As obras disponibilizadas nesta Biblioteca Digital foram publicadas sob expressa autorização dos respectivos autores, em conformidade com a Lei 9610/98.
A consulta aos textos, permitida por seus respectivos autores, é livre, bem como a impressão de trechos ou de um exemplar completo exclusivamente para uso próprio. Não são permitidas a impressão e a reprodução de obras completas com qualquer outra finalidade que não o uso próprio de quem imprime.
A reprodução de pequenos trechos, na forma de citações em trabalhos de terceiros que não o próprio autor do texto consultado,é permitida, na medida justificada para a compreeensão da citação e mediante a informação, junto à citação, do nome do autor do texto original, bem como da fonte da pesquisa.
A violação de direitos autorais é passível de sanções civis e penais.
Título:MICROSTRUCTURAL STABILITY OF ALLOY 33 (CR-FE-NI-N) AND ITS POTENTIAL TO BE SUBMITTED TO FUSION WELDING OPERATIONS Instituição:PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO - PUC-RIO Autor:JULIO CESAR SPADOTTO
This work studies the microstructural stability of alloy 33 (Fe-Cr-Ni-N) aiming at improving the performance of welded joints under in working conditions. Samples of this alloy followed a previously programmed procedure of homogenization and isothermal aging heat treatment at 700 degrees C and 900 degrees C for 1h, 10h and 100h. Under these conditions, the occurrence of homogeneous and heterogeneous conventional precipitation, as well as the discontinuous precipitation phenomena, were identified. The elucidation of the kinetics of the latter is of particular interest because of the well-known negative effect on the mechanical properties and performance of the several alloys applied as structural component. Subsequently, the as-received material was submitted to TIG welding process. Samples of the weld joints followed the same heat treatment schedule of homogenization and isothermal aging temperature of 700 degrees C for 1h, 10h and 100h. In addition, a welded sample was directly aged at this temperature for 100h at 700 degrees C. Microstructural characterization of the material, from the as received condition, to all post-heat treatment, as-welded and post-welding conditions was performed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy, in the conventional (CTEM)and scanning/transmission (STEM) modes. Whenever possible, qualitative microanalysis of different microstructural elements was carried out by characteristic x-ray energy dispersive spectroscopic (XEDS) coupled to SEM and TEM/STEM. Micro-hardness tests were conducted to evaluate the effects of welding and heat treatment on the materials under all above mentioned conditions. The results demonstrate that both the homogeneous and heterogeneous precipitates at grain boundary as well as colonies of discontinuous precipitation are rich in chromium. In the latter, characterized by a lamellar structure growing cooperatively with high angle grain boundary migration, the lamellar precipitates
appear to have nitrogen incorporated by inter granular diffusion mechanism, forming Cr2N.This phenomenon was also detected in the welded joint aged at 700 degrees C for 100 h. The results of the hardness tests show the precipitation hardening effect on the alloy aged at 33 at both temperatures , contrary to the welded joints where no significant change in micro-hardness were detected even after the application of heat treatments.