Electrochemical Properties of CeS Inclusions in Stainless Steel and Inhibiting Effects of Ce³⁺Ions on Pitting