Journal of Materials Research and Technology Journal of Materials Research and Technology
J Mater Res Technol 2017;6:65-70 DOI: 10.1016/j.jmrt.2016.07.001
Original Article
Structural characterization of plasma nitrided interstitial-free steel at different temperatures by SEM, XRD and Rietveld method
Ana Paula de Andrade Manfridini, Geralda Cristina Durães de Godoy, Leandro de Arruda Santos,
Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
Received 03 May 2016, Accepted 05 July 2016
Abstract

Plasma nitriding processes are widely used to improve surface properties of several steels and alloys. In this work, the formation of nitrides in the surface of plasma nitrided IF steels as a function of the temperature was investigated. Three cold-rolled IF steel plates were nitrided for 4h after shot peening at three different temperatures: 450°C, 475°C, and 500°C. The resultant nitrided layers were then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Rietveld method, and hardness measurements. Through SEM images, it was possible to visualize two main sublayers: a compound layer and a diffusion zone. Through XRD, two phases were identified in the compound layer, which were ¿-Fe2–3N and γ′-Fe4N. The diffusion zone presented a ferritic matrix with fine precipitates, possibly α″-Fe16N2. By Rietveld, the calculated quantity of γ′-Fe4N was 68wt.% for the sample treated at 475°C and 58wt.% for the one treated at 500°C. These values were consistent with the hardness measurements. Thus, it is suggested that higher nitriding temperatures facilitate the decreasing of γ′-Fe4N and, consequently, the increasing of ¿-Fe2–3N in the compound layer.

Keywords
Plasma nitriding, IF steels, Structural characterization, Surface properties
J Mater Res Technol 2017;6:65-70 DOI: 10.1016/j.jmrt.2016.07.001