Features of the plasma electrolyte nitrocarburizing of a relief surface

Dependences of the thickness of a layer saturated with interstitial elements on the surface of AISI 304 type stainless steel with an appreciable relief (thread) during anodic plasma electrolyte nitrocarburizing on the processing time and voltage was studied by X-ray diffraction analysis, scanning electron microscopy and optical microscopy. This layer contains two sub-layers: oxygen and nitrogen saturate the upper one, and nitrogen and carbon saturate the second one. This layer grows unevenly depending on three factors: the location on the relief, the processing time, and the voltage on the electrolytic cell. In the relief depressions, the nitrocarburized layer does not grow significantly during all processing times in the range up to 5 min. On the relief protrusions the thickness of the nitrocarburized layer increases with the increase in both the processing time and the voltage on the cell. In the middle of the relief slopes the dependence of layer thickness on processing time and applied voltage is somewhat intermediate between the protrusions and depressions, more similar to that of depressions. Mechanical stresses may occur on relief protrusions during the first minute of processing, leading to cracks and removal of metal from the surface. A zone of base metal with significant grain-boundary carbon diffusion was detected below the nitrocarburized layer.