Dissimilar Friction Stir Welding Between UNS S31603 Austenitic Stainless Steel and UNS S32750 Superduplex Stainless Stee
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THE friction stir welding (FSW) is a solid-state joining process that has, as advantages, reduction or absence of superficial and internal flaws, absence of cracks and porosities caused by material fusion and solidification, and good repeatability. Most of the joints performed by FSW present, transversally, four regions, classified by the type of influence received during welding (Figure 1): the stirred zone (SZ); the thermomechanically affected zone (TMAZ); the heat-affected zone (HAZ), and the base metal (BM). The SZ is the region that suffered intense plastic deformation and mixture of the material due to the passage of the pin and presents very fine recrystallized grains when compared
MARIA CLAUDIA THEODORO, Ph.D Student, is with the Laborato´rio Nacional de Nanotecnologia, Rua Giuseppe Ma´ximo Scolfaro, 10.000, Caixa Postal 6192, CEP 13083-970 Campinas, SP, Brazil, and also with the Fac. Engenharia Mecaˆnica, University of Campinas, Rua Mendeleyev, 200, Cidade Universita´ria "Zeferino Vaz" Bara˜o Geraldo, CEP 13083-860 Campinas, SP, Brazil. Contact e-mail: [email protected] VICTOR FERRINHO PEREIRA, Engineer, is with the Laborat´rio Nacional de Nanotecnologia. PAULO ROBERTO MEI, Professor, is with the Fac. Engenharia Mecaˆnica, University of Campinas. ANTONIO JOSE RAMIREZ, Lead Scientist/Visiting Professor, is with the Laborato´rio Nacional de Nanotecnologia, and also with the School of Mechanical Engineering, University of Campinas, Campinas, Brazil and is now with the Welding Engineering Program, Materials Science and Engineering Department, The Ohio State University, Columbus OH. Manuscript submitted July 25, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
with other zones. The TMAZ is an external region from SZ and receives plastic deformation and microscopic changes caused by pin movement and frictional heating, although there is no mixture of the material. The HAZ is the zone that received influence only from heating, without plastic deformation. The BM is the part of the material that remains unaffected, maintaining the original properties before welding.[1–6] These regions have no symmetrical shape relative to the center of the joint. This is due to the probe rotation and translation, which generates the advancing side (AS) and retreating side (RS). The AS is the side where the direction of the rotation and translation of the pin are the same. On this side, the greatest plastic deformation and relative velocity occur during weld. The lowest relative velocity and most of the material mixing occur in the RS, because the material is forced against the translation direction.[2,4,5] In similar FS welds, in the SZ the material presents a flow pattern and vortices of intercalated bands of grains that have undergone different plastic deformation and rate of deformation.[1,2] These bands present grains with different sizes, indicating dynamic recrystallization. Some authors[1,5–7] have recorded a flow pattern and vortices intercalating both materials in the SZ of dissimilar FS welds. In some materials, the heat
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