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

Abstract

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.

Characterization of the Microstructure, Mechanical Properties, and Corrosion Resistance of a Friction-Stir-Welded Joint of Hyper Duplex Stainless Steel

“…Both of them can produce a recrystallization process, which is followed by grain growth in the ferrite phase. According to earlier studies, DRX, including continuous DRX (CDRX), or discontinuous DRX (DDRX) may exist in the SZ during the FSW of DSSs [24][25][26]29,30]. High stacking fault energy (SFE) of the ferrite phase facilitates CDRX.…”

Dimensionamento de um Sistema Robotizado para a Soldagem pelo Processo Friction Stir Welding

“…O torque resultante na junta é governado pelas características de fluxo dos materiais a serem soldados, e pela velocidade do fuso. Dessa forma, a menor força axial, combinada com maior velocidade de rotação e menor velocidade de avanço resulta em menor torque na junta soldada, pois proporciona maior entrada de calor, o que aumenta a fluidez do material [22].…”

“…Santos et al [22] soldaram aços inoxidáveis duplex e super duplex de 6 mm de espessura, usando um equipamento Technologies Inc. (TTI), dedicado à soldagem pelo processo FSW. Para as soldagens foi utilizada uma ferramenta de PCBN-40% W-Re com ombro de 25 mm de diâmetro e pino com comprimento de 6 mm e 8 mm de diâmetro.…”

Soldagem por Atrito com Pino Não Consumível de Aços Inoxidáveis Duplex

“…Os ensaios não foram realizados para o aço UNS S32205 devido à indisponibilidade de amostras de tamanho adequado. A Tabela 3 apresenta os dados obtidos pelos ensaios de tração em amostras do metal de base e em amostras longitudinais nas juntas soldadas [22]. Tabela 3.…”

“…Tabela 3. Ensaios de tração longitudinais em juntas soldadas [22]. Da análise das superfícies de fratura após os testes de tração, a Figura 6 apresenta as fractografias das juntas soldadas para os aços UNS (a) S32101, (b) S32750 e (c) S32760.…”