Influence of heat treatments of an HDSS alloy on the microstructure and corrosion behavior

Abstract Microstructural changes in grade 7A hyper-duplex stainless steel (HDSS) according to ASTM 890 were examined after various annealing treatments. Electrochemical measurements were then performed to evaluate the impact of these treatments on corrosion behavior. Two initial grades were available, one of which had an austenite-to-ferrite ratio of approximately 1 : 1. The annealing processes altered the ferrite-to-austenite ratio and resulted in the formation of a sigma phase. Following metallographic preparation, various etching methods were employed to highlight the different phases. The Murakami concentrated, Blöch-Wedel 2 and Beraha 2 etching agents were used. Four microstructural states that differed as much as possible were selected for the electrochemical measurements. First, potentiodynamic measurements were performed in an alkaline electrolyte to identify potentials with increased current flow. This was followed by potentiostatic measurements at the selected potentials, using electrochemically controlled etching to identify the corresponding reacting phases.