Microstructure and structural behavior of ion-nitrided AISI 8620 steel

The ion nitriding behavior of AISI 8620 alloy steel has been examined under varying process conditions. The process variables included time (1–8 h), temperature (450–600°C) and a 70% H2–30% N2 gas mixture. The structure of the compound layer was studied by X-ray diffraction (XRD) and light optical microscopy. These studies showed that the thickness of the compound layer increased with increasing time at 500°C and 550°C; however, at 600°C, the thickness of the compound layer decreased with increasing time. Phase changes during ion nitriding at 600°C have been investigated using XRD, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The maximum surface hardness was obtained at 500°C for 8 h and a larger diffusion layer was obtained at 600°C for 8 h. A braunite layer formed at 600°C.