Effect of Pre-Oxidation on Plasma Nitrided Steel AISI4140

Steel AISI4140 is studied after plasma nitriding and preliminary oxidation. The structure of the preliminarily oxidized surfaces after the nitriding is studied by scanning electron microscopy (SEM). The free surface energy is computed from the results of the measurement of the angle of contact between a liquid drop and the surface studied. The thickness of the nitrided layer is determined. The phase transformations on the surface are considered. The effect of oxidation conducted prior to nitriding is shown to be positive. The optimum oxidation mode (300°C, 30 min) for improving the structure of the nitrided layer and more than doubling its thickness is chosen.