Estudo da influência do pH do eletrólito no comportamento eletroquímico das ligas UNS S41003 e ENDUR 300

• Ano de defesa: 2021
• Autor(a) principal: Queiroz, Carlos Henrique Barbosa
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Resistência à corrosão; ENDUR 300®; pH; Dureza; Hardox 400; Aço inoxidável de ultra resistência
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/63698

The Endur 300 alloy is a newly developed alloy with a low chromium content and a predominantly martensitic microstructure. It is marketed with the main focus of application as a structural steel, with potential to replace alloys such as the A36 alloy, which is widely used in this regard. Given the lack of information about this new alloy in the literature and its potential application in environments with a wide pH range, the present work sought to carry out a study and characterization of the electrochemical behavior of the Endur 300 alloy in NaCl solution at different pH values, comparing the results to a UNS S41003 alloy, which is used as base material for the production of the Endur 300 alloy. The methodology for carrying out the work was divided into the stages of: Preparation of the specimens; Conducting electrochemical tests of open circuit potential, linear and cyclic polarization, electrochemical impedance spectroscopy and chronoamperometry; Characterization of the surfaces of both alloys before and after the corrosion process by means of optical (MO) and electron (SEM) microscopy; and also the evaluation of the mechanical property of hardness by means of Vickers hardness and microhardness testing. Results showed that, generally speaking, the Endur 300 alloy processing resulted in microstructural and mechanical changes, with no significant effect on the corrosion resistance properties. An increase of Vickers Hardness of approximately 80% was observed for the Endur 300 samples. The main corrosion mechanism observed was localized corrosion, evidenced by the presence of pits after polarization tests. The effect of the medium pH was observed, being particularly influential on the reaction kinetics, as observed through the increase in corrosion current density of approximately 4 orders of magnitude for both alloys exposed to the pH 2.0 medium, through the linear voltammetry experiments. The impedance tests also showed that the pH reduction resulted in a in a decrease in the polarization resistance, which went from 1.18E5 and 1.31E5 Ω*cm², in the pH 5.8 medium, for UNS S41003 and Endur 300 samples, respectively, to 7.84E2 and 7.10E2 Ω*cm², in the pH 2.0 medium. The hardness analysis showed that after 28 days of immersion there was a reduction in the calculated hardness, where the medium pH was more influential for the Endur 300 alloy, which had a more accentuated hardness reduction for the lowest pH solution.