Welding Metallurgy and Weldability

Lippold, John C.

doi:10.1002/9781118960332

Cited by 514 publications

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“…The chi phase presents lower precipitation fractions and studies have shown that its precipitation is associated with sigma phase formation 1,3 . The precipitation of the sigma and chi phases occurs in the temperature ranges 600-1000 °C and 700-950 °C, respectively 1,[4][5][6] , and the precipitation sites are at the α/γ (ferrite/austenite) interfaces. Chi phase can precipitate at the α/α interface, and both sigma and chi phases also precipitate at triple α/α/γ points.…”

Section: Introductionmentioning

confidence: 99%

Double Kinetics of Intermetallic Phase Precipitation in UNS S32205 Duplex Stainless Steels Submitted to Isothermal Heat Treatment

et al. 2017

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One of the most studied deleterious phases in stainless steels is the sigma phase, due to its high potential to decrease the toughness and corrosion resistance of these steels. Eight samples of as-received cold rolled UNS S32205 duplex stainless steel were submitted to isothermal heat treatments at 850 o C during 10,15, 30, 60, 120, 180, 240, and 300 minutes in order to study the precipitation kinetics of the sigma and chi deleterious phases. Several complementary microstructural analysis techniques were used to determine the volume fraction of the intermetallic phases, including optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Evaluation was made of the kinetics of isothermal formation of sigma and chi phases in commercial duplex stainless steels (UNS S32205). The results indicated two different mechanisms for sigma phase precipitation: sigma phase formed from the chi phase for shorter isothermal heat treatment times, and sigma phase precipitated at the ferrite-austenite interface for longer isothermal heat treatment times, using a temperature of 850 o C. The phase transformation kinetics determined using the JMA equation indicated that chi phase precipitation caused faster sigma phase formation.

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Section: Introductionmentioning

confidence: 99%

Double Kinetics of Intermetallic Phase Precipitation in UNS S32205 Duplex Stainless Steels Submitted to Isothermal Heat Treatment

et al. 2017

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“…Many authors have studied different solutions to restore the equal percentages of the ferrite and austenite phases as well as solutions to avoid precipitation of the detrimental intermetallic compounds such as the sigma (σ), chi (χ) and nitride phases after the welding processes [9,10]; the critical temperatures for the formation of these phases are between 650 and 900 °C. Lippold and Koseki [11] suggested limiting the heat input during welding of the duplex stainless steels in the range of 0.5-2.0 kJ/mm, so that formation and precipitation of the deleterious intermetallic phases can be avoided [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

Tahaei

Pérez²,

Merlin

et al. 2016

Soldag. insp.

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In this research, the effect of the addition of nickel powder and the application of a post weld heat treatment (PWHT) on the welding properties of the UNS S32304 lean duplex stainless steel were investigated in order to improve the microstructure and mechanical properties. Nickel powder was directly poured inside the joint gap and mixed with the filler metal during the Gas Tungsten Arc Welding (GTAW) process; moreover, the solution heat treatment was performed at 1100 °C for 10 min. The joints were characterized by optical microscopy (OM) and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and hardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. The results showed that both the addition of nickel powder during the welding process and the post weld heat treatment made it possible to improve the mechanical properties of the weld joints. PWHT had the best effect in restoring the equal percentage of ferrite and austenite compared to the addition of nickel powder. Key-words:Duplex stainless steel; GTAW process; Nickel powder; PWHT; Microstructure. Efeito da Adição de Pó de Níquel e do Tratamento Pós Soldagem nas Propriedades Metalúrgicas do Aço Inoxidável Duplex UNS S32304 SoldadoResumo: No presente estudo, foi investigado o efeito da adição de pó de níquel e a aplicação de um tratamento térmico pós-soldagem (PWHT) nas propriedades de soldagem do aço inoxidável lean duplex UNS S32304, a fim de melhorar a microestrutura e as propriedades mecânicas. Pó de níquel foi diretamente vertido na abertura da junta e misturado com o metal de adição durante o processo de soldagem a arco com eletrodo de tungsténio e proteção gasosa (GTAW). Além disso, o tratamento térmico foi estabelecido em 1100 °C por 10 min. As juntas foram caracterizadas por microscopia óptica (MO) e a evolução das percentagens de fase nas diferentes zonas foi estudada por meio da técnica de análise de imagem. Os ensaios de tração e de microdureza foram realizados, a fim de avaliar a melhoria das propriedades mecânicas das juntas. Os resultados mostraram que tanto a adição de pó de níquel durante o processo de soldagem e o tratamento térmico pós-soldagem permitiram melhorar as propriedades mecânicas da junta soldada. PWHT mostrou o melhor efeito em restaurar a percentagem igual de ferrita e austenita comparado com a adição de pó de níquel. Palavras-chave:Aços Inoxidáveis Duplex; GTAW; Pó de níquel; PWHT; Microestrutura.

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“…Cr eq = Cr + Mo + 0.7×Nb (1) Ni eq = Ni + 35×C + 20×N + 0.25×Cu (2) Butt joints were made using a dedicated Transformation Technologies, Inc. (TTI) FSW machine, which enables position and force control during welding. Plates (500 mm × 180 mm × 6.0 mm) were friction stir welded using an untilted composite tool consisting of polycrystalline cubic boron nitride in a metallic matrix of 40 vol.% W-Re (PCBN-40% W-Re), with 25.0 and 8.0 mm shoulder and pin diameters, respectively, 6.0 mm pin length, and axial load (in the welding direction) of 15 kN.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, the time that the material remains at elevated temperatures is shorter in FSW, avoiding deleterious precipitation of phases such as sigma phase. Prevention of sigma phase formation from ferrite requires rapid cooling from 900 to 500 ºC 1 . It is known that the presence of deleterious phases in DSS and SDSS strongly compromises corrosion performance.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

“…The chemical composition of these materials provides them with a high level of resistance to localized corrosion (especially pitting) in salt water environments, as well as good mechanical strength and ductility 1 . DSS and SDSS have replaced austenitic stainless steel (ASS) in many applications where stress corrosion cracking and pitting corrosion are concerns, although ASS continues to be studied, due to its good formability 2,3 .…”

Section: Introductionmentioning

confidence: 99%

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Friction stir welding of duplex and superduplex stainless steels and some aspects of microstructural characterization and mechanical performance

et al. 2016

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Friction stir welding was used to produce butt joints on 6 mm thick plates of UNS S32101 lean duplex stainless steel, S32205 duplex stainless steel, and S32750 and S32760 superduplex stainless steels. Fully consolidated joints were achieved, with full penetration, using heat input of 1.37-1.50 kJ/mm. Specimens submitted to tensile testing performed perpendicular to the welding direction showed failure on the base metal, reflecting better mechanical performance of the welded joints. Furthermore, tensile testing along the joints revealed higher yield and tensile strengths in all cases, as well as increased elongation. Microstructural evaluation showed that there was pronounced grain refinement in the welded joints of all the materials studied, achieving grain sizes as small as 1 µm. The differences in the ferrite and austenite grain sizes in the stir zone, such as the degree of grain refinement, could be explained by the combination of dynamic recrystallization of austenite during the welding process and the recrystallization and growth of the ferrite grains, promoted firstly by the severe deformation and secondly by the high temperature inherent to the FSW process. Superduplex stainless steel FSW joints were more able to maintain a balanced microstructure, compared to conventional and lean duplex stainless steels, due to greater homogeneity of recrystallization in the welded joint.

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Welding Metallurgy and Weldability

Cited by 514 publications

References 0 publications

Double Kinetics of Intermetallic Phase Precipitation in UNS S32205 Duplex Stainless Steels Submitted to Isothermal Heat Treatment

Double Kinetics of Intermetallic Phase Precipitation in UNS S32205 Duplex Stainless Steels Submitted to Isothermal Heat Treatment

Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

Friction stir welding of duplex and superduplex stainless steels and some aspects of microstructural characterization and mechanical performance

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