Fatigue Properties and Dislocation Structures of Nitrided Rolled Steel.

Fatigue properties of the nitrided rolled steel are investigated on the basis of the observations of the substructures produced by nitriding and fatigue. It is found that the fatigue limit of the nitrided rolled specimens is much higher than that of the nitrided annealed ones and the substructures before the nitriding are effective for the improvement of the fatigue strength. The substructure of the rolled steel consists of cells with dislocation clusters within them. By means of nitriding treatment, cell structures and twins appear in the inner part of the compound layer, while uniformly distributed dislocation clusters in the region just below the compound layer and the inner part of the diffusion layer. After fatigue test, most of these substructures are preserved except for the region just below the compound layer where the cell structures due to active dislocation motions were formed.