Avaliação da formulação de reativos à base de ácido pícrico visando a revelação do grão austenítico prévio em diferentes tipos de aços
Evaluation of picric acid etchant formulations for the prior austenite grain revelation in different steel types
Natália Aparecida Barbosa Pimenta, Paulo Sérgio Moreira, Geraldo Lúcio de Faria
Resumo
As técnicas de revelação dos contornos de grãos austeníticos prévios em aços são importantes ferramentas de caracterização. O método mais usual faz uso de reativos à base de ácido pícrico, que, na maioria dos casos, não produz resultados satisfatórios. Diante disso, foram investigadas, neste trabalho, formulações de reativos à base de ácido pícrico, variando-se a concentração de ácido clorídrico, com o objetivo de propor condições de ataque eficientes para sete aços fabricados no Brasil. Para cada aço, foram avaliados reativos com cinco concentrações distintas de HCl e diferentes tempos de ataque. Foi possível revelar os contornos de grãos austeníticos eficientemente para todos os tipos de aços estudados adequando-se a concentração de HCl adicionado e o tempo de ataque. Com base nos resultados alcançados, foi possível disponibilizar uma tabela e uma equação de regressão linear múltipla que apresenta o tempo de ataque em função do carbono equivalente do aço e da concentração de HCl. Concluiu-se que a concentração de HCL utilizada no reativo é o parâmetro que exerce maior influência sobre o tempo de ataque.
Palavras-chave
Abstract
Techniques used to reveal the prior austenite grain boundaries in steels are important characterization tools. The most common method used to reveal the austenite grain boundaries is with picric acid based etchant. Unfortunately, it does not produce satisfactory results in most cases. Therefore, in the present study, the formulation of picric acid-based etchant was investigated. Five hydrochloric acid concentration at different etching time were studied in order to determine what would be the most efficient etching condition for seven types of steels currently manufactured in Brazil. It was possible to reveal the austenite grain boundaries efficiently for all studied steels by adjusting the hydrochloric acid concentration and the etching time. Based on the achieved results, it was possible to make available a reference table and a multiple linear regression equation that highlight the optimal etching time as a function of the carbon equivalent and HCl concentration. It was concluded that the used HCl concentration is the parameter which has the greater influence on the etching time.
Keywords
Referências
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Submetido em:
11/06/2020
Aceito em:
28/09/2020
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