Acceleration of Plasma Nitriding at 550 degrees C with Rare Earth on the Surface of 38CrMoAl Steel

In order to explore the effect of the addition of rare earth (RE) to a steel microstructure and the consequent performance of a nitrided layer, plasma nitriding was carried out on 38CrMoAl steel in an atmosphere of NH3 at 550 degrees C for 4, 8, and 12 h. The modified layers were characterized using an optical microscope (OM), a microhardness tester, X-ray diffraction (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electrochemical workstation. After 12 h of nitriding without RE, the modified layer thickness was 355.90 mu m, the weight gain was 3.75 mg/cm(2), and the surface hardness was 882.5 HV0.05. After 12 h of RE nitriding, the thickness of the modified layer was 390.8 mu m, the weight gain was 3.87 mg/cm(2), and the surface hardness was 1027 HV0.05. Compared with nitriding without RE, the epsilon-Fe2-3N diffraction peak was enhanced in the RE nitriding layer. After 12 h of RE nitriding, La, LaFeO3, and a trace amount of Fe2O3 appeared. The corrosion rate of the modified layer was at its lowest (15.089 x 10(-2) mm/a), as was the current density (1.282 x 10(-5) A/cm(2)); therefore, the corrosion resistance improved.