抄録
In order to clarify the effect of strain-aging on fatigue strength, rotating bending tests were made on interference fitted car axles, φ 12mm and φ 50mm, aged after cold surface rolling as well as on those subjected to warm surface rolling. The results obtained are as follows;
(1) The microstructure of specimen was hardly changed by aging, but the surface hardness was increased by 1.1 times in comparison with the cold rolled specimen due to strengthening of ferrite.
(2) The surface compressive residual stress of the aged specimen was 400MPa and the depth of hardened layer was 4mm. Then in comparison with the cold rolled specimen, the residual stress was decreased by 50MPa and the depth of hardened layer increased by 2 times.
(3) The maximum value of fatigue strength of the press-fitted specimen of φ 50mm was obtained at 300°C aging. The value was 216MPa, 1.1 times in comparison with the cold specimen and 2 times in comparison with the normalized specimen. Because of the size effect, the fatigue strength of the φ 50mm aged specimen was decreased by 0.9 times in comparison with the φ 12mm aged specimen.
(4) The fatigue strength of the aged specimen was closer to that of the warm surface rolled specimen than that of the cold rolled one.
