kth.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • 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
In-situ observations on the suppression of phase separation in duplex stainless steel by applying an external magnetic field
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.ORCID iD: 0000-0003-1027-821x
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.ORCID iD: 0000-0002-9920-5393
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In-situ small-angle neutron scattering (SANS) experiments, with and without an applied magnetic field of 1.5 T, were performed for two duplex stainless steels: 22Cr-5Ni and 25Cr-7Ni (wt.%) during isothermal heat treatment at 450 °C. The kinetics of phase separation was suppressed by the external magnetic field in both steels, however, the suppression was much more pronounced in 25Cr-7Ni where phase separation was nearly eliminated. The different magnetic energy contribution from the external field in each alloy explains the different behaviour of the alloys. The findings could have large technical implications for mitigation of low-temperature embrittlement in Fe-Cr-Ni based alloys.

Keywords [en]
In-situ SANS; duplex stainless steel; phase separation; spinodal decomposition; magnetic field; embrittlement.
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-316781OAI: oai:DiVA.org:kth-316781DiVA, id: diva2:1691232
Projects
Vinnova Cooler Lsi
Note

QC 20220902

Available from: 2022-08-29 Created: 2022-08-29 Last updated: 2023-12-07Bibliographically approved
In thesis
1. Phase separation in duplex stainless steel: characterization and mitigation
Open this publication in new window or tab >>Phase separation in duplex stainless steel: characterization and mitigation
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Duplex stainless steel (DSS) is a category of widely used stainlesssteel, which are strategically important in a variety of applications such asin the food industry, chemical engineering plants and nuclear power plants,due to their attractive combination of mechanical properties and corrosionresistance. However, these steel grades are sensitive to the so-called ‘475°Cembrittlement’, because of a phase separation (PS) phenomenon in theferrite phase, which decomposes into Fe-rich ferrite (α) and Cr-rich ferrite(α'), when exposed to temperatures within the miscibility gap. The PS isaccompanied by an increase of micro-hardness of the bcc phase and a severeloss of toughness, leading to the deterioration of the mechanical properties.Therefore, the upper service temperature of DSSs in industrial applicationshas been limited to around 250° C.In the present work, the PS in DSSs was mainly investigated by smallangleneutron scattering (SANS). A quantitative analysis method based onthe SANS data was proposed to evaluate both the wavelength and amplitudeof PS in Fe-Cr based alloys, e.g. DSSs. The wavelength and amplitudequantified by this methodology showed a good agreement with the resultsby atom probe tomography (APT). Then, SANS measurements and thismethod were applied for a comprehensive investigation on the applicationof DSSs and their weldments under industrially relevant conditions, i.e.low/intermediate temperature and prolonged aging time, in order to pursuethe structure-property relation. The current study shows that the measuredCr amplitude is connected to the change of micro-hardness and impacttoughness. Moreover, embrittlement is a function of both the isothermalaging temperature and time.In order to find effective ways to mitigate the PS, this work has alsoattempted to investigate the governing thermodynamics and the kinetics ofPS. First, the effects of alloying elements (e.g. Ni, Al, Co) on the Fe-Crsystem were critically reviewed since such understanding could pave theway for the design of the next generation of DSSs that are less susceptibleto embrittlement; Second, the process route can also influence the PS andit was therefore investigated. It was found that a faster cooling rate aftersolution treatment leads to the lower rate of PS. Moreover, applying anexternal magnetic field may also affect the kinetics of PS: an in-situ SANSstudy showed that a 1.5 T applied magnetic field can significantly delay thePS of DSSs in the early stages.This thesis can be summarized in two parts: i) demonstration of SANSfor characterizing and quantifying PS in DSSs under industrially relevantconditions; ii) discussion of the possibility to mitigate PS in DSSs to becomeless susceptible to low/intermediate temperature embrittlement.

Abstract [sv]

Duplexa rostfria stål (DSS) är en kategori av rostfria stål som ärstrategiskt viktiga i en mängd olika applikationer såsom i livsmedelsindustrin,kemitekniska anläggningar och kärnkraftverk. Detta på grund avderas attraktiva kombination av styrka och korrosionsbeständighet. Dessastålsorter är dock känsliga för den så kallade '475°C försprödningen', pågrund av fasseparation (PS) i ferritfasen, där det sönderdelas till Fe-rikferrit (α) och Cr-rik ferrit (α'), när materialet utsätts för temperaturer inomblandningsluckan. FS åtföljs av en ökning av mikrohårdheten i bcc-fasenoch en kraftigt minskad seghet, vilket leder till försämring av egenskaperna.Därför är den övre användningstemperaturen för DSS i industriellatillämpningar begränsad till cirka 250°C.I denna avhandling har PS undersökts i DSS genom i huvudsaklågvinkel neutronspridning, s.k. SANS. En ny analysmetod baserad påSANS-data har föreslagits för att kvantitativt utvärdera både våglängdenoch amplituden hos PS i Fe-Cr-baserade legeringar, t.ex. DSS. Våglängdenoch amplituden kvantifierades med denna metod och visade en godöverensstämmelse med resultat från atomsondstomografi (APT). SANSmätningaroch denna metod användes vidare för en omfattandeundersökning av DSS och svetsade DSS åldrade under industriellt relevantaförhållanden, d.v.s. låg/mellantemperatur och lång åldringstid. Relationenmellan struktur och egenskaper studerades. Denna avhandling visar hurden uppmätta Cr-amplituden är relaterad till förändringen avmikrohårdhet och slagseghet. Dessutom visas hur försprödningen beror avbåde den isotermiska åldringstemperaturen och tiden.För att hitta effektiva sätt att mildra PS och försprödning av DSS hardetta arbete undersökt dess underliggande termodynamik och kinetik.Först studerades effekterna av tillsatta legeringselement (t.ex. Ni, Al, Co) påFe-Cr-systemet eftersom en sådan förståelse skulle kunna bana väg förutformningen av nästa generations DSS med mindre mottaglighet förförsprödning. Dessutom kan tillverkningsprocessvägen påverka PS underefterföljande åldring av DSS och en snabbare nedkylningshastighet efterupplösningsbehandling visade sig leda till lägre hastighet för PS. Sist meninte minst kan applicering av ett externt magnetfält också påverka kinetikenhos PS och en in-situ SANS-studie visade att ett applicerat magnetfält om1.5 T avsevärt kan fördröja PS för DSS i de tidiga stadierna.Sammanfattningsvis är denna avhandling uppdelad i två delar. Denförsta delen demonstrerar fördelen med SANS när det gäller attkarakterisera och kvantifiera PS i DSS under industri-relevantaförhållanden. Den andra delen diskuterar möjligheten att mildra PS i DSSför att göra dessa mindre mottagliga för försprödning.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2022. p. 151
Series
TRITA-ITM-AVL ; 2022:26
Keywords
duplex stainless steel, 475 °C embrittlement, phase separation, small-angle neutron scattering, mechanical properties, alloying elements, cooling rate, magnetic field
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-316815 (URN)978-91-8040-331-3 (ISBN)
Public defence
2022-09-30, Sal D37 / https://kth-se.zoom.us/j/61392505267, Lindstedtsvägen 5, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Available from: 2022-09-06 Created: 2022-08-30 Last updated: 2023-12-07Bibliographically approved

Open Access in DiVA

No full text in DiVA

Authority records

Liu, JianlingDas, YadunandanKorzhavyi, Pavel A.Hedström, Peter

Search in DiVA

By author/editor
Liu, JianlingDas, YadunandanKorzhavyi, Pavel A.King, StephenHedström, Peter
By organisation
PropertiesStructures
Metallurgy and Metallic Materials

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 123 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • 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