2022 年 62 巻 10 号 p. 2135-2146
The influence of Mn addition on fatigue properties of ferritic steel containing solute carbon was examined using rotating bending fatigue tests on water-quenched Fe–0.016C–1.9Mn ferrite–pearlite steel containing 0.0035 mass% solute carbon in comparison with water-quenched Fe–C ferritic steels containing 0.0063–0.017 mass% solute carbon. The fatigue tests were carried out at ambient temperature around 300 K and a frequency of 50 Hz with a stress ratio of −1. The Fe–C–Mn steel exhibited a comparable hardness and fatigue limit to the water-quenched Fe–0.017C steel which contains about three times the amount of solute carbon than the Fe–C–Mn steel. In addition, the Fe–C–Mn steel exhibited a significant coaxing effect in comparison to the Fe–C steels, when the test was started from a stress amplitude just below the fatigue limit. Crack initiation sites were changed by stress amplitude unlike in the Fe–C steels. Specifically, intergranular cracks were observed at the high stress amplitudes and transgranular cracks were observed at the low stress amplitudes near the fatigue limit. It was concluded that the Mn addition suppresses intergranular cracking at the low stress amplitudes.
