Investigation on the mechanical and pitting corrosion behaviour of solution-treated 22% Cr lean duplex stainless steel with different Mn/N ratio

Abstract

ABSTRACT Effect of Mn/N ratio on the microstructure evolution, mechanical and pitting corrosion properties of solution-treated 22% Cr lean duplex stainless steel (DSS) was investigated. As the Mn/N ratio decreased, tensile and yied strength, as well as elongation,increased due to the strengthening solid solution effect of more nitrogen addition, and two-phase equilibrium was obtained at 17.80 Mn/N ratio. The drop in the amount of Cr2N, more dislocation cell formation in ferrite and the increase of slip bands in austenite contributed to an increase in toughness with increasing Mn/N ratio from 3.28 to 17.80, whereas more σ precipitates and ferrite fraction resulted in a decrease of it at 54.14 Mn/N ratio. Moreover, higher pitting corrosion resistance was obtained for 17.80 Mn/N ratio DSS than that for 2205 DSS due to the thicker and more compact passive film formation, but higher Mn/N ratio of 54.14 decreased it with more loose MnO formation.