Agradecimentos: The authors thank Petrobras and FINEP for financial support and CNPq for scholarships (141686/2009-0 and 201038/2011-0). The assistance provided by LNNano (CNPEM/MCTI) and OSU is gratefully acknowledged. The UNS S322101 DSS and UNS S32750 SDSS steel plates were kindly donated by...

Agradecimentos: The authors thank Petrobras and FINEP for financial support and CNPq for scholarships (141686/2009-0 and 201038/2011-0). The assistance provided by LNNano (CNPEM/MCTI) and OSU is gratefully acknowledged. The UNS S322101 DSS and UNS S32750 SDSS steel plates were kindly donated by Outokumpu, UNS S32760 by Weir Materials, and UNS S32205 by Aperam South America. TFAS thanks UFPE and FACEPE

Duplex stainless steels are successfully used in a wide variety of applications in areas such as the food industry, petrochemical installations, and sea water desalination plants, where high corrosion resistance and high mechanical strength are required. However, during fusion welding operations,...

Duplex stainless steels are successfully used in a wide variety of applications in areas such as the food industry, petrochemical installations, and sea water desalination plants, where high corrosion resistance and high mechanical strength are required. However, during fusion welding operations, there can be changes to the favorable microstructure of these materials that compromise their performance. Friction stir welding with a non-consumable pin enables welded joints to be obtained in the solid state, which avoids typical problems associated with solidification of the molten pool, such as segregation of alloying elements and the formation of solidification and liquefaction cracks. In the case of superduplex stainless steels, use of the technique can avoid unbalanced proportions of ferrite and austenite, formation of deleterious second phases, or growth of ferritic grains in the heat-affected zone. Consolidated joints with full penetration were obtained for 6-mm-thick plates of UNS S32101 and S32205 duplex stainless steels, and S32750 and S32760 superduplex steels. The welding heat cycles employed avoided the conditions required for formation of deleterious phases, except in the case of the welded joint of the S32760 steel, where SEM images indicated the formation of secondary phases, as corroborated by decreased mechanical performance. Analysis using EBSD and transmission electron microscopy revealed continuous dynamic recrystallization by the formation of cellular arrays of dislocations in the ferrite and discontinuous dynamic recrystallization in the austenite. Microtexture evaluation indicated the presence of fibers typical of shear in the thermomechanically affected zone. These fibers were not obviously present in the stir zone, probably due to the intensity of microstructural reformulation to which this region was subjected.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ

141686/2009-0; 201038/2011-0

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