Effect of inclusions on the fatigue strength of a bearing steel

Here are presented results of experimental investigation about effect of inclusions on the fatigue strength of a bearing steel 100Cr6. Fatigue tests were carried out at sinusoidal cyclic tension-compression loading, f = 190 Hz, R = −1, room temperature, in the region ranged from N ≈ 3.5 × 10 5 to N ≈ 1.0 × 10 8 cycles of loading. Initiation of the fatigue cracks was observed in the bulk of the tested specimens and the so-called “fish eyes” were observed, mainly on the TiN inclusions (66 % Ti, 19 % N, 9 % Cr, remainder Fe, V, Zr). The TiN inclusions are hard, with sharp edges causing a significant stress concentration in a small localized area, resulting in an initiation of a fatigue crack. On the other hand, in standard for the chemical composition of this steel, the content of Ti was not prescribed.