The crystalline structure profile of the compound layer obtained by pulsed plasma nitriding in steel gears is reported. The nitrogen depth profile obtained by Radio Frequency Glow Discharge Optical Emission Spectroscopy is correlated with both the nano-hardness and the crystalline epsilon-Fe3N/gamma'-Fe4N phases identified in the nitrided layer by X-ray diffraction. These results show the importance to control the nitriding parameters to avoid abrupt hardness changes along the case that can jeopardize the gear performance. (c) 2008 Elsevier B.V. All rights reserved.2034195314571461