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3D analysis of phase separation in ferritic stainless steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0003-3598-2465
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0003-1102-4342
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2012 (English)In: Proceedings of the 1st International Conference on 3D Materials Science, John Wiley & Sons, 2012, 221-226 p.Conference paper, Published paper (Refereed)
Abstract [en]

The embrittlement of ferritic stainless steels during low temperature aging is attributed to the phase separation with Fe and Cr demixing. The small scale of the decomposed structure with only minor compositional fluctuations and short distances between the enriched and depleted regions has been a challenge for quite some time. A wide selection of experimental and modeling tools have been used to quantify these types of structures. These analyses often focus on rather late stages of decomposition where the mechanical properties are already seriously affected. The recent advance in 3D tools like phase-field and atom probe tomography have created a need for good quantitative procedures of evaluating the structure and also to link results from the continuum approach to the individual atom measurements. This work aims at addressing this need.

Place, publisher, year, edition, pages
John Wiley & Sons, 2012. 221-226 p.
Keyword [en]
Phase separation, Atom Probe Tomography, Phase-field modeling
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-119237ISI: 000324176000034Scopus ID: 2-s2.0-84889868799ISBN: 978-1-11847-039-8 (print)OAI: oai:DiVA.org:kth-119237DiVA: diva2:610021
Conference
1st International Conference on 3D Materials Science (3DMS),Seven Springs, Pennsylvania, Date: Jul 08-12, 2012
Note

QC 20130308

Available from: 2013-03-08 Created: 2013-03-08 Last updated: 2013-12-06Bibliographically approved
In thesis
1. Experimental study of phase separation in Fe-Cr based alloys
Open this publication in new window or tab >>Experimental study of phase separation in Fe-Cr based alloys
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Duplex stainless steels (DSSs) are important engineering materials due to their combination of good mechanical properties and corrosion resistance. However, as a consequence of their ferrite content, DSSs are sensitive to the so-called ‘475°C embrittlement’, which is induced by phase separation, namely, the ferrite decomposed into Fe-rich ferrite (α) and Cr-rich ferrite (α'), respectively. The phase separation is accompanied with a severe loss of toughness. Thus, the ‘475°C embrittlement’ phenomenon limits DSSs’ upper service temperature to around 250°C.

In the present work, Fe-Cr binary model alloys and commercial DSSs from weldments were investigated for the study of phase separation in ferrite. Different techniques were employed to study the phase separation in model alloys and commercial DSSs, including atom probe tomography, transmission electron microscopy and micro-hardness test.

Three different model alloys, Fe-25Cr, Fe-30Cr and Fe-35Cr (wt. %) were analyzed by atom probe tomography after different aging times. A new method based on radial distribution function was developed to evaluate the wavelength and amplitude of phase separation in these Fe-Cr binary alloys. The results were compared with the wavelengths obtained from 1D auto-correlation function and amplitudes from Langer-Bar-On-Miller method. It was found that the wavelengths from 1D auto-correlation function cannot reflect the 3D nano-scaled structures as accurate as those obtained by radial distribution function. Furthermore, the Langer-Bar-On-Miller method underestimates the amplitudes of phase separation.

Commercial DSSs of SAF2205, 2304, 2507 and 25.10.4L were employed to investigate the connections between phase separation and mechanical properties from different microstructures (base metal, heat-affected-zone and welding bead) in welding. Moreover, the effect of external tensile stress during aging on phase separation of ferrite was also investigated. It was found that atom probe tomography is very useful for the analysis of phase separation in ferrite and the radial distribution function (RDF) is an effective method to compare the extent of phase separation at the very early stages. RDF is even more sensitive than frequency diagrams. In addition, the results indicate that the mechanical properties are highly connected with the phase separation in ferrite and other phenomena, such as Ni-Mn-Si-Cu clusters, that can also deteriorate the mechanical properties.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. vi, 28 p.
Keyword
Duplex stainless steels, Ferritic stainless steels, Spinodal decomposition, Phase separation, Atom probe tomography, Clustering, Radial distribution function (RDF)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-119230 (URN)978-91-7501-632-0 (ISBN)
Presentation
2013-03-22, N111, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130308

Available from: 2013-03-08 Created: 2013-03-08 Last updated: 2013-10-31Bibliographically approved

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Odqvist, JoakimSelleby, Malin

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