Structural characterization of ion-nitrided AISI 5140 low-alloy steel

The ion nitriding behavior of AISI 5140 alloy steel was investigated under different process parameters including time (1, 4, 8, and 12 h), temperature (400, 450, 500, and 550 °C), and gas mixture ratio (0.05, 0.33, 1, and 3 N2/H2). The ion nitriding of steels has been assessed by evaluation of phase composition, hardness profile, compound layer thickness, and case depth by using a microhardness tester, X-ray diffraction (XRD), and scanning electron microscopy (SEM). It is observed that the compound layer thickness and the case depth increase with increasing treatment time and temperature. With increasing gas mixture ratio, the compound layer thickness increases, whereas the case depth decreases. The maximum surface hardness was observed at 450 °C temperature, for 0.33 N2/H2 gas mixture ratio, and for 4-h treatment time.