Influência da austenita revertida no grau de sensitização do aço inoxidável supermartensítico
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Citações na Scopus
Tipo de produção
Trabalho de Conclusão de Curso
Data
2023
Autores
Torres, Ana Carolina Tenente
Orientador
Magnabosco, Rodrigo
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Texto completo (DOI)
Palavras-chave
aço inoxidável supermartensítico,sensitização,austenita revertida,supermartensitic stainless steel,sensitization,reversed austenite
Resumo
O objetivo desse trabalho compreende o estudo da influência da austenita revertida no grau de sensitização do aço inoxidável supermartensítico de uma liga experimental doada pela Villares Metals. Foi estudado o comportamento de sensitização da liga para 3 diferentes frações volumétricas de austenita revertida, estimadas inicialmente por meio de uma simulação no Software ThermoCalc em 10%, 30% e 50% dessa fase, a fim de entender sua influência no comportamento do material. A partir dessa simulação foram obtidas as seguintes temperaturas para o revenimento da liga: 540°C, 620°C e 650°C. Para entender seu comportamento, foram utilizadas técnicas de caracterização como: ferritoscopia, difração de raios-X, dureza, ensaios eletroquímicos e análise metalográfica. Por meio da ferritoscopia obteve-se que a condição com a maior formação de fases não magnéticas foi na revenida a 620°C, com 35,7% de fração de fase austenítica. A revenida a 540°C obteve 11,4% de fase não magnética e a 650°C obteve 32,7%, concluindo que o software ThermoCalc falha ao prever esse comportamento, por prever a quantidade de austenita de equilíbrio nas temperaturas de revenimento, não conseguindo avaliar a transformação martensítica ou a formação de austenita retida, já que estas dependem não só do equilíbrio termodinâmico, mas da cinética das transformações de fase envolvidas. Por meio da análise de DRX, foi possível identificar apenas 2 fases: martensita e austenita, diferentemente do que era simulado pelo software, que previa a possível formação de até 7 diferentes fases. Foi medida a dureza e o valor mais alto foi o da amostra temperada, seguida pela amostra revenida a 540°C, enquanto as amostras de 620°C de 650°C tem durezas inferiores e muito semelhantes entre si. A avaliação do grau de sensitização foi feita por meio de ensaios de polarização eletroquímica de reativação de ciclo duplo (DL EPR), obtendo os seguintes valores de: 0,26, 0,79 e 0,54 para os revenimentos a 540°C, 620°C 650°C, respectivamente. Com isso, a amostra que se demonstrou mais sensitizada foi a revenida a 620°C e a com melhor comportamento a revenida a 540°C.
This work studied the influence of reversed austenite on the degree of sensitization of a supermartensitic stainless steel produced by Villares Metals as an experimental alloy. It was analyzed the sensitization behavior of the alloy for three different volumetric fractions of reversed austenite, initially estimated through a simulation in the ThermoCalc software, as 10%, 30%, or 50% of this phase, to understand it’s influence on the behavior of the material obtained. This simulation resulted in the following temperatures for tempering the alloy: 540°C, 620°C or 650°C. Characterization techniques such as ferritoscopy, X-ray diffraction, hardness, electrochemical tests, and metallographic analysis were used to understand its behavior. Through ferritoscopy it was determined that the condition with the greatest formation of non-magnetic phases is the sample tempered at 620°C, with a 35.7% austenitic phase fraction. Tempering at 540°C resulted in 11.4% of the non-magnetic phase and at 650°C, 32.7%, concluding that the ThermoCalc software fails to predict this behavior since it predicts the equilibrium amount of austenite at tempering temperatures, failing to evaluate the martensitic transformation or the formation of retained austenite, as these depend not only on the thermodynamic equilibrium, but on the kinetics of the phase transformations involved. Through XRD analysis, it was possible to identify only two phases, martensite and austenite, despite what was simulated in ThermoCalc, which predicted the formation of up to seven distinct phases. Hardness was measured in two different scales, for both, the highest value was that of the quenched sample, followed by the sample tempered at 540°C, while the 620°C and 650°C samples have lower hardness and are very similar. The degree of sensitization was measured using Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR), obtaining the values: 0.26, 0.79, and 0.54 for tempering at 540°C, 620°C, and 650°C, respectively. The sample that proved to be most sensitized was the one tempered at 620 °C, and the one with the best behavior was the tempered at 540 °C.
This work studied the influence of reversed austenite on the degree of sensitization of a supermartensitic stainless steel produced by Villares Metals as an experimental alloy. It was analyzed the sensitization behavior of the alloy for three different volumetric fractions of reversed austenite, initially estimated through a simulation in the ThermoCalc software, as 10%, 30%, or 50% of this phase, to understand it’s influence on the behavior of the material obtained. This simulation resulted in the following temperatures for tempering the alloy: 540°C, 620°C or 650°C. Characterization techniques such as ferritoscopy, X-ray diffraction, hardness, electrochemical tests, and metallographic analysis were used to understand its behavior. Through ferritoscopy it was determined that the condition with the greatest formation of non-magnetic phases is the sample tempered at 620°C, with a 35.7% austenitic phase fraction. Tempering at 540°C resulted in 11.4% of the non-magnetic phase and at 650°C, 32.7%, concluding that the ThermoCalc software fails to predict this behavior since it predicts the equilibrium amount of austenite at tempering temperatures, failing to evaluate the martensitic transformation or the formation of retained austenite, as these depend not only on the thermodynamic equilibrium, but on the kinetics of the phase transformations involved. Through XRD analysis, it was possible to identify only two phases, martensite and austenite, despite what was simulated in ThermoCalc, which predicted the formation of up to seven distinct phases. Hardness was measured in two different scales, for both, the highest value was that of the quenched sample, followed by the sample tempered at 540°C, while the 620°C and 650°C samples have lower hardness and are very similar. The degree of sensitization was measured using Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR), obtaining the values: 0.26, 0.79, and 0.54 for tempering at 540°C, 620°C, and 650°C, respectively. The sample that proved to be most sensitized was the one tempered at 620 °C, and the one with the best behavior was the tempered at 540 °C.