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
Super duplex stainless steels: Microstructure and propertiesof physically simulated base and weld metal
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-6242-3517
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-temperature processing and application of super duplex stainless steel(SDSS) are associated with the risk of changes in the ferrite/austenite balance and precipitation of secondary phases. This study was therefore aimed at improving knowledge about effects of thermal cycles on the microstructure and properties of SDSS base and weld metal. Controlled and repeatable thermal cycles were physically simulated using the innovative multiple TIG reheating/remelting and the arc heat treatment techniques. In the first technique, one to four autogenous TIG-remelting passes were applied. During arc heat treatment, a stationary arc was applied on a disc mounted on a water-cooled chamber thereby subjecting the material to a steady state temperature gradient from 0.5 minute to 600 minutes. Microstructures and properties were assessed and linked to thermal history through thermal cycle analysis, thermodynamic calculations and temperature field modelling, Remelting studies showed that nitrogen loss from the melt pool was a function of arc energy and initial nitrogen content and could cause highly ferritic microstructures. Heat affected zones were sensitized by nitride formation next to the fusion boundary and sigma phase precipitation in regions subjected to peak temperatures of 828-1028°C. Accumulated time in the critical temperature range, peak temperature and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase precipitation. Arc heat treatment produced graded microstructures in SDSS base and weld metal with the formation of a ferritic region at high temperature due to solid-state nitrogen loss, precipitation of sigma, chi, nitrides, and R-phase with different morphologies at 550-1010°C and spinodal decomposition below 500°C. This caused sensitization and/or increased hardness and embrittlement. Results were summarized as time-temperature-precipitation and properties diagrams for base and weld metal together with guidelines for processing and welding of SDSS.

Place, publisher, year, edition, pages
Trollhättan: University West , 2018. , p. 102
Series
PhD Thesis: University West ; 24
Keywords [en]
Super duplex stainless steel; weld metal; physical simulation; phase balance; precipitation; secondary phases; corrosion; nitrogen loss; arc heat treatment; production technology
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-12850ISBN: 978-91-87531-98-9 (print)ISBN: 978-91-87531-97-2 (electronic)OAI: oai:DiVA.org:hv-12850DiVA, id: diva2:1243217
Public defence
2018-09-28, F127, lhättan, 09:00 (English)
Supervisors
Available from: 2018-09-04 Created: 2018-08-30
List of papers
1. Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel
Open this publication in new window or tab >>Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel
Show others...
2016 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 2, p. 233-245Article in journal (Refereed) Published
Abstract [en]

The influence of heat input and multiple welding cycles on the microstructure of the heat-affected zone in autogenously TIG-welded 6 mm 2507 type super duplex stainless steel plates was investigated. In order to produce multiple thermal cycles, one to four pass bead-on-plate welds were made with arc energies of 0.47 and 1.08 kJ/mm, corresponding to heat inputs of 0.37 and 0.87 kJ/mm. Several thermocouples were attached to record thermal cycles on the front and back sides of the plates. Finite element modelling was successfully done to map and correlate measured and calculated peak temperatures. Only minor changes were seen in the ferrite content at 1 and 2 mm from the fusion boundary. Nitrides formed in all passes of the low heat input samples in a region next to the fusion boundary, but only after the third and fourth passes of the high heat input samples. Sigma phase precipitated only in a zone heated to a peak temperature in the range of approximately 828 to 1028 °C. Multiple reheating was found to promote precipitation of sigma phase relatively more than slower cooling. A precipitation free zone was observed between the nitride and sigma phase bands. The precipitation behaviour could be understood from equilibrium phase diagrams, evaluation of local thermal cycles and by correlating results from the modelling and measurements of peak temperatures. It is suggested that the peak temperature, the accumulated time in the critical temperature range between approximately 828 and 1028 °C, and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase formation.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2016
Keywords
Duplex stainless steels, GTA welding, multirun welding, heat affected zone, microstructure, mathematical models, energy input
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9001 (URN)10.1007/s40194-016-0300-5 (DOI)000374785100007 ()2-s2.0-84958787089 (Scopus ID)
Available from: 2016-02-05 Created: 2016-02-05 Last updated: 2018-08-30Bibliographically approved
2. Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel
Open this publication in new window or tab >>Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel
2016 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 98, no May, p. 88-97Article in journal (Refereed) Published
Abstract [en]

Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28 wt% in the base metal to 0.17 wt% and 0.10 wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and arc energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.

Place, publisher, year, edition, pages
Reigate, Surrey: Scientific and technical P., 2016
Keywords
Nitrogen loss, TIG welding, multipass welding, ferrite content, thermodynamical calculation, super duplex stainless steel
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9189 (URN)10.1016/j.matdes.2016.03.011 (DOI)000373273000010 ()2-s2.0-84963604761 (Scopus ID)
Available from: 2016-03-04 Created: 2016-03-04 Last updated: 2018-08-30Bibliographically approved
3. Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel
Open this publication in new window or tab >>Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel
2018 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 6, article id 933Article in journal (Refereed) Published
Abstract [en]

Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 Όm to 0.5 Όm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800-900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment. © 2018 by the authors.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
Austenite; Corrosion resistance; Heat resistance; Localized corrosion; Microscopic examination; Morphology; Scanning electron microscopy; Stainless steel; Steel testing; Temperature, Chemical compositions; Duplex stainless steel; Electron backscattered diffraction analysis; Sigma-phase precipitation; Steady-state temperature; Super duplex stainless steel; Thermodynamic calculations; Water-cooled chambers, Steel corrosion
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12703 (URN)10.3390/ma11060933 (DOI)000436500300066 ()2-s2.0-85047834414 (Scopus ID)
Available from: 2018-07-05 Created: 2018-07-05 Last updated: 2018-09-14Bibliographically approved
4. A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
Open this publication in new window or tab >>A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
Show others...
2017 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, p. 11-23Article in journal (Refereed) Published
Abstract [en]

This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.

Place, publisher, year, edition, pages
Reigate, Surrey: Scientific and technical P., 2017
Keywords
Stationary arc, Heat treatment, Graded microstructure, Super duplex stainless steels, Physical simulation, Welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-10760 (URN)10.1016/j.matdes.2017.02.042 (DOI)000399625000002 ()2-s2.0-85013031461 (Scopus ID)
Available from: 2017-02-28 Created: 2017-02-28 Last updated: 2018-08-30Bibliographically approved
5. Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
Open this publication in new window or tab >>Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
Show others...
2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed) Published
Abstract [en]

A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures. © 2018 The Authors

Place, publisher, year, edition, pages
Elsevier Inc., 2018
Keywords
Austenite; Chromium compounds; Cold rolling; Embrittlement; Hardness; Heat treatment; Microstructure; Nitrogen; Nitrogen compounds; Phase equilibria; Schematic diagrams; Stainless steel, Chi phase; Functionally graded microstructures; Nitrogen loss; R phase; Sigma phase, Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12235 (URN)10.1016/j.matchar.2018.03.024 (DOI)000431469300042 ()2-s2.0-85044113030 (Scopus ID)
Note

Available online 19 March 2018

Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2018-08-30Bibliographically approved
6. Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals
Open this publication in new window or tab >>Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals
2018 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 3, p. 517-533Article in journal (Refereed) Published
Abstract [en]

Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.

Place, publisher, year, edition, pages
International Institute of Welding, 2018
Keywords
Super duplex stainless steel, Weld metal, Time-temperature-precipitation diagram, Sensitization, Hardness, Sigma phase, Stationary arc, Heat treatment, Secondary austenite
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12054 (URN)10.1007/s40194-018-0548-z (DOI)000441244700007 (Scopus ID)
Note

First Online: 17 January 2018

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2018-09-14Bibliographically approved
7. Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal
Open this publication in new window or tab >>Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal
2018 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 7, p. 2803-2816Article in journal (Refereed) Published
Abstract [en]

Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12263 (URN)10.1007/s11661-018-4600-9 (DOI)000433974400022 ()2-s2.0-85045465335 (Scopus ID)
Note

First Online: 17 April 2018

Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2018-08-30Bibliographically approved
8. Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel
Open this publication in new window or tab >>Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel
2017 (English)In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 68, no 4, p. 405-415Article in journal (Refereed) Published
Abstract [en]

This is a study of the effect of repetitive TIG (tungsten inert gas) welding passes, melting and remelting the same material volume on microstructure and corrosion resistance of 2507 (EN 1.4410) super duplex stainless steel. One to four weld passes were autogenously (no filler added) applied on a plate using two different arc energies and with pure argon shielding gas. Sensitization testing showed that multipass remelting resulted in significant loss of corrosion resistance of the weld metal, in base material next to the fusion boundary, and in a zone 1 to 4 mm from the fusion boundary. Metallography revealed the main reasons for sensitization to be a ferrite-rich weld metal and precipitation of nitrides in the weld metal, and adjacent heat affected zone together with sigma phase formation at some distance from the fusion boundary. Corrosion properties cannot be significantly restored by a post weld heat treatment. Using filler metals with higher nickel contents and nitrogen containing shielding gases, are therefore, recommended. Welding with a higher heat input and fewer passes, in some cases, can also decrease the risk of formation of secondary phases and possible corrosion attack.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2017
Keywords
Welding, corrosion, resistance
National Category
Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9885 (URN)10.1002/maco.201609102 (DOI)000398581800002 ()2-s2.0-84986268706 (Scopus ID)
Available from: 2016-09-13 Created: 2016-09-13 Last updated: 2018-08-30Bibliographically approved

Open Access in DiVA

fulltext(38965 kB)50 downloads
File information
File name FULLTEXT01.pdfFile size 38965 kBChecksum SHA-512
00dedf3b5b6e1f4e41b7f031e1c0a473e7a68682058576f5f5a765d0fa6ad808712883518150f41ceeb7895cb715046a8ac22e918d33ace569b8c697e7ad7084
Type fulltextMimetype application/pdf
Spikblad(62 kB)17 downloads
File information
File name FULLTEXT02.pdfFile size 62 kBChecksum SHA-512
e05574c53a380d535f29debe2ae249e35cf86b517565f3e48f5e5b76edfd81e678c4cb482c32f9a14fe52211b7a0d513ba4c69535e32e7fd3774563f9633dd7c
Type fulltextMimetype application/pdf

Authority records BETA

Hosseini, Vahid

Search in DiVA

By author/editor
Hosseini, Vahid
By organisation
Division of Welding Technology
Manufacturing, Surface and Joining Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 67 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: 409 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