Influência do grau de sensitização na resistência à corrosão de aço inoxidável austenítico com baixo níquel

Abstract

Austenitic stainless steels are widely used in various industrial sectors due to their excellent mechanical properties and high corrosion resistance. The presence of chromium and nickel in the chemical composition of these steels is essential to ensure these characteristics, favoring an austenitic structure at room temperature. However, the high chromium content, combined with exposure to high temperatures, favors the precipitation of carbides (Cr23C6) in the microstructure, a phenomenon known as sensitization. Austenitic stainless steel QN1803, developed with low nickel content in order to reduce costs and with properties similar to those of conventional steels in this class, is also susceptible to this phenomenon. In this study, the degree of sensitization (DOS) of QN1803 steel was analyzed after heat treatment for different exposure times (1, 6, and 24 hours). For this purpose, the double-cycle potentiodynamic electrochemical reactivation (DL-EPR) technique was used in solutions of 0.5M H₂SO₄ + 0.01M KSCN and 0.5M H₂SO₄ + 0.01M NH4SCN, as it offers advantages in the analysis of stainless steels containing nitrogen. In addition, open circuit potential, linear potentiodynamic polarization, and electrochemical impedance spectroscopy analyses were performed in a 3.5% NaCl solution. The results indicated that the increase in the degree of sensitization of the material after heat treatment resulted in a significant reduction in the resistance and quality of the passive film, emphasizing the increase in carbide precipitation with increasing treatment times. In addition, there was a difference in using the 0.5M H₂SO₄ + 0.01M NH4SCN medium in the DL-EPR method, characterized by smaller variations in DOS values, proving to be more appropriate for the study.