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ResumenEl presente trabajo describe las características microestructurales de uniones soldadas de acero súper dúplex fundido (J93404), al ser sometidas a procesos de recocido para inducir la formación de fase sigma a altas temperaturas. Se analizó la influencia del tiempo de calentamiento a 1.073 K, 1.123 K y 1.173 K sobre la precipitación de fase sigma en la zona afectada térmicamente, metal base y zona de fusión de los conjuntos soldados. Los resultados experimentales evidenciaron la formación de este compuesto intermetálico por descomposición de la fase ferrítica en austenita y sigma. Al comienzo de la transformación la fase nuclea y crece rápidamente en los bordes de grano austenita-ferrita, extendiéndose luego masivamente hacia el seno de la zona ferrítica, con mayor efectividad en términos del aumento de la temperatura de proceso. La formación de sigma en todas las uniones soldadas obedece a un mecanismo de nucleación y crecimiento del tipo Jonson-Mehl-Avrami. Palabras claveFase sigma; Acero súper dúplex fundido; Microestructura; Fundición; Soldadura. Sigma-phase formation in weldments of cast super duplex stainless steel AbstractThis paper decribes the microstructural characteristics of weldments of cast super duplex stainless steel (J93404), being subjected to annealing processes to induce formation of sigma-phase at high temperatures. The influence of heating time at 1073 K, 1123 K and 1173 K upon precipitation of sigma in the heat affected zone, base metal and fusion zone of the weldments was analyzed. The experimental results revealed the formation of this intermetallic compound throughout decomposition of the ferritic phase into austenite and sigma. At earlier stages of the transformation the phase rapidly nucleates and growth along the ferrite-austenite grain boundaries, and then massively advances towards the bulk of the ferritic zone with greater effectiveness as temperature increases. The formation of sigma-phase in all weldments resembles the Johnson-Mehl-Avrami's mechanism stated for nucleation and growth. KeywordsSigma-phase; Cast super duplex steel; Microstructure; Casting; Welding. INTRODUCCIÓNEl extenso uso que los aceros inoxidables del tipo dúplex han encontrado en la industria moderna, es una consecuencia de su excelente resistencia al agrietamiento por corrosión bajo tensiones en atmósferas cloradas, resistencia a la corrosión localizada y alta resistencia mecánica a la tracción. Tales propiedades posibilitan una gran variedad de aplicaciones industriales, particularmente en el campo de los combustibles, petroquímica, pulpa y papel, generación de energía, transporte marítimo, minería y contaminación ambiental [1 y 2] . Estas aleaciones presentan una estructura mixta compuesta por cantidades relativas aproximadamente iguales de las fases austenita (estructura FCC) y ferrita (estructura BCC), lo cual se logra mediante un adecuado balance de los elementos aleantes. Las aleaciones de mayores aplicaciones industriales contienen de 22 a 26 % de Cr, de 4 a 7 % de Ni, hasta 4,5 % de Mo, 0,7 % ...

Page s 322 glycol (PEG) concentration on the structural characteristics of Uox uncomplexed and complexed with 8-azaxanthine (AZA) using powder diffraction data collected on ID31 [2] at the ESRF. Previously unknown phases of Uox were observed depending on the presence and type of salt whereas PEG and pH variation had a minor affect on the cell dimensions. All phases have been successfully indexed, and the known I222 orthorhombic phase of Uox complexed with AZA was solved by molecular replacement using software designed for single crystal diffraction data [3]. The phase diagram of Uox and its relevant crystallizing conditions will be presented.

Pure Ni 0.5 TiOPO 4 was prepared via a traditional solid-state reaction, and then Ni 0.5 TiOPO 4 /C composites with core-shell structure were synthesized by hydrothermally treating Ni 0.5 TiOPO 4 in glucose solution. X-ray diffraction patterns confirmed that Ni 0.5 TiOPO 4 /C crystallized in the monoclinic P2 1 /c space group. The morphology and the microstructure were characterized by scanning electron microscopy and transmission electron microscopy. The small particles with irregular shapes were coated with uniform carbon film of ~ 3 nm in thickness. Raman spectroscopy also confirmed the presence of carbon in Ni 0.5 TiOPO 4 /C composites. The electrochemical performances of Ni 0.5 TiOPO 4 /C and Ni 0.5 TiOPO 4 were compared through galvanostatic charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. Ni 0.5 TiOPO 4 /C composites exhibited improved electrochemical performances due to the existence of carbon shell. During the first discharge, the NTP/C electrode delivered a capacity of 530mAh/g Fig 1. This high capacity corresponds the intercalation of more than 3 mol lithium ions per Ni 0.5 TiOPO 4 ; however, not all lithium atoms could be extracted during the subsequent charge [1]. The redox couples of Ti 4+ /Ti 3+ , Ti 3+ /Ti 2+ and Ni 2+ /Ni in NTP/C can involve the insertion of only 3 mol lithium atoms. Therefore, the excess capacity during the first discharge should attribute to the formation of SEI passivation layer [

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