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Effect of homogenization temperatureon subsequent spinodal decompositionduring aging in Fe-46.5Cr alloy
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: 0000-0003-3598-2465
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.
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(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-150799OAI: oai:DiVA.org:kth-150799DiVA: diva2:745218
Note

QS 2014

Available from: 2014-09-10 Created: 2014-09-10 Last updated: 2014-09-10Bibliographically approved
In thesis
1. An Atom-Probe Tomography Study of Phase Separation in Fe-Cr Based Steels
Open this publication in new window or tab >>An Atom-Probe Tomography Study of Phase Separation in Fe-Cr Based Steels
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stainless steels are very important engineering materials in a variety of applications such as in the food industry and nuclear power plants due to their combination of good mechanical properties and high corrosion resistance. However, ferrite-containing stainless steels are sensitive to the so-called ‘475°C embrittlement’, which is induced by phase separation of the ferrite phase, where it decomposes into Fe-rich ferrite (α) and Cr-rich ferrite (α'). The phase separation is accompanied with a severe loss of toughness. Therefore, the upper service temperature of ferrite-containing stainless steels in industrial applications has been limited to around 250°.

In the present work, Fe-Cr based steels were mainly investigated by atom probe tomography. A new method based on the radial distribution function (RDF) was proposed to quantitatively evaluate both the wavelength and amplitude of phase separation in Fe-Cr alloys from the atom probe tomography data. Moreover, a simplified equation was derived to calculate the amplitude of phase separation. The wavelength and amplitude was compared with evaluations using the auto-correlation function (ACF) and Langer-Bar-on-Miller (LBM) method, respectively. The results show that the commonly used LBM method underestimates the amplitude of phase separation and the wavelengths obtained by RDF shows a good exponential relation with aging time which is expected from the theory. The RDF is also an effective method in detecting the phenomena of clustering and elemental partitioning.

Furthermore, atom probe tomography and the developed quantitative analysis method have been applied to investigate the influence of different factors on the phase separation in Fe-Cr based alloys by the help of mainly mechanical property tests and atom probe tomography analysis. The study shows that: (1) the external tensile stress during aging enhances the phase separation in ferrite. (2) Phase separation in weld bead metals decomposes more rapidly than both the heat-affected-zone metals and the base metals mainly due to the high density of dislocations in the welding bead metals which could facilitate the diffusion. (3) The results show that Ni and Mn can enhance the phase separation comparing to the binary Fe-Cr alloy whereas Cu forms clusters during aging. (4) Initial clustering of Cr atoms was found after homogenization. Two factors, namely, clustering of Cr above the miscibility gap and clustering during quenching was suggested as the two responsible mechanisms. (5) The homogenization temperatures significantly influence the evolution of phase separation in Fe-46.5at.%Cr.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xii, 54 p.
Keyword
Fe-Cr alloys, Ferritic stainless steels, Spinodal decomposition, Phase separation, Atom probe tomography, Radial distribution function (RDF)
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-150796 (URN)978-91-7595-195-9 (ISBN)
Public defence
2014-09-29, F3, Lindstedsvägen 26, Kungliga Tekniska Högskolan, Stockholm, Stockhol, 10:00 (English)
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Supervisors
Projects
Spinodal Project
Note

QC 20140910

Available from: 2014-09-10 Created: 2014-09-09 Last updated: 2014-09-10Bibliographically approved

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