Soldagem híbrida GTAW-Laser Nd-YAG Pulsado: Efeitos no Aço Inoxidável Superduplex UNS S32750
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Data
2021-02-10
Autores
Videira, Arthur Moraes e
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Universidade Estadual Paulista (Unesp)
Resumo
O emprego de aços inoxidáveis superduplex na indústria atual está em crescimento devido as suas características que combinam boas propriedades mecânicas e de resistência à corrosão. Esses aços são constituídos por uma estrutura bifásica com frações volumétricas de aproximadamente 50% ferrita e 50% austenita. Portanto, o desenvolvimento de técnicas para melhorar a soldagem dos aços superduplex é necessário, de modo a garantir que o balanço de fases e as propriedades do material não sejam severamente prejudicados neste processo. O objetivo é estabelecer os parâmetros do processo híbrido GTAW (Gas Tungsten Arc Welding) / Laser Nd-YAG (Neodymium-Doped Yttrium Aluminium Garnet) que permitam manter o balanço das fases na zona fundida do aço inoxidável superduplex UNS S32750 próximo ao inicial. Foram executadas soldagens na condição bead on plate, em uma condição ótima do processo laser para o caso, porém variando-se o aporte térmico introduzido pelo processo GTAW. Soldagens com adição de nitrogênio também foram realizadas. A caracterização do metal base, da zona fundida e da zona termicamente afetada foi realizada mediante microscopia óptica, EDS (Espectroscopia por Dispersão de Energia), microscopia eletrônica de varredura (MEV) e ensaios de corrosão (CPT). Os resultados obtidos foram relacionados aos parâmetros de soldagem utilizados e uma relação entre fração volumétrica de austenita na zona fundida e o desempenho no ensaio CPT foi estabelecida. A soldagem híbrida com adição de nitrogênio resultou em uma fração volumétrica de austenita/ferrita balanceadas, próximas a 50% de cada fase, devido a energia inserida pelo processo híbrido, com consequente melhora nas propriedades de resistência a corrosão, quando comparada com os processos isolados.
The use of superduplex stainless steels in today's industry is growing because of its characteristics that combine good mechanical properties and corrosion resistance. These steels consist of a biphasic structure with volumetric fractions about of 50% ferrite and 50% austenite. Therefore, the development of techniques to improve the welding of superduplex steels is necessary in order to ensure that the phase balance and the properties of the material are not affected during this process. The objective is to establish the parameters of the hybrid process GTAW (Gas Tungsten Arc Welding) / Pulsed Laser Nd-YAG (Neodymium-Doped Yttrium Aluminum Garnet) to maintain the phase balance in the fusion zone of the superduplex stainless UNS S32750 close to the base metal. Welds were performed in bead on plate condition, in an optimal condition of the laser process for the case, however varying the heat input introduced by the GTAW process. Also, nitrogen atmosphere welds were performed. After base metal characterization, the analysis of the molten zone and the heat affected zone was performed by optical microscopy, EDS (Energy Dispersion Spectroscopy), Scanning Electron Microscopy (SEM) and corrosion tests (CPT). The results obtained were related to the welding parameters used and a relationship between volumetric fraction of austenite in the fusion zone and performance in the CPT test was established. The hybrid welding with nitrogen addition led to a balanced volumetric austenite/ferrite fraction in the fusion zone, close to 50% of each phase, due to the thermal input provided by the hybrid process, with consequent improvement in corrosion resistance properties, when compared to isolated processes.
The use of superduplex stainless steels in today's industry is growing because of its characteristics that combine good mechanical properties and corrosion resistance. These steels consist of a biphasic structure with volumetric fractions about of 50% ferrite and 50% austenite. Therefore, the development of techniques to improve the welding of superduplex steels is necessary in order to ensure that the phase balance and the properties of the material are not affected during this process. The objective is to establish the parameters of the hybrid process GTAW (Gas Tungsten Arc Welding) / Pulsed Laser Nd-YAG (Neodymium-Doped Yttrium Aluminum Garnet) to maintain the phase balance in the fusion zone of the superduplex stainless UNS S32750 close to the base metal. Welds were performed in bead on plate condition, in an optimal condition of the laser process for the case, however varying the heat input introduced by the GTAW process. Also, nitrogen atmosphere welds were performed. After base metal characterization, the analysis of the molten zone and the heat affected zone was performed by optical microscopy, EDS (Energy Dispersion Spectroscopy), Scanning Electron Microscopy (SEM) and corrosion tests (CPT). The results obtained were related to the welding parameters used and a relationship between volumetric fraction of austenite in the fusion zone and performance in the CPT test was established. The hybrid welding with nitrogen addition led to a balanced volumetric austenite/ferrite fraction in the fusion zone, close to 50% of each phase, due to the thermal input provided by the hybrid process, with consequent improvement in corrosion resistance properties, when compared to isolated processes.
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Palavras-chave
Soldagem híbrida, UNS S32750, GTAW, Laser, Nd:YAG, Superduplex, Aço, Hybrid Welding, Duplex