Structure and Properties of the Glow Discharge Nitrided Layers Produced on Austenitic Steel

The study is concerned with the nitrided layers produced on ‘medical’ steel of the 316L (00H17N14M2) grade at a temperature of 450°C. The results of the microstructural observations performed by TEM and of the phase analysis of the layers are presented and discussed. The examinations were conducted in the regions extending from the surface down to a depth of about 25 um. The near-surface zone appeared to contain nitrogen austenite and fine precipitates. There were also certain phases in the lamellar form. Because of the applicative aspect of the glow discharge nitriding of 316 steel, the examinations also included its mechanical strength, in particular the static tensile strength and the low-cycle fatigue strength. The static tensile tests showed no significant differences in the yield stress between the samples in the starting state and those subjected to the low-temperature glow discharge assisted nitriding. The low-cycle fatigue tests (which, in view of the differences between the properties of the untreated material and the nitrided layers, can be classified among the most severe mechanical tests) either, indicated no essential differences in the fatigue properties of the samples subjected to the surface treatments conducted under various conditions.