Oxidação de aços inoxidáveis ferríticos a altas temperaturas em atmosfera de Argônio

Abstract

Stainless steels have progressed significantly, especially to meet the needs of the oil, aeronautics, automobile and many other industries. The ferritic family has been gradually replacing the austenitic family, for high temperature applications, offering more advantageous cost benefit due to the almost absence of nickel. The objective of this research was to investigate the oxidation behavior of ferritic stainless steels AISI 409, AISI 439 and AISI 441, in a tubular oven in an argon atmosphere, thus establishing a relationship between the stabilizing elements. The samples were polished, on both surfaces, with diamond pastes of 3 and 1μm and oxidized in a tubular oven for 2h, 4h, 8h, 16h, 32h and 50h, the temperature range used was between 850°C and 950°C, in the argon atmosphere, containing 1ppm of O2. The oxidation kinetics was established, measuring the mass gain per unit area as a function of the oxidation time. The microstructure of the oxide films was performed using Scanning Electron Microscopy (SEM). The chemical characterization of the oxide films was done by energy dispersive spectroscopy (EDS). In the analysis of oxidation rates, mass gain per unit area is observed in an increasing way with temperature, and the parabolic law was verified in almost all the steels and temperatures mentioned, which formed a protective film, grown by diffusional process obeying Wagner's theory.