Abstract
The rotating bending and push-pull fatigue tests were carried out on 0.29% carbon steel specimens with four kinds of surface roughness at room temperature, 250°C and 350°C, where the strain aging is most remarkable.
The results obtained are as follows:
(1) At room temperature, the fatigue strength decreases as the degree of the surface roughness increases.
(2) At 250°C and 350°C, it is not possible to find any general tendency for the relation between the surface roughness and the fatigue strength, because of the scatter of fatigue strength data, the difference in stress level between the rotating bending and push-pull, the change in surface roughness caused by the formation of oxide scale, the change of hardness by repeated stress and so on.
(3) At 250°C and 350°C, in spite of the difference in surface roughness, the S-N curves can be divided remarkably into two groups, one for the mechanically finished specimens and the other for the specimens annealed in vacuum after mechanical finishing.
