| 1. |
- Anantha, Krishnan Hariramabadran, et al.
(författare)
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Correlative Microstructure Analysis and In Situ Corrosion Study of AISI 420 Martensitic Stainless Steel for Plastic Molding Applications
- 2017
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 164:4, s. C85-C93
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the corrosion behavior of tempered AISI 420 martensitic stainless steel (MSS) was studied by in-situ atomic force microscopy (AFM) in 0.1M NaCl and correlated with the microstructure. Thermocalc simulation, dilatometry, and X-ray diffraction (XRD) were performed to investigate phase transformation which showed the formation of M3C, M7C3, and M23C6 type of carbides and also retained austenite. Optical microscopy, scanning electron microscopy (SEM), and AFM characterization revealed undissolved carbides and tempering carbides in the martensitic matrix. Volta potential mapping measured by scanning Kelvin probe force microscopy (SKPFM) indicated higher electrochemical (practical) nobility of the carbides with respect to the martensitic matrix whereas regions adjacent to carbides showed lower nobilities due to chromium depletion. Open circuit potential and cyclic potentiodynamic polarization measurements showed metastable corrosion activities associated with a weak passive behavior and a risk for localized corrosion along certain carbide boundaries. In-situ AFM measurements revealed selective dissolution of certain carbide interphases and martensitic inter-lath regions indicating higher propensity to localized corrosion.
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| 2. |
- Anantha, Krishnan Hariramabadran, et al.
(författare)
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In situ AFM study of localized corrosion processes of tempered AISI 420 martensitic stainless steel : Effect of secondary hardening
- 2017
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 164:13, s. C810-C818
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Tidskriftsartikel (refereegranskat)abstract
- The effect of secondary hardening of tempered AISI 420 martensitic stainless steel on the corrosion behavior in aqueous 0.01 M NaCl has been studied, in-situ, using atomic force microscopy (AFM) to monitor real-time localized corrosion processes. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses confirmed the presence of undissolved and secondary carbides (Cr23C6, Cr7C3, Cr3C2, Cr3C, Cr2C, and CrC) as well as retained austenite, all finely dispersed in the tempered martensitic matrix. Electrochemical measurements, consisted of monitoring of the open-circuit potential vs. time and cyclic polarization in 0.01 M NaCl solution, were performed to evaluate the passivity and its breakdown, and it was seen that initiation sites for localized corrosion were predominantly peripheral sites of carbides. In-situ AFM measurements revealed that there was a sequence for localized corrosion in which the neighboring matrix next to secondary carbides dissolved first, followed by corrosive attack on regions adjacent to undissolved carbides. Tempering at 500◦C reduced the corrosion resistance and the ability to passivate in comparison to tempering at 250◦C.
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| 3. |
- Örnek, Cem, et al.
(författare)
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475 degrees C Embrittlement of Duplex Stainless Steel-A Comprehensive Microstructure Characterization Study
- 2017
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Ingår i: Materials Performance and Characterization. - : American society for testing and materials. - 2379-1365 .- 2165-3992. ; 6:3, s. 409-436
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Tidskriftsartikel (refereegranskat)abstract
- The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite, austenite, and at interphase boundaries were characterized using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Microanalyses confirmed the presence of Cr-enriched alpha'' and Cr-depleted alpha' spinodal structures in the ferrite after 5 h of aging at 475 degrees C. Long-term aging for 255 h resulted in heavily-faulted R-phase precipitates with sizes of similar to 50-400 nm, chi-phase, and epsilon-Cu in the ferrite, TiN and Cr2N precipitates in the austenite, and a continuous network of M23C6-carbides at interphase boundaries. A significant hardness increase was observed after 255 h of aging, which was accompanied by a reduction of ferrite fraction. X-ray diffraction (XRD) stress measurements showed a general reduction of residual stresses in both ferrite and austenite with aging. Electron backscatter diffraction (EBSD) showed increased local misorientations, primarily close to precipitate interfaces within the ferrite, indicating the development of strain heterogeneities in the microstructure. The data presented provided a better understanding of 475 degrees C embrittlement in duplex stainless steel, suggesting that not only the ferrite alone is responsible for embrittlement. A comprehensive microstructure characterization study has been provided and the explanation for 475 degrees C embrittlement of duplex stainless steel has been discussed.
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| 4. |
- Örnek, Cem, et al.
(författare)
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748 K (475 A degrees C) Embrittlement of Duplex Stainless Steel : Effect on Microstructure and Fracture Behavior
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : SPRINGER. - 1073-5623 .- 1543-1940. ; 48A:4, s. 1653-1665
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Tidskriftsartikel (refereegranskat)abstract
- 22Cr-5Ni duplex stainless steel (DSS) was aged at 748 K (475 A degrees C) and the microstructure development correlated to changes in mechanical properties and fracture behavior. Tensile testing of aged microstructures confirmed the occurrence of 748 K (475 A degrees C) embrittlement, which was accompanied by an increase of strength and hardness and loss of toughness. Aging caused spinodal decomposition of the ferrite phase, consisting of Cr-enriched alpha aEuro(3) and Fe-rich alpha' and the formation of a large number of R-phase precipitates, with sizes between 50 and 400 nm. Fracture surface analyses revealed a gradual change of the fracture mode from ductile to brittle delamination fracture, associated with slip incompatibility between ferrite and austenite. Ferrite became highly brittle after 255 hours of aging, mainly due to the presence of precipitates, while austenite was ductile and accommodated most plastic strain. The fracture mechanism as a function of 748 K (475 A degrees C) embrittlement is discussed in light of microstructure development.
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| 5. |
- Örnek, Cem, et al.
(författare)
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Characterization of 475 degrees C Embrittlement of Duplex Stainless Steel Microstructure via Scanning Kelvin Probe Force Microscopy and Magnetic Force Microscopy
- 2017
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 164:6, s. C207-C217
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin probe force microscopy (SKPFM) measured local Volta potentials in microstructure of 22Cr-5Ni duplex stainless steel have been correlated to microstructure development with aging treatments at 475 degrees C. Magnetic force microscopy (MFM) was employed to differentiate crystallographic phases to provide complementary information. The absolute Volta potentials of both ferrite and austenite increased after 5 hours of aging, indicating electrochemical ennoblement of the entire microstructure. Longer aging resulted in a gradual decrease of measured Volta potentials in both phases. The microstructure showed after 255 hours aging up to 2.5-times larger potential differences than in the as-received condition, indicating impaired electrochemical nobility. In the as-received microstructure, the ferrite phase was less noble than the austenite, whereas after 5 hours aging both phases had similar, balanced Volta potentials which indicated a balanced nobility of ferrite and austenite. Longer aging treatment caused severe loss of nobility for the entiremicrostructure, with ferrite showing larger changes in Volta potential than the austenite. Spinodal microstructure decomposition and associated phase reactions of the ferrite, with elemental redistribution in the austenite, are the reason for the observed changes in microstructure nobility.
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