Exploratory study of degree sensitization of duplex stainless steel UNS S31803 aged at 800°C by double loop potentiokinetic reactivation method (DL-EPR)

摘要

The main purpose of this research is the study of degree sensitization (DOS) of UNS S31803duplex stainless steel (DSS) aged at 800°C by double loop potentiokinetic reactivation (DL-EPR)method. For this, solution heat treatment was conducted at 1175°C for 30 minutes in originalsamples followed by aging at 800°C between 10 min and 72 h, enabling the formation of different phase contents. The aged samples were mounted as metallography specimens for microstructuralcharacterization, which was carried out by quantitative metallography, magnetic measurementsand scanning electron microscopy. The DL-EPR tests were conducted in polished samples at 30°Cin 3 different solutions: (A) 0,5M H2SO4 + 0,5M NaCl + 0,01M KSCN; (B) 1M H2SO4 + 0,5M NaCl +0,01M KSCN; and (C) 2M H2SO4 + 0,5 M NaCl + 0,01 M KSCN to evaluate the most indicatedsolution to the study of the electrochemical behaviour of each condition. A strong relation between the DOS and the microstructure of the samples for each condition was observed. The solution © is the most indicated for DL-EPR tests between all the solutions tested in this work, because considering the intense Cr-depletion of the material due to sigma formation, only this solution shows significant differences in DOS between aged samples. Oscillations in DOS were observed probably as a consequence of a possible Cr redistribution to depleted areas due to sigma phase formation. However, the low Cr content available to the redistribution does not allow the restoration of DOS values initially registered for the solution-treated sample.