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Study of Corrosion Behavior of a 2507 Super Duplex Stainless Steel: Influence of Quenched-in and Isothermal Nitrides
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
(Sandvik Materials Technology)
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-9453-1333
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-4431-0671
2014 (English)In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 9, no 1, 61-80 p.Article in journal (Refereed) Published
Abstract [en]

Precipitation of different types of chromium nitrides may occur during processing of super duplex stainless steels, affecting the properties of the material. In this study the influence of quenched-in (size range ca. 50-100 nm) and isothermal (size range ca. 80-250 nm) types of nitrides on the corrosion behavior of a 2507 super duplex stainless steel has been investigated at room temperature and at 90 degrees C (above the critical pitting temperature) in 1 M NaCl solution. The microstructure has been characterized by scanning electron microscopy and magnetic force microscopy. The isothermal nitrides exhibit a higher Volta potential compared to the matrix, but such difference could not be observed for the quenched-in nitrides. In-situ electrochemical AFM measurements at room temperature show stable surfaces for a wide range of applied potentials despite the presence of either type of nitrides. In the transpassive region isothermal nitrides appear to be slightly more deleterious than quenched-in nitrides. At 90 degrees C isothermal nitrides largely reduce the corrosion resistance of the austenite phase, while the quenched-in nitrides reduce the corrosion resistance of the material to a much lesser extent. The size difference between isothermal and quenched-in chromium nitrides may be crucial, in particular above the critical pitting temperature.

Place, publisher, year, edition, pages
2014. Vol. 9, no 1, 61-80 p.
Keyword [en]
Duplex stainless steel, nitrides, exposure tempera ture, atomic force microscopy, corrosion
National Category
Corrosion Engineering
Identifiers
URN: urn:nbn:se:kth:diva-129354ISI: 000328931100006Scopus ID: 2-s2.0-84891050891OAI: oai:DiVA.org:kth-129354DiVA: diva2:651801
Note

QC 20140123. Updated from accepted to published.

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Influence of carbides and nitrides on corrosion initiation of advanced alloys: A local probing study
Open this publication in new window or tab >>Influence of carbides and nitrides on corrosion initiation of advanced alloys: A local probing study
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Advanced alloys often present precipitated carbides and nitrides in their microstructure following exposure to elevated temperatures. These secondary phases are usually undesirable, because potentially deleterious for the corrosion and mechanical performances of the material. Carbides and nitrides are enriched in key alloying elements that are subtracted from their surrounding matrix areas, creating alloying element depleted zones, which might become initial sites for corrosion initiation. In this study, the influence of micro- and nano-sized precipitated carbides and nitrides on the corrosion initiation of biomedical CoCrMo alloys and duplex stainless steels has been investigated at microscopic scale, by using a combination of local probing techniques. The microstructures of the alloys were first characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The Volta potential mapping of carbides and nitrides revealed their higher nobility compared to the matrix, and particularly compared to their surrounding areas, suggesting the occurrence of some alloying element depletion in the latter locations, which may lead to a higher susceptibility for corrosion initiation. In-situ electrochemical AFM studies performed at room temperature showed passive behavior for large potential ranges for both alloy families, despite the presence of the precipitated carbides or nitrides. At high anodic applied potential, at which transpassive dissolution occurs, preferential dissolution started from the areas adjacent to the precipitated carbides and nitrides, in accordance with the Volta potential results. Thus, the presence of carbides and nitrides doesn’t largely affect the corrosion resistance of the tested advanced alloys, which maintain passive behavior when exposed to highly concentrated chloride solutions at room temperature with no applied potential. The effect of nitrides on the corrosion initiation of duplex stainless steels was investigated also at temperatures above the critical pitting temperature (CPT). Depending on the type, distribution and size range of the precipitated nitrides different corrosion behaviors were observed. Intragranular (quenched-in) nano-sized nitrides (ca. 50-100 nm) finely dispersed in the ferrite grains have a minor influence on the corrosion resistance of the material at temperatures above the CPT, while larger intergranular (isothermal) nitrides (ca. 80-250 nm) precipitated along the phase boundaries cause a detrimental reduction of the corrosion resistance of the material, in particular of the austenite phase

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiv, 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:34
Keyword
carbides, nitrides, microstructure, CoCrMo alloys, duplex stainless steels, localized corrosion, transpassive dissoluti on, elemental depletion, AFM, TEM, SEM.
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-129356 (URN)978-91-7501-841-6 (ISBN)
Public defence
2013-10-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2013-09-27Bibliographically approved

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