The Microstructure of Tool Steel after Low Temperature Ion Nitriding
  The microstructural development in H13 tool steel upon nitriding by an ion beam process was investigated. The nitriding experiments were performed at a relatively low temperature of about 400\deg C and at constant ion beam energy (400 eV) of different doses in a high-vacuum preparation chamber; the ion source was fed with high purity nitrogen gas. The specimens were characterized by X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), scanning and transmission electron microscopy (SEM and TEM), and grazing incidence and Bragg-Brentano X-ray diffractometry. In particular, the influence of the nitrogen surface concentration on the development of the nitrogen concentration-depth profile and the possible precipitation of alloying element nitrides are discussed. 
L. F. Zagonel, E. J. Mittemeijer, and F. Alvarez
cond-mat.mtrl-sci