Estudo do efeito da precipitação da fase sigma na resistência à corrosão do aço inoxidável duplex sinterizado

• Autor(a) principal: Moura, Milena Jacinto da Silva
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Ceará (UFC)
• Texto Completo: http://www.repositorio.ufc.br/handle/riufc/59355
• topic: Aço inoxidável duplex; Tratamento térmico; Fase sigma

Sintered duplex stainless steels consist of two types of microstructure, ferritic and austenitic, present in similar proportions, which add good corrosion resistance and satisfactory mechanical strength. What differs from these conventional steels is their manufacturing process, which is produced by the sintering of metallic powders, which are united by atomic diffusion, and can happen in the liquid or solid state. In the latter case at temperatures below the melting point. This process has as characteristics: a smaller number of steps, the use of almost all the raw material and consequently the reduction of costs. However, it is necessary to understand the behavior of these steels when subjected to different temperatures, to understand the effect of the sigma phase in these materials. Therefore, the objective of this work is the study of the corrosion resistance in the duplex steel (22% Cr-5% Ni) produced by sintering. When in its matrix there is the formation of the sigma phase (σ), the formation of these precipitates decreases the corrosion resistance. Therefore, to determine if the sigma phase is harmful to this AID, sintered AID samples were prepared, followed by solubilization, aging heat treatment, at temperatures of 700, 750, 800, 850 and 900 ° C and fast cooling in water. For each temperature there was a variation in treatment times of 10 minutes, 1 hour and 10 hours. The microstructural characterization of the steels was performed using optical microscopy (OM), scanning electron microscopy (SEM), Energy dispersive x-ray (EDS) and microhardness measurements. Electrochemical tests of OCP, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), chronoamperometry and critical pite temperature (CPT) were carried out. The characterization by OM showed a gradual increase in the percentage of precipitate as the temperature and the aging time increase. There was an increase in hardness due to the increase in aging time. In the microscopy, optical and scanning, the quantifications of the sigma phase are presented for all the samples. In the electrochemical tests, it was related that the increase of the percentage of precipitation of the sigma phase, directly interferes in reducing the corrosion resistance of this material.