The Effect of the Plasma-Nitriding Process on the Structure and Wear Properties of the Sintered Low Alloy Steel

In this research, the effect of the plasma-nitriding process on the structure and wear properties of the sintered powder of a low alloy steel with the trade name of Astaloy85Mo was investigated. In the first step, powders were pressed by the hydraulic press in a chamber with 5 mbar pressure. In the next step, the sintering process was performed for 30 min in the NH₃ atmosphere at 1120 °C. Afterward, the plasma-nitriding process was performed on the samples at the temperatures of 470 and 570 °C for 3 and 6 h. After plasma nitriding, the shape and nature of the formed layers in the microstructure of the powders were surveyed by the optical microscope, XRD and EDS, as well as SEM. Also, the wear behavior of the samples under the applied load of 45 and 25 N was investigated. The obtained results revealed the formation of Fe₃N (ε) and Fe₄N (γ′) phases, leading to the nucleation and growth of a compound and diffusion nitride layers in the sintered steel. Also, the main phase at the temperature of 470 °C was ε. In contrast, the main phase at the temperature of 570 °C was γ′. As the most important finding of the work, it was realized that the wear rate of the plasma-nitrided sample for 6 h, at the temperature of 570 °C under the applied load of 25 N, was improved by approximately 22 times.