The X6CrNiTi1810 austenitic stainless steel samples nitrided by plasma immersion ion implantation at 300 degreesC/3 hare studied by slow positron implantation and conversion electrons Mossbauer spectroscopies completed with X-ray diffraction (XRD) measurements. The surface layers consist of gamma(N)-Fe expanded austenite and epsilon-Fe2N nitride. The changes in hyperfine parameters and relative representation of both phases during the interrupted long-time annealing at 150 degreesC are discussed from the point of view of nitrogen migration and changes in defect structure. (C) 2002 Elsevier Science B.V. All rights reserved.