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51318-11102-Influence of tungsten on passivity breakdown and repassivation of 25Cr super duplex stainless steels

Picture for Influence of tungsten on passivity breakdown and repassivation of 25Cr super duplex stainless steels
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Two super duplex stainless steels were investigated: a W-free (UNS S32750) and a 2.1 wt% W-containing (UNS S39274) grade. Goals: To study localized corrosion resistance of super duplex stainless steels and how W affects the same.

Product Number: 51318-11102-SG
Author: Cristian Torres / Mariano Kappes / Roy Johnsen / Mariano Iannuzzi
Publication Date: 2018
Industry: Science of Corrosion
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Super duplex stainless steels are ferritic-austenitic stainless steels with 25 wt% Cr and a pitting resistance equivalent (PRE) ≥ 40. Even though other elements, such as Cr and Mo, have been studied in much more detail than W, research has shown that an optimal composition exists, in which W in solid solution improves localized corrosion resistance. Outside this range, W is ineffective or even detrimental. However, the mechanisms by which W improves localized corrosion resistance in stainless steels are unclear. For example, debate still exists as to whether W enhances passivity or facilitates repassivation.

In this work, two super duplex stainless steels were investigated: a W-free (UNS S32750) and a 2.1 wt% W-containing (UNS S39274) grade. The first goal was to study differences in the overall localized corrosion resistance; while the second objective was to gain an insight into the mechanisms by which W affects the localized corrosion performance of super duplex stainless steels. The work was divided into two parts. Firstly, anodic potentiodynamic polarization curves were conducted in different simulated pit environments at various temperatures. Two simulated pit solutions were tested: 1 M HCl and 7 M LiCl adjusted to a pH of 0. In the second part, crevice repassivation potentials were measured using the potentiodynamic-galvanostatic-potentiodynamic technique in 3.5 wt% NaCl pH = 6.5 solution. This investigation will provide evidence regarding the influence of W in passive film stability and repassivation kinetics

Key words: localized corrosion, super duplex stainless steel, crevice repassivation potential, pit-like-solutions, tungsten

Super duplex stainless steels are ferritic-austenitic stainless steels with 25 wt% Cr and a pitting resistance equivalent (PRE) ≥ 40. Even though other elements, such as Cr and Mo, have been studied in much more detail than W, research has shown that an optimal composition exists, in which W in solid solution improves localized corrosion resistance. Outside this range, W is ineffective or even detrimental. However, the mechanisms by which W improves localized corrosion resistance in stainless steels are unclear. For example, debate still exists as to whether W enhances passivity or facilitates repassivation.

In this work, two super duplex stainless steels were investigated: a W-free (UNS S32750) and a 2.1 wt% W-containing (UNS S39274) grade. The first goal was to study differences in the overall localized corrosion resistance; while the second objective was to gain an insight into the mechanisms by which W affects the localized corrosion performance of super duplex stainless steels. The work was divided into two parts. Firstly, anodic potentiodynamic polarization curves were conducted in different simulated pit environments at various temperatures. Two simulated pit solutions were tested: 1 M HCl and 7 M LiCl adjusted to a pH of 0. In the second part, crevice repassivation potentials were measured using the potentiodynamic-galvanostatic-potentiodynamic technique in 3.5 wt% NaCl pH = 6.5 solution. This investigation will provide evidence regarding the influence of W in passive film stability and repassivation kinetics

Key words: localized corrosion, super duplex stainless steel, crevice repassivation potential, pit-like-solutions, tungsten

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51318-11105-Effect of tungsten on the precipitation kinetics and localized corrosion resistance of super duplex

Product Number: 51318-11105-SG
Author: Mia Bernås / Ida Westermann / Anders Jernberg, Atle H. Qvale / Roy Johnsen / Cristian Torres / Mariano Iannuzzi
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The effect of W on the precipitation kinetics of three 25Cr SDSS grades was quantified in Time-Temperature-Transformation (TTT) diagrams. Optical microscopy, scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), and Electron backscatter diffraction (EBSD) were used.
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51318-11084-The Application Limitation Boundary of Duplex Stainless Steel under Sour Condition in Oil Fields

Product Number: 51318-11084-SG
Author: Ziru Zhang / Zhu Wang / Junpeng Xue / Lei Zhang / Xian Tang / Minxu Lu
Publication Date: 2018
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Pitting failure boundary of duplex stainless steel under sour condition was investigated by electrochemical and immersion tests. Polarization measurements investigate the effect of temperature and H2S on the corrosion behavior.
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51318-11107-Effect of Oxygen in Back Shielding Gas on Corrosion Resistance of Super Duplex Stainless Steel Pipe

Product Number: 51318-11107-SG
Author: Takayuki Tokumine / Takanori Mimoto / Gen Ogita / Yoshiyuki Shimizu / Masanori Gokou / Fu-Gao Wei / Toshiaki Ashitani / Masayuki Tanaka
Publication Date: 2018
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The effect of back shielding gas types and contained oxygen level on the corrosion resistance of welds was investigated for gas tungsten arc welding (GTAW) of UNS S32750 super duplex stainless steel (SDSS) pipes.
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