Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
An Atom-Probe Tomography Study of Phase Separation in Fe-Cr Based Steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-4180-2486
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 [en]
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: urn:nbn:se:kth:diva-150796ISBN: 978-91-7595-195-9 (print)OAI: oai:DiVA.org:kth-150796DiVA: diva2:745089
Public defence
2014-09-29, F3, Lindstedsvägen 26, Kungliga Tekniska Högskolan, Stockholm, Stockhol, 10:00 (English)
Opponent
Supervisors
Projects
Spinodal Project
Note

QC 20140910

Available from: 2014-09-10 Created: 2014-09-09 Last updated: 2014-09-10Bibliographically approved
List of papers
1. Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis
Open this publication in new window or tab >>Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis
2013 (English)In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 19, no 3, 665-675 p.Article in journal (Refereed) Published
Abstract [en]

Nanostructure evolution during low temperature aging of three binary Fe-Cr alloys has been investigated by atom probe tomography. A new method based on radial distribution function (RDF) analysis to quantify the composition wavelength and amplitude of spinodal decomposition is proposed. Wavelengths estimated from RDF have a power-law type evolution and are in reasonable agreement with wavelengths estimated using other more conventional methods. The main advantages of the proposed method are the following: (1) Selecting a box size to generate the frequency diagram, which is known to generate bias in the evaluation of amplitude, is avoided. (2) The determination of amplitude is systematic and utilizes the wavelength evaluated first to subsequently evaluate the amplitude. (3) The RDF is capable of representing very subtle decomposition, which is not possible using frequency diagrams, and thus a proposed theoretical treatment of the experimental RDF creates the possibility to determine amplitude at very early stages of spinodal decomposition.

Keyword
atom probe tomography (APT), spinodal decomposition, radial distribution function (RDF), phase separation, stainless steels
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-124038 (URN)10.1017/S1431927613000470 (DOI)000319126300018 ()2-s2.0-84877973197 (Scopus ID)
Funder
Swedish Research Council, 621-2009-5289Vinnova
Note

QC 20130628. Updated from "Accepted" to "Published"

Available from: 2013-06-28 Created: 2013-06-25 Last updated: 2017-12-06Bibliographically approved
2. Observations of copper clustering in a 25Cr-7Ni super duplex stainless steel during low-temperature aging under load
Open this publication in new window or tab >>Observations of copper clustering in a 25Cr-7Ni super duplex stainless steel during low-temperature aging under load
Show others...
2012 (English)In: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 92, no 7, 336-343 p.Article in journal (Refereed) Published
Abstract [en]

Atom-probe tomography was used to investigate phase separation and copper (Cu) clustering in the ferrite phase of a 25Cr-7Ni super duplex stainless steel. The steel was subjected to a tensile load during aging at 325 degrees C for 5800 h. The degree of phase separation into alpha (Fe-rich) and alpha' (Cr-rich) was small, but still, it was the highest in the steel subjected to the highest load. Cu was found to cluster, and the number density of clusters increased with increasing load. In the material subjected to the highest load, Cu was enriched in regions that were neither Fe-rich nor Cr-rich. These regions also had the highest number density of Cu clusters.

Keyword
3DAP, stainless steels, phase decomposition, clusters, copper, duplex steels
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-85491 (URN)10.1080/09500839.2012.672773 (DOI)000305682200004 ()2-s2.0-84863190061 (Scopus ID)
Funder
Swedish Research Council, 621-2009-5289Vinnova
Note

QC 20140910

Available from: 2012-02-13 Created: 2012-02-13 Last updated: 2017-12-07Bibliographically approved
3. Concurrent phase separation and clustering in the ferrite phase during low temperature stress aging of duplex stainless steel weldments
Open this publication in new window or tab >>Concurrent phase separation and clustering in the ferrite phase during low temperature stress aging of duplex stainless steel weldments
Show others...
2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 16, 5818-5827 p.Article in journal (Refereed) Published
Abstract [en]

The concurrent phase separation and clustering of alloying elements in the ferrite phase of duplex stainless steel weldments after stress aging at 325 degrees C have been investigated by atom probe tomography analysis. Both phase separation, into Fe-rich and Cr-rich ferrite, and solute clustering were observed. Phase separation in the heat-affected zone (HAZ) is most pronounced in the high alloyed SAF 2507, followed by SAF 2205 and SAF 2304. Moreover Cu clustering was observed in the HAZ of SAF 2507. However, decomposition in the weld bead (25.10.4L) was more pronounced than in the HAZs, with both phase separation and clustering of Ni-Mn-Si-Cu. The observed differences in the decomposition behaviors in the HAZ and weld bead can be attributed to the high Ni content and the characteristic microstructure of the weld bead with high internal strains. In addition, an applied tensile stress during aging of weldments has been found to further promote the kinetics of phase separation and clustering.

Keyword
Duplex stainless steels, Phase separation, Atom probe tomography, Spinodal decomposition, Clustering
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-104382 (URN)10.1016/j.actamat.2012.07.022 (DOI)000309438500016 ()2-s2.0-84866129827 (Scopus ID)
Funder
Swedish Research Council, 621-2009-5289Vinnova
Note

QC 20121105

Available from: 2012-11-05 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
4. Initial clustering - A key factor for phase separation kinetics in Fe-Cr-based alloys
Open this publication in new window or tab >>Initial clustering - A key factor for phase separation kinetics in Fe-Cr-based alloys
Show others...
2014 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 75, 62-65 p.Article in journal (Refereed) Published
Abstract [en]

Clustering of alloying elements in solution-treated Fe-Cr-based alloys is of considerable importance for their microstructure stability upon aging. The clustering of Cr after solution treatment in three stainless steel alloy categories has been studied by atom probe tomography. Furthermore, phase-field simulations are applied to examine the effect of initial clustering on phase separation evolution. It is concluded that the clustering of Cr found in solution-treated ferritic and duplex alloys plays a critical role in the nanostructure evolution during aging.

Keyword
Atom probe tomography (APT), Clustering, Phase separation, Phase-field modeling, Stainless steels
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-142330 (URN)10.1016/j.scriptamat.2013.11.020 (DOI)000331025200016 ()2-s2.0-84892369660 (Scopus ID)
Funder
Vinnova
Note

QC 20140228

Available from: 2014-02-28 Created: 2014-02-28 Last updated: 2017-12-05Bibliographically approved
5. The 475 degrees C embrittlement in Fe-20Cr and Fe-20Cr-X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography
Open this publication in new window or tab >>The 475 degrees C embrittlement in Fe-20Cr and Fe-20Cr-X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography
Show others...
2013 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 574, 123-129 p.Article in journal (Refereed) Published
Abstract [en]

In the present work the 475 degrees C embrittlement in binary Fe-Cr and ternary Fe-Cr-X (X=Ni, Cu and Mn) alloys have been investigated. The mechanical properties were evaluated using microhardness and impact testing, and the structural evolution was evaluated using atom probe tomography (APT). The APT results after aging at 500 degrees C for 10 h clearly showed that both Ni and Mn accelerate the ferrite decomposition. No evident phase separation of either the Fe-20Cr or Fe-20Cr-1.5Cu samples was detected after 10 h of aging and thus no conclusions on the effect of Cu can be drawn. Cu clustering was however found in the Fe-20Cr-1.5Cu sample after 10 h aging at 500 degrees C. The mechanical property evolution was consistent with the structural evolution found from APT. Samples aged at 450 and 500 degrees C all showed increasing hardness and decreasing impact energy. The embrittlement was observed to take place mainly during the first 10 h of aging and it could primarily be attributed to phase separation, but also substitutional solute clustering and possibly carbon and nitrogen segregation may contribute in a negative way.

Keyword
Phase separation, Spinodal decomposition, 475 degrees C embrittlement, Atom probe tomography, Ferritic stainless steels, Mechanical properties
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-124438 (URN)10.1016/j.msea.2013.03.016 (DOI)000319088100016 ()2-s2.0-84875954170 (Scopus ID)
Funder
Vinnova
Note

QC 20130710

Available from: 2013-07-10 Created: 2013-07-05 Last updated: 2017-12-06Bibliographically approved
6. Direct atom probe tomography observations of concentration fluctuationsin Fe-Cr solid solution
Open this publication in new window or tab >>Direct atom probe tomography observations of concentration fluctuationsin Fe-Cr solid solution
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-150797 (URN)
Note

QS 2014

Available from: 2014-09-10 Created: 2014-09-10 Last updated: 2014-09-10Bibliographically approved
7. Effect of homogenization temperatureon subsequent spinodal decompositionduring aging in Fe-46.5Cr alloy
Open this publication in new window or tab >>Effect of homogenization temperatureon subsequent spinodal decompositionduring aging in Fe-46.5Cr alloy
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-150799 (URN)
Note

QS 2014

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

Open Access in DiVA

Ph.D thesis_Jing Zhou_KTH(3030 kB)5144 downloads
File information
File name FULLTEXT02.pdfFile size 3030 kBChecksum SHA-512
7ef7a265d92b96e63285b9dbac8e024c5fb8f270552244f77142a35ed5e7ad75e79aca211e7a5f454a04c3feb2cdb28b74210e0a20a66c6c8902d9dfa03cc88f
Type fulltextMimetype application/pdf

Authority records BETA

Zhou, Jing

Search in DiVA

By author/editor
Zhou, Jing
By organisation
Physical Metallurgy
Metallurgy and Metallic Materials

Search outside of DiVA

GoogleGoogle Scholar
Total: 5144 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 486 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf