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In recent years some progress has been made about the addition of Carbon Nanotubes (CNTs) in the stainless steel metal matrix by pulsed Gas Tungsten Arc Welding (P-GTAW). Despite that, there is lack of information regarding to microstructural modifications induced by CNTs in dissimilar welding. In this sense, we present the welding of nanocomposite based on Nickel/Carbon Nanotubes-stainless steel 316L alloy (Ni/CNTs-SS 316L), as the welding metal, on carbon-manganese (C-Mn) non-alloyed structural steel, as the base metal. The microstructure of manufactured specimens with/without nanocomposite was characterized by: optical microscopy; Raman spectroscopy; scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and electron backscattering diffraction (EBSD). Moreover, Vickers tests were performed from the welding metal (WM) to the base metal (BM) before/after temper treatment in order to investigate the microhardness changes. The results show that dilution rate and grain size for specimen with nanocomposite was higher than without nanocomposite; the CNTs affected the misorientation angle and texture of the WM; the topside microhardness from WM with Ni-CNTs was on average 30.40% higher than BM; and, in transverse cross-section microhardness was 31% higher than control sample on average at fusion line zone. These results indicate that addition of CNTs in the metallic matrix by dissimilar welding is a fertile ground for new studies applicable to manufacturing industry.

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ResumoA liga de níquel 718 encontra aplicações variadas nas indústrias aeronáutica, aeroespacial, óleo e gás e nuclear em função da excelente combinação entre resistência e ductilidade. As diferentes formas de processamento utilizadas para sua elaboração tendem a unir processos de deformação com temperatura, a fim de melhorar as propriedades mecânicas do material. Sendo assim, o presente trabalho tem como objetivo a caracterização e investigação do efeito de rotas de processamento termomecânicos distintas, avaliando a repercussão na fração de contornos especiais, dos carbetos (Nb,Ti)C e nas propriedades mecânicas do material endurecido por precipitação. Palavras-chave: Liga 718; Engenharia de contorno de grão; Tratamento termomecânico; Carbetos. EFFECT OF DIFFERENT PROCESSING ROUTES ASSOCIATED WITH GRAIN BOUNDARY ENGINEERING AND IMPROVEMENT OF MECHANICAL PROPERTIES AbstractThe nickel alloy 718 are the most varied applications in the aerospace, oil and gas and nuclear industries in excellent combination of function between resistance and ductility. The different forms of mechanical process used for their preparation usually combine deformation processes and temperature in order to improve the mechanical properties of the material. Thus, this study aims to characterize and investigate the effect of different thermomechanical process routes, evaluating the impact on the special boundary fraction, the carbides (Nb,Ti)C and mechanical properties of a precipitation hardenend material.