Soldagem dissimilar autógena com laser pulsado nd:yag dos aços austenítico aisi 316l e superduplex uns s32750
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Data
2021-03-08
Autores
Leite, Carla Gabriela da Silva
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Universidade Estadual Paulista (Unesp)
Resumo
As constantes mudanças no cenário global, tanto do ponto de vista econômico quanto tecnológico, forçam uma busca constante pelo aperfeiçoamento de novos materiais e processos. Dentro desse escopo, destacam-se os aços inoxidáveis com estrutura duplex. Por possuírem uma microestrutura binária, composta por ferrita e austenita, em proporções iguais, esses aços apresentam excelente resistência à corrosão e resistência mecânica. A soldagem laser dos aços duplex faz com que ocorra um desbalanceamento entre as fases ferrita e austenita no metal de solda, ocasionando uma microestrutura predominantemente ferrítica, e assim, perdendo suas características de boa resistência à corrosão e resistência mecânica. O presente trabalho teve como objetivo analisar uma junta dissimilar soldada com laser Nd:YAG pulsado, na condição autógena, entre os aços inoxidáveis superduplex UNS S32750 e austenítico AISI 316L, condição presente em muitas situações da indústria química e petroquímica. As soldagens foram realizadas em juntas topo e sem abertura de raiz. A energia do pulso foi fixada em 10J, com potência de pico de 2kw e largura temporal de 5ms. A frequência variou de 1,8 Hz a 9 Hz. Dessa forma, as juntas soldadas foram obtidas com taxas de sobreposição de 50%, 60%, 70%, 80% e 90%. Utilizou-se argônio puro como gás de proteção, com vazão de 15l/min. A velocidade de soldagem foi fixada em 1,0 mm/s. Foram realizadas análises macrográficas e micrográficas da junta soldada através de microscopia ótica e microscopia eletrônica de varredura. Foram realizados ensaios mecânicos de tração e ensaios de corrosão. Os resultados mostraram que a soldagem dissimilar entre o aço inoxidável superduplex UNS S32750 e o aço inoxidável austenítico AISI 316L gera uma microestrutura duplex na zona fundida, com balanço de fase próximo ao do metal base duplex. A zona termicamente afetada apresentou dimensões muito reduzidas, característica da soldagem laser. As juntas obtidas com taxa de sobreposição de 50%, 60% e 70% romperam no metal de solda enquanto que as juntas com 80% e 90% romperam no metal base. Os ensaios de corrosão mostraram que as juntas soldadas apresentam uma resistência à corrosão superior ao aço AISI 316L porém inferior ao aço duplex UNS S32750.
The constant changes in the global scenario, both from an economic and technological point of view, force a constant search for the improvement of new materials and processes. Within this scope, stainless steel with a duplex structure stands out. Because they have a binary microstructure, composed of ferrite and austenite, in equal proportions, these steels have excellent resistance to corrosion and mechanical resistance. The laser welding of duplex steels causes an imbalance between the ferrite and austenite phases in the weld metal, causing a predominantly ferritic microstructure, and thus losing its characteristics of good corrosion resistance. This work aimed to analyze a dissimilar joint welded with pulsed Nd: YAG laser, in autogenous condition, between UNS S32750 and AISI 316L austenitic stainless steel, a condition present in many situations in the chemical and petrochemical industry. Welding was carried out on top joints and without root opening. The pulse energy was fixed at 10J, with a peak power of 2kw and a temporal width of 5ms. The frequency varied from 1.8 Hz to 9 Hz. Thus, the welded joints were obtained with overlapping rates of 50%, 60%, 70%, 80% and 90%. Pure argon was used as the shielding gas, with a flow rate of 15l / min. The welding speed was fixed at 1.0 mm / s. Macrographic and micrographic analyzes of the welded joint were performed using optical microscopy and scanning electron microscopy. Mechanical tensile tests and corrosion tests were carried out. The results showed that dissimilar welding between UNS S32750 superduplex stainless steel and AISI 316L austenitic stainless steel generates a duplex microstructure in the molten zone, with phase balance close to that of the duplex base metal. The thermally affected area had very small dimensions, characteristic of laser welding. The joints obtained with an overlapping rate of 50%, 60% and 70% broke in the weld metal while the joints with 80% and 90% broke in the base metal. The corrosion tests showed that the welded joints present a corrosion resistance superior to AISI 316L steel but inferior to the UNS S32750 duplex steel.
The constant changes in the global scenario, both from an economic and technological point of view, force a constant search for the improvement of new materials and processes. Within this scope, stainless steel with a duplex structure stands out. Because they have a binary microstructure, composed of ferrite and austenite, in equal proportions, these steels have excellent resistance to corrosion and mechanical resistance. The laser welding of duplex steels causes an imbalance between the ferrite and austenite phases in the weld metal, causing a predominantly ferritic microstructure, and thus losing its characteristics of good corrosion resistance. This work aimed to analyze a dissimilar joint welded with pulsed Nd: YAG laser, in autogenous condition, between UNS S32750 and AISI 316L austenitic stainless steel, a condition present in many situations in the chemical and petrochemical industry. Welding was carried out on top joints and without root opening. The pulse energy was fixed at 10J, with a peak power of 2kw and a temporal width of 5ms. The frequency varied from 1.8 Hz to 9 Hz. Thus, the welded joints were obtained with overlapping rates of 50%, 60%, 70%, 80% and 90%. Pure argon was used as the shielding gas, with a flow rate of 15l / min. The welding speed was fixed at 1.0 mm / s. Macrographic and micrographic analyzes of the welded joint were performed using optical microscopy and scanning electron microscopy. Mechanical tensile tests and corrosion tests were carried out. The results showed that dissimilar welding between UNS S32750 superduplex stainless steel and AISI 316L austenitic stainless steel generates a duplex microstructure in the molten zone, with phase balance close to that of the duplex base metal. The thermally affected area had very small dimensions, characteristic of laser welding. The joints obtained with an overlapping rate of 50%, 60% and 70% broke in the weld metal while the joints with 80% and 90% broke in the base metal. The corrosion tests showed that the welded joints present a corrosion resistance superior to AISI 316L steel but inferior to the UNS S32750 duplex steel.
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Palavras-chave
Soldagem laser, Junta dissimilar, Aço duplex, UNS S32750, AISI 316L, Laser welding, Dissimilar joint