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A study of duplex stainless steels aged at 325°C under applied tensile load
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, Physical Metallurgy.ORCID iD: 0000-0003-1102-4342
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, Computational Thermodynamics. Outokumpu Stainless Research Foundation, Sweden .
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2011 (English)In: 7th European Stainless Steel Conference: Science and Market, Proceedings, Associazione Italiana di Metallurgia , 2011Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Associazione Italiana di Metallurgia , 2011.
Keyword [en]
Duplex stainless steels, Embrittlement, Load effect, Mechanical properties, Microstructure, Phase separation, Welding
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-85479Scopus ID: 2-s2.0-84909606309ISBN: 978-888529884-2 (print)OAI: oai:DiVA.org:kth-85479DiVA: diva2:499884
Conference
7th European Stainless Steel Conference: Science and Market, Como, Italy, 21 September 2011 through 23 September 2011
Note

QC 20120411

Available from: 2012-02-13 Created: 2012-02-13 Last updated: 2015-04-23Bibliographically 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, Joakim

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