In this work we report a study of the structural modifications and corrosion behavior of martensitic stainless steels (MSS) nitrided by plasma immersion ion implantation (PI3). The samples were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, photoemission electron spectroscopy, and potentiodynamic electrochemical measurements. Depending on the PI3 treatment temperature, three different material property trends are observed. At lower implantation temperatures (e.g., 360 degrees C), the material corrosion resistance is improved and a compact phase of epsilon-(Fe,Cr)(3)N, without changes in the crystal morphology, is obtained. At intermediate temperatures (e.g., 430 degrees C), CrN precipitates form principally at grain boundaries, leading to a degradation in the corrosion resistance compared to the original MSS material. At higher temperatures (e.g., 500 degrees C), the relatively great mobility of the nitrogen and chromium in the matrix induced random precipitates of CrN, transforming the original martensitic phase into alpha-Fe (ferrite), and causing a further degradation in the corrosion resistance. (c) 2005 American Vacuum Society.