抄録
The changes of thermal residual stressed in low-carbon steel by quench-aging and repeated stressing were investigated using plate specimens of 0.16%C steel. For the study of the effect of quench-aging, aging at room temperature as well as aging at the temperature 100°C were chosen. In repeated stressing, four stress amplitudes above and below the endurance limit were employed. The aspects of precipitates due to various aging treatments were studied by electron micrographs. The results obtained were as follows: (1) The surface residual stresses decrease first and then increase noticeably, thenceforward diminish gradually both by aging at room temperature and accelerated aging with repeated stressing. In the latter, the increase as well as the fading of surface residual stresses are larger by the higher atress amplitudes. (2) The surface residual stress and the hardness both show their maximum value under the same condition by aging at room temperature as well as by aging at the temperature 100°C. (3) The surface residual stress and the hardness both show higher values by aging at the temperature 100°C for 1 hr than by other aging treatments. (4) In the electron micrographs, precipitates were seen in grobular forms at the early stage of aging and then they grew into plate-like forms. In repeated stressing, their features were quite similar to that of aging, indicating the accelerating effect of aging with repeated stressing. (5) The endurance limit heightens and the life lengthens considerably by this quenching. In this experiment, the rise of the endurance limit was about 53% and that of endurance life was almost 400%. It shoud be noted that the residual stresses play an important role in these improvements.
