Microstructural thermostability of high nitrogen austenitic stainless steel

A high nitrogen austenitic stainless steel, Fe–24Mn–18Cr–3Ni–0.62N, was isothermally annealed from 750 to 900 °C for different times to investigate the thermostability of its microstructures. Results show that the precipitates were Cr2N and initially formed along the grain boundary. The time–temperature–precipitation diagram was established, according to which the critical cooling rate of this material with less than 0.1–0.5 vol.% of precipitated Cr2N was specified as 30 °C/min. The microhardness of the matrix in samples annealed at different temperatures decreased with the diffusion of nitrogen from the matrix to grain boundaries.