Precipitation behavior of M2N in a high-nitrogen austenitic stainless steel during isothermal aging

The precipitation behavior of M2N and the microstructural evolution in a Cr-Mn austenitic stainless steel with a high nitrogen content of 0.43mass% during isothermal aging has been investigated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The aging treatments have led to the decomposition of nitrogen supersaturated austenitic matrix through discontinuous cellular precipitation. The precipitated cells comprise alternate lamellae of M2N precipitate and austenitic matrix. This kind of precipitate morphology is similar to that of pearlite. However, owing to the non-eutectoidic mechanism of the reaction, the growth characteristic of the cellular precipitates is different from that of pearlite in Fe-C binary alloys. M2N precipitate in the cell possesses a hexagonal crystal structure with the parameters a = 0.4752nnm and c = 0.4429nm, and the orientation relationship between the M2N precipitates and austenite determined from the SADP is [0110]M2N//[101]γ, [2110]M2N//[010]γ,