Aplicação de aço inoxidável AISI 316L como metal de adição na soldagem do aço inoxidável duplex UNS S32205 com laser pulsado Nd: YAG
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Data
2022-06-09
Autores
Nakashima, Paulino Yoshiaki
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A indústria de óleo e gás enfrenta ambientes extremamente agressivos, o que exige a utilização de materiais com elevadas resistências à corrosão e tenacidade, propriedades essas normalmente encontradas em ligas especiais, como os aços inoxidáveis duplex e superduplex. Esses aços apresentam microestrutura balanceada, com frações volumétricas de aproximadamente 50% de ferrita e 50% de austenita. Porém, ao serem soldados, devido à alta velocidade de resfriamento, assoaciado a um elevado aporte térmico, a zona fundida resultante é predominantemente ferrítica. O processo a laser Nd: YAG representa uma boa alternativa para esses materiais, visto que oferece energia relativamente baixa, concentrada no cordão de solda, consequentemente em uma ZTA (Zona Termicamente Afetada) estreita. Embora esse processo apresente uma boa qualidade na soldagem de aços inoxidáveis duplex e superduplex, ainda enfrentamos desbalanceamento das fases ferrita e austenita na zona fundida. O presente trabalho investigou a variação no balanceamento dessas fases na região de solda, por meio da adição de uma lâmina fina de aço inoxidável AISI 316L, na união de chapas finas de aço inoxidável duplex UNS S32205. Foram confeccionadas 4 amostras com diferentes espessuras para o metal de adição (0,050mm, 0,100mm, 0,200mm e 0,300mm). As amostras foram soldadas em juntas de topo, sem abertura de raiz, com laser Nd:YAG na condição pulsado. A análise de EDS na junta soldada apontou uma maior presença de Ni à medida em que houve aumento da espessura do metal de adição, com o Ni contribuindo em um aumento na formação de austenita. A amostra com 0,300mm de metal de adição foi a amostra que apresentou os melhores resultados, com uma boa formação do cordão, sem porosidades e trincas, fração volumétrica similar à encontrada no metal base com 51,9% de austenita e 48,1% de ferrita, menor variação de dureza, em relação ao metal base, maior resistência à corrosão no ensaio de corrosão por pites.
The oil and gas industry faces extremely aggressive environments, which require the use of materials with high corrosion resistance and toughness, properties normally found in special alloys, such as duplex and superduplex stainless steels. These steels have a balanced microstructure, with volume fractions of approximately 50% ferrite and 50% austenite. However, when they are welded, due to the high cooling speed, associated with a high heat input, the resulting fused zone is predominantly ferritic. The Nd:YAG laser process represents a good alternative for these materials, as it offers relatively low energy, concentrated in the weld bead, consequently in a narrow HAZ (Thermally Affected Zone). Although this process presents a good quality in the welding of duplex and superduplex stainless steels, we still face unbalance of the ferrite and austenite phases in the fused zone. The present work investigated the variation in the balance of these phases in the weld region, through the addition of a thin blade of AISI 316L stainless steel, in the union of thin blades of duplex stainless steel UNS S32205. Four samples were made with different thicknesses for the filler metal (0.050mm, 0.100mm, 0.200mm and 0.300mm). The samples were welded in butt joints, without root opening, with Nd:YAG laser in pulsed condition. The EDS analysis in the welded joint showed a greater presence of Ni as the filler metal thickness increased, with Ni contributing to an increase in austenite formation. The sample with 0.300 mm of filler metal was the sample that presented the best results, with good bead formation, without porosities and cracks, volumetric fraction similar to that found in the base metal with 51.9% austenite and 48.1% of ferrite, less hardness variation, in relation to the base metal, greater corrosion resistance in the pitting corrosion test.
The oil and gas industry faces extremely aggressive environments, which require the use of materials with high corrosion resistance and toughness, properties normally found in special alloys, such as duplex and superduplex stainless steels. These steels have a balanced microstructure, with volume fractions of approximately 50% ferrite and 50% austenite. However, when they are welded, due to the high cooling speed, associated with a high heat input, the resulting fused zone is predominantly ferritic. The Nd:YAG laser process represents a good alternative for these materials, as it offers relatively low energy, concentrated in the weld bead, consequently in a narrow HAZ (Thermally Affected Zone). Although this process presents a good quality in the welding of duplex and superduplex stainless steels, we still face unbalance of the ferrite and austenite phases in the fused zone. The present work investigated the variation in the balance of these phases in the weld region, through the addition of a thin blade of AISI 316L stainless steel, in the union of thin blades of duplex stainless steel UNS S32205. Four samples were made with different thicknesses for the filler metal (0.050mm, 0.100mm, 0.200mm and 0.300mm). The samples were welded in butt joints, without root opening, with Nd:YAG laser in pulsed condition. The EDS analysis in the welded joint showed a greater presence of Ni as the filler metal thickness increased, with Ni contributing to an increase in austenite formation. The sample with 0.300 mm of filler metal was the sample that presented the best results, with good bead formation, without porosities and cracks, volumetric fraction similar to that found in the base metal with 51.9% austenite and 48.1% of ferrite, less hardness variation, in relation to the base metal, greater corrosion resistance in the pitting corrosion test.
Descrição
Palavras-chave
Soldagem laser, Nd:YAG, UNS S32205, AISI 316L, Duplex, Laser welding