Atom probe tomography characterization of nitrogen induced decomposition in low temperature plasma nitrided 304L austenitic stainless steel

A three-dimensional atomic characterization of AISI 304L plasma nitrided at 400 °C has been carried out with atom probe tomography (APT). While only a single phase, usually called γN phase or expanded austenite, can be detected by the X-ray diffraction, APT reveals the formation of nanometric MN (M=Cr, Fe) precipitates. Preferential precipitation of MN at planar defects has been observed. These results suggest that even at moderate nitriding temperatures the diffusion of Cr takes place resulting in slow but nevertheless detectable precipitation kinetics.