Influence of the microstructure on the mechanical properties in pulsed plasma nitriding AISI P20 steel

Plasma technologies are widely used in surface engineering processes of metals. Basically, these treatments improve the mechanical, tribological, and chemical properties of the material such as wear resistance, hardness, fatigue resistance, friction, and corrosion resistance. In this work, a comprehensive study of the influence of the microstructure on the mechanical properties of AISI P20 steel treated at different temperatures by pulsed plasma nitriding is reported. The processes were done by using a pulsed plasma industrial system. The samples were characterized by nano-indentation (hardness), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray dispersion spectroscopy (EDS). At lower treatment temperatures (360degC), a high density of small lamellar precipitates, constituted by more epsiv-Fe_2,3N phase than gamma-Fe₄N phase, is formed. At intermediate treatment temperatures (480degC), big lamellar precipitates, constituted by more gamma-Fe₄N phase than epsiv-Fe_2,3N phase, are formed at grain boundary. At higher treatment temperatures (520degC), the nitrided layer does not contain lamellar precipitates and it is only constituted by alpha-Fe phase saturated in nitrogen. Hardness depends on distribution of precipitates and crystalline phases (microstructure). The higher hardness values are obtained when more and smaller lamellar precipitates are presented and constituted by more epsiv-Fe_2,3N phase.