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Wessman, S. (2019). On the use of computational thermodynamics for predicting the precipitation and growth of secondary phases in stainless steels. In: ESSC and DUPLEX 2019 - 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition: . Paper presented at 10th European Stainless Steel Conference - Science and Market, ESSC 2019 and 6th European Duplex Stainless Steel Conference and Exhibition, DUPLEX 2019; Vienna; Austria; 30 September 2019 through 2 October 2019 (pp. 198-206). Austrian Society for Metallurgy and Materials (ASMET)
Open this publication in new window or tab >>On the use of computational thermodynamics for predicting the precipitation and growth of secondary phases in stainless steels
2019 (English)In: ESSC and DUPLEX 2019 - 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition, Austrian Society for Metallurgy and Materials (ASMET) , 2019, p. 198-206Conference paper, Published paper (Refereed)
Abstract [en]

Stainless steels are high-Alloyed, usually with multiple components and often also dual matrix phases, as for duplex stainless steels. This makes predictions and calculations of alloying effects on equilibria and phase transformations a challenge. Computational thermodynamics has emerged as an indispensable tool for calculations within these complex systems on predictions of equilibria and precipitation & growth. This paper offers examples illustrating how computational methods can be applied both to thermodynamics and kinetics of stainless steels in order to predict microstructure comprising of the desired matrix phases ferrite and/or austenite, as also the less desired secondary phases such as intermetallic phases and nitrides. © 2019 ESSC and DUPLEX 2019 - 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition. All rights reserved.

Place, publisher, year, edition, pages
Austrian Society for Metallurgy and Materials (ASMET), 2019
Keywords
Commerce; Forecasting; Nickel steel; Phase equilibria; Thermodynamics, Alloying effect; Computational thermodynamics; Indispensable tools; Intermetallic phasis; Matrix phasis; Multiple components; Secondary phasis; Thermodynamics and kinetics, Duplex stainless steel
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-15016 (URN)2-s2.0-85079324358 (Scopus ID)
Conference
10th European Stainless Steel Conference - Science and Market, ESSC 2019 and 6th European Duplex Stainless Steel Conference and Exhibition, DUPLEX 2019; Vienna; Austria; 30 September 2019 through 2 October 2019
Funder
Vinnova, 2016-02834
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-03-04Bibliographically approved
Hosseini, V., Wessman, S., Hurtig, K. & Karlsson, L. (2019). Predicting ferrite fractions in single pass super duplex stainless steel welds: thermal cycle analysis and phase transformation modeling. In: ESSC and DUPLEX 2019: 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition. Paper presented at 10th European Stainless Steel Conference - Science and Market, ESSC 2019 and 6th European Duplex Stainless Steel Conference and Exhibition, DUPLEX 2019; Vienna; Austria; 30 September 2019 through 2 October 2019 (pp. 180-197). Wien: Austrian Society for Metallurgy and Materials (ASMET)
Open this publication in new window or tab >>Predicting ferrite fractions in single pass super duplex stainless steel welds: thermal cycle analysis and phase transformation modeling
2019 (English)In: ESSC and DUPLEX 2019: 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition, Wien: Austrian Society for Metallurgy and Materials (ASMET) , 2019, p. 180-197Conference paper, Published paper (Refereed)
Abstract [en]

The relationship between welding process parameters, welding thermal cycle, and the final microstructure is of great importance for reliable fabrication of welded super duplex stainless steels (SDSS) structures. The present study was primarily aimed at investigating the relationship for root/single pass welding of type 2507 SDSS. Fourteen welds were produced using GMAW, GTAW, SAW, and SMAW with different joints geometries, plate thicknesses, and welding parameters. Thermal cycles were recorded using several thermocouples attached to the plates and thermocouples were also harpooned into the weld pool. Weld pool geometries and base metal dilution in the weld metal were determined for all welds. The general trend was that the ferrite fraction of the weld zone increased with increasing cooling rate and base metal dilution in the weld metal. The ferrite fraction was in the range 49-64% for all welds. Kinetics of austenite formation was modeled using computational thermodynamics (Thermo-Calc & DICTRA) to predict the ferrite fractions in the weld zone and calculated fractions were in good agreement with experimental results. Some conflicting results showed that in addition to dilution and cooling rate, the possible nitrogen loss must be taken into account when evaluating and predicting ferrite fraction. It was concluded that the above approach can be used for prediction of the ferrite fraction of super duplex stainless steel single pass welds. Â 2019 ESSC and DUPLEX 2019 - 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition. All rights reserved.

Place, publisher, year, edition, pages
Wien: Austrian Society for Metallurgy and Materials (ASMET), 2019
Keywords
Commerce; Cooling; Electric arc welding; Electric welding; Ferrite; Forecasting; Metals; Nickel steel; Phase transitions; Plates (structural components); Thermal cycling; Thermocouples; Welds, Computational thermodynamics; Dictra; Ferrite fraction; Kinetics of austenite formation; Simulation; Super duplex stainless steel; Welding process parameters; Welding thermal cycles, 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-15015 (URN)2-s2.0-85079330776 (Scopus ID)
Conference
10th European Stainless Steel Conference - Science and Market, ESSC 2019 and 6th European Duplex Stainless Steel Conference and Exhibition, DUPLEX 2019; Vienna; Austria; 30 September 2019 through 2 October 2019
Funder
Vinnova, 2016-02834
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-02-24Bibliographically approved
Hosseini, V., Karlsson, L., Engelberg, D. & Wessman, S. (2018). Correction to: Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals (Welding in the World, (2018), 62, 3, (517-533), 10.1007/s40194-018-0548-z). Welding in the World, 62(4), 893
Open this publication in new window or tab >>Correction to: Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals (Welding in the World, (2018), 62, 3, (517-533), 10.1007/s40194-018-0548-z)
2018 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 4, p. 893-Article in journal (Refereed) Published
Abstract [en]

Unfortunately due to typesetting mistakes, Tables 4-€“6 have been displayed erroneously in the article. © 2018, International Institute of Welding.

National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12659 (URN)10.1007/s40194-018-0565-y (DOI)2-s2.0-85048496813 (Scopus ID)
Funder
Vinnova, 2016-02834Knowledge Foundation, DNr 20140130
Available from: 2018-07-04 Created: 2018-07-04 Last updated: 2019-05-28Bibliographically approved
Hosseini, V., Karlsson, L., Wessman, S. & Fuertes, N. (2018). Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel. Materials, 11(6), Article ID 933.
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.

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)
Funder
Knowledge Foundation, 20140130
Available from: 2018-07-05 Created: 2018-07-05 Last updated: 2019-05-27Bibliographically approved
Hosseini, V., Karlsson, L., Örnek, C., Reccagni, P., Wessman, S. & Engelberg, D. (2018). Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method. Materials Characterization, 139, 390-400
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
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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

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)
Funder
Vinnova, 2016-02834Knowledge Foundation, 20140130
Note

Available online 19 March 2018

Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2019-05-27Bibliographically approved
Hosseini, V., Thuvander, M., Wessman, S. & Karlsson, L. (2018). Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal. Metallurgical and Materials Transactions. A, 49A(7), 2803-2816
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)
Funder
Knowledge Foundation, 20140130
Note

First Online: 17 April 2018

Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2019-03-21Bibliographically approved
Hosseini, V., Karlsson, L., Engelberg, D. & Wessman, S. (2018). Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals. Welding in the World, 62(3), 517-533
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.

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 ()
Funder
Vinnova, 2016-02834Knowledge Foundation, DNr 20140130
Note

First Online: 17 January 2018

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2019-05-28Bibliographically approved
Hosseini, V. A., Wessman, S., Hurtig, K. & Karlsson, L. (2016). Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel. Materials & design, 98(May), 88-97
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.

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)
Funder
Knowledge Foundation, 2014-01910
Available from: 2016-03-04 Created: 2016-03-04 Last updated: 2019-05-20Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5110-449X

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