Resistência à corrosão dos aços inoxidáveis super duplex ASTM a 890/A 890M grau 5A e 6A

Abstract

The super duplex stainless steel is widely used in aggressive corrosion environments. This type of steel has attractive combination of good mechanical strength in addition to excellent corrosion and impact resistance. However, when undergoing a heat treatment in temperature range between 300°C and 550°C a precipitation of '-phase can occur causing a reduction of corrosion resistance and ductility. Therefore, the aim of this study is to evaluate the corrosion resistance of super duplex stainless steel grade 5A and 6A after heat treatment at 475oC for different aging time. The difference in chemical composition between these steel grades is copper and tungsten content. The corrosion resistance of the samples was evaluated employing following electrochemical techniques: open circuit potential measurement, anodic polarization, cyclic polarization, electrochemical impedance spectroscopy and critical pitting temperature. The electrochemical results indicate a strong influence of aging time on corrosion resistance. Microstructural examination revealed a dual phase structure composed of a ferritic matrix with austenite islands in equal proportion. The hardness increases rapidly in the early hours of heat treatment, then with progressing time the hardening rate decreases.