Friction Stir Welding Of Duplex And Superduplex Stainless Steels And Some Aspects Of Microstructural Characterization And Mechanical Performance

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)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 mu m. 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.191117131PetrobrasFINEPCNPqFAPESPConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Friction Stir Welding Of Duplex Stainless Steels

Duplex stainless steels are successful in a variety of applications such as the food industry, petrochemical and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may be change during fusion welding steps and it can compromise the performance of these materials. Friction stir welding is a solid state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. For superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat affected zone. Consolidated friction stir welded joints with full penetration of 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints showing increased of yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding gran refinement was observed in the welded joint achieving grain sizes as small as 1 mu m. This refinement was associated with the combination of microstructural restoration mechanisms in the dual phase microstructure promoted by severe deformation associated with a high temperature during the welding process.211596

Friction Stir Welding of Duplex Stainless Steels

Duplex stainless steels are successful in a variety of applications such as the food industry, petrochemical and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may be change during fusion welding steps and it can compromise the performance of these materials. Friction stir welding is a solid state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. For superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat affected zone. Consolidated friction stir welded joints with full penetration of 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints showing increased of yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding gran refinement was observed in the welded joint achieving grain sizes as small as 1 ?m. This refinement was associated with the combination of microstructural restoration mechanisms in the dual phase microstructure promoted by severe deformation associated with a high temperature during the welding process.Os aços inoxidáveis duplex são bem sucedidos em uma variedade de aplicações como a indústria alimentícia, petroquímica e para plantas de dessalinização da água do mar, onde alta a resistência à corrosão e alta resistência mecânica são exigidas. Contudo, durante operações de soldagem por fusão pode haver alteração da microestrutura favorável destes materiais comprometendo seu desempenho. O processo de soldagem por atrito com pino não consumível pode gerar juntas no estado sólido evitando os típicos problemas da solidificação da poça fundida como segregação de elementos de liga, formação de trincas de solidificação e liquação; para o caso de aços inoxidáveis superduplex, pode-se evitar proporções desbalanceadas de ferrita e austenita, formação de fases secundárias deletérias e crescimento de grão ferrítico na zona termicamente afetada. Juntas consolidadas com penetração completa foram obtidas usando chapas de 6 mm de espessura para os aços inoxidáveis duplex UNS S32101 e S32205 e superduplex S32750 e S32760. As amostras foram submetidas a ensaios de tração indicando uma melhoria do desempenho mecânica das juntas soldadas com o aumento da tensão de escoamento e do limite de resistência à tração para todos os casos. Em relação à caracterização microestrutural, um pronunciado refinamento da ordem de 1 ?m foi observado na junta soldada. Este refinamento foi associado à combinação de mecanismos de restauração na microestrutura bifásica promovida pela deformação severa junto com a alta temperatura durante o processo de soldagem.211596

Friction stir welding of duplex stainless steels

Os aços inoxidáveis duplex são bem sucedidos em uma variedade de aplicações como a indústria alimentícia, petroquímica e para plantas de dessalinização da água do mar, onde alta a resistência à corrosão e alta resistência mecânica são exigidas. Contudo, durante operações de soldagem por fusão pode haver alteração da microestrutura favorável destes materiais comprometendo seu desempenho. O processo de soldagem por atrito com pino não consumível pode gerar juntas no estado sólido evitando os típicos problemas da solidificação da poça fundida como segregação de elementos de liga, formação de trincas de solidificação e liquação; para o caso de aços inoxidáveis superduplex, pode-se evitar proporções desbalanceadas de ferrita e austenita, formação de fases secundárias deletérias e crescimento de grão ferrítico na zona termicamente afetada. Juntas consolidadas com penetração completa foram obtidas usando chapas de 6 mm de espessura para os aços inoxidáveis duplex UNS S32101 e S32205 e superduplex S32750 e S32760. As amostras foram submetidas a ensaios de tração indicando uma melhoria do desempenho mecânica das juntas soldadas com o aumento da tensão de escoamento e do limite de resistência à tração para todos os casos. Em relação à caracterização microestrutural, um pronunciado refinamento da ordem de 1 μm foi observado na junta soldada. Este refinamento foi associado à combinação de mecanismos de restauração na microestrutura bifásica promovida pela deformação severa junto com a alta temperatura durante o processo de soldagem2115969CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPFUNDAÇÃO DE AMPARO À CIÊNCIA E TECNOLOGIA DO ESTADO DE PERNAMBUCO - FACEPEFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçãoSem informaçãoSem informaçãoDuplex stainless steels are successful in a variety of applications such as the food industry, petrochemical and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may be change during fusion welding steps and it can compromise the performance of these materials. Friction stir welding is a solid state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. For superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat affected zone. Consolidated friction stir welded joints with full penetration of 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints showing increased of yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding gran refinement was observed in the welded joint achieving grain sizes as small as 1 μm. This refinement was associated with the combination of microstructural restoration mechanisms in the dual phase microstructure promoted by severe deformation associated with a high temperature during the welding proces

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

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.191117131FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçã

Influence of heating rate on the reversion of strain-induced martensite in AISI 304 austenitic stainless steel

Austenitic stainless steels specimens were deformed by tension from 0.03 to 0.12 of true strain at -50ºC and -10ºC, in order to obtain different volumetric fractions of e and α' strain induced martensites. The morphology, distribution and volumetric fractions of the strain induced martensites were characterized by metallography and dilatometry analysis and quantified by ferrite detector measurements. The reverse transformation temperatures of ε→γ and α'→γwere detected by dilatometry tests. The e and α' martensites reversion was observed in the temperature range of 50-200ºC and 500-800ºC, respectively. The heating rate did not influence the reversing of ε→α' temperatures but did affect the α'→γtransformation temperatures.Ensaios de tração foram realizados em corpos-de-prova de aço inoxidável austenítico, nas temperaturas de -50 e -10ºC e quantidades de deformação de 3 a 12%, com a finalidade de se obterem diferentes quantidades de fases martensíticas dos tipos e e a'. As martensitas induzidas por deformação foram caracterizadas quanto a sua morfologia, distribuição e quantidade por meio de análises metalográficas, dilatometria, e medidas com um detector de ferrita. As temperaturas de transformações reversas, ε→γ e α'→γ, foram determinadas por ensaios dilatométricos. A reversão das martensitas e e α' foi observada nas faixas de temperaturas de 50-200ºC e 500-800ºC, respectivamente. A taxa de aquecimento praticamente não influencia as temperaturas de reversão de ε→γ. A reversão da martensita α', ao contrário, mostrou-se dependente da taxa de aquecimento.5358Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Evaluation of two-step transformation in Ni-rich titanium-nickel alloys using thermal and internal friction analyses

The use of Ti-Ni memory alloys covers several fields of application such as medicine, dentistry, actuators,sensors among others. Because of the thermomechanical behavior of these materials, they are an object ofcontinuous studies and their properties are related to the occurrence of thermoelastic martensitic phase transformations.The thermal analyzes were performed using dilatometry and differential scanning calorimetry todetermine the temperatures that occurred transformations during the cooling and heating, as well as to evaluatethe influence of the thermal treatments performed by dilatometry. The thermomechanical behavior wasalso evaluated by the internal friction that measured behavior damping considering the structural and microstructuralchanges. The calorimetry measurements indicated suppression of the R phase through decompositionof precipitates of Ti3N4after the thermal treatments, that were corroborated by dilatometry and microhardness.This phase was also studied by the technique of internal friction, which showed that the mechanicaldamping coefficient increased as a function of temperature, due to the movement of the defects induced bytension.Keywords: Ti-Ni, shape-memory effect, internal friction, dilatometry, calorimetry