Effect of a Novel Heat Treatment on the Corrosion Resistance of Duplex Stainless Steel S32101

Abstract

In this paper, the effect of a novel heat treatment on the microstructure evolution and corrosion resistance of S32101 was investigated, and the nucleation of equiaxial austenite and pitting mechanism during secondary solution treatment was revealed. The results demonstrated that the nucleation of austenite was concentrated within the ferrite, α/α grain boundaries and α/γ phase boundaries, with a preferential nucleation occurring at the α/α grain boundaries. Following solution treatment at 1050 °C, the corrosion current density reached its minimum value of 8.153 nAcm⁻², accompanied by the highest E_pit-E_corr potential difference, indicating optimal resistance to pitting nucleation and superior pitting corrosion resistance. Furthermore, as the holding time increased, the break potential exhibited a trend of first increasing and then decreasing, with a maximum break potential of 691.32 mV observed after holding for 5 min, at which point the highest E_pit-E_corr was recorded at 907.37 mV. The ferrite, characterized by low PREN values, significantly influenced the overall pitting resistance of S32101. The pitting mechanism of S32101 in a 3.5% NaCl solution was attributed to the selective corrosion of ferrite.