Cavitation erosion behavior of high‑nitrogen austenitic stainless steel: Effect and design of grain-boundary characteristics

Abstract

An understanding of the cavitation erosion behavior and mechanisms of high‑nitrogen austenitic stainless steel is of interest for scientific and economic reasons. The original microstructure of 18Mn18Cr0.6 N steel was examined using electron backscatter diffraction analysis. Specimens were eroded using an ultrasonic cavitation erosion facility. The damaged surfaces were observed using scanning electron microscopy. Coherent Σ3 boundaries had the worst cavitation erosion resistance; the cavitation damage was located primarily at the same sides of the twins with a low Taylor factor. The cavitation erosion resistance decreased in the order: random high-angle grain boundaries and Σ27 boundaries; incoherent Σ3 boundaries; Σ9 boundaries; and coherent Σ3 boundaries. The Taylor factor was important in the analyses of metal material cavitation erosion. A large difference between the two grains or twins in the Taylor factor yielded a higher cracking risk of the boundary between them. Grain rotation led to a step formation at a boundary and the cavitation damage was accelerated. Three types of cavitation erosion were identified. A cavitation mechanism model for coherent Σ3 boundaries was proposed. Finally, the design of grain-boundary characteristics to improve the cavitation erosion resistance was discussed.