Journal
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE
Volume 29, Issue 4, Pages 2612-2622Publisher
SPRINGER
DOI: 10.1007/s11665-020-04753-6
Keywords
corrosion; low-temperature plasma nitriding; metastable pitting; UNS S32205
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Funding
- CNPq Brazilian Funding Agency
- CAPES Brazilian Funding Agency
- Fundacion Universitaria Los Libertadores
- Federal University of Technology - Parana (UTFPR)
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The duplex stainless steel UNS S32205 was plasma nitrided at 380 degrees C for 10 h using a gas mixture of 25% N-2-75% H-2. The thickness of the nitrided layer was 4.5 +/- 0.5 mu m, composed mainly of nitrogen-expanded austenite and iron nitrides precipitates. There was an increase in surface hardness around 2.6 and 3.8 times in the nitrided layer formed on the austenite and the ferrite phases, respectively, in relation to the untreated samples. The surface texture parameters skewness (S-sk), maximum peak height (S-p) and texture aspect ratio (S-tr) were the most appropriate parameters for studying the topography changes after treatment. An improvement in the localized corrosion properties after the nitriding treatment was revealed by the cyclic polarization curves. The nitrided samples showed higher pitting corrosion and repassivation potentials compared to the untreated material. The ferritic phases and grain boundaries were more susceptible to corrosion in the nitrided samples. The potentiodynamic curves of the nitrided samples exhibited a hillside on the passive-to-transpassive transition. This feature was already observed by other researchers, but it has not been well investigated. Potentiostatic studies demonstrated that metastable pitting took place on this transition.
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