抄録
The fatigue phenomenon of mild steel is characterized by the existence of fatigue limit and coaxing effect. Although many researches have been made from the viewpoint of strain ageing brought about by interstitial solute atoms of carbon and nitrogen, the effect of strain ageing on fatigue limit has not been fully understood.
The objective of this work is to clarify the effect of strain ageing on the fatigue phenomenon. The experiments were undertaken from the viewpoint that fatigue is a competitive process of two mechanisms of damage and strengthening of the material. Two techniques were applied for this purpose. One was the measurement of the change in solute contents of C and N atoms by internal friction, and the other the reversion of Cottrell atmosphere.
The experimental results are summarized as follows;
It was recognized that there occurred strain ageing in the fatigue process. By removing the strain ageing effect, the specimen fractured even under the stress lower than the fatigue limit. Fatigue limit by suppressing the dislocation multiplication in the fatigue process became higher than the original value. It was also observed that, as the time rate of strain ageing increased at higher temperatures, the knee of S-N curve shifted to the smaller number of cycles.
