Influence of N on precipitation behavior, associated corrosion and mechanical properties of super austenitic stainless steel S32654

Abstract

The influence of N on the precipitation behavior, associated corrosion, and mechanical properties of S32654 were investigated by microstructural, electrochemical, and mechanical analyses. Increasing the N content results in several alterations: (1) grain refinement, which promotes intergranular precipitation; (2) a linear increase in the driving force for Cr2N and Mo activity, which accelerates the precipitation of intergranular Cr2N and π phase, respectively; (3) a linear decrease in the driving force for σ phase and Cr activity, which suppresses the formation of intragranular σ phase. The total amount of precipitates first decreased and then increased with the N content increasing. Furthermore, the intergranular corrosion susceptibility depended substantially on the total amount of precipitates and also first exhibited a decreasing and then an increasing trend as the N content increased. In addition, aging precipitation caused a considerable decrement in the ultimate tensile strength (UTS) and a remarkable increment in the yield strength (YS). Both the UTS and YS always increased with N content increasing throughout the solution and aging process. Whereas the elongation was considerably sensitive to the aging treatment, it exhibited marginal variation with the N content increasing.