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Hosseini, V., Hurtig, K. & Karlsson, L. (2020). Bead by bead study of a multipass shielded metal arc-welded super-duplex stainless steel. Welding in the World
Open this publication in new window or tab >>Bead by bead study of a multipass shielded metal arc-welded super-duplex stainless steel
2020 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669Article in journal (Refereed) Epub ahead of print
Abstract [en]

The present study aims at investigating bead geometry and the evolution of microstructure with thermal cycles in multipass shielded metal arc welding of a V-groove 13-mm type-2507 super-duplex stainless steel (SDSS) plate. The weld consisted of 4 beads produced with arc energies of 0.81-1.06 kJ/mm. The upper beads showed lower base metal (BM) dilution than the first bead. Thermal cycles were recorded with thermocouples, indicating that the cooling rate decreased in the as-deposited weld zone when adding a new bead. Ferrite fraction in the as-welded condition was lower for the upper beads. The austenite grain morphology in reheated passes varied depending on the local peak temperatures and the number of reheating passes. Sigma phase precipitated in a location reheated by the third and fourth passes that was subjected to a critical peak temperature for sigma precipitation. Ferrite content, measured using image analysis and Fisher FERITSCOPE technique, showed that the ferrite fraction moved toward 50/50% in the weld metal with an increasing number of reheating cycles. Finally, a schematic map showing an overview of the microstructure in the multipass SDSS weld was introduced.

Keywords
Multipass welding; Super-duplex stainless steel; Ferrite content; Sigma phase; Nitrides
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14753 (URN)10.1007/s40194-019-00829-7 (DOI)000498097900001 ()2-s2.0-85075381068 (Scopus ID)
Funder
Vinnova, 2016-02834EU, Horizon 2020, 823786
Available from: 2019-12-12 Created: 2019-12-12 Last updated: 2020-01-30Bibliographically approved
Hosseini, V., Hurtig, K., Eyzop, D., Östberg, A., Janiak, P. & Karlsson, L. (2019). Ferrite content measurement in super duplex stainless steel welds. Welding in the World, 63(2), 551-563
Open this publication in new window or tab >>Ferrite content measurement in super duplex stainless steel welds
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2019 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, no 2, p. 551-563Article in journal (Refereed) Published
Abstract [en]

Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.

Keywords
Ferrite fraction, Ferrite number, Image analysis, Round Robin, Super duplex stainless stee, l Point counting
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13198 (URN)10.1007/s40194-018-00681-1 (DOI)000462318600028 ()2-s2.0-85063276679 (Scopus ID)
Funder
Vinnova, 2016-02834Knowledge Foundation, 20140130
Note

First Online: 05 December 2018

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2020-02-04Bibliographically approved
Hosseini, V. & Karlsson, L. (2019). Physical and kinetic simulation of nitrogen loss in high temperature heat affected zone of duplex stainless steels. Materialia, 6, Article ID 100325.
Open this publication in new window or tab >>Physical and kinetic simulation of nitrogen loss in high temperature heat affected zone of duplex stainless steels
2019 (English)In: Materialia, ISSN 2589-1529, Vol. 6, article id 100325Article in journal (Refereed) Published
Abstract [en]

High temperature heat affected zone (HTHAZ) of duplex stainless steels is prone to local corrosion attack due to a high ferrite fraction and nitride formation. Literature commonly attributes formation of this undesirable microstructure to rapid cooling from high peak temperatures. However, this study investigated the possible role of nitrogen loss in HTHAZ using a combination of physical and kinetics simulation. Applying a stationary gas-tungsten arc (GTA) on a water-cooled plate, a technique known as arc heat treatment, showed that considerable nitrogen loss occurred already after 0.5 min up to 150 µm from the fusion boundary. This zone was extended to 1300 µm after 600 min arc heat treatment. The results of bead-on-plate GTA welding and Gleeble testing replicating the thermal cycle in HTHAZ showed that the ferrite fraction of the real HTHAZ was 7% higher than that for Gleeble samples. This agrees with results from arc heat treatment, where ferrite fraction was found to increase due to nitrogen loss. Numerical and Dictra approaches were developed to simulate the kinetics of nitrogen loss in HTHAZ considering ferrite as the nitrogen rapid diffusion path towards the weld pool. Simulation showed good agreement with both welding and physical simulation. A combination of thermodynamic and kinetics simulations properly predicted the ferrite fraction at 1100 °C for different arc heat treatment times. In conclusion, the experiments (physical simulations and GTA welding) and kinetics simulation showed that nitrogen was lost from HTHAZ to the weld pool. © 2019 Acta Materialia Inc.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Diffusion simulation, Duplex stainless steels, High temperature heat affected zone, Nitrogen loss, Thermodynamic simulation, Welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13858 (URN)10.1016/j.mtla.2019.100325 (DOI)2-s2.0-85064890131 (Scopus ID)
Funder
Knowledge Foundation, 20140130
Available from: 2019-05-24 Created: 2019-05-24 Last updated: 2020-01-15Bibliographically 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. (2019). Super duplex stainless steels Microstructure and propertiesof physically simulated base and weld metal. Stainless Steel World (December), 8-9
Open this publication in new window or tab >>Super duplex stainless steels Microstructure and propertiesof physically simulated base and weld metal
2019 (English)In: Stainless Steel World, ISSN 1383-7184, no December, p. 8-9Article in journal (Other academic) Published
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.

National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-14990 (URN)978-91-87531-97-2 (ISBN)
Available from: 2020-02-25 Created: 2020-02-25 Last updated: 2020-02-25Bibliographically approved
Hosseini, V., Högström, M., Hurtig, K., Valiente Bermejo, M. A., Stridh, L.-E. & Karlsson, L. (2019). Wire-arc additive manufacturing of a duplex stainless steel: thermal cycle analysis and microstructure characterization. Welding in the World, 63(4), 975-987
Open this publication in new window or tab >>Wire-arc additive manufacturing of a duplex stainless steel: thermal cycle analysis and microstructure characterization
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2019 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, no 4, p. 975-987Article in journal (Refereed) Published
Abstract [en]

The evolution of microstructures with thermal cycles was studied for wire-arc additive manufacturing of duplex stainless steel blocks. To produce samples, arc energy of 0.5kJ/mm and interlayer temperature of 150 degrees C were used as low heat input-low interlayer temperature (LHLT) and arc energy of 0.8kJ/mm and interlayer temperature of 250 degrees C as high heat input-high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers4 beads in each layerfor LHLT and 15 layers3 beads in each layerfor HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 degrees C, compared with HHHT. A higher austenite fraction (+8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 degrees C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-arc additively manufactured duplex stainless steel samples (35-60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800-1200 degrees C).

Keywords
Duplex stainless steels; Additive manufacturing; GMAW; Thermal cycles; Austenite fraction; Secondary phases
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13947 (URN)10.1007/s40194-019-00735-y (DOI)000468518900005 ()2-s2.0-85066099481 (Scopus ID)
Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2020-02-03
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
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