Precipitation behavior of the Cr23C6 and Cr2(C, N) phase within the medium-nitrogen austenitic stainless steel and its mechanism of induced formation of thin film at grain boundaries

In the global shortage of nickel resources, it is imperative to optimize the production process of nickel-saving stainless steel and further improve the quality of its products. Among the various types of nickel-saving stainless steel, Cr-Mn-N stainless steel has the widest application range. This study investigates a novel as-rolled medium-nitrogen austenitic stainless steel (A-ss-N). Annealing treatments were conducted at 800°C, 850°C, 900°C, and 1000°C for 30 minutes. The microstructures of as-rolled and heat-treated A-ss-N were characterized, its tensile properties were tested. Results demonstrate that annealing at 800°C/850°C for 30 minutes induces substantial precipitation of granular Cr 23 C 6 and Cr 2 (C, N) precipitates at grain boundaries. The low intragranular Cr content facilitates nucleation and growth of thin films adjacent to these precipitates, forming interconnected thin film along grain boundaries that develop into continuous network structures. However, annealing at 900°C/1000°C for 30 minutes eliminates the thin film, while Cr 23 C 6 and Cr 2 (C, N) precipitates gradually dissolve. Mechanical tests indicate that after 900°C annealing to eliminate the network structure, the room-temperature tensile properties of A-ss-N were significantly enhanced, with its elongation increasing from 29.5% (after 850°C annealing) to 67.5% (after 900°C annealing), and the strength-ductility product improving from 23.01 GPa·% to 61.56 GPa·%.