The plane bending fatigue tests were made on a low carbon steel plate with a precrack under the stress ratio of 0.05 at room temperature. In some specimens, the precrack introduced by load cycle at room temperature was aged statically by heating in the short brittleness temperature range. By this procedure, the dislocation-relocking structures were introduced in the plastic zone left ahead of the precrack tip. In the other specimens, the precrack was introduced by load cycle in the temperature range above mentioned too. Therefore the plastic zone was aged cyclically. The crack propagation rate da/dn and the effective stress range ratio U were compared between the specimens aged and unaged. For the cyclically aged specimens, a decrease in da/dn was observed transiently. This behavior was similar to the well-known delayed retardation after a single high load. A decrease in U corresponding to that in da/dn was observed, too. The analysis based on the effective stress intensity factor range ΔK_eff, however, showed that the crack closure concept could not perfectly account for the retardation effect in crack propagation. For the statically aged specimens, the retardation effect was observed too. The effect was smaller than that for the cyclically aged specimens.
Both the statically and cyclically aged specimens showed the most remarkable effect on crack propagation behavior when aged at 375°C.