Influence of crack-like surface defects on the fatigue limit of nitrocarburized carbon steel

Abstract

Abstract. The aim of this study was to evaluate the influence of surface crack on the bending fatigue limit of nitrocarburized steel. Semicircular slits with depths of 0.040, 0.075, and 0.100 mm were introduced on the surface of nitrocarburized medium carbon steel specimens to simulate the presence of small cracks. Bending fatigue tests were performed at room temperature in air with the stress ratio R = −1. It was observed that the fatigue limit decreased as the depth of the slit increased. The acceptable crack size was estimated based on fracture mechanics. The predicted acceptable crack size was consistent with the experimental result. Therefore, the acceptable crack size of nitrocarburized carbon steel could be predicted via analysis based on fracture mechanics.

Effect of Salt Bath Nitrocarburizing and Post-Oxidation on Static and Fatigue Behaviours of a Construction Steel

“…In previous contributions, several authors have analysed the effect of nitrocarburizing on the fatigue limit of the plain material [26][27][28][29][30][31], while only few contributions [10,24] have been devoted to investigating the effect of nitrocarburizing on the medium-high cycle fatigue regime, considering both plain and notched specimens. Moreover, the effects of the combination of salt bath nitrocarburization and post-oxidation, i.e., QPQ treatment, have been mainly analysed from the point of view of microstructure, hardness, wear and corrosion resistance [14][15][16][17][18]32], while the effects of QPQ treatment on the fatigue behaviour have been investigated in detail only for some steel categories, such as carbon steels [33][34][35], alloyed steels [36,37], tool steel [38]; and also for ductile cast iron [39].…”