Evaluación de los electrodos UTP 8 y UTP 86FN para el posible reacondicionamiento por soldadura de carcasas de las turbinas de un turbocompresor de los Grupos Electrógenos
Fecha
2019
Autores
Machado Rodríguez, Luis Alberto
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Editor
Universidad Central ``Marta Abreu`` de Las Villas. Facultad de Ingeniería Mecánica e Industrial. Departamento de Ingeniería Mecánica
Resumen
En el presente trabajo se aborda la caracterización microestructural y química de las carcasas tanto la tradicional como la modificada, encontrándose que ambas están fabricadas de hierro fundido nodular y esferoidal respectivamente, con una matriz ferrifica. Se describen las grietas producidas en estas carcasas, dándose según su fabricante las longitudes permisibles de acuerdo en la dirección y zona en donde estas aparezcan y las causas que permiten la iniciación y propagación de las grietas, dichas causas son choque y fatiga térmica. Se determinó el valor de la amplitud máxima del esfuerzo térmico durante el choque térmico (Sm), teniendo como valor 560 MPa para un concentrador de esfuerzos (kf) igual 1. Se utilizó los electrodos UTP 8 y UTP 86FN para el reacondicionamiento por soldadura de la carcasa modificada, valorándose los resultados obtenidos por cada uno de ellos. En el electrodo UTP 8 se obtuvo en la zona fundida una estructura dendrítica típica de los depósitos de soldadura con alto contenido de Ni y en la interface se observaron estructura martensita y cementita altamente endurecida, lo cual no es recomendable. El electrodo UTP 86FN deposita una estructura similar al metal base, siendo recomendable para el reacondicionamiento por soldadura de piezas que trabajen a altas temperaturas, en la zona fundida presenta una microestructura muy similar al metal base con diferencia que el tamaño de grafito es menor, garantizando buenas propiedades del cordón, en la zona de interface no se encontró presencia de martensita, ni cementita altamente endurecida. Los valores de microdureza alcanzado en el metal depositado para el electrodo UTP 8 y UTP 86FN fue 236 y 265 HV50 respectivamente, mientras que en la zona de transición la microdureza del primero es del orden de 1565 HV50 y del segundo es 575 HV50. En la determinación de la dureza HB, para ambos electrodos, se observó que la dureza en el centro del cordón de soldadura corresponde con el rango de dureza dado por el fabricante UTP.
In the present work the microstructural and chemical characterization of the carcasses is approached, both the traditional and the modified ones, finding that both are made of nodular cast iron and spheroidal respectively, with a ferrite matrix. The cracks produced in these housings are described, according to their manufacturer the permissible lengths according to the direction and area where they appear and the causes that allow the initiation and propagation of cracks, these causes are shock and thermal fatigue. The value of the maximum amplitude of the thermal stress during the thermal shock (Sm) was determined, having as value 560 MPa for an equal stress concentrator (kf) 1. The UTP 8 and UTP 86FN electrodes were used for welding reconditioning. the modified housing, evaluating the results obtained by each of them. In the UTP 8 electrode, a typical dendritic structure of the solder deposits with a high Ni content was obtained in the melted zone and martensite and highly hardened cementite structure were observed in the interface, which is not recommended. The UTP 86FN electrode deposits a structure similar to the base metal, being recommendable for the reconditioning by welding of parts that work at high temperatures, in the melted zone it presents a microstructure very similar to the base metal with difference that the size of graphite is smaller, guaranteeing good cord properties, in the interface area there was no presence of martensite, nor highly hardened cementite. The microhardness values reached in the metal deposited for the electrode UTP 8 and UTP 86FN were 236 and 265 HV50 respectively, while in the transition zone the microhardness of the first is of the order of 1565 HV50 and of the second is 575 HV50. In the determination of the HB hardness, for both electrodes, it was observed that the hardness in the center of the weld bead corresponds to the hardness range given by the manufacturer UTP.
In the present work the microstructural and chemical characterization of the carcasses is approached, both the traditional and the modified ones, finding that both are made of nodular cast iron and spheroidal respectively, with a ferrite matrix. The cracks produced in these housings are described, according to their manufacturer the permissible lengths according to the direction and area where they appear and the causes that allow the initiation and propagation of cracks, these causes are shock and thermal fatigue. The value of the maximum amplitude of the thermal stress during the thermal shock (Sm) was determined, having as value 560 MPa for an equal stress concentrator (kf) 1. The UTP 8 and UTP 86FN electrodes were used for welding reconditioning. the modified housing, evaluating the results obtained by each of them. In the UTP 8 electrode, a typical dendritic structure of the solder deposits with a high Ni content was obtained in the melted zone and martensite and highly hardened cementite structure were observed in the interface, which is not recommended. The UTP 86FN electrode deposits a structure similar to the base metal, being recommendable for the reconditioning by welding of parts that work at high temperatures, in the melted zone it presents a microstructure very similar to the base metal with difference that the size of graphite is smaller, guaranteeing good cord properties, in the interface area there was no presence of martensite, nor highly hardened cementite. The microhardness values reached in the metal deposited for the electrode UTP 8 and UTP 86FN were 236 and 265 HV50 respectively, while in the transition zone the microhardness of the first is of the order of 1565 HV50 and of the second is 575 HV50. In the determination of the HB hardness, for both electrodes, it was observed that the hardness in the center of the weld bead corresponds to the hardness range given by the manufacturer UTP.
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Procedimientos de Soldadura, Soldadura, Centro de Investigaciones de Soldadura (CIS), Proceso Metalúrgico, Tratamientos Térmicos, Grupos Electrógenos, Turbocompresor, Electrodo UTP-8, Electrodo UTP-86FN, Soldadura de Carcasas.